Merge from rust-lang/rust

15 files changed, 19330 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
new file mode 100644
index 00000000000..a57eb70c705
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -0,0 +1,445 @@
+use crate::errors;
+use crate::fluent_generated as fluent;
+use crate::maybe_whole;
+
+use super::{AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle};
+use rustc_ast as ast;
+use rustc_ast::attr;
+use rustc_ast::token::{self, Delimiter};
+use rustc_errors::{codes::*, Diag, PResult};
+use rustc_span::{sym, BytePos, Span};
+use thin_vec::ThinVec;
+use tracing::debug;
+
+// Public for rustfmt usage
+#[derive(Debug)]
+pub enum InnerAttrPolicy {
+    Permitted,
+    Forbidden(Option<InnerAttrForbiddenReason>),
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum InnerAttrForbiddenReason {
+    InCodeBlock,
+    AfterOuterDocComment { prev_doc_comment_span: Span },
+    AfterOuterAttribute { prev_outer_attr_sp: Span },
+}
+
+enum OuterAttributeType {
+    DocComment,
+    DocBlockComment,
+    Attribute,
+}
+
+impl<'a> Parser<'a> {
+    /// Parses attributes that appear before an item.
+    pub(super) fn parse_outer_attributes(&mut self) -> PResult<'a, AttrWrapper> {
+        let mut outer_attrs = ast::AttrVec::new();
+        let mut just_parsed_doc_comment = false;
+        let start_pos = self.num_bump_calls;
+        loop {
+            let attr = if self.check(&token::Pound) {
+                let prev_outer_attr_sp = outer_attrs.last().map(|attr| attr.span);
+
+                let inner_error_reason = if just_parsed_doc_comment {
+                    Some(InnerAttrForbiddenReason::AfterOuterDocComment {
+                        prev_doc_comment_span: prev_outer_attr_sp.unwrap(),
+                    })
+                } else {
+                    prev_outer_attr_sp.map(|prev_outer_attr_sp| {
+                        InnerAttrForbiddenReason::AfterOuterAttribute { prev_outer_attr_sp }
+                    })
+                };
+                let inner_parse_policy = InnerAttrPolicy::Forbidden(inner_error_reason);
+                just_parsed_doc_comment = false;
+                Some(self.parse_attribute(inner_parse_policy)?)
+            } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
+                if attr_style != ast::AttrStyle::Outer {
+                    let span = self.token.span;
+                    let mut err = self
+                        .dcx()
+                        .struct_span_err(span, fluent::parse_inner_doc_comment_not_permitted);
+                    err.code(E0753);
+                    if let Some(replacement_span) = self.annotate_following_item_if_applicable(
+                        &mut err,
+                        span,
+                        match comment_kind {
+                            token::CommentKind::Line => OuterAttributeType::DocComment,
+                            token::CommentKind::Block => OuterAttributeType::DocBlockComment,
+                        },
+                    ) {
+                        err.note(fluent::parse_note);
+                        err.span_suggestion_verbose(
+                            replacement_span,
+                            fluent::parse_suggestion,
+                            "",
+                            rustc_errors::Applicability::MachineApplicable,
+                        );
+                    }
+                    err.emit();
+                }
+                self.bump();
+                just_parsed_doc_comment = true;
+                // Always make an outer attribute - this allows us to recover from a misplaced
+                // inner attribute.
+                Some(attr::mk_doc_comment(
+                    &self.psess.attr_id_generator,
+                    comment_kind,
+                    ast::AttrStyle::Outer,
+                    data,
+                    self.prev_token.span,
+                ))
+            } else {
+                None
+            };
+
+            if let Some(attr) = attr {
+                if attr.style == ast::AttrStyle::Outer {
+                    outer_attrs.push(attr);
+                }
+            } else {
+                break;
+            }
+        }
+        Ok(AttrWrapper::new(outer_attrs, start_pos))
+    }
+
+    /// Matches `attribute = # ! [ meta_item ]`.
+    /// `inner_parse_policy` prescribes how to handle inner attributes.
+    // Public for rustfmt usage.
+    pub fn parse_attribute(
+        &mut self,
+        inner_parse_policy: InnerAttrPolicy,
+    ) -> PResult<'a, ast::Attribute> {
+        debug!(
+            "parse_attribute: inner_parse_policy={:?} self.token={:?}",
+            inner_parse_policy, self.token
+        );
+        let lo = self.token.span;
+        // Attributes can't have attributes of their own [Editor's note: not with that attitude]
+        self.collect_tokens_no_attrs(|this| {
+            assert!(this.eat(&token::Pound), "parse_attribute called in non-attribute position");
+
+            let style =
+                if this.eat(&token::Not) { ast::AttrStyle::Inner } else { ast::AttrStyle::Outer };
+
+            this.expect(&token::OpenDelim(Delimiter::Bracket))?;
+            let item = this.parse_attr_item(false)?;
+            this.expect(&token::CloseDelim(Delimiter::Bracket))?;
+            let attr_sp = lo.to(this.prev_token.span);
+
+            // Emit error if inner attribute is encountered and forbidden.
+            if style == ast::AttrStyle::Inner {
+                this.error_on_forbidden_inner_attr(attr_sp, inner_parse_policy);
+            }
+
+            Ok(attr::mk_attr_from_item(&self.psess.attr_id_generator, item, None, style, attr_sp))
+        })
+    }
+
+    fn annotate_following_item_if_applicable(
+        &self,
+        err: &mut Diag<'_>,
+        span: Span,
+        attr_type: OuterAttributeType,
+    ) -> Option<Span> {
+        let mut snapshot = self.create_snapshot_for_diagnostic();
+        let lo = span.lo()
+            + BytePos(match attr_type {
+                OuterAttributeType::Attribute => 1,
+                _ => 2,
+            });
+        let hi = lo + BytePos(1);
+        let replacement_span = span.with_lo(lo).with_hi(hi);
+        if let OuterAttributeType::DocBlockComment | OuterAttributeType::DocComment = attr_type {
+            snapshot.bump();
+        }
+        loop {
+            // skip any other attributes, we want the item
+            if snapshot.token.kind == token::Pound {
+                if let Err(err) = snapshot.parse_attribute(InnerAttrPolicy::Permitted) {
+                    err.cancel();
+                    return Some(replacement_span);
+                }
+            } else {
+                break;
+            }
+        }
+        match snapshot.parse_item_common(
+            AttrWrapper::empty(),
+            true,
+            false,
+            FnParseMode { req_name: |_| true, req_body: true },
+            ForceCollect::No,
+        ) {
+            Ok(Some(item)) => {
+                // FIXME(#100717)
+                err.arg("item", item.kind.descr());
+                err.span_label(item.span, fluent::parse_label_does_not_annotate_this);
+                err.span_suggestion_verbose(
+                    replacement_span,
+                    fluent::parse_sugg_change_inner_to_outer,
+                    match attr_type {
+                        OuterAttributeType::Attribute => "",
+                        OuterAttributeType::DocBlockComment => "*",
+                        OuterAttributeType::DocComment => "/",
+                    },
+                    rustc_errors::Applicability::MachineApplicable,
+                );
+                return None;
+            }
+            Err(item_err) => {
+                item_err.cancel();
+            }
+            Ok(None) => {}
+        }
+        Some(replacement_span)
+    }
+
+    pub(super) fn error_on_forbidden_inner_attr(&self, attr_sp: Span, policy: InnerAttrPolicy) {
+        if let InnerAttrPolicy::Forbidden(reason) = policy {
+            let mut diag = match reason.as_ref().copied() {
+                Some(InnerAttrForbiddenReason::AfterOuterDocComment { prev_doc_comment_span }) => {
+                    self.dcx()
+                        .struct_span_err(
+                            attr_sp,
+                            fluent::parse_inner_attr_not_permitted_after_outer_doc_comment,
+                        )
+                        .with_span_label(attr_sp, fluent::parse_label_attr)
+                        .with_span_label(
+                            prev_doc_comment_span,
+                            fluent::parse_label_prev_doc_comment,
+                        )
+                }
+                Some(InnerAttrForbiddenReason::AfterOuterAttribute { prev_outer_attr_sp }) => self
+                    .dcx()
+                    .struct_span_err(
+                        attr_sp,
+                        fluent::parse_inner_attr_not_permitted_after_outer_attr,
+                    )
+                    .with_span_label(attr_sp, fluent::parse_label_attr)
+                    .with_span_label(prev_outer_attr_sp, fluent::parse_label_prev_attr),
+                Some(InnerAttrForbiddenReason::InCodeBlock) | None => {
+                    self.dcx().struct_span_err(attr_sp, fluent::parse_inner_attr_not_permitted)
+                }
+            };
+
+            diag.note(fluent::parse_inner_attr_explanation);
+            if self
+                .annotate_following_item_if_applicable(
+                    &mut diag,
+                    attr_sp,
+                    OuterAttributeType::Attribute,
+                )
+                .is_some()
+            {
+                diag.note(fluent::parse_outer_attr_explanation);
+            };
+            diag.emit();
+        }
+    }
+
+    /// Parses an inner part of an attribute (the path and following tokens).
+    /// The tokens must be either a delimited token stream, or empty token stream,
+    /// or the "legacy" key-value form.
+    ///     PATH `(` TOKEN_STREAM `)`
+    ///     PATH `[` TOKEN_STREAM `]`
+    ///     PATH `{` TOKEN_STREAM `}`
+    ///     PATH
+    ///     PATH `=` UNSUFFIXED_LIT
+    /// The delimiters or `=` are still put into the resulting token stream.
+    pub fn parse_attr_item(&mut self, capture_tokens: bool) -> PResult<'a, ast::AttrItem> {
+        maybe_whole!(self, NtMeta, |attr| attr.into_inner());
+
+        let do_parse = |this: &mut Self| {
+            let path = this.parse_path(PathStyle::Mod)?;
+            let args = this.parse_attr_args()?;
+            Ok(ast::AttrItem { path, args, tokens: None })
+        };
+        // Attr items don't have attributes
+        if capture_tokens { self.collect_tokens_no_attrs(do_parse) } else { do_parse(self) }
+    }
+
+    /// Parses attributes that appear after the opening of an item. These should
+    /// be preceded by an exclamation mark, but we accept and warn about one
+    /// terminated by a semicolon.
+    ///
+    /// Matches `inner_attrs*`.
+    pub(crate) fn parse_inner_attributes(&mut self) -> PResult<'a, ast::AttrVec> {
+        let mut attrs = ast::AttrVec::new();
+        loop {
+            let start_pos: u32 = self.num_bump_calls.try_into().unwrap();
+            // Only try to parse if it is an inner attribute (has `!`).
+            let attr = if self.check(&token::Pound) && self.look_ahead(1, |t| t == &token::Not) {
+                Some(self.parse_attribute(InnerAttrPolicy::Permitted)?)
+            } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
+                if attr_style == ast::AttrStyle::Inner {
+                    self.bump();
+                    Some(attr::mk_doc_comment(
+                        &self.psess.attr_id_generator,
+                        comment_kind,
+                        attr_style,
+                        data,
+                        self.prev_token.span,
+                    ))
+                } else {
+                    None
+                }
+            } else {
+                None
+            };
+            if let Some(attr) = attr {
+                let end_pos: u32 = self.num_bump_calls.try_into().unwrap();
+                // If we are currently capturing tokens, mark the location of this inner attribute.
+                // If capturing ends up creating a `LazyAttrTokenStream`, we will include
+                // this replace range with it, removing the inner attribute from the final
+                // `AttrTokenStream`. Inner attributes are stored in the parsed AST note.
+                // During macro expansion, they are selectively inserted back into the
+                // token stream (the first inner attribute is removed each time we invoke the
+                // corresponding macro).
+                let range = start_pos..end_pos;
+                if let Capturing::Yes = self.capture_state.capturing {
+                    self.capture_state.inner_attr_ranges.insert(attr.id, (range, vec![]));
+                }
+                attrs.push(attr);
+            } else {
+                break;
+            }
+        }
+        Ok(attrs)
+    }
+
+    // Note: must be unsuffixed.
+    pub(crate) fn parse_unsuffixed_meta_item_lit(&mut self) -> PResult<'a, ast::MetaItemLit> {
+        let lit = self.parse_meta_item_lit()?;
+        debug!("checking if {:?} is unsuffixed", lit);
+
+        if !lit.kind.is_unsuffixed() {
+            self.dcx().emit_err(errors::SuffixedLiteralInAttribute { span: lit.span });
+        }
+
+        Ok(lit)
+    }
+
+    /// Parses `cfg_attr(pred, attr_item_list)` where `attr_item_list` is comma-delimited.
+    pub fn parse_cfg_attr(&mut self) -> PResult<'a, (ast::MetaItem, Vec<(ast::AttrItem, Span)>)> {
+        let cfg_predicate = self.parse_meta_item()?;
+        self.expect(&token::Comma)?;
+
+        // Presumably, the majority of the time there will only be one attr.
+        let mut expanded_attrs = Vec::with_capacity(1);
+        while self.token.kind != token::Eof {
+            let lo = self.token.span;
+            let item = self.parse_attr_item(true)?;
+            expanded_attrs.push((item, lo.to(self.prev_token.span)));
+            if !self.eat(&token::Comma) {
+                break;
+            }
+        }
+
+        Ok((cfg_predicate, expanded_attrs))
+    }
+
+    /// Matches `COMMASEP(meta_item_inner)`.
+    pub(crate) fn parse_meta_seq_top(&mut self) -> PResult<'a, ThinVec<ast::NestedMetaItem>> {
+        // Presumably, the majority of the time there will only be one attr.
+        let mut nmis = ThinVec::with_capacity(1);
+        while self.token.kind != token::Eof {
+            nmis.push(self.parse_meta_item_inner()?);
+            if !self.eat(&token::Comma) {
+                break;
+            }
+        }
+        Ok(nmis)
+    }
+
+    /// Parse a meta item per RFC 1559.
+    ///
+    /// ```ebnf
+    /// MetaItem = SimplePath ( '=' UNSUFFIXED_LIT | '(' MetaSeq? ')' )? ;
+    /// MetaSeq = MetaItemInner (',' MetaItemInner)* ','? ;
+    /// ```
+    pub fn parse_meta_item(&mut self) -> PResult<'a, ast::MetaItem> {
+        // We can't use `maybe_whole` here because it would bump in the `None`
+        // case, which we don't want.
+        if let token::Interpolated(nt) = &self.token.kind
+            && let token::NtMeta(attr_item) = &**nt
+        {
+            match attr_item.meta(attr_item.path.span) {
+                Some(meta) => {
+                    self.bump();
+                    return Ok(meta);
+                }
+                None => self.unexpected()?,
+            }
+        }
+
+        let lo = self.token.span;
+        let path = self.parse_path(PathStyle::Mod)?;
+        let kind = self.parse_meta_item_kind()?;
+        let span = lo.to(self.prev_token.span);
+        Ok(ast::MetaItem { path, kind, span })
+    }
+
+    pub(crate) fn parse_meta_item_kind(&mut self) -> PResult<'a, ast::MetaItemKind> {
+        Ok(if self.eat(&token::Eq) {
+            ast::MetaItemKind::NameValue(self.parse_unsuffixed_meta_item_lit()?)
+        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            let (list, _) = self.parse_paren_comma_seq(|p| p.parse_meta_item_inner())?;
+            ast::MetaItemKind::List(list)
+        } else {
+            ast::MetaItemKind::Word
+        })
+    }
+
+    /// Parse an inner meta item per RFC 1559.
+    ///
+    /// ```ebnf
+    /// MetaItemInner = UNSUFFIXED_LIT | MetaItem ;
+    /// ```
+    fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
+        match self.parse_unsuffixed_meta_item_lit() {
+            Ok(lit) => return Ok(ast::NestedMetaItem::Lit(lit)),
+            Err(err) => err.cancel(), // we provide a better error below
+        }
+
+        match self.parse_meta_item() {
+            Ok(mi) => return Ok(ast::NestedMetaItem::MetaItem(mi)),
+            Err(err) => err.cancel(), // we provide a better error below
+        }
+
+        let mut err = errors::InvalidMetaItem {
+            span: self.token.span,
+            token: self.token.clone(),
+            quote_ident_sugg: None,
+        };
+
+        // Suggest quoting idents, e.g. in `#[cfg(key = value)]`. We don't use `Token::ident` and
+        // don't `uninterpolate` the token to avoid suggesting anything butchered or questionable
+        // when macro metavariables are involved.
+        if self.prev_token == token::Eq
+            && let token::Ident(..) = self.token.kind
+        {
+            let before = self.token.span.shrink_to_lo();
+            while let token::Ident(..) = self.token.kind {
+                self.bump();
+            }
+            err.quote_ident_sugg = Some(errors::InvalidMetaItemQuoteIdentSugg {
+                before,
+                after: self.prev_token.span.shrink_to_hi(),
+            });
+        }
+
+        Err(self.dcx().create_err(err))
+    }
+}
+
+/// The attributes are complete if all attributes are either a doc comment or a builtin attribute other than `cfg_attr`
+pub fn is_complete(attrs: &[ast::Attribute]) -> bool {
+    attrs.iter().all(|attr| {
+        attr.is_doc_comment()
+            || attr.ident().is_some_and(|ident| {
+                ident.name != sym::cfg_attr && rustc_feature::is_builtin_attr_name(ident.name)
+            })
+    })
+}
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
new file mode 100644
index 00000000000..62c8f9f5dac
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -0,0 +1,465 @@
+use super::{Capturing, FlatToken, ForceCollect, Parser, ReplaceRange, TokenCursor, TrailingToken};
+use rustc_ast::token::{self, Delimiter, Token, TokenKind};
+use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree, AttributesData, DelimSpacing};
+use rustc_ast::tokenstream::{DelimSpan, LazyAttrTokenStream, Spacing, ToAttrTokenStream};
+use rustc_ast::{self as ast};
+use rustc_ast::{AttrVec, Attribute, HasAttrs, HasTokens};
+use rustc_errors::PResult;
+use rustc_session::parse::ParseSess;
+use rustc_span::{sym, Span, DUMMY_SP};
+
+use std::ops::Range;
+
+/// A wrapper type to ensure that the parser handles outer attributes correctly.
+/// When we parse outer attributes, we need to ensure that we capture tokens
+/// for the attribute target. This allows us to perform cfg-expansion on
+/// a token stream before we invoke a derive proc-macro.
+///
+/// This wrapper prevents direct access to the underlying `ast::AttrVec>`.
+/// Parsing code can only get access to the underlying attributes
+/// by passing an `AttrWrapper` to `collect_tokens_trailing_tokens`.
+/// This makes it difficult to accidentally construct an AST node
+/// (which stores an `ast::AttrVec`) without first collecting tokens.
+///
+/// This struct has its own module, to ensure that the parser code
+/// cannot directly access the `attrs` field
+#[derive(Debug, Clone)]
+pub struct AttrWrapper {
+    attrs: AttrVec,
+    // The start of the outer attributes in the token cursor.
+    // This allows us to create a `ReplaceRange` for the entire attribute
+    // target, including outer attributes.
+    start_pos: usize,
+}
+
+impl AttrWrapper {
+    pub(super) fn new(attrs: AttrVec, start_pos: usize) -> AttrWrapper {
+        AttrWrapper { attrs, start_pos }
+    }
+    pub fn empty() -> AttrWrapper {
+        AttrWrapper { attrs: AttrVec::new(), start_pos: usize::MAX }
+    }
+
+    pub(crate) fn take_for_recovery(self, psess: &ParseSess) -> AttrVec {
+        psess.dcx.span_delayed_bug(
+            self.attrs.get(0).map(|attr| attr.span).unwrap_or(DUMMY_SP),
+            "AttrVec is taken for recovery but no error is produced",
+        );
+
+        self.attrs
+    }
+
+    /// Prepend `self.attrs` to `attrs`.
+    // FIXME: require passing an NT to prevent misuse of this method
+    pub(crate) fn prepend_to_nt_inner(self, attrs: &mut AttrVec) {
+        let mut self_attrs = self.attrs;
+        std::mem::swap(attrs, &mut self_attrs);
+        attrs.extend(self_attrs);
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.attrs.is_empty()
+    }
+
+    pub fn is_complete(&self) -> bool {
+        crate::parser::attr::is_complete(&self.attrs)
+    }
+}
+
+/// Returns `true` if `attrs` contains a `cfg` or `cfg_attr` attribute
+fn has_cfg_or_cfg_attr(attrs: &[Attribute]) -> bool {
+    // NOTE: Builtin attributes like `cfg` and `cfg_attr` cannot be renamed via imports.
+    // Therefore, the absence of a literal `cfg` or `cfg_attr` guarantees that
+    // we don't need to do any eager expansion.
+    attrs.iter().any(|attr| {
+        attr.ident().is_some_and(|ident| ident.name == sym::cfg || ident.name == sym::cfg_attr)
+    })
+}
+
+// Produces a `TokenStream` on-demand. Using `cursor_snapshot`
+// and `num_calls`, we can reconstruct the `TokenStream` seen
+// by the callback. This allows us to avoid producing a `TokenStream`
+// if it is never needed - for example, a captured `macro_rules!`
+// argument that is never passed to a proc macro.
+// In practice token stream creation happens rarely compared to
+// calls to `collect_tokens` (see some statistics in #78736),
+// so we are doing as little up-front work as possible.
+//
+// This also makes `Parser` very cheap to clone, since
+// there is no intermediate collection buffer to clone.
+#[derive(Clone)]
+struct LazyAttrTokenStreamImpl {
+    start_token: (Token, Spacing),
+    cursor_snapshot: TokenCursor,
+    num_calls: usize,
+    break_last_token: bool,
+    replace_ranges: Box<[ReplaceRange]>,
+}
+
+impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
+    fn to_attr_token_stream(&self) -> AttrTokenStream {
+        // The token produced by the final call to `{,inlined_}next` was not
+        // actually consumed by the callback. The combination of chaining the
+        // initial token and using `take` produces the desired result - we
+        // produce an empty `TokenStream` if no calls were made, and omit the
+        // final token otherwise.
+        let mut cursor_snapshot = self.cursor_snapshot.clone();
+        let tokens =
+            std::iter::once((FlatToken::Token(self.start_token.0.clone()), self.start_token.1))
+                .chain(std::iter::repeat_with(|| {
+                    let token = cursor_snapshot.next();
+                    (FlatToken::Token(token.0), token.1)
+                }))
+                .take(self.num_calls);
+
+        if !self.replace_ranges.is_empty() {
+            let mut tokens: Vec<_> = tokens.collect();
+            let mut replace_ranges = self.replace_ranges.to_vec();
+            replace_ranges.sort_by_key(|(range, _)| range.start);
+
+            #[cfg(debug_assertions)]
+            {
+                for [(range, tokens), (next_range, next_tokens)] in replace_ranges.array_windows() {
+                    assert!(
+                        range.end <= next_range.start || range.end >= next_range.end,
+                        "Replace ranges should either be disjoint or nested: ({:?}, {:?}) ({:?}, {:?})",
+                        range,
+                        tokens,
+                        next_range,
+                        next_tokens,
+                    );
+                }
+            }
+
+            // Process the replace ranges, starting from the highest start
+            // position and working our way back. If have tokens like:
+            //
+            // `#[cfg(FALSE)] struct Foo { #[cfg(FALSE)] field: bool }`
+            //
+            // Then we will generate replace ranges for both
+            // the `#[cfg(FALSE)] field: bool` and the entire
+            // `#[cfg(FALSE)] struct Foo { #[cfg(FALSE)] field: bool }`
+            //
+            // By starting processing from the replace range with the greatest
+            // start position, we ensure that any replace range which encloses
+            // another replace range will capture the *replaced* tokens for the inner
+            // range, not the original tokens.
+            for (range, new_tokens) in replace_ranges.into_iter().rev() {
+                assert!(!range.is_empty(), "Cannot replace an empty range: {range:?}");
+                // Replace ranges are only allowed to decrease the number of tokens.
+                assert!(
+                    range.len() >= new_tokens.len(),
+                    "Range {range:?} has greater len than {new_tokens:?}"
+                );
+
+                // Replace any removed tokens with `FlatToken::Empty`.
+                // This keeps the total length of `tokens` constant throughout the
+                // replacement process, allowing us to use all of the `ReplaceRanges` entries
+                // without adjusting indices.
+                let filler = std::iter::repeat((FlatToken::Empty, Spacing::Alone))
+                    .take(range.len() - new_tokens.len());
+
+                tokens.splice(
+                    (range.start as usize)..(range.end as usize),
+                    new_tokens.into_iter().chain(filler),
+                );
+            }
+            make_token_stream(tokens.into_iter(), self.break_last_token)
+        } else {
+            make_token_stream(tokens, self.break_last_token)
+        }
+    }
+}
+
+impl<'a> Parser<'a> {
+    /// Records all tokens consumed by the provided callback,
+    /// including the current token. These tokens are collected
+    /// into a `LazyAttrTokenStream`, and returned along with the result
+    /// of the callback.
+    ///
+    /// Note: If your callback consumes an opening delimiter
+    /// (including the case where you call `collect_tokens`
+    /// when the current token is an opening delimiter),
+    /// you must also consume the corresponding closing delimiter.
+    ///
+    /// That is, you can consume
+    /// `something ([{ }])` or `([{}])`, but not `([{}]`
+    ///
+    /// This restriction shouldn't be an issue in practice,
+    /// since this function is used to record the tokens for
+    /// a parsed AST item, which always has matching delimiters.
+    pub fn collect_tokens_trailing_token<R: HasAttrs + HasTokens>(
+        &mut self,
+        attrs: AttrWrapper,
+        force_collect: ForceCollect,
+        f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, (R, TrailingToken)>,
+    ) -> PResult<'a, R> {
+        // We only bail out when nothing could possibly observe the collected tokens:
+        // 1. We cannot be force collecting tokens (since force-collecting requires tokens
+        //    by definition
+        if matches!(force_collect, ForceCollect::No)
+            // None of our outer attributes can require tokens (e.g. a proc-macro)
+            && attrs.is_complete()
+            // If our target supports custom inner attributes, then we cannot bail
+            // out early, since we may need to capture tokens for a custom inner attribute
+            // invocation.
+            && !R::SUPPORTS_CUSTOM_INNER_ATTRS
+            // Never bail out early in `capture_cfg` mode, since there might be `#[cfg]`
+            // or `#[cfg_attr]` attributes.
+            && !self.capture_cfg
+        {
+            return Ok(f(self, attrs.attrs)?.0);
+        }
+
+        let start_token = (self.token.clone(), self.token_spacing);
+        let cursor_snapshot = self.token_cursor.clone();
+        let start_pos = self.num_bump_calls;
+
+        let has_outer_attrs = !attrs.attrs.is_empty();
+        let prev_capturing = std::mem::replace(&mut self.capture_state.capturing, Capturing::Yes);
+        let replace_ranges_start = self.capture_state.replace_ranges.len();
+
+        let ret = f(self, attrs.attrs);
+
+        self.capture_state.capturing = prev_capturing;
+
+        let (mut ret, trailing) = ret?;
+
+        // When we're not in `capture-cfg` mode, then bail out early if:
+        // 1. Our target doesn't support tokens at all (e.g we're parsing an `NtIdent`)
+        //    so there's nothing for us to do.
+        // 2. Our target already has tokens set (e.g. we've parsed something
+        // like `#[my_attr] $item`. The actual parsing code takes care of prepending
+        // any attributes to the nonterminal, so we don't need to modify the
+        // already captured tokens.
+        // Note that this check is independent of `force_collect`- if we already
+        // have tokens, or can't even store them, then there's never a need to
+        // force collection of new tokens.
+        if !self.capture_cfg && matches!(ret.tokens_mut(), None | Some(Some(_))) {
+            return Ok(ret);
+        }
+
+        // This is very similar to the bail out check at the start of this function.
+        // Now that we've parsed an AST node, we have more information available.
+        if matches!(force_collect, ForceCollect::No)
+            // We now have inner attributes available, so this check is more precise
+            // than `attrs.is_complete()` at the start of the function.
+            // As a result, we don't need to check `R::SUPPORTS_CUSTOM_INNER_ATTRS`
+            && crate::parser::attr::is_complete(ret.attrs())
+            // Subtle: We call `has_cfg_or_cfg_attr` with the attrs from `ret`.
+            // This ensures that we consider inner attributes (e.g. `#![cfg]`),
+            // which require us to have tokens available
+            // We also call `has_cfg_or_cfg_attr` at the beginning of this function,
+            // but we only bail out if there's no possibility of inner attributes
+            // (!R::SUPPORTS_CUSTOM_INNER_ATTRS)
+            // We only capture about `#[cfg]` or `#[cfg_attr]` in `capture_cfg`
+            // mode - during normal parsing, we don't need any special capturing
+            // for those attributes, since they're builtin.
+            && !(self.capture_cfg && has_cfg_or_cfg_attr(ret.attrs()))
+        {
+            return Ok(ret);
+        }
+
+        let mut inner_attr_replace_ranges = Vec::new();
+        // Take the captured ranges for any inner attributes that we parsed.
+        for inner_attr in ret.attrs().iter().filter(|a| a.style == ast::AttrStyle::Inner) {
+            if let Some(attr_range) = self.capture_state.inner_attr_ranges.remove(&inner_attr.id) {
+                inner_attr_replace_ranges.push(attr_range);
+            } else {
+                self.dcx().span_delayed_bug(inner_attr.span, "Missing token range for attribute");
+            }
+        }
+
+        let replace_ranges_end = self.capture_state.replace_ranges.len();
+
+        let mut end_pos = self.num_bump_calls;
+
+        let mut captured_trailing = false;
+
+        // Capture a trailing token if requested by the callback 'f'
+        match trailing {
+            TrailingToken::None => {}
+            TrailingToken::Gt => {
+                assert_eq!(self.token.kind, token::Gt);
+            }
+            TrailingToken::Semi => {
+                assert_eq!(self.token.kind, token::Semi);
+                end_pos += 1;
+                captured_trailing = true;
+            }
+            TrailingToken::MaybeComma => {
+                if self.token.kind == token::Comma {
+                    end_pos += 1;
+                    captured_trailing = true;
+                }
+            }
+        }
+
+        // If we 'broke' the last token (e.g. breaking a '>>' token to two '>' tokens),
+        // then extend the range of captured tokens to include it, since the parser
+        // was not actually bumped past it. When the `LazyAttrTokenStream` gets converted
+        // into an `AttrTokenStream`, we will create the proper token.
+        if self.break_last_token {
+            assert!(!captured_trailing, "Cannot set break_last_token and have trailing token");
+            end_pos += 1;
+        }
+
+        let num_calls = end_pos - start_pos;
+
+        // If we have no attributes, then we will never need to
+        // use any replace ranges.
+        let replace_ranges: Box<[ReplaceRange]> = if ret.attrs().is_empty() && !self.capture_cfg {
+            Box::new([])
+        } else {
+            // Grab any replace ranges that occur *inside* the current AST node.
+            // We will perform the actual replacement when we convert the `LazyAttrTokenStream`
+            // to an `AttrTokenStream`.
+            let start_calls: u32 = start_pos.try_into().unwrap();
+            self.capture_state.replace_ranges[replace_ranges_start..replace_ranges_end]
+                .iter()
+                .cloned()
+                .chain(inner_attr_replace_ranges.iter().cloned())
+                .map(|(range, tokens)| {
+                    ((range.start - start_calls)..(range.end - start_calls), tokens)
+                })
+                .collect()
+        };
+
+        let tokens = LazyAttrTokenStream::new(LazyAttrTokenStreamImpl {
+            start_token,
+            num_calls,
+            cursor_snapshot,
+            break_last_token: self.break_last_token,
+            replace_ranges,
+        });
+
+        // If we support tokens at all
+        if let Some(target_tokens) = ret.tokens_mut() {
+            if target_tokens.is_none() {
+                // Store se our newly captured tokens into the AST node
+                *target_tokens = Some(tokens.clone());
+            }
+        }
+
+        let final_attrs = ret.attrs();
+
+        // If `capture_cfg` is set and we're inside a recursive call to
+        // `collect_tokens_trailing_token`, then we need to register a replace range
+        // if we have `#[cfg]` or `#[cfg_attr]`. This allows us to run eager cfg-expansion
+        // on the captured token stream.
+        if self.capture_cfg
+            && matches!(self.capture_state.capturing, Capturing::Yes)
+            && has_cfg_or_cfg_attr(final_attrs)
+        {
+            let attr_data = AttributesData { attrs: final_attrs.iter().cloned().collect(), tokens };
+
+            // Replace the entire AST node that we just parsed, including attributes,
+            // with a `FlatToken::AttrTarget`. If this AST node is inside an item
+            // that has `#[derive]`, then this will allow us to cfg-expand this
+            // AST node.
+            let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
+            let new_tokens = vec![(FlatToken::AttrTarget(attr_data), Spacing::Alone)];
+
+            assert!(!self.break_last_token, "Should not have unglued last token with cfg attr");
+            let range: Range<u32> = (start_pos.try_into().unwrap())..(end_pos.try_into().unwrap());
+            self.capture_state.replace_ranges.push((range, new_tokens));
+            self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
+        }
+
+        // Only clear our `replace_ranges` when we're finished capturing entirely.
+        if matches!(self.capture_state.capturing, Capturing::No) {
+            self.capture_state.replace_ranges.clear();
+            // We don't clear `inner_attr_ranges`, as doing so repeatedly
+            // had a measurable performance impact. Most inner attributes that
+            // we insert will get removed - when we drop the parser, we'll free
+            // up the memory used by any attributes that we didn't remove from the map.
+        }
+        Ok(ret)
+    }
+}
+
+/// Converts a flattened iterator of tokens (including open and close delimiter tokens)
+/// into a `TokenStream`, creating a `TokenTree::Delimited` for each matching pair
+/// of open and close delims.
+fn make_token_stream(
+    mut iter: impl Iterator<Item = (FlatToken, Spacing)>,
+    break_last_token: bool,
+) -> AttrTokenStream {
+    #[derive(Debug)]
+    struct FrameData {
+        // This is `None` for the first frame, `Some` for all others.
+        open_delim_sp: Option<(Delimiter, Span, Spacing)>,
+        inner: Vec<AttrTokenTree>,
+    }
+    let mut stack = vec![FrameData { open_delim_sp: None, inner: vec![] }];
+    let mut token_and_spacing = iter.next();
+    while let Some((token, spacing)) = token_and_spacing {
+        match token {
+            FlatToken::Token(Token { kind: TokenKind::OpenDelim(delim), span }) => {
+                stack
+                    .push(FrameData { open_delim_sp: Some((delim, span, spacing)), inner: vec![] });
+            }
+            FlatToken::Token(Token { kind: TokenKind::CloseDelim(delim), span }) => {
+                let frame_data = stack
+                    .pop()
+                    .unwrap_or_else(|| panic!("Token stack was empty for token: {token:?}"));
+
+                let (open_delim, open_sp, open_spacing) = frame_data.open_delim_sp.unwrap();
+                assert_eq!(
+                    open_delim, delim,
+                    "Mismatched open/close delims: open={open_delim:?} close={span:?}"
+                );
+                let dspan = DelimSpan::from_pair(open_sp, span);
+                let dspacing = DelimSpacing::new(open_spacing, spacing);
+                let stream = AttrTokenStream::new(frame_data.inner);
+                let delimited = AttrTokenTree::Delimited(dspan, dspacing, delim, stream);
+                stack
+                    .last_mut()
+                    .unwrap_or_else(|| panic!("Bottom token frame is missing for token: {token:?}"))
+                    .inner
+                    .push(delimited);
+            }
+            FlatToken::Token(token) => stack
+                .last_mut()
+                .expect("Bottom token frame is missing!")
+                .inner
+                .push(AttrTokenTree::Token(token, spacing)),
+            FlatToken::AttrTarget(data) => stack
+                .last_mut()
+                .expect("Bottom token frame is missing!")
+                .inner
+                .push(AttrTokenTree::Attributes(data)),
+            FlatToken::Empty => {}
+        }
+        token_and_spacing = iter.next();
+    }
+    let mut final_buf = stack.pop().expect("Missing final buf!");
+    if break_last_token {
+        let last_token = final_buf.inner.pop().unwrap();
+        if let AttrTokenTree::Token(last_token, spacing) = last_token {
+            let unglued_first = last_token.kind.break_two_token_op().unwrap().0;
+
+            // An 'unglued' token is always two ASCII characters
+            let mut first_span = last_token.span.shrink_to_lo();
+            first_span = first_span.with_hi(first_span.lo() + rustc_span::BytePos(1));
+
+            final_buf
+                .inner
+                .push(AttrTokenTree::Token(Token::new(unglued_first, first_span), spacing));
+        } else {
+            panic!("Unexpected last token {last_token:?}")
+        }
+    }
+    AttrTokenStream::new(final_buf.inner)
+}
+
+// Some types are used a lot. Make sure they don't unintentionally get bigger.
+#[cfg(target_pointer_width = "64")]
+mod size_asserts {
+    use super::*;
+    use rustc_data_structures::static_assert_size;
+    // tidy-alphabetical-start
+    static_assert_size!(AttrWrapper, 16);
+    static_assert_size!(LazyAttrTokenStreamImpl, 104);
+    // tidy-alphabetical-end
+}
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
new file mode 100644
index 00000000000..ac12787f2ef
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -0,0 +1,3056 @@
+use super::pat::Expected;
+use super::{
+    BlockMode, CommaRecoveryMode, Parser, PathStyle, Restrictions, SemiColonMode, SeqSep,
+    TokenExpectType, TokenType,
+};
+use crate::errors::{
+    AmbiguousPlus, AsyncMoveBlockIn2015, AttributeOnParamType, BadQPathStage2, BadTypePlus,
+    BadTypePlusSub, ColonAsSemi, ComparisonOperatorsCannotBeChained,
+    ComparisonOperatorsCannotBeChainedSugg, ConstGenericWithoutBraces,
+    ConstGenericWithoutBracesSugg, DocCommentDoesNotDocumentAnything, DocCommentOnParamType,
+    DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
+    GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg,
+    HelpIdentifierStartsWithNumber, HelpUseLatestEdition, InInTypo, IncorrectAwait,
+    IncorrectSemicolon, IncorrectUseOfAwait, PatternMethodParamWithoutBody, QuestionMarkInType,
+    QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
+    StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens, StructLiteralNeedingParensSugg,
+    SuggAddMissingLetStmt, SuggEscapeIdentifier, SuggRemoveComma, TernaryOperator,
+    UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
+    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead, WrapType,
+};
+use crate::fluent_generated as fluent;
+use crate::parser;
+use crate::parser::attr::InnerAttrPolicy;
+use ast::token::IdentIsRaw;
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Lit, LitKind, Token, TokenKind};
+use rustc_ast::tokenstream::AttrTokenTree;
+use rustc_ast::util::parser::AssocOp;
+use rustc_ast::{
+    AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingMode, Block,
+    BlockCheckMode, Expr, ExprKind, GenericArg, Generics, HasTokens, Item, ItemKind, Param, Pat,
+    PatKind, Path, PathSegment, QSelf, Recovered, Ty, TyKind,
+};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{
+    pluralize, Applicability, Diag, DiagCtxt, ErrorGuaranteed, FatalError, PErr, PResult,
+    Subdiagnostic,
+};
+use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::source_map::Spanned;
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{BytePos, Span, SpanSnippetError, Symbol, DUMMY_SP};
+use std::mem::take;
+use std::ops::{Deref, DerefMut};
+use thin_vec::{thin_vec, ThinVec};
+
+/// Creates a placeholder argument.
+pub(super) fn dummy_arg(ident: Ident, guar: ErrorGuaranteed) -> Param {
+    let pat = P(Pat {
+        id: ast::DUMMY_NODE_ID,
+        kind: PatKind::Ident(BindingMode::NONE, ident, None),
+        span: ident.span,
+        tokens: None,
+    });
+    let ty = Ty { kind: TyKind::Err(guar), span: ident.span, id: ast::DUMMY_NODE_ID, tokens: None };
+    Param {
+        attrs: AttrVec::default(),
+        id: ast::DUMMY_NODE_ID,
+        pat,
+        span: ident.span,
+        ty: P(ty),
+        is_placeholder: false,
+    }
+}
+
+pub(super) trait RecoverQPath: Sized + 'static {
+    const PATH_STYLE: PathStyle = PathStyle::Expr;
+    fn to_ty(&self) -> Option<P<Ty>>;
+    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self;
+}
+
+impl RecoverQPath for Ty {
+    const PATH_STYLE: PathStyle = PathStyle::Type;
+    fn to_ty(&self) -> Option<P<Ty>> {
+        Some(P(self.clone()))
+    }
+    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: TyKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+impl RecoverQPath for Pat {
+    const PATH_STYLE: PathStyle = PathStyle::Pat;
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: PatKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+impl RecoverQPath for Expr {
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: ExprKind::Path(qself, path),
+            attrs: AttrVec::new(),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+/// Control whether the closing delimiter should be consumed when calling `Parser::consume_block`.
+pub(crate) enum ConsumeClosingDelim {
+    Yes,
+    No,
+}
+
+#[derive(Clone, Copy)]
+pub enum AttemptLocalParseRecovery {
+    Yes,
+    No,
+}
+
+impl AttemptLocalParseRecovery {
+    pub fn yes(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => true,
+            AttemptLocalParseRecovery::No => false,
+        }
+    }
+
+    pub fn no(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => false,
+            AttemptLocalParseRecovery::No => true,
+        }
+    }
+}
+
+/// Information for emitting suggestions and recovering from
+/// C-style `i++`, `--i`, etc.
+#[derive(Debug, Copy, Clone)]
+struct IncDecRecovery {
+    /// Is this increment/decrement its own statement?
+    standalone: IsStandalone,
+    /// Is this an increment or decrement?
+    op: IncOrDec,
+    /// Is this pre- or postfix?
+    fixity: UnaryFixity,
+}
+
+/// Is an increment or decrement expression its own statement?
+#[derive(Debug, Copy, Clone)]
+enum IsStandalone {
+    /// It's standalone, i.e., its own statement.
+    Standalone,
+    /// It's a subexpression, i.e., *not* standalone.
+    Subexpr,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum IncOrDec {
+    Inc,
+    Dec,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum UnaryFixity {
+    Pre,
+    Post,
+}
+
+impl IncOrDec {
+    fn chr(&self) -> char {
+        match self {
+            Self::Inc => '+',
+            Self::Dec => '-',
+        }
+    }
+
+    fn name(&self) -> &'static str {
+        match self {
+            Self::Inc => "increment",
+            Self::Dec => "decrement",
+        }
+    }
+}
+
+impl std::fmt::Display for UnaryFixity {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Pre => write!(f, "prefix"),
+            Self::Post => write!(f, "postfix"),
+        }
+    }
+}
+
+struct MultiSugg {
+    msg: String,
+    patches: Vec<(Span, String)>,
+    applicability: Applicability,
+}
+
+impl MultiSugg {
+    fn emit(self, err: &mut Diag<'_>) {
+        err.multipart_suggestion(self.msg, self.patches, self.applicability);
+    }
+
+    fn emit_verbose(self, err: &mut Diag<'_>) {
+        err.multipart_suggestion_verbose(self.msg, self.patches, self.applicability);
+    }
+}
+
+/// SnapshotParser is used to create a snapshot of the parser
+/// without causing duplicate errors being emitted when the `Parser`
+/// is dropped.
+pub struct SnapshotParser<'a> {
+    parser: Parser<'a>,
+}
+
+impl<'a> Deref for SnapshotParser<'a> {
+    type Target = Parser<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.parser
+    }
+}
+
+impl<'a> DerefMut for SnapshotParser<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.parser
+    }
+}
+
+impl<'a> Parser<'a> {
+    pub fn dcx(&self) -> &'a DiagCtxt {
+        &self.psess.dcx
+    }
+
+    /// Replace `self` with `snapshot.parser`.
+    pub(super) fn restore_snapshot(&mut self, snapshot: SnapshotParser<'a>) {
+        *self = snapshot.parser;
+    }
+
+    /// Create a snapshot of the `Parser`.
+    pub fn create_snapshot_for_diagnostic(&self) -> SnapshotParser<'a> {
+        let snapshot = self.clone();
+        SnapshotParser { parser: snapshot }
+    }
+
+    pub(super) fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
+        self.psess.source_map().span_to_snippet(span)
+    }
+
+    /// Emits an error with suggestions if an identifier was expected but not found.
+    ///
+    /// Returns a possibly recovered identifier.
+    pub(super) fn expected_ident_found(
+        &mut self,
+        recover: bool,
+    ) -> PResult<'a, (Ident, IdentIsRaw)> {
+        if let TokenKind::DocComment(..) = self.prev_token.kind {
+            return Err(self.dcx().create_err(DocCommentDoesNotDocumentAnything {
+                span: self.prev_token.span,
+                missing_comma: None,
+            }));
+        }
+
+        let valid_follow = &[
+            TokenKind::Eq,
+            TokenKind::Colon,
+            TokenKind::Comma,
+            TokenKind::Semi,
+            TokenKind::PathSep,
+            TokenKind::OpenDelim(Delimiter::Brace),
+            TokenKind::OpenDelim(Delimiter::Parenthesis),
+            TokenKind::CloseDelim(Delimiter::Brace),
+            TokenKind::CloseDelim(Delimiter::Parenthesis),
+        ];
+
+        let mut recovered_ident = None;
+        // we take this here so that the correct original token is retained in
+        // the diagnostic, regardless of eager recovery.
+        let bad_token = self.token.clone();
+
+        // suggest prepending a keyword in identifier position with `r#`
+        let suggest_raw = if let Some((ident, IdentIsRaw::No)) = self.token.ident()
+            && ident.is_raw_guess()
+            && self.look_ahead(1, |t| valid_follow.contains(&t.kind))
+        {
+            recovered_ident = Some((ident, IdentIsRaw::Yes));
+
+            // `Symbol::to_string()` is different from `Symbol::into_diag_arg()`,
+            // which uses `Symbol::to_ident_string()` and "helpfully" adds an implicit `r#`
+            let ident_name = ident.name.to_string();
+
+            Some(SuggEscapeIdentifier { span: ident.span.shrink_to_lo(), ident_name })
+        } else {
+            None
+        };
+
+        let suggest_remove_comma =
+            if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
+                if recover {
+                    self.bump();
+                    recovered_ident = self.ident_or_err(false).ok();
+                };
+
+                Some(SuggRemoveComma { span: bad_token.span })
+            } else {
+                None
+            };
+
+        let help_cannot_start_number = self.is_lit_bad_ident().map(|(len, valid_portion)| {
+            let (invalid, valid) = self.token.span.split_at(len as u32);
+
+            recovered_ident = Some((Ident::new(valid_portion, valid), IdentIsRaw::No));
+
+            HelpIdentifierStartsWithNumber { num_span: invalid }
+        });
+
+        let err = ExpectedIdentifier {
+            span: bad_token.span,
+            token: bad_token,
+            suggest_raw,
+            suggest_remove_comma,
+            help_cannot_start_number,
+        };
+        let mut err = self.dcx().create_err(err);
+
+        // if the token we have is a `<`
+        // it *might* be a misplaced generic
+        // FIXME: could we recover with this?
+        if self.token == token::Lt {
+            // all keywords that could have generic applied
+            let valid_prev_keywords =
+                [kw::Fn, kw::Type, kw::Struct, kw::Enum, kw::Union, kw::Trait];
+
+            // If we've expected an identifier,
+            // and the current token is a '<'
+            // if the previous token is a valid keyword
+            // that might use a generic, then suggest a correct
+            // generic placement (later on)
+            let maybe_keyword = self.prev_token.clone();
+            if valid_prev_keywords.into_iter().any(|x| maybe_keyword.is_keyword(x)) {
+                // if we have a valid keyword, attempt to parse generics
+                // also obtain the keywords symbol
+                match self.parse_generics() {
+                    Ok(generic) => {
+                        if let TokenKind::Ident(symbol, _) = maybe_keyword.kind {
+                            let ident_name = symbol;
+                            // at this point, we've found something like
+                            // `fn <T>id`
+                            // and current token should be Ident with the item name (i.e. the function name)
+                            // if there is a `<` after the fn name, then don't show a suggestion, show help
+
+                            if !self.look_ahead(1, |t| *t == token::Lt)
+                                && let Ok(snippet) =
+                                    self.psess.source_map().span_to_snippet(generic.span)
+                            {
+                                err.multipart_suggestion_verbose(
+                                        format!("place the generic parameter name after the {ident_name} name"),
+                                        vec![
+                                            (self.token.span.shrink_to_hi(), snippet),
+                                            (generic.span, String::new())
+                                        ],
+                                        Applicability::MaybeIncorrect,
+                                    );
+                            } else {
+                                err.help(format!(
+                                    "place the generic parameter name after the {ident_name} name"
+                                ));
+                            }
+                        }
+                    }
+                    Err(err) => {
+                        // if there's an error parsing the generics,
+                        // then don't do a misplaced generics suggestion
+                        // and emit the expected ident error instead;
+                        err.cancel();
+                    }
+                }
+            }
+        }
+
+        if let Some(recovered_ident) = recovered_ident
+            && recover
+        {
+            err.emit();
+            Ok(recovered_ident)
+        } else {
+            Err(err)
+        }
+    }
+
+    pub(super) fn expected_ident_found_err(&mut self) -> Diag<'a> {
+        self.expected_ident_found(false).unwrap_err()
+    }
+
+    /// Checks if the current token is a integer or float literal and looks like
+    /// it could be a invalid identifier with digits at the start.
+    ///
+    /// Returns the number of characters (bytes) composing the invalid portion
+    /// of the identifier and the valid portion of the identifier.
+    pub(super) fn is_lit_bad_ident(&mut self) -> Option<(usize, Symbol)> {
+        // ensure that the integer literal is followed by a *invalid*
+        // suffix: this is how we know that it is a identifier with an
+        // invalid beginning.
+        if let token::Literal(Lit {
+            kind: token::LitKind::Integer | token::LitKind::Float,
+            symbol,
+            suffix: Some(suffix), // no suffix makes it a valid literal
+        }) = self.token.kind
+            && rustc_ast::MetaItemLit::from_token(&self.token).is_none()
+        {
+            Some((symbol.as_str().len(), suffix))
+        } else {
+            None
+        }
+    }
+
+    pub(super) fn expected_one_of_not_found(
+        &mut self,
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
+    ) -> PResult<'a, Recovered> {
+        debug!("expected_one_of_not_found(edible: {:?}, inedible: {:?})", edible, inedible);
+        fn tokens_to_string(tokens: &[TokenType]) -> String {
+            let mut i = tokens.iter();
+            // This might be a sign we need a connect method on `Iterator`.
+            let b = i.next().map_or_else(String::new, |t| t.to_string());
+            i.enumerate().fold(b, |mut b, (i, a)| {
+                if tokens.len() > 2 && i == tokens.len() - 2 {
+                    b.push_str(", or ");
+                } else if tokens.len() == 2 && i == tokens.len() - 2 {
+                    b.push_str(" or ");
+                } else {
+                    b.push_str(", ");
+                }
+                b.push_str(&a.to_string());
+                b
+            })
+        }
+
+        self.expected_tokens.extend(edible.iter().chain(inedible).cloned().map(TokenType::Token));
+        let mut expected = self
+            .expected_tokens
+            .iter()
+            .filter(|token| {
+                // Filter out suggestions that suggest the same token which was found and deemed incorrect.
+                fn is_ident_eq_keyword(found: &TokenKind, expected: &TokenType) -> bool {
+                    if let TokenKind::Ident(current_sym, _) = found
+                        && let TokenType::Keyword(suggested_sym) = expected
+                    {
+                        return current_sym == suggested_sym;
+                    }
+                    false
+                }
+
+                if **token != parser::TokenType::Token(self.token.kind.clone()) {
+                    let eq = is_ident_eq_keyword(&self.token.kind, &token);
+                    // If the suggestion is a keyword and the found token is an ident,
+                    // the content of which are equal to the suggestion's content,
+                    // we can remove that suggestion (see the `return false` below).
+
+                    // If this isn't the case however, and the suggestion is a token the
+                    // content of which is the same as the found token's, we remove it as well.
+                    if !eq {
+                        if let TokenType::Token(kind) = &token {
+                            if kind == &self.token.kind {
+                                return false;
+                            }
+                        }
+                        return true;
+                    }
+                }
+                false
+            })
+            .cloned()
+            .collect::<Vec<_>>();
+        expected.sort_by_cached_key(|x| x.to_string());
+        expected.dedup();
+
+        let sm = self.psess.source_map();
+
+        // Special-case "expected `;`" errors.
+        if expected.contains(&TokenType::Token(token::Semi)) {
+            // If the user is trying to write a ternary expression, recover it and
+            // return an Err to prevent a cascade of irrelevant diagnostics.
+            if self.prev_token == token::Question
+                && let Err(e) = self.maybe_recover_from_ternary_operator()
+            {
+                return Err(e);
+            }
+
+            if self.token.span == DUMMY_SP || self.prev_token.span == DUMMY_SP {
+                // Likely inside a macro, can't provide meaningful suggestions.
+            } else if !sm.is_multiline(self.prev_token.span.until(self.token.span)) {
+                // The current token is in the same line as the prior token, not recoverable.
+            } else if [token::Comma, token::Colon].contains(&self.token.kind)
+                && self.prev_token.kind == token::CloseDelim(Delimiter::Parenthesis)
+            {
+                // Likely typo: The current token is on a new line and is expected to be
+                // `.`, `;`, `?`, or an operator after a close delimiter token.
+                //
+                // let a = std::process::Command::new("echo")
+                //         .arg("1")
+                //         ,arg("2")
+                //         ^
+                // https://github.com/rust-lang/rust/issues/72253
+            } else if self.look_ahead(1, |t| {
+                t == &token::CloseDelim(Delimiter::Brace)
+                    || t.can_begin_expr() && t.kind != token::Colon
+            }) && [token::Comma, token::Colon].contains(&self.token.kind)
+            {
+                // Likely typo: `,` → `;` or `:` → `;`. This is triggered if the current token is
+                // either `,` or `:`, and the next token could either start a new statement or is a
+                // block close. For example:
+                //
+                //   let x = 32:
+                //   let y = 42;
+                let guar = self.dcx().emit_err(ExpectedSemi {
+                    span: self.token.span,
+                    token: self.token.clone(),
+                    unexpected_token_label: None,
+                    sugg: ExpectedSemiSugg::ChangeToSemi(self.token.span),
+                });
+                self.bump();
+                return Ok(Recovered::Yes(guar));
+            } else if self.look_ahead(0, |t| {
+                t == &token::CloseDelim(Delimiter::Brace)
+                    || ((t.can_begin_expr() || t.can_begin_item())
+                        && t != &token::Semi
+                        && t != &token::Pound)
+                    // Avoid triggering with too many trailing `#` in raw string.
+                    || (sm.is_multiline(
+                        self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo()),
+                    ) && t == &token::Pound)
+            }) && !expected.contains(&TokenType::Token(token::Comma))
+            {
+                // Missing semicolon typo. This is triggered if the next token could either start a
+                // new statement or is a block close. For example:
+                //
+                //   let x = 32
+                //   let y = 42;
+                let span = self.prev_token.span.shrink_to_hi();
+                let guar = self.dcx().emit_err(ExpectedSemi {
+                    span,
+                    token: self.token.clone(),
+                    unexpected_token_label: Some(self.token.span),
+                    sugg: ExpectedSemiSugg::AddSemi(span),
+                });
+                return Ok(Recovered::Yes(guar));
+            }
+        }
+
+        if self.token.kind == TokenKind::EqEq
+            && self.prev_token.is_ident()
+            && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Eq)))
+        {
+            // Likely typo: `=` → `==` in let expr or enum item
+            return Err(self.dcx().create_err(UseEqInstead { span: self.token.span }));
+        }
+
+        if self.token.is_keyword(kw::Move) && self.prev_token.is_keyword(kw::Async) {
+            // The 2015 edition is in use because parsing of `async move` has failed.
+            let span = self.prev_token.span.to(self.token.span);
+            return Err(self.dcx().create_err(AsyncMoveBlockIn2015 { span }));
+        }
+
+        let expect = tokens_to_string(&expected);
+        let actual = super::token_descr(&self.token);
+        let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
+            let fmt = format!("expected one of {expect}, found {actual}");
+            let short_expect = if expected.len() > 6 {
+                format!("{} possible tokens", expected.len())
+            } else {
+                expect
+            };
+            (fmt, (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")))
+        } else if expected.is_empty() {
+            (
+                format!("unexpected token: {actual}"),
+                (self.prev_token.span, "unexpected token after this".to_string()),
+            )
+        } else {
+            (
+                format!("expected {expect}, found {actual}"),
+                (self.prev_token.span.shrink_to_hi(), format!("expected {expect}")),
+            )
+        };
+        self.last_unexpected_token_span = Some(self.token.span);
+        // FIXME: translation requires list formatting (for `expect`)
+        let mut err = self.dcx().struct_span_err(self.token.span, msg_exp);
+
+        // Look for usages of '=>' where '>=' was probably intended
+        if self.token == token::FatArrow
+            && expected
+                .iter()
+                .any(|tok| matches!(tok, TokenType::Operator | TokenType::Token(TokenKind::Le)))
+            && !expected.iter().any(|tok| {
+                matches!(
+                    tok,
+                    TokenType::Token(TokenKind::FatArrow) | TokenType::Token(TokenKind::Comma)
+                )
+            })
+        {
+            err.span_suggestion(
+                self.token.span,
+                "you might have meant to write a \"greater than or equal to\" comparison",
+                ">=",
+                Applicability::MaybeIncorrect,
+            );
+        }
+
+        if let TokenKind::Ident(symbol, _) = &self.prev_token.kind {
+            if ["def", "fun", "func", "function"].contains(&symbol.as_str()) {
+                err.span_suggestion_short(
+                    self.prev_token.span,
+                    format!("write `fn` instead of `{symbol}` to declare a function"),
+                    "fn",
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+
+        if let TokenKind::Ident(prev, _) = &self.prev_token.kind
+            && let TokenKind::Ident(cur, _) = &self.token.kind
+        {
+            let concat = Symbol::intern(&format!("{prev}{cur}"));
+            let ident = Ident::new(concat, DUMMY_SP);
+            if ident.is_used_keyword() || ident.is_reserved() || ident.is_raw_guess() {
+                let span = self.prev_token.span.to(self.token.span);
+                err.span_suggestion_verbose(
+                    span,
+                    format!("consider removing the space to spell keyword `{concat}`"),
+                    concat,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+
+        // Try to detect an intended c-string literal while using a pre-2021 edition. The heuristic
+        // here is to identify a cooked, uninterpolated `c` id immediately followed by a string, or
+        // a cooked, uninterpolated `cr` id immediately followed by a string or a `#`, in an edition
+        // where c-string literals are not allowed. There is the very slight possibility of a false
+        // positive for a `cr#` that wasn't intended to start a c-string literal, but identifying
+        // that in the parser requires unbounded lookahead, so we only add a hint to the existing
+        // error rather than replacing it entirely.
+        if ((self.prev_token.kind == TokenKind::Ident(sym::c, IdentIsRaw::No)
+            && matches!(&self.token.kind, TokenKind::Literal(token::Lit { kind: token::Str, .. })))
+            || (self.prev_token.kind == TokenKind::Ident(sym::cr, IdentIsRaw::No)
+                && matches!(
+                    &self.token.kind,
+                    TokenKind::Literal(token::Lit { kind: token::Str, .. }) | token::Pound
+                )))
+            && self.prev_token.span.hi() == self.token.span.lo()
+            && !self.token.span.at_least_rust_2021()
+        {
+            err.note("you may be trying to write a c-string literal");
+            err.note("c-string literals require Rust 2021 or later");
+            err.subdiagnostic(self.dcx(), HelpUseLatestEdition::new());
+        }
+
+        // `pub` may be used for an item or `pub(crate)`
+        if self.prev_token.is_ident_named(sym::public)
+            && (self.token.can_begin_item()
+                || self.token.kind == TokenKind::OpenDelim(Delimiter::Parenthesis))
+        {
+            err.span_suggestion_short(
+                self.prev_token.span,
+                "write `pub` instead of `public` to make the item public",
+                "pub",
+                Applicability::MachineApplicable,
+            );
+        }
+
+        if let token::DocComment(kind, style, _) = self.token.kind {
+            // We have something like `expr //!val` where the user likely meant `expr // !val`
+            let pos = self.token.span.lo() + BytePos(2);
+            let span = self.token.span.with_lo(pos).with_hi(pos);
+            err.span_suggestion_verbose(
+                span,
+                format!(
+                    "add a space before {} to write a regular comment",
+                    match (kind, style) {
+                        (token::CommentKind::Line, ast::AttrStyle::Inner) => "`!`",
+                        (token::CommentKind::Block, ast::AttrStyle::Inner) => "`!`",
+                        (token::CommentKind::Line, ast::AttrStyle::Outer) => "the last `/`",
+                        (token::CommentKind::Block, ast::AttrStyle::Outer) => "the last `*`",
+                    },
+                ),
+                " ".to_string(),
+                Applicability::MachineApplicable,
+            );
+        }
+
+        let sp = if self.token == token::Eof {
+            // This is EOF; don't want to point at the following char, but rather the last token.
+            self.prev_token.span
+        } else {
+            label_sp
+        };
+
+        if self.check_too_many_raw_str_terminators(&mut err) {
+            if expected.contains(&TokenType::Token(token::Semi)) && self.eat(&token::Semi) {
+                let guar = err.emit();
+                return Ok(Recovered::Yes(guar));
+            } else {
+                return Err(err);
+            }
+        }
+
+        if self.prev_token.span == DUMMY_SP {
+            // Account for macro context where the previous span might not be
+            // available to avoid incorrect output (#54841).
+            err.span_label(self.token.span, label_exp);
+        } else if !sm.is_multiline(self.token.span.shrink_to_hi().until(sp.shrink_to_lo())) {
+            // When the spans are in the same line, it means that the only content between
+            // them is whitespace, point at the found token in that case:
+            //
+            // X |     () => { syntax error };
+            //   |                    ^^^^^ expected one of 8 possible tokens here
+            //
+            // instead of having:
+            //
+            // X |     () => { syntax error };
+            //   |                   -^^^^^ unexpected token
+            //   |                   |
+            //   |                   expected one of 8 possible tokens here
+            err.span_label(self.token.span, label_exp);
+        } else {
+            err.span_label(sp, label_exp);
+            err.span_label(self.token.span, "unexpected token");
+        }
+        Err(err)
+    }
+
+    /// The user has written `#[attr] expr` which is unsupported. (#106020)
+    pub(super) fn attr_on_non_tail_expr(&self, expr: &Expr) -> ErrorGuaranteed {
+        // Missing semicolon typo error.
+        let span = self.prev_token.span.shrink_to_hi();
+        let mut err = self.dcx().create_err(ExpectedSemi {
+            span,
+            token: self.token.clone(),
+            unexpected_token_label: Some(self.token.span),
+            sugg: ExpectedSemiSugg::AddSemi(span),
+        });
+        let attr_span = match &expr.attrs[..] {
+            [] => unreachable!(),
+            [only] => only.span,
+            [first, rest @ ..] => {
+                for attr in rest {
+                    err.span_label(attr.span, "");
+                }
+                first.span
+            }
+        };
+        err.span_label(
+            attr_span,
+            format!(
+                "only `;` terminated statements or tail expressions are allowed after {}",
+                if expr.attrs.len() == 1 { "this attribute" } else { "these attributes" },
+            ),
+        );
+        if self.token == token::Pound
+            && self.look_ahead(1, |t| t.kind == token::OpenDelim(Delimiter::Bracket))
+        {
+            // We have
+            // #[attr]
+            // expr
+            // #[not_attr]
+            // other_expr
+            err.span_label(span, "expected `;` here");
+            err.multipart_suggestion(
+                "alternatively, consider surrounding the expression with a block",
+                vec![
+                    (expr.span.shrink_to_lo(), "{ ".to_string()),
+                    (expr.span.shrink_to_hi(), " }".to_string()),
+                ],
+                Applicability::MachineApplicable,
+            );
+
+            // Special handling for `#[cfg(...)]` chains
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            if let [attr] = &expr.attrs[..]
+                && let ast::AttrKind::Normal(attr_kind) = &attr.kind
+                && let [segment] = &attr_kind.item.path.segments[..]
+                && segment.ident.name == sym::cfg
+                && let Some(args_span) = attr_kind.item.args.span()
+                && let next_attr = match snapshot.parse_attribute(InnerAttrPolicy::Forbidden(None))
+                {
+                    Ok(next_attr) => next_attr,
+                    Err(inner_err) => {
+                        inner_err.cancel();
+                        return err.emit();
+                    }
+                }
+                && let ast::AttrKind::Normal(next_attr_kind) = next_attr.kind
+                && let Some(next_attr_args_span) = next_attr_kind.item.args.span()
+                && let [next_segment] = &next_attr_kind.item.path.segments[..]
+                && segment.ident.name == sym::cfg
+            {
+                let next_expr = match snapshot.parse_expr() {
+                    Ok(next_expr) => next_expr,
+                    Err(inner_err) => {
+                        inner_err.cancel();
+                        return err.emit();
+                    }
+                };
+                // We have for sure
+                // #[cfg(..)]
+                // expr
+                // #[cfg(..)]
+                // other_expr
+                // So we suggest using `if cfg!(..) { expr } else if cfg!(..) { other_expr }`.
+                let margin = self.psess.source_map().span_to_margin(next_expr.span).unwrap_or(0);
+                let sugg = vec![
+                    (attr.span.with_hi(segment.span().hi()), "if cfg!".to_string()),
+                    (args_span.shrink_to_hi().with_hi(attr.span.hi()), " {".to_string()),
+                    (expr.span.shrink_to_lo(), "    ".to_string()),
+                    (
+                        next_attr.span.with_hi(next_segment.span().hi()),
+                        "} else if cfg!".to_string(),
+                    ),
+                    (
+                        next_attr_args_span.shrink_to_hi().with_hi(next_attr.span.hi()),
+                        " {".to_string(),
+                    ),
+                    (next_expr.span.shrink_to_lo(), "    ".to_string()),
+                    (next_expr.span.shrink_to_hi(), format!("\n{}}}", " ".repeat(margin))),
+                ];
+                err.multipart_suggestion(
+                    "it seems like you are trying to provide different expressions depending on \
+                     `cfg`, consider using `if cfg!(..)`",
+                    sugg,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        err.emit()
+    }
+
+    fn check_too_many_raw_str_terminators(&mut self, err: &mut Diag<'_>) -> bool {
+        let sm = self.psess.source_map();
+        match (&self.prev_token.kind, &self.token.kind) {
+            (
+                TokenKind::Literal(Lit {
+                    kind: LitKind::StrRaw(n_hashes) | LitKind::ByteStrRaw(n_hashes),
+                    ..
+                }),
+                TokenKind::Pound,
+            ) if !sm.is_multiline(
+                self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo()),
+            ) =>
+            {
+                let n_hashes: u8 = *n_hashes;
+                err.primary_message("too many `#` when terminating raw string");
+                let str_span = self.prev_token.span;
+                let mut span = self.token.span;
+                let mut count = 0;
+                while self.token.kind == TokenKind::Pound
+                    && !sm.is_multiline(span.shrink_to_hi().until(self.token.span.shrink_to_lo()))
+                {
+                    span = span.with_hi(self.token.span.hi());
+                    self.bump();
+                    count += 1;
+                }
+                err.span(span);
+                err.span_suggestion(
+                    span,
+                    format!("remove the extra `#`{}", pluralize!(count)),
+                    "",
+                    Applicability::MachineApplicable,
+                );
+                err.span_label(
+                    str_span,
+                    format!("this raw string started with {n_hashes} `#`{}", pluralize!(n_hashes)),
+                );
+                true
+            }
+            _ => false,
+        }
+    }
+
+    pub fn maybe_suggest_struct_literal(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode,
+        maybe_struct_name: token::Token,
+        can_be_struct_literal: bool,
+    ) -> Option<PResult<'a, P<Block>>> {
+        if self.token.is_ident() && self.look_ahead(1, |t| t == &token::Colon) {
+            // We might be having a struct literal where people forgot to include the path:
+            // fn foo() -> Foo {
+            //     field: value,
+            // }
+            debug!(?maybe_struct_name, ?self.token);
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            let path = Path {
+                segments: ThinVec::new(),
+                span: self.prev_token.span.shrink_to_lo(),
+                tokens: None,
+            };
+            let struct_expr = snapshot.parse_expr_struct(None, path, false);
+            let block_tail = self.parse_block_tail(lo, s, AttemptLocalParseRecovery::No);
+            return Some(match (struct_expr, block_tail) {
+                (Ok(expr), Err(err)) => {
+                    // We have encountered the following:
+                    // fn foo() -> Foo {
+                    //     field: value,
+                    // }
+                    // Suggest:
+                    // fn foo() -> Foo { Path {
+                    //     field: value,
+                    // } }
+                    let guar = err.delay_as_bug();
+                    self.restore_snapshot(snapshot);
+                    let mut tail = self.mk_block(
+                        thin_vec![self.mk_stmt_err(expr.span, guar)],
+                        s,
+                        lo.to(self.prev_token.span),
+                    );
+                    tail.could_be_bare_literal = true;
+                    if maybe_struct_name.is_ident() && can_be_struct_literal {
+                        // Account for `if Example { a: one(), }.is_pos() {}`.
+                        // expand `before` so that we take care of module path such as:
+                        // `foo::Bar { ... } `
+                        // we expect to suggest `(foo::Bar { ... })` instead of `foo::(Bar { ... })`
+                        let sm = self.psess.source_map();
+                        let before = maybe_struct_name.span.shrink_to_lo();
+                        if let Ok(extend_before) = sm.span_extend_prev_while(before, |t| {
+                            t.is_alphanumeric() || t == ':' || t == '_'
+                        }) {
+                            Err(self.dcx().create_err(StructLiteralNeedingParens {
+                                span: maybe_struct_name.span.to(expr.span),
+                                sugg: StructLiteralNeedingParensSugg {
+                                    before: extend_before.shrink_to_lo(),
+                                    after: expr.span.shrink_to_hi(),
+                                },
+                            }))
+                        } else {
+                            return None;
+                        }
+                    } else {
+                        self.dcx().emit_err(StructLiteralBodyWithoutPath {
+                            span: expr.span,
+                            sugg: StructLiteralBodyWithoutPathSugg {
+                                before: expr.span.shrink_to_lo(),
+                                after: expr.span.shrink_to_hi(),
+                            },
+                        });
+                        Ok(tail)
+                    }
+                }
+                (Err(err), Ok(tail)) => {
+                    // We have a block tail that contains a somehow valid type ascription expr.
+                    err.cancel();
+                    Ok(tail)
+                }
+                (Err(snapshot_err), Err(err)) => {
+                    // We don't know what went wrong, emit the normal error.
+                    snapshot_err.cancel();
+                    self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
+                    Err(err)
+                }
+                (Ok(_), Ok(mut tail)) => {
+                    tail.could_be_bare_literal = true;
+                    Ok(tail)
+                }
+            });
+        }
+        None
+    }
+
+    pub(super) fn recover_closure_body(
+        &mut self,
+        mut err: Diag<'a>,
+        before: token::Token,
+        prev: token::Token,
+        token: token::Token,
+        lo: Span,
+        decl_hi: Span,
+    ) -> PResult<'a, P<Expr>> {
+        err.span_label(lo.to(decl_hi), "while parsing the body of this closure");
+        let guar = match before.kind {
+            token::OpenDelim(Delimiter::Brace)
+                if !matches!(token.kind, token::OpenDelim(Delimiter::Brace)) =>
+            {
+                // `{ || () }` should have been `|| { () }`
+                err.multipart_suggestion(
+                    "you might have meant to open the body of the closure, instead of enclosing \
+                     the closure in a block",
+                    vec![
+                        (before.span, String::new()),
+                        (prev.span.shrink_to_hi(), " {".to_string()),
+                    ],
+                    Applicability::MaybeIncorrect,
+                );
+                let guar = err.emit();
+                self.eat_to_tokens(&[&token::CloseDelim(Delimiter::Brace)]);
+                guar
+            }
+            token::OpenDelim(Delimiter::Parenthesis)
+                if !matches!(token.kind, token::OpenDelim(Delimiter::Brace)) =>
+            {
+                // We are within a function call or tuple, we can emit the error
+                // and recover.
+                self.eat_to_tokens(&[&token::CloseDelim(Delimiter::Parenthesis), &token::Comma]);
+
+                err.multipart_suggestion_verbose(
+                    "you might have meant to open the body of the closure",
+                    vec![
+                        (prev.span.shrink_to_hi(), " {".to_string()),
+                        (self.token.span.shrink_to_lo(), "}".to_string()),
+                    ],
+                    Applicability::MaybeIncorrect,
+                );
+                err.emit()
+            }
+            _ if !matches!(token.kind, token::OpenDelim(Delimiter::Brace)) => {
+                // We don't have a heuristic to correctly identify where the block
+                // should be closed.
+                err.multipart_suggestion_verbose(
+                    "you might have meant to open the body of the closure",
+                    vec![(prev.span.shrink_to_hi(), " {".to_string())],
+                    Applicability::HasPlaceholders,
+                );
+                return Err(err);
+            }
+            _ => return Err(err),
+        };
+        Ok(self.mk_expr_err(lo.to(self.token.span), guar))
+    }
+
+    /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
+    /// passes through any errors encountered. Used for error recovery.
+    pub(super) fn eat_to_tokens(&mut self, kets: &[&TokenKind]) {
+        if let Err(err) =
+            self.parse_seq_to_before_tokens(kets, SeqSep::none(), TokenExpectType::Expect, |p| {
+                Ok(p.parse_token_tree())
+            })
+        {
+            err.cancel();
+        }
+    }
+
+    /// This function checks if there are trailing angle brackets and produces
+    /// a diagnostic to suggest removing them.
+    ///
+    /// ```ignore (diagnostic)
+    /// let _ = [1, 2, 3].into_iter().collect::<Vec<usize>>>>();
+    ///                                                    ^^ help: remove extra angle brackets
+    /// ```
+    ///
+    /// If `true` is returned, then trailing brackets were recovered, tokens were consumed
+    /// up until one of the tokens in 'end' was encountered, and an error was emitted.
+    pub(super) fn check_trailing_angle_brackets(
+        &mut self,
+        segment: &PathSegment,
+        end: &[&TokenKind],
+    ) -> Option<ErrorGuaranteed> {
+        if !self.may_recover() {
+            return None;
+        }
+
+        // This function is intended to be invoked after parsing a path segment where there are two
+        // cases:
+        //
+        // 1. A specific token is expected after the path segment.
+        //    eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
+        //        `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
+        // 2. No specific token is expected after the path segment.
+        //    eg. `x.foo` (field access)
+        //
+        // This function is called after parsing `.foo` and before parsing the token `end` (if
+        // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
+        // `Foo::<Bar>`.
+
+        // We only care about trailing angle brackets if we previously parsed angle bracket
+        // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
+        // removed in this case:
+        //
+        // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
+        //
+        // This case is particularly tricky as we won't notice it just looking at the tokens -
+        // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
+        // have already been parsed):
+        //
+        // `x.foo::<u32>>>(3)`
+        let parsed_angle_bracket_args =
+            segment.args.as_ref().is_some_and(|args| args.is_angle_bracketed());
+
+        debug!(
+            "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
+            parsed_angle_bracket_args,
+        );
+        if !parsed_angle_bracket_args {
+            return None;
+        }
+
+        // Keep the span at the start so we can highlight the sequence of `>` characters to be
+        // removed.
+        let lo = self.token.span;
+
+        // We need to look-ahead to see if we have `>` characters without moving the cursor forward
+        // (since we might have the field access case and the characters we're eating are
+        // actual operators and not trailing characters - ie `x.foo >> 3`).
+        let mut position = 0;
+
+        // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
+        // many of each (so we can correctly pluralize our error messages) and continue to
+        // advance.
+        let mut number_of_shr = 0;
+        let mut number_of_gt = 0;
+        while self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            if *t == token::BinOp(token::BinOpToken::Shr) {
+                number_of_shr += 1;
+                true
+            } else if *t == token::Gt {
+                number_of_gt += 1;
+                true
+            } else {
+                false
+            }
+        }) {
+            position += 1;
+        }
+
+        // If we didn't find any trailing `>` characters, then we have nothing to error about.
+        debug!(
+            "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
+            number_of_gt, number_of_shr,
+        );
+        if number_of_gt < 1 && number_of_shr < 1 {
+            return None;
+        }
+
+        // Finally, double check that we have our end token as otherwise this is the
+        // second case.
+        if self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            end.contains(&&t.kind)
+        }) {
+            // Eat from where we started until the end token so that parsing can continue
+            // as if we didn't have those extra angle brackets.
+            self.eat_to_tokens(end);
+            let span = lo.until(self.token.span);
+
+            let num_extra_brackets = number_of_gt + number_of_shr * 2;
+            return Some(self.dcx().emit_err(UnmatchedAngleBrackets { span, num_extra_brackets }));
+        }
+        None
+    }
+
+    /// Check if a method call with an intended turbofish has been written without surrounding
+    /// angle brackets.
+    pub(super) fn check_turbofish_missing_angle_brackets(&mut self, segment: &mut PathSegment) {
+        if !self.may_recover() {
+            return;
+        }
+
+        if token::PathSep == self.token.kind && segment.args.is_none() {
+            let snapshot = self.create_snapshot_for_diagnostic();
+            self.bump();
+            let lo = self.token.span;
+            match self.parse_angle_args(None) {
+                Ok(args) => {
+                    let span = lo.to(self.prev_token.span);
+                    // Detect trailing `>` like in `x.collect::Vec<_>>()`.
+                    let mut trailing_span = self.prev_token.span.shrink_to_hi();
+                    while self.token.kind == token::BinOp(token::Shr)
+                        || self.token.kind == token::Gt
+                    {
+                        trailing_span = trailing_span.to(self.token.span);
+                        self.bump();
+                    }
+                    if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
+                        // Recover from bad turbofish: `foo.collect::Vec<_>()`.
+                        segment.args = Some(AngleBracketedArgs { args, span }.into());
+
+                        self.dcx().emit_err(GenericParamsWithoutAngleBrackets {
+                            span,
+                            sugg: GenericParamsWithoutAngleBracketsSugg {
+                                left: span.shrink_to_lo(),
+                                right: trailing_span,
+                            },
+                        });
+                    } else {
+                        // This doesn't look like an invalid turbofish, can't recover parse state.
+                        self.restore_snapshot(snapshot);
+                    }
+                }
+                Err(err) => {
+                    // We couldn't parse generic parameters, unlikely to be a turbofish. Rely on
+                    // generic parse error instead.
+                    err.cancel();
+                    self.restore_snapshot(snapshot);
+                }
+            }
+        }
+    }
+
+    /// When writing a turbofish with multiple type parameters missing the leading `::`, we will
+    /// encounter a parse error when encountering the first `,`.
+    pub(super) fn check_mistyped_turbofish_with_multiple_type_params(
+        &mut self,
+        mut e: Diag<'a>,
+        expr: &mut P<Expr>,
+    ) -> PResult<'a, ErrorGuaranteed> {
+        if let ExprKind::Binary(binop, _, _) = &expr.kind
+            && let ast::BinOpKind::Lt = binop.node
+            && self.eat(&token::Comma)
+        {
+            let x = self.parse_seq_to_before_end(
+                &token::Gt,
+                SeqSep::trailing_allowed(token::Comma),
+                |p| match p.parse_generic_arg(None)? {
+                    Some(arg) => Ok(arg),
+                    // If we didn't eat a generic arg, then we should error.
+                    None => p.unexpected_any(),
+                },
+            );
+            match x {
+                Ok((_, _, Recovered::No)) => {
+                    if self.eat(&token::Gt) {
+                        // We made sense of it. Improve the error message.
+                        e.span_suggestion_verbose(
+                            binop.span.shrink_to_lo(),
+                            fluent::parse_sugg_turbofish_syntax,
+                            "::",
+                            Applicability::MaybeIncorrect,
+                        );
+                        match self.parse_expr() {
+                            Ok(_) => {
+                                // The subsequent expression is valid. Mark
+                                // `expr` as erroneous and emit `e` now, but
+                                // return `Ok` so parsing can continue.
+                                let guar = e.emit();
+                                *expr = self.mk_expr_err(expr.span.to(self.prev_token.span), guar);
+                                return Ok(guar);
+                            }
+                            Err(err) => {
+                                err.cancel();
+                            }
+                        }
+                    }
+                }
+                Ok((_, _, Recovered::Yes(_))) => {}
+                Err(err) => {
+                    err.cancel();
+                }
+            }
+        }
+        Err(e)
+    }
+
+    /// Suggest add the missing `let` before the identifier in stmt
+    /// `a: Ty = 1` -> `let a: Ty = 1`
+    pub(super) fn suggest_add_missing_let_for_stmt(&mut self, err: &mut Diag<'a>) {
+        if self.token == token::Colon {
+            let prev_span = self.prev_token.span.shrink_to_lo();
+            let snapshot = self.create_snapshot_for_diagnostic();
+            self.bump();
+            match self.parse_ty() {
+                Ok(_) => {
+                    if self.token == token::Eq {
+                        let sugg = SuggAddMissingLetStmt { span: prev_span };
+                        sugg.add_to_diag(err);
+                    }
+                }
+                Err(e) => {
+                    e.cancel();
+                }
+            }
+            self.restore_snapshot(snapshot);
+        }
+    }
+
+    /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
+    /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
+    /// parenthesising the leftmost comparison. The return value indicates if recovery happened.
+    fn attempt_chained_comparison_suggestion(
+        &mut self,
+        err: &mut ComparisonOperatorsCannotBeChained,
+        inner_op: &Expr,
+        outer_op: &Spanned<AssocOp>,
+    ) -> bool {
+        if let ExprKind::Binary(op, l1, r1) = &inner_op.kind {
+            if let ExprKind::Field(_, ident) = l1.kind
+                && ident.as_str().parse::<i32>().is_err()
+                && !matches!(r1.kind, ExprKind::Lit(_))
+            {
+                // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
+                // suggestion being the only one to apply is high.
+                return false;
+            }
+            return match (op.node, &outer_op.node) {
+                // `x == y == z`
+                (BinOpKind::Eq, AssocOp::Equal) |
+                // `x < y < z` and friends.
+                (BinOpKind::Lt, AssocOp::Less | AssocOp::LessEqual) |
+                (BinOpKind::Le, AssocOp::LessEqual | AssocOp::Less) |
+                // `x > y > z` and friends.
+                (BinOpKind::Gt, AssocOp::Greater | AssocOp::GreaterEqual) |
+                (BinOpKind::Ge, AssocOp::GreaterEqual | AssocOp::Greater) => {
+                    let expr_to_str = |e: &Expr| {
+                        self.span_to_snippet(e.span)
+                            .unwrap_or_else(|_| pprust::expr_to_string(e))
+                    };
+                    err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::SplitComparison {
+                        span: inner_op.span.shrink_to_hi(),
+                        middle_term: expr_to_str(r1),
+                    });
+                    false // Keep the current parse behavior, where the AST is `(x < y) < z`.
+                }
+                // `x == y < z`
+                (BinOpKind::Eq, AssocOp::Less | AssocOp::LessEqual | AssocOp::Greater | AssocOp::GreaterEqual) => {
+                    // Consume `z`/outer-op-rhs.
+                    let snapshot = self.create_snapshot_for_diagnostic();
+                    match self.parse_expr() {
+                        Ok(r2) => {
+                            // We are sure that outer-op-rhs could be consumed, the suggestion is
+                            // likely correct.
+                            err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::Parenthesize {
+                                left: r1.span.shrink_to_lo(),
+                                right: r2.span.shrink_to_hi(),
+                            });
+                            true
+                        }
+                        Err(expr_err) => {
+                            expr_err.cancel();
+                            self.restore_snapshot(snapshot);
+                            true
+                        }
+                    }
+                }
+                // `x > y == z`
+                (BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge, AssocOp::Equal) => {
+                    let snapshot = self.create_snapshot_for_diagnostic();
+                    // At this point it is always valid to enclose the lhs in parentheses, no
+                    // further checks are necessary.
+                    match self.parse_expr() {
+                        Ok(_) => {
+                            err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::Parenthesize {
+                                left: l1.span.shrink_to_lo(),
+                                right: r1.span.shrink_to_hi(),
+                            });
+                            true
+                        }
+                        Err(expr_err) => {
+                            expr_err.cancel();
+                            self.restore_snapshot(snapshot);
+                            false
+                        }
+                    }
+                }
+                _ => false
+            };
+        }
+        false
+    }
+
+    /// Produces an error if comparison operators are chained (RFC #558).
+    /// We only need to check the LHS, not the RHS, because all comparison ops have same
+    /// precedence (see `fn precedence`) and are left-associative (see `fn fixity`).
+    ///
+    /// This can also be hit if someone incorrectly writes `foo<bar>()` when they should have used
+    /// the turbofish (`foo::<bar>()`) syntax. We attempt some heuristic recovery if that is the
+    /// case.
+    ///
+    /// Keep in mind that given that `outer_op.is_comparison()` holds and comparison ops are left
+    /// associative we can infer that we have:
+    ///
+    /// ```text
+    ///           outer_op
+    ///           /   \
+    ///     inner_op   r2
+    ///        /  \
+    ///      l1    r1
+    /// ```
+    pub(super) fn check_no_chained_comparison(
+        &mut self,
+        inner_op: &Expr,
+        outer_op: &Spanned<AssocOp>,
+    ) -> PResult<'a, Option<P<Expr>>> {
+        debug_assert!(
+            outer_op.node.is_comparison(),
+            "check_no_chained_comparison: {:?} is not comparison",
+            outer_op.node,
+        );
+
+        let mk_err_expr =
+            |this: &Self, span, guar| Ok(Some(this.mk_expr(span, ExprKind::Err(guar))));
+
+        match &inner_op.kind {
+            ExprKind::Binary(op, l1, r1) if op.node.is_comparison() => {
+                let mut err = ComparisonOperatorsCannotBeChained {
+                    span: vec![op.span, self.prev_token.span],
+                    suggest_turbofish: None,
+                    help_turbofish: None,
+                    chaining_sugg: None,
+                };
+
+                // Include `<` to provide this recommendation even in a case like
+                // `Foo<Bar<Baz<Qux, ()>>>`
+                if op.node == BinOpKind::Lt && outer_op.node == AssocOp::Less
+                    || outer_op.node == AssocOp::Greater
+                {
+                    if outer_op.node == AssocOp::Less {
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump();
+                        // So far we have parsed `foo<bar<`, consume the rest of the type args.
+                        let modifiers =
+                            [(token::Lt, 1), (token::Gt, -1), (token::BinOp(token::Shr), -2)];
+                        self.consume_tts(1, &modifiers);
+
+                        if !&[token::OpenDelim(Delimiter::Parenthesis), token::PathSep]
+                            .contains(&self.token.kind)
+                        {
+                            // We don't have `foo< bar >(` or `foo< bar >::`, so we rewind the
+                            // parser and bail out.
+                            self.restore_snapshot(snapshot);
+                        }
+                    }
+                    return if token::PathSep == self.token.kind {
+                        // We have some certainty that this was a bad turbofish at this point.
+                        // `foo< bar >::`
+                        if let ExprKind::Binary(o, ..) = inner_op.kind
+                            && o.node == BinOpKind::Lt
+                        {
+                            err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        } else {
+                            err.help_turbofish = Some(());
+                        }
+
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump(); // `::`
+
+                        // Consume the rest of the likely `foo<bar>::new()` or return at `foo<bar>`.
+                        match self.parse_expr() {
+                            Ok(_) => {
+                                // 99% certain that the suggestion is correct, continue parsing.
+                                let guar = self.dcx().emit_err(err);
+                                // FIXME: actually check that the two expressions in the binop are
+                                // paths and resynthesize new fn call expression instead of using
+                                // `ExprKind::Err` placeholder.
+                                mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar)
+                            }
+                            Err(expr_err) => {
+                                expr_err.cancel();
+                                // Not entirely sure now, but we bubble the error up with the
+                                // suggestion.
+                                self.restore_snapshot(snapshot);
+                                Err(self.dcx().create_err(err))
+                            }
+                        }
+                    } else if token::OpenDelim(Delimiter::Parenthesis) == self.token.kind {
+                        // We have high certainty that this was a bad turbofish at this point.
+                        // `foo< bar >(`
+                        if let ExprKind::Binary(o, ..) = inner_op.kind
+                            && o.node == BinOpKind::Lt
+                        {
+                            err.suggest_turbofish = Some(op.span.shrink_to_lo());
+                        } else {
+                            err.help_turbofish = Some(());
+                        }
+                        // Consume the fn call arguments.
+                        match self.consume_fn_args() {
+                            Err(()) => Err(self.dcx().create_err(err)),
+                            Ok(()) => {
+                                let guar = self.dcx().emit_err(err);
+                                // FIXME: actually check that the two expressions in the binop are
+                                // paths and resynthesize new fn call expression instead of using
+                                // `ExprKind::Err` placeholder.
+                                mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar)
+                            }
+                        }
+                    } else {
+                        if !matches!(l1.kind, ExprKind::Lit(_))
+                            && !matches!(r1.kind, ExprKind::Lit(_))
+                        {
+                            // All we know is that this is `foo < bar >` and *nothing* else. Try to
+                            // be helpful, but don't attempt to recover.
+                            err.help_turbofish = Some(());
+                        }
+
+                        // If it looks like a genuine attempt to chain operators (as opposed to a
+                        // misformatted turbofish, for instance), suggest a correct form.
+                        let recovered = self
+                            .attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
+                        if recovered {
+                            let guar = self.dcx().emit_err(err);
+                            mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar)
+                        } else {
+                            // These cases cause too many knock-down errors, bail out (#61329).
+                            Err(self.dcx().create_err(err))
+                        }
+                    };
+                }
+                let recovered =
+                    self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
+                let guar = self.dcx().emit_err(err);
+                if recovered {
+                    return mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar);
+                }
+            }
+            _ => {}
+        }
+        Ok(None)
+    }
+
+    fn consume_fn_args(&mut self) -> Result<(), ()> {
+        let snapshot = self.create_snapshot_for_diagnostic();
+        self.bump(); // `(`
+
+        // Consume the fn call arguments.
+        let modifiers = [
+            (token::OpenDelim(Delimiter::Parenthesis), 1),
+            (token::CloseDelim(Delimiter::Parenthesis), -1),
+        ];
+        self.consume_tts(1, &modifiers);
+
+        if self.token.kind == token::Eof {
+            // Not entirely sure that what we consumed were fn arguments, rollback.
+            self.restore_snapshot(snapshot);
+            Err(())
+        } else {
+            // 99% certain that the suggestion is correct, continue parsing.
+            Ok(())
+        }
+    }
+
+    pub(super) fn maybe_report_ambiguous_plus(&mut self, impl_dyn_multi: bool, ty: &Ty) {
+        if impl_dyn_multi {
+            self.dcx().emit_err(AmbiguousPlus { sum_ty: pprust::ty_to_string(ty), span: ty.span });
+        }
+    }
+
+    /// Swift lets users write `Ty?` to mean `Option<Ty>`. Parse the construct and recover from it.
+    pub(super) fn maybe_recover_from_question_mark(&mut self, ty: P<Ty>) -> P<Ty> {
+        if self.token == token::Question {
+            self.bump();
+            let guar = self.dcx().emit_err(QuestionMarkInType {
+                span: self.prev_token.span,
+                sugg: QuestionMarkInTypeSugg {
+                    left: ty.span.shrink_to_lo(),
+                    right: self.prev_token.span,
+                },
+            });
+            self.mk_ty(ty.span.to(self.prev_token.span), TyKind::Err(guar))
+        } else {
+            ty
+        }
+    }
+
+    /// Rust has no ternary operator (`cond ? then : else`). Parse it and try
+    /// to recover from it if `then` and `else` are valid expressions. Returns
+    /// an err if this appears to be a ternary expression.
+    pub(super) fn maybe_recover_from_ternary_operator(&mut self) -> PResult<'a, ()> {
+        if self.prev_token != token::Question {
+            return PResult::Ok(());
+        }
+
+        let lo = self.prev_token.span.lo();
+        let snapshot = self.create_snapshot_for_diagnostic();
+
+        if match self.parse_expr() {
+            Ok(_) => true,
+            Err(err) => {
+                err.cancel();
+                // The colon can sometimes be mistaken for type
+                // ascription. Catch when this happens and continue.
+                self.token == token::Colon
+            }
+        } {
+            if self.eat_noexpect(&token::Colon) {
+                match self.parse_expr() {
+                    Ok(_) => {
+                        return Err(self
+                            .dcx()
+                            .create_err(TernaryOperator { span: self.token.span.with_lo(lo) }));
+                    }
+                    Err(err) => {
+                        err.cancel();
+                    }
+                };
+            }
+        }
+        self.restore_snapshot(snapshot);
+        Ok(())
+    }
+
+    pub(super) fn maybe_recover_from_bad_type_plus(&mut self, ty: &Ty) -> PResult<'a, ()> {
+        // Do not add `+` to expected tokens.
+        if !self.token.is_like_plus() {
+            return Ok(());
+        }
+
+        self.bump(); // `+`
+        let bounds = self.parse_generic_bounds()?;
+        let sum_span = ty.span.to(self.prev_token.span);
+
+        let sub = match &ty.kind {
+            TyKind::Ref(lifetime, mut_ty) => {
+                let sum_with_parens = pprust::to_string(|s| {
+                    s.s.word("&");
+                    s.print_opt_lifetime(lifetime);
+                    s.print_mutability(mut_ty.mutbl, false);
+                    s.popen();
+                    s.print_type(&mut_ty.ty);
+                    if !bounds.is_empty() {
+                        s.word(" + ");
+                        s.print_type_bounds(&bounds);
+                    }
+                    s.pclose()
+                });
+
+                BadTypePlusSub::AddParen { sum_with_parens, span: sum_span }
+            }
+            TyKind::Ptr(..) | TyKind::BareFn(..) => BadTypePlusSub::ForgotParen { span: sum_span },
+            _ => BadTypePlusSub::ExpectPath { span: sum_span },
+        };
+
+        self.dcx().emit_err(BadTypePlus { ty: pprust::ty_to_string(ty), span: sum_span, sub });
+
+        Ok(())
+    }
+
+    pub(super) fn recover_from_prefix_increment(
+        &mut self,
+        operand_expr: P<Expr>,
+        op_span: Span,
+        start_stmt: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let standalone = if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr };
+        let kind = IncDecRecovery { standalone, op: IncOrDec::Inc, fixity: UnaryFixity::Pre };
+        self.recover_from_inc_dec(operand_expr, kind, op_span)
+    }
+
+    pub(super) fn recover_from_postfix_increment(
+        &mut self,
+        operand_expr: P<Expr>,
+        op_span: Span,
+        start_stmt: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let kind = IncDecRecovery {
+            standalone: if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr },
+            op: IncOrDec::Inc,
+            fixity: UnaryFixity::Post,
+        };
+        self.recover_from_inc_dec(operand_expr, kind, op_span)
+    }
+
+    pub(super) fn recover_from_postfix_decrement(
+        &mut self,
+        operand_expr: P<Expr>,
+        op_span: Span,
+        start_stmt: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let kind = IncDecRecovery {
+            standalone: if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr },
+            op: IncOrDec::Dec,
+            fixity: UnaryFixity::Post,
+        };
+        self.recover_from_inc_dec(operand_expr, kind, op_span)
+    }
+
+    fn recover_from_inc_dec(
+        &mut self,
+        base: P<Expr>,
+        kind: IncDecRecovery,
+        op_span: Span,
+    ) -> PResult<'a, P<Expr>> {
+        let mut err = self.dcx().struct_span_err(
+            op_span,
+            format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
+        );
+        err.span_label(op_span, format!("not a valid {} operator", kind.fixity));
+
+        let help_base_case = |mut err: Diag<'_, _>, base| {
+            err.help(format!("use `{}= 1` instead", kind.op.chr()));
+            err.emit();
+            Ok(base)
+        };
+
+        // (pre, post)
+        let spans = match kind.fixity {
+            UnaryFixity::Pre => (op_span, base.span.shrink_to_hi()),
+            UnaryFixity::Post => (base.span.shrink_to_lo(), op_span),
+        };
+
+        match kind.standalone {
+            IsStandalone::Standalone => {
+                self.inc_dec_standalone_suggest(kind, spans).emit_verbose(&mut err)
+            }
+            IsStandalone::Subexpr => {
+                let Ok(base_src) = self.span_to_snippet(base.span) else {
+                    return help_base_case(err, base);
+                };
+                match kind.fixity {
+                    UnaryFixity::Pre => {
+                        self.prefix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
+                    }
+                    UnaryFixity::Post => {
+                        // won't suggest since we can not handle the precedences
+                        // for example: `a + b++` has been parsed (a + b)++ and we can not suggest here
+                        if !matches!(base.kind, ExprKind::Binary(_, _, _)) {
+                            self.postfix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
+                        }
+                    }
+                }
+            }
+        }
+        Err(err)
+    }
+
+    fn prefix_inc_dec_suggest(
+        &mut self,
+        base_src: String,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches: vec![
+                (pre_span, "{ ".to_string()),
+                (post_span, format!(" {}= 1; {} }}", kind.op.chr(), base_src)),
+            ],
+            applicability: Applicability::MachineApplicable,
+        }
+    }
+
+    fn postfix_inc_dec_suggest(
+        &mut self,
+        base_src: String,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        let tmp_var = if base_src.trim() == "tmp" { "tmp_" } else { "tmp" };
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches: vec![
+                (pre_span, format!("{{ let {tmp_var} = ")),
+                (post_span, format!("; {} {}= 1; {} }}", base_src, kind.op.chr(), tmp_var)),
+            ],
+            applicability: Applicability::HasPlaceholders,
+        }
+    }
+
+    fn inc_dec_standalone_suggest(
+        &mut self,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        let mut patches = Vec::new();
+
+        if !pre_span.is_empty() {
+            patches.push((pre_span, String::new()));
+        }
+
+        patches.push((post_span, format!(" {}= 1", kind.op.chr())));
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches,
+            applicability: Applicability::MachineApplicable,
+        }
+    }
+
+    /// Tries to recover from associated item paths like `[T]::AssocItem` / `(T, U)::AssocItem`.
+    /// Attempts to convert the base expression/pattern/type into a type, parses the `::AssocItem`
+    /// tail, and combines them into a `<Ty>::AssocItem` expression/pattern/type.
+    pub(super) fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
+        &mut self,
+        base: P<T>,
+    ) -> PResult<'a, P<T>> {
+        if !self.may_recover() {
+            return Ok(base);
+        }
+
+        // Do not add `::` to expected tokens.
+        if self.token == token::PathSep {
+            if let Some(ty) = base.to_ty() {
+                return self.maybe_recover_from_bad_qpath_stage_2(ty.span, ty);
+            }
+        }
+        Ok(base)
+    }
+
+    /// Given an already parsed `Ty`, parses the `::AssocItem` tail and
+    /// combines them into a `<Ty>::AssocItem` expression/pattern/type.
+    pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
+        &mut self,
+        ty_span: Span,
+        ty: P<Ty>,
+    ) -> PResult<'a, P<T>> {
+        self.expect(&token::PathSep)?;
+
+        let mut path = ast::Path { segments: ThinVec::new(), span: DUMMY_SP, tokens: None };
+        self.parse_path_segments(&mut path.segments, T::PATH_STYLE, None)?;
+        path.span = ty_span.to(self.prev_token.span);
+
+        self.dcx().emit_err(BadQPathStage2 {
+            span: ty_span,
+            wrap: WrapType { lo: ty_span.shrink_to_lo(), hi: ty_span.shrink_to_hi() },
+        });
+
+        let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
+        Ok(P(T::recovered(Some(P(QSelf { ty, path_span, position: 0 })), path)))
+    }
+
+    /// This function gets called in places where a semicolon is NOT expected and if there's a
+    /// semicolon it emits the appropriate error and returns true.
+    pub fn maybe_consume_incorrect_semicolon(&mut self, previous_item: Option<&Item>) -> bool {
+        if self.token.kind != TokenKind::Semi {
+            return false;
+        }
+
+        // Check previous item to add it to the diagnostic, for example to say
+        // `enum declarations are not followed by a semicolon`
+        let err = match previous_item {
+            Some(previous_item) => {
+                let name = match previous_item.kind {
+                    // Say "braced struct" because tuple-structs and
+                    // braceless-empty-struct declarations do take a semicolon.
+                    ItemKind::Struct(..) => "braced struct",
+                    _ => previous_item.kind.descr(),
+                };
+                IncorrectSemicolon { span: self.token.span, name, show_help: true }
+            }
+            None => IncorrectSemicolon { span: self.token.span, name: "", show_help: false },
+        };
+        self.dcx().emit_err(err);
+
+        self.bump();
+        true
+    }
+
+    /// Creates a `Diag` for an unexpected token `t` and tries to recover if it is a
+    /// closing delimiter.
+    pub(super) fn unexpected_try_recover(&mut self, t: &TokenKind) -> PResult<'a, Recovered> {
+        let token_str = pprust::token_kind_to_string(t);
+        let this_token_str = super::token_descr(&self.token);
+        let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
+            // Point at the end of the macro call when reaching end of macro arguments.
+            (token::Eof, Some(_)) => {
+                let sp = self.prev_token.span.shrink_to_hi();
+                (sp, sp)
+            }
+            // We don't want to point at the following span after DUMMY_SP.
+            // This happens when the parser finds an empty TokenStream.
+            _ if self.prev_token.span == DUMMY_SP => (self.token.span, self.token.span),
+            // EOF, don't want to point at the following char, but rather the last token.
+            (token::Eof, None) => (self.prev_token.span, self.token.span),
+            _ => (self.prev_token.span.shrink_to_hi(), self.token.span),
+        };
+        let msg = format!(
+            "expected `{}`, found {}",
+            token_str,
+            match (&self.token.kind, self.subparser_name) {
+                (token::Eof, Some(origin)) => format!("end of {origin}"),
+                _ => this_token_str,
+            },
+        );
+        let mut err = self.dcx().struct_span_err(sp, msg);
+        let label_exp = format!("expected `{token_str}`");
+        let sm = self.psess.source_map();
+        if !sm.is_multiline(prev_sp.until(sp)) {
+            // When the spans are in the same line, it means that the only content
+            // between them is whitespace, point only at the found token.
+            err.span_label(sp, label_exp);
+        } else {
+            err.span_label(prev_sp, label_exp);
+            err.span_label(sp, "unexpected token");
+        }
+        Err(err)
+    }
+
+    pub(super) fn expect_semi(&mut self) -> PResult<'a, ()> {
+        if self.eat(&token::Semi) || self.recover_colon_as_semi() {
+            return Ok(());
+        }
+        self.expect(&token::Semi).map(drop) // Error unconditionally
+    }
+
+    pub(super) fn recover_colon_as_semi(&mut self) -> bool {
+        let line_idx = |span: Span| {
+            self.psess
+                .source_map()
+                .span_to_lines(span)
+                .ok()
+                .and_then(|lines| Some(lines.lines.get(0)?.line_index))
+        };
+
+        if self.may_recover()
+            && self.token == token::Colon
+            && self.look_ahead(1, |next| line_idx(self.token.span) < line_idx(next.span))
+        {
+            self.dcx().emit_err(ColonAsSemi {
+                span: self.token.span,
+                type_ascription: self.psess.unstable_features.is_nightly_build().then_some(()),
+            });
+            self.bump();
+            return true;
+        }
+
+        false
+    }
+
+    /// Consumes alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
+    /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
+    pub(super) fn recover_incorrect_await_syntax(
+        &mut self,
+        lo: Span,
+        await_sp: Span,
+    ) -> PResult<'a, P<Expr>> {
+        let (hi, expr, is_question) = if self.token == token::Not {
+            // Handle `await!(<expr>)`.
+            self.recover_await_macro()?
+        } else {
+            self.recover_await_prefix(await_sp)?
+        };
+        let (sp, guar) = self.error_on_incorrect_await(lo, hi, &expr, is_question);
+        let expr = self.mk_expr_err(lo.to(sp), guar);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    fn recover_await_macro(&mut self) -> PResult<'a, (Span, P<Expr>, bool)> {
+        self.expect(&token::Not)?;
+        self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
+        let expr = self.parse_expr()?;
+        self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+        Ok((self.prev_token.span, expr, false))
+    }
+
+    fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, P<Expr>, bool)> {
+        let is_question = self.eat(&token::Question); // Handle `await? <expr>`.
+        let expr = if self.token == token::OpenDelim(Delimiter::Brace) {
+            // Handle `await { <expr> }`.
+            // This needs to be handled separately from the next arm to avoid
+            // interpreting `await { <expr> }?` as `<expr>?.await`.
+            self.parse_expr_block(None, self.token.span, BlockCheckMode::Default)
+        } else {
+            self.parse_expr()
+        }
+        .map_err(|mut err| {
+            err.span_label(await_sp, "while parsing this incorrect await expression");
+            err
+        })?;
+        Ok((expr.span, expr, is_question))
+    }
+
+    fn error_on_incorrect_await(
+        &self,
+        lo: Span,
+        hi: Span,
+        expr: &Expr,
+        is_question: bool,
+    ) -> (Span, ErrorGuaranteed) {
+        let span = lo.to(hi);
+        let applicability = match expr.kind {
+            ExprKind::Try(_) => Applicability::MaybeIncorrect, // `await <expr>?`
+            _ => Applicability::MachineApplicable,
+        };
+
+        let guar = self.dcx().emit_err(IncorrectAwait {
+            span,
+            sugg_span: (span, applicability),
+            expr: self.span_to_snippet(expr.span).unwrap_or_else(|_| pprust::expr_to_string(expr)),
+            question_mark: if is_question { "?" } else { "" },
+        });
+
+        (span, guar)
+    }
+
+    /// If encountering `future.await()`, consumes and emits an error.
+    pub(super) fn recover_from_await_method_call(&mut self) {
+        if self.token == token::OpenDelim(Delimiter::Parenthesis)
+            && self.look_ahead(1, |t| t == &token::CloseDelim(Delimiter::Parenthesis))
+        {
+            // future.await()
+            let lo = self.token.span;
+            self.bump(); // (
+            let span = lo.to(self.token.span);
+            self.bump(); // )
+
+            self.dcx().emit_err(IncorrectUseOfAwait { span });
+        }
+    }
+
+    pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, P<Expr>> {
+        let is_try = self.token.is_keyword(kw::Try);
+        let is_questionmark = self.look_ahead(1, |t| t == &token::Not); //check for !
+        let is_open = self.look_ahead(2, |t| t == &token::OpenDelim(Delimiter::Parenthesis)); //check for (
+
+        if is_try && is_questionmark && is_open {
+            let lo = self.token.span;
+            self.bump(); //remove try
+            self.bump(); //remove !
+            let try_span = lo.to(self.token.span); //we take the try!( span
+            self.bump(); //remove (
+            let is_empty = self.token == token::CloseDelim(Delimiter::Parenthesis); //check if the block is empty
+            self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::No); //eat the block
+            let hi = self.token.span;
+            self.bump(); //remove )
+            let mut err = self.dcx().struct_span_err(lo.to(hi), "use of deprecated `try` macro");
+            err.note("in the 2018 edition `try` is a reserved keyword, and the `try!()` macro is deprecated");
+            let prefix = if is_empty { "" } else { "alternatively, " };
+            if !is_empty {
+                err.multipart_suggestion(
+                    "you can use the `?` operator instead",
+                    vec![(try_span, "".to_owned()), (hi, "?".to_owned())],
+                    Applicability::MachineApplicable,
+                );
+            }
+            err.span_suggestion(lo.shrink_to_lo(), format!("{prefix}you can still access the deprecated `try!()` macro using the \"raw identifier\" syntax"), "r#", Applicability::MachineApplicable);
+            let guar = err.emit();
+            Ok(self.mk_expr_err(lo.to(hi), guar))
+        } else {
+            Err(self.expected_expression_found()) // The user isn't trying to invoke the try! macro
+        }
+    }
+
+    /// When trying to close a generics list and encountering code like
+    /// ```text
+    /// impl<S: Into<std::borrow::Cow<'static, str>> From<S> for Canonical {}
+    ///                                          // ^ missing > here
+    /// ```
+    /// we provide a structured suggestion on the error from `expect_gt`.
+    pub(super) fn expect_gt_or_maybe_suggest_closing_generics(
+        &mut self,
+        params: &[ast::GenericParam],
+    ) -> PResult<'a, ()> {
+        let Err(mut err) = self.expect_gt() else {
+            return Ok(());
+        };
+        // Attempt to find places where a missing `>` might belong.
+        if let [.., ast::GenericParam { bounds, .. }] = params
+            && let Some(poly) = bounds
+                .iter()
+                .filter_map(|bound| match bound {
+                    ast::GenericBound::Trait(poly, _) => Some(poly),
+                    _ => None,
+                })
+                .last()
+        {
+            err.span_suggestion_verbose(
+                poly.span.shrink_to_hi(),
+                "you might have meant to end the type parameters here",
+                ">",
+                Applicability::MaybeIncorrect,
+            );
+        }
+        Err(err)
+    }
+
+    pub(super) fn recover_seq_parse_error(
+        &mut self,
+        delim: Delimiter,
+        lo: Span,
+        err: PErr<'a>,
+    ) -> P<Expr> {
+        let guar = err.emit();
+        // Recover from parse error, callers expect the closing delim to be consumed.
+        self.consume_block(delim, ConsumeClosingDelim::Yes);
+        self.mk_expr(lo.to(self.prev_token.span), ExprKind::Err(guar))
+    }
+
+    /// Eats tokens until we can be relatively sure we reached the end of the
+    /// statement. This is something of a best-effort heuristic.
+    ///
+    /// We terminate when we find an unmatched `}` (without consuming it).
+    pub(super) fn recover_stmt(&mut self) {
+        self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore)
+    }
+
+    /// If `break_on_semi` is `Break`, then we will stop consuming tokens after
+    /// finding (and consuming) a `;` outside of `{}` or `[]` (note that this is
+    /// approximate -- it can mean we break too early due to macros, but that
+    /// should only lead to sub-optimal recovery, not inaccurate parsing).
+    ///
+    /// If `break_on_block` is `Break`, then we will stop consuming tokens
+    /// after finding (and consuming) a brace-delimited block.
+    pub(super) fn recover_stmt_(
+        &mut self,
+        break_on_semi: SemiColonMode,
+        break_on_block: BlockMode,
+    ) {
+        let mut brace_depth = 0;
+        let mut bracket_depth = 0;
+        let mut in_block = false;
+        debug!("recover_stmt_ enter loop (semi={:?}, block={:?})", break_on_semi, break_on_block);
+        loop {
+            debug!("recover_stmt_ loop {:?}", self.token);
+            match self.token.kind {
+                token::OpenDelim(Delimiter::Brace) => {
+                    brace_depth += 1;
+                    self.bump();
+                    if break_on_block == BlockMode::Break && brace_depth == 1 && bracket_depth == 0
+                    {
+                        in_block = true;
+                    }
+                }
+                token::OpenDelim(Delimiter::Bracket) => {
+                    bracket_depth += 1;
+                    self.bump();
+                }
+                token::CloseDelim(Delimiter::Brace) => {
+                    if brace_depth == 0 {
+                        debug!("recover_stmt_ return - close delim {:?}", self.token);
+                        break;
+                    }
+                    brace_depth -= 1;
+                    self.bump();
+                    if in_block && bracket_depth == 0 && brace_depth == 0 {
+                        debug!("recover_stmt_ return - block end {:?}", self.token);
+                        break;
+                    }
+                }
+                token::CloseDelim(Delimiter::Bracket) => {
+                    bracket_depth -= 1;
+                    if bracket_depth < 0 {
+                        bracket_depth = 0;
+                    }
+                    self.bump();
+                }
+                token::Eof => {
+                    debug!("recover_stmt_ return - Eof");
+                    break;
+                }
+                token::Semi => {
+                    self.bump();
+                    if break_on_semi == SemiColonMode::Break
+                        && brace_depth == 0
+                        && bracket_depth == 0
+                    {
+                        debug!("recover_stmt_ return - Semi");
+                        break;
+                    }
+                }
+                token::Comma
+                    if break_on_semi == SemiColonMode::Comma
+                        && brace_depth == 0
+                        && bracket_depth == 0 =>
+                {
+                    break;
+                }
+                _ => self.bump(),
+            }
+        }
+    }
+
+    pub(super) fn check_for_for_in_in_typo(&mut self, in_span: Span) {
+        if self.eat_keyword(kw::In) {
+            // a common typo: `for _ in in bar {}`
+            self.dcx().emit_err(InInTypo {
+                span: self.prev_token.span,
+                sugg_span: in_span.until(self.prev_token.span),
+            });
+        }
+    }
+
+    pub(super) fn eat_incorrect_doc_comment_for_param_type(&mut self) {
+        if let token::DocComment(..) = self.token.kind {
+            self.dcx().emit_err(DocCommentOnParamType { span: self.token.span });
+            self.bump();
+        } else if self.token == token::Pound
+            && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Bracket))
+        {
+            let lo = self.token.span;
+            // Skip every token until next possible arg.
+            while self.token != token::CloseDelim(Delimiter::Bracket) {
+                self.bump();
+            }
+            let sp = lo.to(self.token.span);
+            self.bump();
+            self.dcx().emit_err(AttributeOnParamType { span: sp });
+        }
+    }
+
+    pub(super) fn parameter_without_type(
+        &mut self,
+        err: &mut Diag<'_>,
+        pat: P<ast::Pat>,
+        require_name: bool,
+        first_param: bool,
+    ) -> Option<Ident> {
+        // If we find a pattern followed by an identifier, it could be an (incorrect)
+        // C-style parameter declaration.
+        if self.check_ident()
+            && self.look_ahead(1, |t| {
+                *t == token::Comma || *t == token::CloseDelim(Delimiter::Parenthesis)
+            })
+        {
+            // `fn foo(String s) {}`
+            let ident = self.parse_ident().unwrap();
+            let span = pat.span.with_hi(ident.span.hi());
+
+            err.span_suggestion(
+                span,
+                "declare the type after the parameter binding",
+                "<identifier>: <type>",
+                Applicability::HasPlaceholders,
+            );
+            return Some(ident);
+        } else if require_name
+            && (self.token == token::Comma
+                || self.token == token::Lt
+                || self.token == token::CloseDelim(Delimiter::Parenthesis))
+        {
+            let rfc_note = "anonymous parameters are removed in the 2018 edition (see RFC 1685)";
+
+            let (ident, self_sugg, param_sugg, type_sugg, self_span, param_span, type_span) =
+                match pat.kind {
+                    PatKind::Ident(_, ident, _) => (
+                        ident,
+                        "self: ",
+                        ": TypeName".to_string(),
+                        "_: ",
+                        pat.span.shrink_to_lo(),
+                        pat.span.shrink_to_hi(),
+                        pat.span.shrink_to_lo(),
+                    ),
+                    // Also catches `fn foo(&a)`.
+                    PatKind::Ref(ref inner_pat, mutab)
+                        if matches!(inner_pat.clone().into_inner().kind, PatKind::Ident(..)) =>
+                    {
+                        match inner_pat.clone().into_inner().kind {
+                            PatKind::Ident(_, ident, _) => {
+                                let mutab = mutab.prefix_str();
+                                (
+                                    ident,
+                                    "self: ",
+                                    format!("{ident}: &{mutab}TypeName"),
+                                    "_: ",
+                                    pat.span.shrink_to_lo(),
+                                    pat.span,
+                                    pat.span.shrink_to_lo(),
+                                )
+                            }
+                            _ => unreachable!(),
+                        }
+                    }
+                    _ => {
+                        // Otherwise, try to get a type and emit a suggestion.
+                        if let Some(ty) = pat.to_ty() {
+                            err.span_suggestion_verbose(
+                                pat.span,
+                                "explicitly ignore the parameter name",
+                                format!("_: {}", pprust::ty_to_string(&ty)),
+                                Applicability::MachineApplicable,
+                            );
+                            err.note(rfc_note);
+                        }
+
+                        return None;
+                    }
+                };
+
+            // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
+            if first_param {
+                err.span_suggestion(
+                    self_span,
+                    "if this is a `self` type, give it a parameter name",
+                    self_sugg,
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            // Avoid suggesting that `fn foo(HashMap<u32>)` is fixed with a change to
+            // `fn foo(HashMap: TypeName<u32>)`.
+            if self.token != token::Lt {
+                err.span_suggestion(
+                    param_span,
+                    "if this is a parameter name, give it a type",
+                    param_sugg,
+                    Applicability::HasPlaceholders,
+                );
+            }
+            err.span_suggestion(
+                type_span,
+                "if this is a type, explicitly ignore the parameter name",
+                type_sugg,
+                Applicability::MachineApplicable,
+            );
+            err.note(rfc_note);
+
+            // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
+            return if self.token == token::Lt { None } else { Some(ident) };
+        }
+        None
+    }
+
+    pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
+        let pat = self.parse_pat_no_top_alt(Some(Expected::ArgumentName), None)?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        self.dcx().emit_err(PatternMethodParamWithoutBody { span: pat.span });
+
+        // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
+        let pat =
+            P(Pat { kind: PatKind::Wild, span: pat.span, id: ast::DUMMY_NODE_ID, tokens: None });
+        Ok((pat, ty))
+    }
+
+    pub(super) fn recover_bad_self_param(&mut self, mut param: Param) -> PResult<'a, Param> {
+        let span = param.pat.span;
+        let guar = self.dcx().emit_err(SelfParamNotFirst { span });
+        param.ty.kind = TyKind::Err(guar);
+        Ok(param)
+    }
+
+    pub(super) fn consume_block(&mut self, delim: Delimiter, consume_close: ConsumeClosingDelim) {
+        let mut brace_depth = 0;
+        loop {
+            if self.eat(&token::OpenDelim(delim)) {
+                brace_depth += 1;
+            } else if self.check(&token::CloseDelim(delim)) {
+                if brace_depth == 0 {
+                    if let ConsumeClosingDelim::Yes = consume_close {
+                        // Some of the callers of this method expect to be able to parse the
+                        // closing delimiter themselves, so we leave it alone. Otherwise we advance
+                        // the parser.
+                        self.bump();
+                    }
+                    return;
+                } else {
+                    self.bump();
+                    brace_depth -= 1;
+                    continue;
+                }
+            } else if self.token == token::Eof {
+                return;
+            } else {
+                self.bump();
+            }
+        }
+    }
+
+    pub(super) fn expected_expression_found(&self) -> Diag<'a> {
+        let (span, msg) = match (&self.token.kind, self.subparser_name) {
+            (&token::Eof, Some(origin)) => {
+                let sp = self.prev_token.span.shrink_to_hi();
+                (sp, format!("expected expression, found end of {origin}"))
+            }
+            _ => (
+                self.token.span,
+                format!("expected expression, found {}", super::token_descr(&self.token)),
+            ),
+        };
+        let mut err = self.dcx().struct_span_err(span, msg);
+        let sp = self.psess.source_map().start_point(self.token.span);
+        if let Some(sp) = self.psess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
+        }
+        err.span_label(span, "expected expression");
+
+        // Walk the chain of macro expansions for the current token to point at how the original
+        // code was interpreted. This helps the user realize when a macro argument of one type is
+        // later reinterpreted as a different type, like `$x:expr` being reinterpreted as `$x:pat`
+        // in a subsequent macro invocation (#71039).
+        let mut tok = self.token.clone();
+        let mut labels = vec![];
+        while let TokenKind::Interpolated(nt) = &tok.kind {
+            let tokens = nt.tokens();
+            labels.push(nt.clone());
+            if let Some(tokens) = tokens
+                && let tokens = tokens.to_attr_token_stream()
+                && let tokens = tokens.0.deref()
+                && let [AttrTokenTree::Token(token, _)] = &tokens[..]
+            {
+                tok = token.clone();
+            } else {
+                break;
+            }
+        }
+        let mut iter = labels.into_iter().peekable();
+        let mut show_link = false;
+        while let Some(nt) = iter.next() {
+            let descr = nt.descr();
+            if let Some(next) = iter.peek() {
+                let next_descr = next.descr();
+                if next_descr != descr {
+                    err.span_label(next.use_span(), format!("this is expected to be {next_descr}"));
+                    err.span_label(
+                        nt.use_span(),
+                        format!(
+                            "this is interpreted as {}, but it is expected to be {}",
+                            next_descr, descr,
+                        ),
+                    );
+                    show_link = true;
+                }
+            }
+        }
+        if show_link {
+            err.note(
+                "when forwarding a matched fragment to another macro-by-example, matchers in the \
+                 second macro will see an opaque AST of the fragment type, not the underlying \
+                 tokens",
+            );
+        }
+        err
+    }
+
+    fn consume_tts(
+        &mut self,
+        mut acc: i64, // `i64` because malformed code can have more closing delims than opening.
+        // Not using `FxHashMap` due to `token::TokenKind: !Eq + !Hash`.
+        modifier: &[(token::TokenKind, i64)],
+    ) {
+        while acc > 0 {
+            if let Some((_, val)) = modifier.iter().find(|(t, _)| *t == self.token.kind) {
+                acc += *val;
+            }
+            if self.token.kind == token::Eof {
+                break;
+            }
+            self.bump();
+        }
+    }
+
+    /// Replace duplicated recovered parameters with `_` pattern to avoid unnecessary errors.
+    ///
+    /// This is necessary because at this point we don't know whether we parsed a function with
+    /// anonymous parameters or a function with names but no types. In order to minimize
+    /// unnecessary errors, we assume the parameters are in the shape of `fn foo(a, b, c)` where
+    /// the parameters are *names* (so we don't emit errors about not being able to find `b` in
+    /// the local scope), but if we find the same name multiple times, like in `fn foo(i8, i8)`,
+    /// we deduplicate them to not complain about duplicated parameter names.
+    pub(super) fn deduplicate_recovered_params_names(&self, fn_inputs: &mut ThinVec<Param>) {
+        let mut seen_inputs = FxHashSet::default();
+        for input in fn_inputs.iter_mut() {
+            let opt_ident = if let (PatKind::Ident(_, ident, _), TyKind::Err(_)) =
+                (&input.pat.kind, &input.ty.kind)
+            {
+                Some(*ident)
+            } else {
+                None
+            };
+            if let Some(ident) = opt_ident {
+                if seen_inputs.contains(&ident) {
+                    input.pat.kind = PatKind::Wild;
+                }
+                seen_inputs.insert(ident);
+            }
+        }
+    }
+
+    /// Handle encountering a symbol in a generic argument list that is not a `,` or `>`. In this
+    /// case, we emit an error and try to suggest enclosing a const argument in braces if it looks
+    /// like the user has forgotten them.
+    pub fn handle_ambiguous_unbraced_const_arg(
+        &mut self,
+        args: &mut ThinVec<AngleBracketedArg>,
+    ) -> PResult<'a, bool> {
+        // If we haven't encountered a closing `>`, then the argument is malformed.
+        // It's likely that the user has written a const expression without enclosing it
+        // in braces, so we try to recover here.
+        let arg = args.pop().unwrap();
+        // FIXME: for some reason using `unexpected` or `expected_one_of_not_found` has
+        // adverse side-effects to subsequent errors and seems to advance the parser.
+        // We are causing this error here exclusively in case that a `const` expression
+        // could be recovered from the current parser state, even if followed by more
+        // arguments after a comma.
+        let mut err = self.dcx().struct_span_err(
+            self.token.span,
+            format!("expected one of `,` or `>`, found {}", super::token_descr(&self.token)),
+        );
+        err.span_label(self.token.span, "expected one of `,` or `>`");
+        match self.recover_const_arg(arg.span(), err) {
+            Ok(arg) => {
+                args.push(AngleBracketedArg::Arg(arg));
+                if self.eat(&token::Comma) {
+                    return Ok(true); // Continue
+                }
+            }
+            Err(err) => {
+                args.push(arg);
+                // We will emit a more generic error later.
+                err.delay_as_bug();
+            }
+        }
+        return Ok(false); // Don't continue.
+    }
+
+    /// Attempt to parse a generic const argument that has not been enclosed in braces.
+    /// There are a limited number of expressions that are permitted without being encoded
+    /// in braces:
+    /// - Literals.
+    /// - Single-segment paths (i.e. standalone generic const parameters).
+    /// All other expressions that can be parsed will emit an error suggesting the expression be
+    /// wrapped in braces.
+    pub fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, P<Expr>> {
+        let start = self.token.span;
+        let expr = self.parse_expr_res(Restrictions::CONST_EXPR, None).map_err(|mut err| {
+            err.span_label(
+                start.shrink_to_lo(),
+                "while parsing a const generic argument starting here",
+            );
+            err
+        })?;
+        if !self.expr_is_valid_const_arg(&expr) {
+            self.dcx().emit_err(ConstGenericWithoutBraces {
+                span: expr.span,
+                sugg: ConstGenericWithoutBracesSugg {
+                    left: expr.span.shrink_to_lo(),
+                    right: expr.span.shrink_to_hi(),
+                },
+            });
+        }
+        Ok(expr)
+    }
+
+    fn recover_const_param_decl(&mut self, ty_generics: Option<&Generics>) -> Option<GenericArg> {
+        let snapshot = self.create_snapshot_for_diagnostic();
+        let param = match self.parse_const_param(AttrVec::new()) {
+            Ok(param) => param,
+            Err(err) => {
+                err.cancel();
+                self.restore_snapshot(snapshot);
+                return None;
+            }
+        };
+
+        let ident = param.ident.to_string();
+        let sugg = match (ty_generics, self.psess.source_map().span_to_snippet(param.span())) {
+            (Some(Generics { params, span: impl_generics, .. }), Ok(snippet)) => {
+                Some(match &params[..] {
+                    [] => UnexpectedConstParamDeclarationSugg::AddParam {
+                        impl_generics: *impl_generics,
+                        incorrect_decl: param.span(),
+                        snippet,
+                        ident,
+                    },
+                    [.., generic] => UnexpectedConstParamDeclarationSugg::AppendParam {
+                        impl_generics_end: generic.span().shrink_to_hi(),
+                        incorrect_decl: param.span(),
+                        snippet,
+                        ident,
+                    },
+                })
+            }
+            _ => None,
+        };
+        let guar =
+            self.dcx().emit_err(UnexpectedConstParamDeclaration { span: param.span(), sugg });
+
+        let value = self.mk_expr_err(param.span(), guar);
+        Some(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }))
+    }
+
+    pub fn recover_const_param_declaration(
+        &mut self,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, Option<GenericArg>> {
+        // We have to check for a few different cases.
+        if let Some(arg) = self.recover_const_param_decl(ty_generics) {
+            return Ok(Some(arg));
+        }
+
+        // We haven't consumed `const` yet.
+        let start = self.token.span;
+        self.bump(); // `const`
+
+        // Detect and recover from the old, pre-RFC2000 syntax for const generics.
+        let mut err = UnexpectedConstInGenericParam { span: start, to_remove: None };
+        if self.check_const_arg() {
+            err.to_remove = Some(start.until(self.token.span));
+            self.dcx().emit_err(err);
+            Ok(Some(GenericArg::Const(self.parse_const_arg()?)))
+        } else {
+            let after_kw_const = self.token.span;
+            self.recover_const_arg(after_kw_const, self.dcx().create_err(err)).map(Some)
+        }
+    }
+
+    /// Try to recover from possible generic const argument without `{` and `}`.
+    ///
+    /// When encountering code like `foo::< bar + 3 >` or `foo::< bar - baz >` we suggest
+    /// `foo::<{ bar + 3 }>` and `foo::<{ bar - baz }>`, respectively. We only provide a suggestion
+    /// if we think that the resulting expression would be well formed.
+    pub fn recover_const_arg(&mut self, start: Span, mut err: Diag<'a>) -> PResult<'a, GenericArg> {
+        let is_op_or_dot = AssocOp::from_token(&self.token)
+            .and_then(|op| {
+                if let AssocOp::Greater
+                | AssocOp::Less
+                | AssocOp::ShiftRight
+                | AssocOp::GreaterEqual
+                // Don't recover from `foo::<bar = baz>`, because this could be an attempt to
+                // assign a value to a defaulted generic parameter.
+                | AssocOp::Assign
+                | AssocOp::AssignOp(_) = op
+                {
+                    None
+                } else {
+                    Some(op)
+                }
+            })
+            .is_some()
+            || self.token.kind == TokenKind::Dot;
+        // This will be true when a trait object type `Foo +` or a path which was a `const fn` with
+        // type params has been parsed.
+        let was_op =
+            matches!(self.prev_token.kind, token::BinOp(token::Plus | token::Shr) | token::Gt);
+        if !is_op_or_dot && !was_op {
+            // We perform these checks and early return to avoid taking a snapshot unnecessarily.
+            return Err(err);
+        }
+        let snapshot = self.create_snapshot_for_diagnostic();
+        if is_op_or_dot {
+            self.bump();
+        }
+        match self.parse_expr_res(Restrictions::CONST_EXPR, None) {
+            Ok(expr) => {
+                // Find a mistake like `MyTrait<Assoc == S::Assoc>`.
+                if token::EqEq == snapshot.token.kind {
+                    err.span_suggestion(
+                        snapshot.token.span,
+                        "if you meant to use an associated type binding, replace `==` with `=`",
+                        "=",
+                        Applicability::MaybeIncorrect,
+                    );
+                    let guar = err.emit();
+                    let value = self.mk_expr_err(start.to(expr.span), guar);
+                    return Ok(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }));
+                } else if token::Colon == snapshot.token.kind
+                    && expr.span.lo() == snapshot.token.span.hi()
+                    && matches!(expr.kind, ExprKind::Path(..))
+                {
+                    // Find a mistake like "foo::var:A".
+                    err.span_suggestion(
+                        snapshot.token.span,
+                        "write a path separator here",
+                        "::",
+                        Applicability::MaybeIncorrect,
+                    );
+                    let guar = err.emit();
+                    return Ok(GenericArg::Type(
+                        self.mk_ty(start.to(expr.span), TyKind::Err(guar)),
+                    ));
+                } else if token::Comma == self.token.kind || self.token.kind.should_end_const_arg()
+                {
+                    // Avoid the following output by checking that we consumed a full const arg:
+                    // help: expressions must be enclosed in braces to be used as const generic
+                    //       arguments
+                    //    |
+                    // LL |     let sr: Vec<{ (u32, _, _) = vec![] };
+                    //    |                 ^                      ^
+                    return Ok(self.dummy_const_arg_needs_braces(err, start.to(expr.span)));
+                }
+            }
+            Err(err) => {
+                err.cancel();
+            }
+        }
+        self.restore_snapshot(snapshot);
+        Err(err)
+    }
+
+    /// Try to recover from an unbraced const argument whose first token [could begin a type][ty].
+    ///
+    /// [ty]: token::Token::can_begin_type
+    pub(crate) fn recover_unbraced_const_arg_that_can_begin_ty(
+        &mut self,
+        mut snapshot: SnapshotParser<'a>,
+    ) -> Option<P<ast::Expr>> {
+        match snapshot.parse_expr_res(Restrictions::CONST_EXPR, None) {
+            // Since we don't know the exact reason why we failed to parse the type or the
+            // expression, employ a simple heuristic to weed out some pathological cases.
+            Ok(expr) if let token::Comma | token::Gt = snapshot.token.kind => {
+                self.restore_snapshot(snapshot);
+                Some(expr)
+            }
+            Ok(_) => None,
+            Err(err) => {
+                err.cancel();
+                None
+            }
+        }
+    }
+
+    /// Creates a dummy const argument, and reports that the expression must be enclosed in braces
+    pub fn dummy_const_arg_needs_braces(&self, mut err: Diag<'a>, span: Span) -> GenericArg {
+        err.multipart_suggestion(
+            "expressions must be enclosed in braces to be used as const generic \
+             arguments",
+            vec![(span.shrink_to_lo(), "{ ".to_string()), (span.shrink_to_hi(), " }".to_string())],
+            Applicability::MaybeIncorrect,
+        );
+        let guar = err.emit();
+        let value = self.mk_expr_err(span, guar);
+        GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value })
+    }
+
+    /// Some special error handling for the "top-level" patterns in a match arm,
+    /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
+    pub(crate) fn maybe_recover_colon_colon_in_pat_typo(
+        &mut self,
+        mut first_pat: P<Pat>,
+        expected: Option<Expected>,
+    ) -> P<Pat> {
+        if token::Colon != self.token.kind {
+            return first_pat;
+        }
+        if !matches!(first_pat.kind, PatKind::Ident(_, _, None) | PatKind::Path(..))
+            || !self.look_ahead(1, |token| token.is_ident() && !token.is_reserved_ident())
+        {
+            let mut snapshot_type = self.create_snapshot_for_diagnostic();
+            snapshot_type.bump(); // `:`
+            match snapshot_type.parse_ty() {
+                Err(inner_err) => {
+                    inner_err.cancel();
+                }
+                Ok(ty) => {
+                    let Err(mut err) = self.expected_one_of_not_found(&[], &[]) else {
+                        return first_pat;
+                    };
+                    err.span_label(ty.span, "specifying the type of a pattern isn't supported");
+                    self.restore_snapshot(snapshot_type);
+                    let span = first_pat.span.to(ty.span);
+                    first_pat = self.mk_pat(span, PatKind::Wild);
+                    err.emit();
+                }
+            }
+            return first_pat;
+        }
+        // The pattern looks like it might be a path with a `::` -> `:` typo:
+        // `match foo { bar:baz => {} }`
+        let colon_span = self.token.span;
+        // We only emit "unexpected `:`" error here if we can successfully parse the
+        // whole pattern correctly in that case.
+        let mut snapshot_pat = self.create_snapshot_for_diagnostic();
+        let mut snapshot_type = self.create_snapshot_for_diagnostic();
+
+        // Create error for "unexpected `:`".
+        match self.expected_one_of_not_found(&[], &[]) {
+            Err(mut err) => {
+                // Skip the `:`.
+                snapshot_pat.bump();
+                snapshot_type.bump();
+                match snapshot_pat.parse_pat_no_top_alt(expected, None) {
+                    Err(inner_err) => {
+                        inner_err.cancel();
+                    }
+                    Ok(mut pat) => {
+                        // We've parsed the rest of the pattern.
+                        let new_span = first_pat.span.to(pat.span);
+                        let mut show_sugg = false;
+                        // Try to construct a recovered pattern.
+                        match &mut pat.kind {
+                            PatKind::Struct(qself @ None, path, ..)
+                            | PatKind::TupleStruct(qself @ None, path, _)
+                            | PatKind::Path(qself @ None, path) => match &first_pat.kind {
+                                PatKind::Ident(_, ident, _) => {
+                                    path.segments.insert(0, PathSegment::from_ident(*ident));
+                                    path.span = new_span;
+                                    show_sugg = true;
+                                    first_pat = pat;
+                                }
+                                PatKind::Path(old_qself, old_path) => {
+                                    path.segments = old_path
+                                        .segments
+                                        .iter()
+                                        .cloned()
+                                        .chain(take(&mut path.segments))
+                                        .collect();
+                                    path.span = new_span;
+                                    *qself = old_qself.clone();
+                                    first_pat = pat;
+                                    show_sugg = true;
+                                }
+                                _ => {}
+                            },
+                            PatKind::Ident(BindingMode::NONE, ident, None) => {
+                                match &first_pat.kind {
+                                    PatKind::Ident(_, old_ident, _) => {
+                                        let path = PatKind::Path(
+                                            None,
+                                            Path {
+                                                span: new_span,
+                                                segments: thin_vec![
+                                                    PathSegment::from_ident(*old_ident),
+                                                    PathSegment::from_ident(*ident),
+                                                ],
+                                                tokens: None,
+                                            },
+                                        );
+                                        first_pat = self.mk_pat(new_span, path);
+                                        show_sugg = true;
+                                    }
+                                    PatKind::Path(old_qself, old_path) => {
+                                        let mut segments = old_path.segments.clone();
+                                        segments.push(PathSegment::from_ident(*ident));
+                                        let path = PatKind::Path(
+                                            old_qself.clone(),
+                                            Path { span: new_span, segments, tokens: None },
+                                        );
+                                        first_pat = self.mk_pat(new_span, path);
+                                        show_sugg = true;
+                                    }
+                                    _ => {}
+                                }
+                            }
+                            _ => {}
+                        }
+                        if show_sugg {
+                            err.span_suggestion_verbose(
+                                colon_span.until(self.look_ahead(1, |t| t.span)),
+                                "maybe write a path separator here",
+                                "::",
+                                Applicability::MaybeIncorrect,
+                            );
+                        } else {
+                            first_pat = self.mk_pat(new_span, PatKind::Wild);
+                        }
+                        self.restore_snapshot(snapshot_pat);
+                    }
+                }
+                match snapshot_type.parse_ty() {
+                    Err(inner_err) => {
+                        inner_err.cancel();
+                    }
+                    Ok(ty) => {
+                        err.span_label(ty.span, "specifying the type of a pattern isn't supported");
+                        self.restore_snapshot(snapshot_type);
+                        let new_span = first_pat.span.to(ty.span);
+                        first_pat = self.mk_pat(new_span, PatKind::Wild);
+                    }
+                }
+                err.emit();
+            }
+            _ => {
+                // Carry on as if we had not done anything. This should be unreachable.
+            }
+        };
+        first_pat
+    }
+
+    pub(crate) fn maybe_recover_unexpected_block_label(&mut self) -> bool {
+        // Check for `'a : {`
+        if !(self.check_lifetime()
+            && self.look_ahead(1, |tok| tok.kind == token::Colon)
+            && self.look_ahead(2, |tok| tok.kind == token::OpenDelim(Delimiter::Brace)))
+        {
+            return false;
+        }
+        let label = self.eat_label().expect("just checked if a label exists");
+        self.bump(); // eat `:`
+        let span = label.ident.span.to(self.prev_token.span);
+        self.dcx()
+            .struct_span_err(span, "block label not supported here")
+            .with_span_label(span, "not supported here")
+            .with_tool_only_span_suggestion(
+                label.ident.span.until(self.token.span),
+                "remove this block label",
+                "",
+                Applicability::MachineApplicable,
+            )
+            .emit();
+        true
+    }
+
+    /// Some special error handling for the "top-level" patterns in a match arm,
+    /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
+    pub(crate) fn maybe_recover_unexpected_comma(
+        &mut self,
+        lo: Span,
+        rt: CommaRecoveryMode,
+    ) -> PResult<'a, ()> {
+        if self.token != token::Comma {
+            return Ok(());
+        }
+
+        // An unexpected comma after a top-level pattern is a clue that the
+        // user (perhaps more accustomed to some other language) forgot the
+        // parentheses in what should have been a tuple pattern; return a
+        // suggestion-enhanced error here rather than choking on the comma later.
+        let comma_span = self.token.span;
+        self.bump();
+        if let Err(err) = self.skip_pat_list() {
+            // We didn't expect this to work anyway; we just wanted to advance to the
+            // end of the comma-sequence so we know the span to suggest parenthesizing.
+            err.cancel();
+        }
+        let seq_span = lo.to(self.prev_token.span);
+        let mut err = self.dcx().struct_span_err(comma_span, "unexpected `,` in pattern");
+        if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
+            err.multipart_suggestion(
+                format!(
+                    "try adding parentheses to match on a tuple{}",
+                    if let CommaRecoveryMode::LikelyTuple = rt { "" } else { "..." },
+                ),
+                vec![
+                    (seq_span.shrink_to_lo(), "(".to_string()),
+                    (seq_span.shrink_to_hi(), ")".to_string()),
+                ],
+                Applicability::MachineApplicable,
+            );
+            if let CommaRecoveryMode::EitherTupleOrPipe = rt {
+                err.span_suggestion(
+                    seq_span,
+                    "...or a vertical bar to match on multiple alternatives",
+                    seq_snippet.replace(',', " |"),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        Err(err)
+    }
+
+    pub(crate) fn maybe_recover_bounds_doubled_colon(&mut self, ty: &Ty) -> PResult<'a, ()> {
+        let TyKind::Path(qself, path) = &ty.kind else { return Ok(()) };
+        let qself_position = qself.as_ref().map(|qself| qself.position);
+        for (i, segments) in path.segments.windows(2).enumerate() {
+            if qself_position.is_some_and(|pos| i < pos) {
+                continue;
+            }
+            if let [a, b] = segments {
+                let (a_span, b_span) = (a.span(), b.span());
+                let between_span = a_span.shrink_to_hi().to(b_span.shrink_to_lo());
+                if self.span_to_snippet(between_span).as_deref() == Ok(":: ") {
+                    return Err(self.dcx().create_err(DoubleColonInBound {
+                        span: path.span.shrink_to_hi(),
+                        between: between_span,
+                    }));
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Check for exclusive ranges written as `..<`
+    pub(crate) fn maybe_err_dotdotlt_syntax(&self, maybe_lt: Token, mut err: PErr<'a>) -> PErr<'a> {
+        if maybe_lt == token::Lt
+            && (self.expected_tokens.contains(&TokenType::Token(token::Gt))
+                || matches!(self.token.kind, token::Literal(..)))
+        {
+            err.span_suggestion(
+                maybe_lt.span,
+                "remove the `<` to write an exclusive range",
+                "",
+                Applicability::MachineApplicable,
+            );
+        }
+        err
+    }
+
+    /// This checks if this is a conflict marker, depending of the parameter passed.
+    ///
+    /// * `>>>>>`
+    /// * `=====`
+    /// * `<<<<<`
+    ///
+    pub fn is_vcs_conflict_marker(
+        &mut self,
+        long_kind: &TokenKind,
+        short_kind: &TokenKind,
+    ) -> bool {
+        (0..3).all(|i| self.look_ahead(i, |tok| tok == long_kind))
+            && self.look_ahead(3, |tok| tok == short_kind)
+    }
+
+    fn conflict_marker(&mut self, long_kind: &TokenKind, short_kind: &TokenKind) -> Option<Span> {
+        if self.is_vcs_conflict_marker(long_kind, short_kind) {
+            let lo = self.token.span;
+            for _ in 0..4 {
+                self.bump();
+            }
+            return Some(lo.to(self.prev_token.span));
+        }
+        None
+    }
+
+    pub fn recover_vcs_conflict_marker(&mut self) {
+        if let Err(err) = self.err_vcs_conflict_marker() {
+            err.emit();
+            FatalError.raise();
+        }
+    }
+
+    pub fn err_vcs_conflict_marker(&mut self) -> PResult<'a, ()> {
+        let Some(start) = self.conflict_marker(&TokenKind::BinOp(token::Shl), &TokenKind::Lt)
+        else {
+            return Ok(());
+        };
+        let mut spans = Vec::with_capacity(3);
+        spans.push(start);
+        let mut middlediff3 = None;
+        let mut middle = None;
+        let mut end = None;
+        loop {
+            if self.token.kind == TokenKind::Eof {
+                break;
+            }
+            if let Some(span) = self.conflict_marker(&TokenKind::OrOr, &TokenKind::BinOp(token::Or))
+            {
+                middlediff3 = Some(span);
+            }
+            if let Some(span) = self.conflict_marker(&TokenKind::EqEq, &TokenKind::Eq) {
+                middle = Some(span);
+            }
+            if let Some(span) = self.conflict_marker(&TokenKind::BinOp(token::Shr), &TokenKind::Gt)
+            {
+                spans.push(span);
+                end = Some(span);
+                break;
+            }
+            self.bump();
+        }
+        let mut err = self.dcx().struct_span_err(spans, "encountered diff marker");
+        err.span_label(start, "after this is the code before the merge");
+        if let Some(middle) = middlediff3 {
+            err.span_label(middle, "");
+        }
+        if let Some(middle) = middle {
+            err.span_label(middle, "");
+        }
+        if let Some(end) = end {
+            err.span_label(end, "above this are the incoming code changes");
+        }
+        err.help(
+            "if you're having merge conflicts after pulling new code, the top section is the code \
+             you already had and the bottom section is the remote code",
+        );
+        err.help(
+            "if you're in the middle of a rebase, the top section is the code being rebased onto \
+             and the bottom section is the code coming from the current commit being rebased",
+        );
+        err.note(
+            "for an explanation on these markers from the `git` documentation, visit \
+             <https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging#_checking_out_conflicts>",
+        );
+        Err(err)
+    }
+
+    /// Parse and throw away a parenthesized comma separated
+    /// sequence of patterns until `)` is reached.
+    fn skip_pat_list(&mut self) -> PResult<'a, ()> {
+        while !self.check(&token::CloseDelim(Delimiter::Parenthesis)) {
+            self.parse_pat_no_top_alt(None, None)?;
+            if !self.eat(&token::Comma) {
+                return Ok(());
+            }
+        }
+        Ok(())
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
new file mode 100644
index 00000000000..d2d21624150
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -0,0 +1,4047 @@
+// ignore-tidy-filelength
+use super::diagnostics::SnapshotParser;
+use super::pat::{CommaRecoveryMode, Expected, RecoverColon, RecoverComma};
+use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
+use super::{
+    AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
+    SemiColonMode, SeqSep, TokenExpectType, TokenType, Trailing, TrailingToken,
+};
+
+use crate::errors;
+use crate::maybe_recover_from_interpolated_ty_qpath;
+use ast::mut_visit::{noop_visit_expr, MutVisitor};
+use ast::token::IdentIsRaw;
+use ast::{CoroutineKind, ForLoopKind, GenBlockKind, MatchKind, Pat, Path, PathSegment, Recovered};
+use core::mem;
+use core::ops::ControlFlow;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Token, TokenKind};
+use rustc_ast::util::case::Case;
+use rustc_ast::util::classify;
+use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
+use rustc_ast::visit::{walk_expr, Visitor};
+use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, UnOp, DUMMY_NODE_ID};
+use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
+use rustc_ast::{Arm, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
+use rustc_ast::{ClosureBinder, MetaItemLit, StmtKind};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::stack::ensure_sufficient_stack;
+use rustc_errors::{Applicability, Diag, PResult, StashKey, Subdiagnostic};
+use rustc_lexer::unescape::unescape_char;
+use rustc_macros::Subdiagnostic;
+use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
+use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
+use rustc_session::lint::BuiltinLintDiag;
+use rustc_span::source_map::{self, Spanned};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{BytePos, ErrorGuaranteed, Pos, Span};
+use thin_vec::{thin_vec, ThinVec};
+
+/// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
+/// dropped into the token stream, which happens while parsing the result of
+/// macro expansion). Placement of these is not as complex as I feared it would
+/// be. The important thing is to make sure that lookahead doesn't balk at
+/// `token::Interpolated` tokens.
+macro_rules! maybe_whole_expr {
+    ($p:expr) => {
+        if let token::Interpolated(nt) = &$p.token.kind {
+            match &**nt {
+                token::NtExpr(e) | token::NtLiteral(e) => {
+                    let e = e.clone();
+                    $p.bump();
+                    return Ok(e);
+                }
+                token::NtPath(path) => {
+                    let path = (**path).clone();
+                    $p.bump();
+                    return Ok($p.mk_expr($p.prev_token.span, ExprKind::Path(None, path)));
+                }
+                token::NtBlock(block) => {
+                    let block = block.clone();
+                    $p.bump();
+                    return Ok($p.mk_expr($p.prev_token.span, ExprKind::Block(block, None)));
+                }
+                _ => {}
+            };
+        }
+    };
+}
+
+#[derive(Debug)]
+pub(super) enum LhsExpr {
+    NotYetParsed,
+    AttributesParsed(AttrWrapper),
+    AlreadyParsed { expr: P<Expr>, starts_statement: bool },
+}
+
+impl From<Option<AttrWrapper>> for LhsExpr {
+    /// Converts `Some(attrs)` into `LhsExpr::AttributesParsed(attrs)`
+    /// and `None` into `LhsExpr::NotYetParsed`.
+    ///
+    /// This conversion does not allocate.
+    fn from(o: Option<AttrWrapper>) -> Self {
+        if let Some(attrs) = o { LhsExpr::AttributesParsed(attrs) } else { LhsExpr::NotYetParsed }
+    }
+}
+
+impl From<P<Expr>> for LhsExpr {
+    /// Converts the `expr: P<Expr>` into `LhsExpr::AlreadyParsed { expr, starts_statement: false }`.
+    ///
+    /// This conversion does not allocate.
+    fn from(expr: P<Expr>) -> Self {
+        LhsExpr::AlreadyParsed { expr, starts_statement: false }
+    }
+}
+
+#[derive(Debug)]
+enum DestructuredFloat {
+    /// 1e2
+    Single(Symbol, Span),
+    /// 1.
+    TrailingDot(Symbol, Span, Span),
+    /// 1.2 | 1.2e3
+    MiddleDot(Symbol, Span, Span, Symbol, Span),
+    /// Invalid
+    Error,
+}
+
+impl<'a> Parser<'a> {
+    /// Parses an expression.
+    #[inline]
+    pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
+        self.current_closure.take();
+
+        self.parse_expr_res(Restrictions::empty(), None)
+    }
+
+    /// Parses an expression, forcing tokens to be collected
+    pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
+        self.collect_tokens_no_attrs(|this| this.parse_expr())
+    }
+
+    pub fn parse_expr_anon_const(&mut self) -> PResult<'a, AnonConst> {
+        self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
+    }
+
+    fn parse_expr_catch_underscore(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+        match self.parse_expr_res(restrictions, None) {
+            Ok(expr) => Ok(expr),
+            Err(err) => match self.token.ident() {
+                Some((Ident { name: kw::Underscore, .. }, IdentIsRaw::No))
+                    if self.may_recover() && self.look_ahead(1, |t| t == &token::Comma) =>
+                {
+                    // Special-case handling of `foo(_, _, _)`
+                    let guar = err.emit();
+                    self.bump();
+                    Ok(self.mk_expr(self.prev_token.span, ExprKind::Err(guar)))
+                }
+                _ => Err(err),
+            },
+        }
+    }
+
+    /// Parses a sequence of expressions delimited by parentheses.
+    fn parse_expr_paren_seq(&mut self) -> PResult<'a, ThinVec<P<Expr>>> {
+        self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore(Restrictions::empty()))
+            .map(|(r, _)| r)
+    }
+
+    /// Parses an expression, subject to the given restrictions.
+    #[inline]
+    pub(super) fn parse_expr_res(
+        &mut self,
+        r: Restrictions,
+        already_parsed_attrs: Option<AttrWrapper>,
+    ) -> PResult<'a, P<Expr>> {
+        self.with_res(r, |this| this.parse_expr_assoc(already_parsed_attrs))
+    }
+
+    /// Parses an associative expression.
+    ///
+    /// This parses an expression accounting for associativity and precedence of the operators in
+    /// the expression.
+    #[inline]
+    fn parse_expr_assoc(
+        &mut self,
+        already_parsed_attrs: Option<AttrWrapper>,
+    ) -> PResult<'a, P<Expr>> {
+        self.parse_expr_assoc_with(0, already_parsed_attrs.into())
+    }
+
+    /// Parses an associative expression with operators of at least `min_prec` precedence.
+    pub(super) fn parse_expr_assoc_with(
+        &mut self,
+        min_prec: usize,
+        lhs: LhsExpr,
+    ) -> PResult<'a, P<Expr>> {
+        let mut starts_stmt = false;
+        let mut lhs = if let LhsExpr::AlreadyParsed { expr, starts_statement } = lhs {
+            starts_stmt = starts_statement;
+            expr
+        } else {
+            let attrs = match lhs {
+                LhsExpr::AttributesParsed(attrs) => Some(attrs),
+                _ => None,
+            };
+            if self.token.is_range_separator() {
+                return self.parse_expr_prefix_range(attrs);
+            } else {
+                self.parse_expr_prefix(attrs)?
+            }
+        };
+
+        if !self.should_continue_as_assoc_expr(&lhs) {
+            return Ok(lhs);
+        }
+
+        self.expected_tokens.push(TokenType::Operator);
+        while let Some(op) = self.check_assoc_op() {
+            let lhs_span = self.interpolated_or_expr_span(&lhs);
+            let cur_op_span = self.token.span;
+            let restrictions = if op.node.is_assign_like() {
+                self.restrictions & Restrictions::NO_STRUCT_LITERAL
+            } else {
+                self.restrictions
+            };
+            let prec = op.node.precedence();
+            if prec < min_prec {
+                break;
+            }
+            // Check for deprecated `...` syntax
+            if self.token == token::DotDotDot && op.node == AssocOp::DotDotEq {
+                self.err_dotdotdot_syntax(self.token.span);
+            }
+
+            if self.token == token::LArrow {
+                self.err_larrow_operator(self.token.span);
+            }
+
+            self.bump();
+            if op.node.is_comparison() {
+                if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
+                    return Ok(expr);
+                }
+            }
+
+            // Look for JS' `===` and `!==` and recover
+            if (op.node == AssocOp::Equal || op.node == AssocOp::NotEqual)
+                && self.token.kind == token::Eq
+                && self.prev_token.span.hi() == self.token.span.lo()
+            {
+                let sp = op.span.to(self.token.span);
+                let sugg = match op.node {
+                    AssocOp::Equal => "==",
+                    AssocOp::NotEqual => "!=",
+                    _ => unreachable!(),
+                }
+                .into();
+                let invalid = format!("{sugg}=");
+                self.dcx().emit_err(errors::InvalidComparisonOperator {
+                    span: sp,
+                    invalid: invalid.clone(),
+                    sub: errors::InvalidComparisonOperatorSub::Correctable {
+                        span: sp,
+                        invalid,
+                        correct: sugg,
+                    },
+                });
+                self.bump();
+            }
+
+            // Look for PHP's `<>` and recover
+            if op.node == AssocOp::Less
+                && self.token.kind == token::Gt
+                && self.prev_token.span.hi() == self.token.span.lo()
+            {
+                let sp = op.span.to(self.token.span);
+                self.dcx().emit_err(errors::InvalidComparisonOperator {
+                    span: sp,
+                    invalid: "<>".into(),
+                    sub: errors::InvalidComparisonOperatorSub::Correctable {
+                        span: sp,
+                        invalid: "<>".into(),
+                        correct: "!=".into(),
+                    },
+                });
+                self.bump();
+            }
+
+            // Look for C++'s `<=>` and recover
+            if op.node == AssocOp::LessEqual
+                && self.token.kind == token::Gt
+                && self.prev_token.span.hi() == self.token.span.lo()
+            {
+                let sp = op.span.to(self.token.span);
+                self.dcx().emit_err(errors::InvalidComparisonOperator {
+                    span: sp,
+                    invalid: "<=>".into(),
+                    sub: errors::InvalidComparisonOperatorSub::Spaceship(sp),
+                });
+                self.bump();
+            }
+
+            if self.prev_token == token::BinOp(token::Plus)
+                && self.token == token::BinOp(token::Plus)
+                && self.prev_token.span.between(self.token.span).is_empty()
+            {
+                let op_span = self.prev_token.span.to(self.token.span);
+                // Eat the second `+`
+                self.bump();
+                lhs = self.recover_from_postfix_increment(lhs, op_span, starts_stmt)?;
+                continue;
+            }
+
+            if self.prev_token == token::BinOp(token::Minus)
+                && self.token == token::BinOp(token::Minus)
+                && self.prev_token.span.between(self.token.span).is_empty()
+                && !self.look_ahead(1, |tok| tok.can_begin_expr())
+            {
+                let op_span = self.prev_token.span.to(self.token.span);
+                // Eat the second `-`
+                self.bump();
+                lhs = self.recover_from_postfix_decrement(lhs, op_span, starts_stmt)?;
+                continue;
+            }
+
+            let op = op.node;
+            // Special cases:
+            if op == AssocOp::As {
+                lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
+                continue;
+            } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
+                // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
+                // generalise it to the Fixity::None code.
+                lhs = self.parse_expr_range(prec, lhs, op, cur_op_span)?;
+                break;
+            }
+
+            let fixity = op.fixity();
+            let prec_adjustment = match fixity {
+                Fixity::Right => 0,
+                Fixity::Left => 1,
+                // We currently have no non-associative operators that are not handled above by
+                // the special cases. The code is here only for future convenience.
+                Fixity::None => 1,
+            };
+            let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
+                this.parse_expr_assoc_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
+            })?;
+
+            self.error_ambiguous_outer_attrs(&lhs, lhs_span, rhs.span);
+            let span = lhs_span.to(rhs.span);
+
+            lhs = match op {
+                AssocOp::Add
+                | AssocOp::Subtract
+                | AssocOp::Multiply
+                | AssocOp::Divide
+                | AssocOp::Modulus
+                | AssocOp::LAnd
+                | AssocOp::LOr
+                | AssocOp::BitXor
+                | AssocOp::BitAnd
+                | AssocOp::BitOr
+                | AssocOp::ShiftLeft
+                | AssocOp::ShiftRight
+                | AssocOp::Equal
+                | AssocOp::Less
+                | AssocOp::LessEqual
+                | AssocOp::NotEqual
+                | AssocOp::Greater
+                | AssocOp::GreaterEqual => {
+                    let ast_op = op.to_ast_binop().unwrap();
+                    let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
+                    self.mk_expr(span, binary)
+                }
+                AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs, cur_op_span)),
+                AssocOp::AssignOp(k) => {
+                    let aop = match k {
+                        token::Plus => BinOpKind::Add,
+                        token::Minus => BinOpKind::Sub,
+                        token::Star => BinOpKind::Mul,
+                        token::Slash => BinOpKind::Div,
+                        token::Percent => BinOpKind::Rem,
+                        token::Caret => BinOpKind::BitXor,
+                        token::And => BinOpKind::BitAnd,
+                        token::Or => BinOpKind::BitOr,
+                        token::Shl => BinOpKind::Shl,
+                        token::Shr => BinOpKind::Shr,
+                    };
+                    let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
+                    self.mk_expr(span, aopexpr)
+                }
+                AssocOp::As | AssocOp::DotDot | AssocOp::DotDotEq => {
+                    self.dcx().span_bug(span, "AssocOp should have been handled by special case")
+                }
+            };
+
+            if let Fixity::None = fixity {
+                break;
+            }
+        }
+
+        Ok(lhs)
+    }
+
+    fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
+        match (self.expr_is_complete(lhs), AssocOp::from_token(&self.token)) {
+            // Semi-statement forms are odd:
+            // See https://github.com/rust-lang/rust/issues/29071
+            (true, None) => false,
+            (false, _) => true, // Continue parsing the expression.
+            // An exhaustive check is done in the following block, but these are checked first
+            // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
+            // want to keep their span info to improve diagnostics in these cases in a later stage.
+            (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
+            (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
+            (true, Some(AssocOp::Add)) | // `{ 42 } + 42` (unary plus)
+            (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
+            (true, Some(AssocOp::LOr)) | // `{ 42 } || 42` ("logical or" or closure)
+            (true, Some(AssocOp::BitOr)) // `{ 42 } | 42` or `{ 42 } |x| 42`
+            => {
+                // These cases are ambiguous and can't be identified in the parser alone.
+                //
+                // Bitwise AND is left out because guessing intent is hard. We can make
+                // suggestions based on the assumption that double-refs are rarely intentional,
+                // and closures are distinct enough that they don't get mixed up with their
+                // return value.
+                let sp = self.psess.source_map().start_point(self.token.span);
+                self.psess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
+                false
+            }
+            (true, Some(op)) if !op.can_continue_expr_unambiguously() => false,
+            (true, Some(_)) => {
+                self.error_found_expr_would_be_stmt(lhs);
+                true
+            }
+        }
+    }
+
+    /// We've found an expression that would be parsed as a statement,
+    /// but the next token implies this should be parsed as an expression.
+    /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
+    fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
+        self.dcx().emit_err(errors::FoundExprWouldBeStmt {
+            span: self.token.span,
+            token: self.token.clone(),
+            suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
+        });
+    }
+
+    fn error_ambiguous_outer_attrs(&self, lhs: &P<Expr>, lhs_span: Span, rhs_span: Span) {
+        if let Some(attr) = lhs.attrs.iter().find(|a| a.style == AttrStyle::Outer) {
+            self.dcx().emit_err(errors::AmbiguousOuterAttributes {
+                span: attr.span.to(rhs_span),
+                sugg: errors::WrapInParentheses::Expression {
+                    left: attr.span.shrink_to_lo(),
+                    right: lhs_span.shrink_to_hi(),
+                },
+            });
+        }
+    }
+
+    /// Possibly translate the current token to an associative operator.
+    /// The method does not advance the current token.
+    ///
+    /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
+    pub fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
+        let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
+            // When parsing const expressions, stop parsing when encountering `>`.
+            (
+                Some(
+                    AssocOp::ShiftRight
+                    | AssocOp::Greater
+                    | AssocOp::GreaterEqual
+                    | AssocOp::AssignOp(token::BinOpToken::Shr),
+                ),
+                _,
+            ) if self.restrictions.contains(Restrictions::CONST_EXPR) => {
+                return None;
+            }
+            // When recovering patterns as expressions, stop parsing when encountering an assignment `=`, an alternative `|`, or a range `..`.
+            (
+                Some(
+                    AssocOp::Assign
+                    | AssocOp::AssignOp(_)
+                    | AssocOp::BitOr
+                    | AssocOp::DotDot
+                    | AssocOp::DotDotEq,
+                ),
+                _,
+            ) if self.restrictions.contains(Restrictions::IS_PAT) => {
+                return None;
+            }
+            (Some(op), _) => (op, self.token.span),
+            (None, Some((Ident { name: sym::and, span }, IdentIsRaw::No)))
+                if self.may_recover() =>
+            {
+                self.dcx().emit_err(errors::InvalidLogicalOperator {
+                    span: self.token.span,
+                    incorrect: "and".into(),
+                    sub: errors::InvalidLogicalOperatorSub::Conjunction(self.token.span),
+                });
+                (AssocOp::LAnd, span)
+            }
+            (None, Some((Ident { name: sym::or, span }, IdentIsRaw::No))) if self.may_recover() => {
+                self.dcx().emit_err(errors::InvalidLogicalOperator {
+                    span: self.token.span,
+                    incorrect: "or".into(),
+                    sub: errors::InvalidLogicalOperatorSub::Disjunction(self.token.span),
+                });
+                (AssocOp::LOr, span)
+            }
+            _ => return None,
+        };
+        Some(source_map::respan(span, op))
+    }
+
+    /// Checks if this expression is a successfully parsed statement.
+    fn expr_is_complete(&self, e: &Expr) -> bool {
+        self.restrictions.contains(Restrictions::STMT_EXPR) && classify::expr_is_complete(e)
+    }
+
+    /// Parses `x..y`, `x..=y`, and `x..`/`x..=`.
+    /// The other two variants are handled in `parse_prefix_range_expr` below.
+    fn parse_expr_range(
+        &mut self,
+        prec: usize,
+        lhs: P<Expr>,
+        op: AssocOp,
+        cur_op_span: Span,
+    ) -> PResult<'a, P<Expr>> {
+        let rhs = if self.is_at_start_of_range_notation_rhs() {
+            let maybe_lt = self.token.clone();
+            Some(
+                self.parse_expr_assoc_with(prec + 1, LhsExpr::NotYetParsed)
+                    .map_err(|err| self.maybe_err_dotdotlt_syntax(maybe_lt, err))?,
+            )
+        } else {
+            None
+        };
+        let rhs_span = rhs.as_ref().map_or(cur_op_span, |x| x.span);
+        self.error_ambiguous_outer_attrs(&lhs, lhs.span, rhs_span);
+        let span = lhs.span.to(rhs_span);
+        let limits =
+            if op == AssocOp::DotDot { RangeLimits::HalfOpen } else { RangeLimits::Closed };
+        let range = self.mk_range(Some(lhs), rhs, limits);
+        Ok(self.mk_expr(span, range))
+    }
+
+    fn is_at_start_of_range_notation_rhs(&self) -> bool {
+        if self.token.can_begin_expr() {
+            // Parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
+            if self.token == token::OpenDelim(Delimiter::Brace) {
+                return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
+            }
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
+    fn parse_expr_prefix_range(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
+        // Check for deprecated `...` syntax.
+        if self.token == token::DotDotDot {
+            self.err_dotdotdot_syntax(self.token.span);
+        }
+
+        debug_assert!(
+            self.token.is_range_separator(),
+            "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
+            self.token
+        );
+
+        let limits = match self.token.kind {
+            token::DotDot => RangeLimits::HalfOpen,
+            _ => RangeLimits::Closed,
+        };
+        let op = AssocOp::from_token(&self.token);
+        // FIXME: `parse_prefix_range_expr` is called when the current
+        // token is `DotDot`, `DotDotDot`, or `DotDotEq`. If we haven't already
+        // parsed attributes, then trying to parse them here will always fail.
+        // We should figure out how we want attributes on range expressions to work.
+        let attrs = self.parse_or_use_outer_attributes(attrs)?;
+        self.collect_tokens_for_expr(attrs, |this, attrs| {
+            let lo = this.token.span;
+            let maybe_lt = this.look_ahead(1, |t| t.clone());
+            this.bump();
+            let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
+                // RHS must be parsed with more associativity than the dots.
+                this.parse_expr_assoc_with(op.unwrap().precedence() + 1, LhsExpr::NotYetParsed)
+                    .map(|x| (lo.to(x.span), Some(x)))
+                    .map_err(|err| this.maybe_err_dotdotlt_syntax(maybe_lt, err))?
+            } else {
+                (lo, None)
+            };
+            let range = this.mk_range(None, opt_end, limits);
+            Ok(this.mk_expr_with_attrs(span, range, attrs))
+        })
+    }
+
+    /// Parses a prefix-unary-operator expr.
+    fn parse_expr_prefix(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
+        let attrs = self.parse_or_use_outer_attributes(attrs)?;
+        let lo = self.token.span;
+
+        macro_rules! make_it {
+            ($this:ident, $attrs:expr, |this, _| $body:expr) => {
+                $this.collect_tokens_for_expr($attrs, |$this, attrs| {
+                    let (hi, ex) = $body?;
+                    Ok($this.mk_expr_with_attrs(lo.to(hi), ex, attrs))
+                })
+            };
+        }
+
+        let this = self;
+
+        // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
+        match this.token.uninterpolate().kind {
+            // `!expr`
+            token::Not => make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Not)),
+            // `~expr`
+            token::Tilde => make_it!(this, attrs, |this, _| this.recover_tilde_expr(lo)),
+            // `-expr`
+            token::BinOp(token::Minus) => {
+                make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Neg))
+            }
+            // `*expr`
+            token::BinOp(token::Star) => {
+                make_it!(this, attrs, |this, _| this.parse_expr_unary(lo, UnOp::Deref))
+            }
+            // `&expr` and `&&expr`
+            token::BinOp(token::And) | token::AndAnd => {
+                make_it!(this, attrs, |this, _| this.parse_expr_borrow(lo))
+            }
+            // `+lit`
+            token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
+                let mut err = errors::LeadingPlusNotSupported {
+                    span: lo,
+                    remove_plus: None,
+                    add_parentheses: None,
+                };
+
+                // a block on the LHS might have been intended to be an expression instead
+                if let Some(sp) = this.psess.ambiguous_block_expr_parse.borrow().get(&lo) {
+                    err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
+                } else {
+                    err.remove_plus = Some(lo);
+                }
+                this.dcx().emit_err(err);
+
+                this.bump();
+                this.parse_expr_prefix(None)
+            }
+            // Recover from `++x`:
+            token::BinOp(token::Plus)
+                if this.look_ahead(1, |t| *t == token::BinOp(token::Plus)) =>
+            {
+                let starts_stmt = this.prev_token == token::Semi
+                    || this.prev_token == token::CloseDelim(Delimiter::Brace);
+                let pre_span = this.token.span.to(this.look_ahead(1, |t| t.span));
+                // Eat both `+`s.
+                this.bump();
+                this.bump();
+
+                let operand_expr = this.parse_expr_dot_or_call(Default::default())?;
+                this.recover_from_prefix_increment(operand_expr, pre_span, starts_stmt)
+            }
+            token::Ident(..) if this.token.is_keyword(kw::Box) => {
+                make_it!(this, attrs, |this, _| this.parse_expr_box(lo))
+            }
+            token::Ident(..) if this.may_recover() && this.is_mistaken_not_ident_negation() => {
+                make_it!(this, attrs, |this, _| this.recover_not_expr(lo))
+            }
+            _ => return this.parse_expr_dot_or_call(Some(attrs)),
+        }
+    }
+
+    fn parse_expr_prefix_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
+        self.bump();
+        let expr = self.parse_expr_prefix(None)?;
+        let span = self.interpolated_or_expr_span(&expr);
+        Ok((lo.to(span), expr))
+    }
+
+    fn parse_expr_unary(&mut self, lo: Span, op: UnOp) -> PResult<'a, (Span, ExprKind)> {
+        let (span, expr) = self.parse_expr_prefix_common(lo)?;
+        Ok((span, self.mk_unary(op, expr)))
+    }
+
+    /// Recover on `~expr` in favor of `!expr`.
+    fn recover_tilde_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
+        self.dcx().emit_err(errors::TildeAsUnaryOperator(lo));
+
+        self.parse_expr_unary(lo, UnOp::Not)
+    }
+
+    /// Parse `box expr` - this syntax has been removed, but we still parse this
+    /// for now to provide a more useful error
+    fn parse_expr_box(&mut self, box_kw: Span) -> PResult<'a, (Span, ExprKind)> {
+        let (span, _) = self.parse_expr_prefix_common(box_kw)?;
+        let inner_span = span.with_lo(box_kw.hi());
+        let code = self.psess.source_map().span_to_snippet(inner_span).unwrap();
+        let guar = self.dcx().emit_err(errors::BoxSyntaxRemoved { span: span, code: code.trim() });
+        Ok((span, ExprKind::Err(guar)))
+    }
+
+    fn is_mistaken_not_ident_negation(&self) -> bool {
+        let token_cannot_continue_expr = |t: &Token| match t.uninterpolate().kind {
+            // These tokens can start an expression after `!`, but
+            // can't continue an expression after an ident
+            token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
+            token::Literal(..) | token::Pound => true,
+            _ => t.is_whole_expr(),
+        };
+        self.token.is_ident_named(sym::not) && self.look_ahead(1, token_cannot_continue_expr)
+    }
+
+    /// Recover on `not expr` in favor of `!expr`.
+    fn recover_not_expr(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
+        let negated_token = self.look_ahead(1, |t| t.clone());
+
+        let sub_diag = if negated_token.is_numeric_lit() {
+            errors::NotAsNegationOperatorSub::SuggestNotBitwise
+        } else if negated_token.is_bool_lit() {
+            errors::NotAsNegationOperatorSub::SuggestNotLogical
+        } else {
+            errors::NotAsNegationOperatorSub::SuggestNotDefault
+        };
+
+        self.dcx().emit_err(errors::NotAsNegationOperator {
+            negated: negated_token.span,
+            negated_desc: super::token_descr(&negated_token),
+            // Span the `not` plus trailing whitespace to avoid
+            // trailing whitespace after the `!` in our suggestion
+            sub: sub_diag(
+                self.psess.source_map().span_until_non_whitespace(lo.to(negated_token.span)),
+            ),
+        });
+
+        self.parse_expr_unary(lo, UnOp::Not)
+    }
+
+    /// Returns the span of expr if it was not interpolated, or the span of the interpolated token.
+    fn interpolated_or_expr_span(&self, expr: &Expr) -> Span {
+        match self.prev_token.kind {
+            TokenKind::NtIdent(..) | TokenKind::NtLifetime(..) | TokenKind::Interpolated(..) => {
+                self.prev_token.span
+            }
+            _ => expr.span,
+        }
+    }
+
+    fn parse_assoc_op_cast(
+        &mut self,
+        lhs: P<Expr>,
+        lhs_span: Span,
+        expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
+    ) -> PResult<'a, P<Expr>> {
+        let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
+            this.error_ambiguous_outer_attrs(&lhs, lhs_span, rhs.span);
+            this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs))
+        };
+
+        // Save the state of the parser before parsing type normally, in case there is a
+        // LessThan comparison after this cast.
+        let parser_snapshot_before_type = self.clone();
+        let cast_expr = match self.parse_as_cast_ty() {
+            Ok(rhs) => mk_expr(self, lhs, rhs),
+            Err(type_err) => {
+                if !self.may_recover() {
+                    return Err(type_err);
+                }
+
+                // Rewind to before attempting to parse the type with generics, to recover
+                // from situations like `x as usize < y` in which we first tried to parse
+                // `usize < y` as a type with generic arguments.
+                let parser_snapshot_after_type = mem::replace(self, parser_snapshot_before_type);
+
+                // Check for typo of `'a: loop { break 'a }` with a missing `'`.
+                match (&lhs.kind, &self.token.kind) {
+                    (
+                        // `foo: `
+                        ExprKind::Path(None, ast::Path { segments, .. }),
+                        token::Ident(kw::For | kw::Loop | kw::While, IdentIsRaw::No),
+                    ) if segments.len() == 1 => {
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        let label = Label {
+                            ident: Ident::from_str_and_span(
+                                &format!("'{}", segments[0].ident),
+                                segments[0].ident.span,
+                            ),
+                        };
+                        match self.parse_expr_labeled(label, false) {
+                            Ok(expr) => {
+                                type_err.cancel();
+                                self.dcx().emit_err(errors::MalformedLoopLabel {
+                                    span: label.ident.span,
+                                    correct_label: label.ident,
+                                });
+                                return Ok(expr);
+                            }
+                            Err(err) => {
+                                err.cancel();
+                                self.restore_snapshot(snapshot);
+                            }
+                        }
+                    }
+                    _ => {}
+                }
+
+                match self.parse_path(PathStyle::Expr) {
+                    Ok(path) => {
+                        let span_after_type = parser_snapshot_after_type.token.span;
+                        let expr = mk_expr(
+                            self,
+                            lhs,
+                            self.mk_ty(path.span, TyKind::Path(None, path.clone())),
+                        );
+
+                        let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
+                        let suggestion = errors::ComparisonOrShiftInterpretedAsGenericSugg {
+                            left: expr.span.shrink_to_lo(),
+                            right: expr.span.shrink_to_hi(),
+                        };
+
+                        match self.token.kind {
+                            token::Lt => {
+                                self.dcx().emit_err(errors::ComparisonInterpretedAsGeneric {
+                                    comparison: self.token.span,
+                                    r#type: path,
+                                    args: args_span,
+                                    suggestion,
+                                })
+                            }
+                            token::BinOp(token::Shl) => {
+                                self.dcx().emit_err(errors::ShiftInterpretedAsGeneric {
+                                    shift: self.token.span,
+                                    r#type: path,
+                                    args: args_span,
+                                    suggestion,
+                                })
+                            }
+                            _ => {
+                                // We can end up here even without `<` being the next token, for
+                                // example because `parse_ty_no_plus` returns `Err` on keywords,
+                                // but `parse_path` returns `Ok` on them due to error recovery.
+                                // Return original error and parser state.
+                                *self = parser_snapshot_after_type;
+                                return Err(type_err);
+                            }
+                        };
+
+                        // Successfully parsed the type path leaving a `<` yet to parse.
+                        type_err.cancel();
+
+                        // Keep `x as usize` as an expression in AST and continue parsing.
+                        expr
+                    }
+                    Err(path_err) => {
+                        // Couldn't parse as a path, return original error and parser state.
+                        path_err.cancel();
+                        *self = parser_snapshot_after_type;
+                        return Err(type_err);
+                    }
+                }
+            }
+        };
+
+        self.parse_and_disallow_postfix_after_cast(cast_expr)
+    }
+
+    /// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
+    /// then emits an error and returns the newly parsed tree.
+    /// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
+    fn parse_and_disallow_postfix_after_cast(
+        &mut self,
+        cast_expr: P<Expr>,
+    ) -> PResult<'a, P<Expr>> {
+        if let ExprKind::Type(_, _) = cast_expr.kind {
+            panic!("ExprKind::Type must not be parsed");
+        }
+
+        let span = cast_expr.span;
+
+        let with_postfix = self.parse_expr_dot_or_call_with_(cast_expr, span)?;
+
+        // Check if an illegal postfix operator has been added after the cast.
+        // If the resulting expression is not a cast, it is an illegal postfix operator.
+        if !matches!(with_postfix.kind, ExprKind::Cast(_, _)) {
+            let msg = format!(
+                "cast cannot be followed by {}",
+                match with_postfix.kind {
+                    ExprKind::Index(..) => "indexing",
+                    ExprKind::Try(_) => "`?`",
+                    ExprKind::Field(_, _) => "a field access",
+                    ExprKind::MethodCall(_) => "a method call",
+                    ExprKind::Call(_, _) => "a function call",
+                    ExprKind::Await(_, _) => "`.await`",
+                    ExprKind::Match(_, _, MatchKind::Postfix) => "a postfix match",
+                    ExprKind::Err(_) => return Ok(with_postfix),
+                    _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
+                }
+            );
+            let mut err = self.dcx().struct_span_err(span, msg);
+
+            let suggest_parens = |err: &mut Diag<'_>| {
+                let suggestions = vec![
+                    (span.shrink_to_lo(), "(".to_string()),
+                    (span.shrink_to_hi(), ")".to_string()),
+                ];
+                err.multipart_suggestion(
+                    "try surrounding the expression in parentheses",
+                    suggestions,
+                    Applicability::MachineApplicable,
+                );
+            };
+
+            suggest_parens(&mut err);
+
+            err.emit();
+        };
+        Ok(with_postfix)
+    }
+
+    /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
+    fn parse_expr_borrow(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
+        self.expect_and()?;
+        let has_lifetime = self.token.is_lifetime() && self.look_ahead(1, |t| t != &token::Colon);
+        let lifetime = has_lifetime.then(|| self.expect_lifetime()); // For recovery, see below.
+        let (borrow_kind, mutbl) = self.parse_borrow_modifiers(lo);
+        let expr = if self.token.is_range_separator() {
+            self.parse_expr_prefix_range(None)
+        } else {
+            self.parse_expr_prefix(None)
+        }?;
+        let hi = self.interpolated_or_expr_span(&expr);
+        let span = lo.to(hi);
+        if let Some(lt) = lifetime {
+            self.error_remove_borrow_lifetime(span, lt.ident.span);
+        }
+        Ok((span, ExprKind::AddrOf(borrow_kind, mutbl, expr)))
+    }
+
+    fn error_remove_borrow_lifetime(&self, span: Span, lt_span: Span) {
+        self.dcx().emit_err(errors::LifetimeInBorrowExpression { span, lifetime_span: lt_span });
+    }
+
+    /// Parse `mut?` or `raw [ const | mut ]`.
+    fn parse_borrow_modifiers(&mut self, lo: Span) -> (ast::BorrowKind, ast::Mutability) {
+        if self.check_keyword(kw::Raw) && self.look_ahead(1, Token::is_mutability) {
+            // `raw [ const | mut ]`.
+            let found_raw = self.eat_keyword(kw::Raw);
+            assert!(found_raw);
+            let mutability = self.parse_const_or_mut().unwrap();
+            self.psess.gated_spans.gate(sym::raw_ref_op, lo.to(self.prev_token.span));
+            (ast::BorrowKind::Raw, mutability)
+        } else {
+            // `mut?`
+            (ast::BorrowKind::Ref, self.parse_mutability())
+        }
+    }
+
+    /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
+    fn parse_expr_dot_or_call(&mut self, attrs: Option<AttrWrapper>) -> PResult<'a, P<Expr>> {
+        let attrs = self.parse_or_use_outer_attributes(attrs)?;
+        self.collect_tokens_for_expr(attrs, |this, attrs| {
+            let base = this.parse_expr_bottom()?;
+            let span = this.interpolated_or_expr_span(&base);
+            this.parse_expr_dot_or_call_with(base, span, attrs)
+        })
+    }
+
+    pub(super) fn parse_expr_dot_or_call_with(
+        &mut self,
+        e0: P<Expr>,
+        lo: Span,
+        mut attrs: ast::AttrVec,
+    ) -> PResult<'a, P<Expr>> {
+        // Stitch the list of outer attributes onto the return value.
+        // A little bit ugly, but the best way given the current code
+        // structure
+        let res = ensure_sufficient_stack(
+            // this expr demonstrates the recursion it guards against
+            || self.parse_expr_dot_or_call_with_(e0, lo),
+        );
+        if attrs.is_empty() {
+            res
+        } else {
+            res.map(|expr| {
+                expr.map(|mut expr| {
+                    attrs.extend(expr.attrs);
+                    expr.attrs = attrs;
+                    expr
+                })
+            })
+        }
+    }
+
+    fn parse_expr_dot_or_call_with_(&mut self, mut e: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+        loop {
+            let has_question =
+                if self.prev_token.kind == TokenKind::Ident(kw::Return, IdentIsRaw::No) {
+                    // we are using noexpect here because we don't expect a `?` directly after a `return`
+                    // which could be suggested otherwise
+                    self.eat_noexpect(&token::Question)
+                } else {
+                    self.eat(&token::Question)
+                };
+            if has_question {
+                // `expr?`
+                e = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Try(e));
+                continue;
+            }
+            let has_dot = if self.prev_token.kind == TokenKind::Ident(kw::Return, IdentIsRaw::No) {
+                // we are using noexpect here because we don't expect a `.` directly after a `return`
+                // which could be suggested otherwise
+                self.eat_noexpect(&token::Dot)
+            } else if self.token.kind == TokenKind::RArrow && self.may_recover() {
+                // Recovery for `expr->suffix`.
+                self.bump();
+                let span = self.prev_token.span;
+                self.dcx().emit_err(errors::ExprRArrowCall { span });
+                true
+            } else {
+                self.eat(&token::Dot)
+            };
+            if has_dot {
+                // expr.f
+                e = self.parse_dot_suffix_expr(lo, e)?;
+                continue;
+            }
+            if self.expr_is_complete(&e) {
+                return Ok(e);
+            }
+            e = match self.token.kind {
+                token::OpenDelim(Delimiter::Parenthesis) => self.parse_expr_fn_call(lo, e),
+                token::OpenDelim(Delimiter::Bracket) => self.parse_expr_index(lo, e)?,
+                _ => return Ok(e),
+            }
+        }
+    }
+
+    pub fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
+        // At this point we've consumed something like `expr.` and `self.token` holds the token
+        // after the dot.
+        match self.token.uninterpolate().kind {
+            token::Ident(..) => self.parse_dot_suffix(base, lo),
+            token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
+                let ident_span = self.token.span;
+                self.bump();
+                Ok(self.mk_expr_tuple_field_access(lo, ident_span, base, symbol, suffix))
+            }
+            token::Literal(token::Lit { kind: token::Float, symbol, suffix }) => {
+                Ok(match self.break_up_float(symbol, self.token.span) {
+                    // 1e2
+                    DestructuredFloat::Single(sym, _sp) => {
+                        // `foo.1e2`: a single complete dot access, fully consumed. We end up with
+                        // the `1e2` token in `self.prev_token` and the following token in
+                        // `self.token`.
+                        let ident_span = self.token.span;
+                        self.bump();
+                        self.mk_expr_tuple_field_access(lo, ident_span, base, sym, suffix)
+                    }
+                    // 1.
+                    DestructuredFloat::TrailingDot(sym, ident_span, dot_span) => {
+                        // `foo.1.`: a single complete dot access and the start of another.
+                        // We end up with the `sym` (`1`) token in `self.prev_token` and a dot in
+                        // `self.token`.
+                        assert!(suffix.is_none());
+                        self.token = Token::new(token::Ident(sym, IdentIsRaw::No), ident_span);
+                        self.bump_with((Token::new(token::Dot, dot_span), self.token_spacing));
+                        self.mk_expr_tuple_field_access(lo, ident_span, base, sym, None)
+                    }
+                    // 1.2 | 1.2e3
+                    DestructuredFloat::MiddleDot(
+                        sym1,
+                        ident1_span,
+                        _dot_span,
+                        sym2,
+                        ident2_span,
+                    ) => {
+                        // `foo.1.2` (or `foo.1.2e3`): two complete dot accesses. We end up with
+                        // the `sym2` (`2` or `2e3`) token in `self.prev_token` and the following
+                        // token in `self.token`.
+                        let next_token2 =
+                            Token::new(token::Ident(sym2, IdentIsRaw::No), ident2_span);
+                        self.bump_with((next_token2, self.token_spacing));
+                        self.bump();
+                        let base1 =
+                            self.mk_expr_tuple_field_access(lo, ident1_span, base, sym1, None);
+                        self.mk_expr_tuple_field_access(lo, ident2_span, base1, sym2, suffix)
+                    }
+                    DestructuredFloat::Error => base,
+                })
+            }
+            _ => {
+                self.error_unexpected_after_dot();
+                Ok(base)
+            }
+        }
+    }
+
+    fn error_unexpected_after_dot(&self) {
+        let actual = pprust::token_to_string(&self.token);
+        let span = self.token.span;
+        let sm = self.psess.source_map();
+        let (span, actual) = match (&self.token.kind, self.subparser_name) {
+            (token::Eof, Some(_)) if let Ok(actual) = sm.span_to_snippet(sm.next_point(span)) => {
+                (span.shrink_to_hi(), actual.into())
+            }
+            _ => (span, actual),
+        };
+        self.dcx().emit_err(errors::UnexpectedTokenAfterDot { span, actual });
+    }
+
+    // We need an identifier or integer, but the next token is a float.
+    // Break the float into components to extract the identifier or integer.
+    // FIXME: With current `TokenCursor` it's hard to break tokens into more than 2
+    // parts unless those parts are processed immediately. `TokenCursor` should either
+    // support pushing "future tokens" (would be also helpful to `break_and_eat`), or
+    // we should break everything including floats into more basic proc-macro style
+    // tokens in the lexer (probably preferable).
+    // See also `TokenKind::break_two_token_op` which does similar splitting of `>>` into `>`.
+    fn break_up_float(&self, float: Symbol, span: Span) -> DestructuredFloat {
+        #[derive(Debug)]
+        enum FloatComponent {
+            IdentLike(String),
+            Punct(char),
+        }
+        use FloatComponent::*;
+
+        let float_str = float.as_str();
+        let mut components = Vec::new();
+        let mut ident_like = String::new();
+        for c in float_str.chars() {
+            if c == '_' || c.is_ascii_alphanumeric() {
+                ident_like.push(c);
+            } else if matches!(c, '.' | '+' | '-') {
+                if !ident_like.is_empty() {
+                    components.push(IdentLike(mem::take(&mut ident_like)));
+                }
+                components.push(Punct(c));
+            } else {
+                panic!("unexpected character in a float token: {c:?}")
+            }
+        }
+        if !ident_like.is_empty() {
+            components.push(IdentLike(ident_like));
+        }
+
+        // With proc macros the span can refer to anything, the source may be too short,
+        // or too long, or non-ASCII. It only makes sense to break our span into components
+        // if its underlying text is identical to our float literal.
+        let can_take_span_apart =
+            || self.span_to_snippet(span).as_deref() == Ok(float_str).as_deref();
+
+        match &*components {
+            // 1e2
+            [IdentLike(i)] => {
+                DestructuredFloat::Single(Symbol::intern(i), span)
+            }
+            // 1.
+            [IdentLike(i), Punct('.')] => {
+                let (ident_span, dot_span) = if can_take_span_apart() {
+                    let (span, ident_len) = (span.data(), BytePos::from_usize(i.len()));
+                    let ident_span = span.with_hi(span.lo + ident_len);
+                    let dot_span = span.with_lo(span.lo + ident_len);
+                    (ident_span, dot_span)
+                } else {
+                    (span, span)
+                };
+                let symbol = Symbol::intern(i);
+                DestructuredFloat::TrailingDot(symbol, ident_span, dot_span)
+            }
+            // 1.2 | 1.2e3
+            [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
+                let (ident1_span, dot_span, ident2_span) = if can_take_span_apart() {
+                    let (span, ident1_len) = (span.data(), BytePos::from_usize(i1.len()));
+                    let ident1_span = span.with_hi(span.lo + ident1_len);
+                    let dot_span = span
+                        .with_lo(span.lo + ident1_len)
+                        .with_hi(span.lo + ident1_len + BytePos(1));
+                    let ident2_span = self.token.span.with_lo(span.lo + ident1_len + BytePos(1));
+                    (ident1_span, dot_span, ident2_span)
+                } else {
+                    (span, span, span)
+                };
+                let symbol1 = Symbol::intern(i1);
+                let symbol2 = Symbol::intern(i2);
+                DestructuredFloat::MiddleDot(symbol1, ident1_span, dot_span, symbol2, ident2_span)
+            }
+            // 1e+ | 1e- (recovered)
+            [IdentLike(_), Punct('+' | '-')] |
+            // 1e+2 | 1e-2
+            [IdentLike(_), Punct('+' | '-'), IdentLike(_)] |
+            // 1.2e+ | 1.2e-
+            [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-')] |
+            // 1.2e+3 | 1.2e-3
+            [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
+                // See the FIXME about `TokenCursor` above.
+                self.error_unexpected_after_dot();
+                DestructuredFloat::Error
+            }
+            _ => panic!("unexpected components in a float token: {components:?}"),
+        }
+    }
+
+    /// Parse the field access used in offset_of, matched by `$(e:expr)+`.
+    /// Currently returns a list of idents. However, it should be possible in
+    /// future to also do array indices, which might be arbitrary expressions.
+    fn parse_floating_field_access(&mut self) -> PResult<'a, P<[Ident]>> {
+        let mut fields = Vec::new();
+        let mut trailing_dot = None;
+
+        loop {
+            // This is expected to use a metavariable $(args:expr)+, but the builtin syntax
+            // could be called directly. Calling `parse_expr` allows this function to only
+            // consider `Expr`s.
+            let expr = self.parse_expr()?;
+            let mut current = &expr;
+            let start_idx = fields.len();
+            loop {
+                match current.kind {
+                    ExprKind::Field(ref left, right) => {
+                        // Field access is read right-to-left.
+                        fields.insert(start_idx, right);
+                        trailing_dot = None;
+                        current = left;
+                    }
+                    // Parse this both to give helpful error messages and to
+                    // verify it can be done with this parser setup.
+                    ExprKind::Index(ref left, ref _right, span) => {
+                        self.dcx().emit_err(errors::ArrayIndexInOffsetOf(span));
+                        current = left;
+                    }
+                    ExprKind::Lit(token::Lit {
+                        kind: token::Float | token::Integer,
+                        symbol,
+                        suffix,
+                    }) => {
+                        if let Some(suffix) = suffix {
+                            self.expect_no_tuple_index_suffix(current.span, suffix);
+                        }
+                        match self.break_up_float(symbol, current.span) {
+                            // 1e2
+                            DestructuredFloat::Single(sym, sp) => {
+                                trailing_dot = None;
+                                fields.insert(start_idx, Ident::new(sym, sp));
+                            }
+                            // 1.
+                            DestructuredFloat::TrailingDot(sym, sym_span, dot_span) => {
+                                assert!(suffix.is_none());
+                                trailing_dot = Some(dot_span);
+                                fields.insert(start_idx, Ident::new(sym, sym_span));
+                            }
+                            // 1.2 | 1.2e3
+                            DestructuredFloat::MiddleDot(
+                                symbol1,
+                                span1,
+                                _dot_span,
+                                symbol2,
+                                span2,
+                            ) => {
+                                trailing_dot = None;
+                                fields.insert(start_idx, Ident::new(symbol2, span2));
+                                fields.insert(start_idx, Ident::new(symbol1, span1));
+                            }
+                            DestructuredFloat::Error => {
+                                trailing_dot = None;
+                                fields.insert(start_idx, Ident::new(symbol, self.prev_token.span));
+                            }
+                        }
+                        break;
+                    }
+                    ExprKind::Path(None, Path { ref segments, .. }) => {
+                        match &segments[..] {
+                            [PathSegment { ident, args: None, .. }] => {
+                                trailing_dot = None;
+                                fields.insert(start_idx, *ident)
+                            }
+                            _ => {
+                                self.dcx().emit_err(errors::InvalidOffsetOf(current.span));
+                                break;
+                            }
+                        }
+                        break;
+                    }
+                    _ => {
+                        self.dcx().emit_err(errors::InvalidOffsetOf(current.span));
+                        break;
+                    }
+                }
+            }
+
+            if matches!(self.token.kind, token::CloseDelim(..) | token::Comma) {
+                break;
+            } else if trailing_dot.is_none() {
+                // This loop should only repeat if there is a trailing dot.
+                self.dcx().emit_err(errors::InvalidOffsetOf(self.token.span));
+                break;
+            }
+        }
+        if let Some(dot) = trailing_dot {
+            self.dcx().emit_err(errors::InvalidOffsetOf(dot));
+        }
+        Ok(fields.into_iter().collect())
+    }
+
+    fn mk_expr_tuple_field_access(
+        &mut self,
+        lo: Span,
+        ident_span: Span,
+        base: P<Expr>,
+        field: Symbol,
+        suffix: Option<Symbol>,
+    ) -> P<Expr> {
+        if let Some(suffix) = suffix {
+            self.expect_no_tuple_index_suffix(ident_span, suffix);
+        }
+        self.mk_expr(lo.to(ident_span), ExprKind::Field(base, Ident::new(field, ident_span)))
+    }
+
+    /// Parse a function call expression, `expr(...)`.
+    fn parse_expr_fn_call(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
+        let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
+            Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
+        } else {
+            None
+        };
+        let open_paren = self.token.span;
+
+        let seq = self
+            .parse_expr_paren_seq()
+            .map(|args| self.mk_expr(lo.to(self.prev_token.span), self.mk_call(fun, args)));
+        match self.maybe_recover_struct_lit_bad_delims(lo, open_paren, seq, snapshot) {
+            Ok(expr) => expr,
+            Err(err) => self.recover_seq_parse_error(Delimiter::Parenthesis, lo, err),
+        }
+    }
+
+    /// If we encounter a parser state that looks like the user has written a `struct` literal with
+    /// parentheses instead of braces, recover the parser state and provide suggestions.
+    #[instrument(skip(self, seq, snapshot), level = "trace")]
+    fn maybe_recover_struct_lit_bad_delims(
+        &mut self,
+        lo: Span,
+        open_paren: Span,
+        seq: PResult<'a, P<Expr>>,
+        snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
+    ) -> PResult<'a, P<Expr>> {
+        match (self.may_recover(), seq, snapshot) {
+            (true, Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
+                snapshot.bump(); // `(`
+                match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
+                    Ok((fields, ..))
+                        if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
+                    {
+                        // We are certain we have `Enum::Foo(a: 3, b: 4)`, suggest
+                        // `Enum::Foo { a: 3, b: 4 }` or `Enum::Foo(3, 4)`.
+                        self.restore_snapshot(snapshot);
+                        let close_paren = self.prev_token.span;
+                        let span = lo.to(close_paren);
+                        // filter shorthand fields
+                        let fields: Vec<_> =
+                            fields.into_iter().filter(|field| !field.is_shorthand).collect();
+
+                        let guar = if !fields.is_empty() &&
+                            // `token.kind` should not be compared here.
+                            // This is because the `snapshot.token.kind` is treated as the same as
+                            // that of the open delim in `TokenTreesReader::parse_token_tree`, even
+                            // if they are different.
+                            self.span_to_snippet(close_paren).is_ok_and(|snippet| snippet == ")")
+                        {
+                            err.cancel();
+                            self.dcx()
+                                .create_err(errors::ParenthesesWithStructFields {
+                                    span,
+                                    r#type: path,
+                                    braces_for_struct: errors::BracesForStructLiteral {
+                                        first: open_paren,
+                                        second: close_paren,
+                                    },
+                                    no_fields_for_fn: errors::NoFieldsForFnCall {
+                                        fields: fields
+                                            .into_iter()
+                                            .map(|field| field.span.until(field.expr.span))
+                                            .collect(),
+                                    },
+                                })
+                                .emit()
+                        } else {
+                            err.emit()
+                        };
+                        Ok(self.mk_expr_err(span, guar))
+                    }
+                    Ok(_) => Err(err),
+                    Err(err2) => {
+                        err2.cancel();
+                        Err(err)
+                    }
+                }
+            }
+            (_, seq, _) => seq,
+        }
+    }
+
+    /// Parse an indexing expression `expr[...]`.
+    fn parse_expr_index(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
+        let prev_span = self.prev_token.span;
+        let open_delim_span = self.token.span;
+        self.bump(); // `[`
+        let index = self.parse_expr()?;
+        self.suggest_missing_semicolon_before_array(prev_span, open_delim_span)?;
+        self.expect(&token::CloseDelim(Delimiter::Bracket))?;
+        Ok(self.mk_expr(
+            lo.to(self.prev_token.span),
+            self.mk_index(base, index, open_delim_span.to(self.prev_token.span)),
+        ))
+    }
+
+    /// Assuming we have just parsed `.`, continue parsing into an expression.
+    fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+        if self.token.uninterpolated_span().at_least_rust_2018() && self.eat_keyword(kw::Await) {
+            return Ok(self.mk_await_expr(self_arg, lo));
+        }
+
+        // Post-fix match
+        if self.eat_keyword(kw::Match) {
+            let match_span = self.prev_token.span;
+            self.psess.gated_spans.gate(sym::postfix_match, match_span);
+            return self.parse_match_block(lo, match_span, self_arg, MatchKind::Postfix);
+        }
+
+        let fn_span_lo = self.token.span;
+        let mut seg = self.parse_path_segment(PathStyle::Expr, None)?;
+        self.check_trailing_angle_brackets(&seg, &[&token::OpenDelim(Delimiter::Parenthesis)]);
+        self.check_turbofish_missing_angle_brackets(&mut seg);
+
+        if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            // Method call `expr.f()`
+            let args = self.parse_expr_paren_seq()?;
+            let fn_span = fn_span_lo.to(self.prev_token.span);
+            let span = lo.to(self.prev_token.span);
+            Ok(self.mk_expr(
+                span,
+                ExprKind::MethodCall(Box::new(ast::MethodCall {
+                    seg,
+                    receiver: self_arg,
+                    args,
+                    span: fn_span,
+                })),
+            ))
+        } else {
+            // Field access `expr.f`
+            if let Some(args) = seg.args {
+                self.dcx().emit_err(errors::FieldExpressionWithGeneric(args.span()));
+            }
+
+            let span = lo.to(self.prev_token.span);
+            Ok(self.mk_expr(span, ExprKind::Field(self_arg, seg.ident)))
+        }
+    }
+
+    /// At the bottom (top?) of the precedence hierarchy,
+    /// Parses things like parenthesized exprs, macros, `return`, etc.
+    ///
+    /// N.B., this does not parse outer attributes, and is private because it only works
+    /// correctly if called from `parse_dot_or_call_expr()`.
+    fn parse_expr_bottom(&mut self) -> PResult<'a, P<Expr>> {
+        maybe_recover_from_interpolated_ty_qpath!(self, true);
+        maybe_whole_expr!(self);
+
+        // Outer attributes are already parsed and will be
+        // added to the return value after the fact.
+
+        let restrictions = self.restrictions;
+        self.with_res(restrictions - Restrictions::ALLOW_LET, |this| {
+            // Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
+            let lo = this.token.span;
+            if let token::Literal(_) = this.token.kind {
+                // This match arm is a special-case of the `_` match arm below and
+                // could be removed without changing functionality, but it's faster
+                // to have it here, especially for programs with large constants.
+                this.parse_expr_lit()
+            } else if this.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+                this.parse_expr_tuple_parens(restrictions)
+            } else if this.check(&token::OpenDelim(Delimiter::Brace)) {
+                this.parse_expr_block(None, lo, BlockCheckMode::Default)
+            } else if this.check(&token::BinOp(token::Or)) || this.check(&token::OrOr) {
+                this.parse_expr_closure().map_err(|mut err| {
+                    // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
+                    // then suggest parens around the lhs.
+                    if let Some(sp) = this.psess.ambiguous_block_expr_parse.borrow().get(&lo) {
+                        err.subdiagnostic(this.dcx(), ExprParenthesesNeeded::surrounding(*sp));
+                    }
+                    err
+                })
+            } else if this.check(&token::OpenDelim(Delimiter::Bracket)) {
+                this.parse_expr_array_or_repeat(Delimiter::Bracket)
+            } else if this.is_builtin() {
+                this.parse_expr_builtin()
+            } else if this.check_path() {
+                this.parse_expr_path_start()
+            } else if this.check_keyword(kw::Move)
+                || this.check_keyword(kw::Static)
+                || this.check_const_closure()
+            {
+                this.parse_expr_closure()
+            } else if this.eat_keyword(kw::If) {
+                this.parse_expr_if()
+            } else if this.check_keyword(kw::For) {
+                if this.choose_generics_over_qpath(1) {
+                    this.parse_expr_closure()
+                } else {
+                    assert!(this.eat_keyword(kw::For));
+                    this.parse_expr_for(None, this.prev_token.span)
+                }
+            } else if this.eat_keyword(kw::While) {
+                this.parse_expr_while(None, this.prev_token.span)
+            } else if let Some(label) = this.eat_label() {
+                this.parse_expr_labeled(label, true)
+            } else if this.eat_keyword(kw::Loop) {
+                let sp = this.prev_token.span;
+                this.parse_expr_loop(None, this.prev_token.span).map_err(|mut err| {
+                    err.span_label(sp, "while parsing this `loop` expression");
+                    err
+                })
+            } else if this.eat_keyword(kw::Match) {
+                let match_sp = this.prev_token.span;
+                this.parse_expr_match().map_err(|mut err| {
+                    err.span_label(match_sp, "while parsing this `match` expression");
+                    err
+                })
+            } else if this.eat_keyword(kw::Unsafe) {
+                let sp = this.prev_token.span;
+                this.parse_expr_block(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
+                    |mut err| {
+                        err.span_label(sp, "while parsing this `unsafe` expression");
+                        err
+                    },
+                )
+            } else if this.check_inline_const(0) {
+                this.parse_const_block(lo.to(this.token.span), false)
+            } else if this.may_recover() && this.is_do_catch_block() {
+                this.recover_do_catch()
+            } else if this.is_try_block() {
+                this.expect_keyword(kw::Try)?;
+                this.parse_try_block(lo)
+            } else if this.eat_keyword(kw::Return) {
+                this.parse_expr_return()
+            } else if this.eat_keyword(kw::Continue) {
+                this.parse_expr_continue(lo)
+            } else if this.eat_keyword(kw::Break) {
+                this.parse_expr_break()
+            } else if this.eat_keyword(kw::Yield) {
+                this.parse_expr_yield()
+            } else if this.is_do_yeet() {
+                this.parse_expr_yeet()
+            } else if this.eat_keyword(kw::Become) {
+                this.parse_expr_become()
+            } else if this.check_keyword(kw::Let) {
+                this.parse_expr_let(restrictions)
+            } else if this.eat_keyword(kw::Underscore) {
+                Ok(this.mk_expr(this.prev_token.span, ExprKind::Underscore))
+            } else if this.token.uninterpolated_span().at_least_rust_2018() {
+                // `Span::at_least_rust_2018()` is somewhat expensive; don't get it repeatedly.
+                if this.token.uninterpolated_span().at_least_rust_2024()
+                    // check for `gen {}` and `gen move {}`
+                    // or `async gen {}` and `async gen move {}`
+                    && (this.is_gen_block(kw::Gen, 0)
+                        || (this.check_keyword(kw::Async) && this.is_gen_block(kw::Gen, 1)))
+                {
+                    // FIXME: (async) gen closures aren't yet parsed.
+                    this.parse_gen_block()
+                } else if this.check_keyword(kw::Async) {
+                    // FIXME(gen_blocks): Parse `gen async` and suggest swap
+                    if this.is_gen_block(kw::Async, 0) {
+                        // Check for `async {` and `async move {`,
+                        this.parse_gen_block()
+                    } else {
+                        this.parse_expr_closure()
+                    }
+                } else if this.eat_keyword_noexpect(kw::Await) {
+                    this.recover_incorrect_await_syntax(lo, this.prev_token.span)
+                } else {
+                    this.parse_expr_lit()
+                }
+            } else {
+                this.parse_expr_lit()
+            }
+        })
+    }
+
+    fn parse_expr_lit(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+        match self.parse_opt_token_lit() {
+            Some((token_lit, _)) => {
+                let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Lit(token_lit));
+                self.maybe_recover_from_bad_qpath(expr)
+            }
+            None => self.try_macro_suggestion(),
+        }
+    }
+
+    fn parse_expr_tuple_parens(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+        self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
+        let (es, trailing_comma) = match self.parse_seq_to_end(
+            &token::CloseDelim(Delimiter::Parenthesis),
+            SeqSep::trailing_allowed(token::Comma),
+            |p| p.parse_expr_catch_underscore(restrictions.intersection(Restrictions::ALLOW_LET)),
+        ) {
+            Ok(x) => x,
+            Err(err) => {
+                return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, err));
+            }
+        };
+        let kind = if es.len() == 1 && matches!(trailing_comma, Trailing::No) {
+            // `(e)` is parenthesized `e`.
+            ExprKind::Paren(es.into_iter().next().unwrap())
+        } else {
+            // `(e,)` is a tuple with only one field, `e`.
+            ExprKind::Tup(es)
+        };
+        let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    fn parse_expr_array_or_repeat(&mut self, close_delim: Delimiter) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+        self.bump(); // `[` or other open delim
+
+        let close = &token::CloseDelim(close_delim);
+        let kind = if self.eat(close) {
+            // Empty vector
+            ExprKind::Array(ThinVec::new())
+        } else {
+            // Non-empty vector
+            let first_expr = self.parse_expr()?;
+            if self.eat(&token::Semi) {
+                // Repeating array syntax: `[ 0; 512 ]`
+                let count = self.parse_expr_anon_const()?;
+                self.expect(close)?;
+                ExprKind::Repeat(first_expr, count)
+            } else if self.eat(&token::Comma) {
+                // Vector with two or more elements.
+                let sep = SeqSep::trailing_allowed(token::Comma);
+                let (mut exprs, _) = self.parse_seq_to_end(close, sep, |p| p.parse_expr())?;
+                exprs.insert(0, first_expr);
+                ExprKind::Array(exprs)
+            } else {
+                // Vector with one element
+                self.expect(close)?;
+                ExprKind::Array(thin_vec![first_expr])
+            }
+        };
+        let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    fn parse_expr_path_start(&mut self) -> PResult<'a, P<Expr>> {
+        let maybe_eq_tok = self.prev_token.clone();
+        let (qself, path) = if self.eat_lt() {
+            let lt_span = self.prev_token.span;
+            let (qself, path) = self.parse_qpath(PathStyle::Expr).map_err(|mut err| {
+                // Suggests using '<=' if there is an error parsing qpath when the previous token
+                // is an '=' token. Only emits suggestion if the '<' token and '=' token are
+                // directly adjacent (i.e. '=<')
+                if maybe_eq_tok.kind == TokenKind::Eq && maybe_eq_tok.span.hi() == lt_span.lo() {
+                    let eq_lt = maybe_eq_tok.span.to(lt_span);
+                    err.span_suggestion(eq_lt, "did you mean", "<=", Applicability::Unspecified);
+                }
+                err
+            })?;
+            (Some(qself), path)
+        } else {
+            (None, self.parse_path(PathStyle::Expr)?)
+        };
+
+        // `!`, as an operator, is prefix, so we know this isn't that.
+        let (span, kind) = if self.eat(&token::Not) {
+            // MACRO INVOCATION expression
+            if qself.is_some() {
+                self.dcx().emit_err(errors::MacroInvocationWithQualifiedPath(path.span));
+            }
+            let lo = path.span;
+            let mac = P(MacCall { path, args: self.parse_delim_args()? });
+            (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
+        } else if self.check(&token::OpenDelim(Delimiter::Brace))
+            && let Some(expr) = self.maybe_parse_struct_expr(&qself, &path)
+        {
+            if qself.is_some() {
+                self.psess.gated_spans.gate(sym::more_qualified_paths, path.span);
+            }
+            return expr;
+        } else {
+            (path.span, ExprKind::Path(qself, path))
+        };
+
+        let expr = self.mk_expr(span, kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `'label: $expr`. The label is already parsed.
+    pub(super) fn parse_expr_labeled(
+        &mut self,
+        label_: Label,
+        mut consume_colon: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let lo = label_.ident.span;
+        let label = Some(label_);
+        let ate_colon = self.eat(&token::Colon);
+        let expr = if self.eat_keyword(kw::While) {
+            self.parse_expr_while(label, lo)
+        } else if self.eat_keyword(kw::For) {
+            self.parse_expr_for(label, lo)
+        } else if self.eat_keyword(kw::Loop) {
+            self.parse_expr_loop(label, lo)
+        } else if self.check_noexpect(&token::OpenDelim(Delimiter::Brace))
+            || self.token.is_whole_block()
+        {
+            self.parse_expr_block(label, lo, BlockCheckMode::Default)
+        } else if !ate_colon
+            && self.may_recover()
+            && (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
+                || self.token.is_punct())
+            && could_be_unclosed_char_literal(label_.ident)
+        {
+            let (lit, _) =
+                self.recover_unclosed_char(label_.ident, Parser::mk_token_lit_char, |self_| {
+                    self_.dcx().create_err(errors::UnexpectedTokenAfterLabel {
+                        span: self_.token.span,
+                        remove_label: None,
+                        enclose_in_block: None,
+                    })
+                });
+            consume_colon = false;
+            Ok(self.mk_expr(lo, ExprKind::Lit(lit)))
+        } else if !ate_colon
+            && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
+        {
+            // We're probably inside of a `Path<'a>` that needs a turbofish
+            let guar = self.dcx().emit_err(errors::UnexpectedTokenAfterLabel {
+                span: self.token.span,
+                remove_label: None,
+                enclose_in_block: None,
+            });
+            consume_colon = false;
+            Ok(self.mk_expr_err(lo, guar))
+        } else {
+            let mut err = errors::UnexpectedTokenAfterLabel {
+                span: self.token.span,
+                remove_label: None,
+                enclose_in_block: None,
+            };
+
+            // Continue as an expression in an effort to recover on `'label: non_block_expr`.
+            let expr = self.parse_expr().map(|expr| {
+                let span = expr.span;
+
+                let found_labeled_breaks = {
+                    struct FindLabeledBreaksVisitor;
+
+                    impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
+                        type Result = ControlFlow<()>;
+                        fn visit_expr(&mut self, ex: &'ast Expr) -> ControlFlow<()> {
+                            if let ExprKind::Break(Some(_label), _) = ex.kind {
+                                ControlFlow::Break(())
+                            } else {
+                                walk_expr(self, ex)
+                            }
+                        }
+                    }
+
+                    FindLabeledBreaksVisitor.visit_expr(&expr).is_break()
+                };
+
+                // Suggestion involves adding a labeled block.
+                //
+                // If there are no breaks that may use this label, suggest removing the label and
+                // recover to the unmodified expression.
+                if !found_labeled_breaks {
+                    err.remove_label = Some(lo.until(span));
+
+                    return expr;
+                }
+
+                err.enclose_in_block = Some(errors::UnexpectedTokenAfterLabelSugg {
+                    left: span.shrink_to_lo(),
+                    right: span.shrink_to_hi(),
+                });
+
+                // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
+                let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
+                let blk = self.mk_block(thin_vec![stmt], BlockCheckMode::Default, span);
+                self.mk_expr(span, ExprKind::Block(blk, label))
+            });
+
+            self.dcx().emit_err(err);
+            expr
+        }?;
+
+        if !ate_colon && consume_colon {
+            self.dcx().emit_err(errors::RequireColonAfterLabeledExpression {
+                span: expr.span,
+                label: lo,
+                label_end: lo.shrink_to_hi(),
+            });
+        }
+
+        Ok(expr)
+    }
+
+    /// Emit an error when a char is parsed as a lifetime or label because of a missing quote.
+    pub(super) fn recover_unclosed_char<L>(
+        &self,
+        ident: Ident,
+        mk_lit_char: impl FnOnce(Symbol, Span) -> L,
+        err: impl FnOnce(&Self) -> Diag<'a>,
+    ) -> L {
+        assert!(could_be_unclosed_char_literal(ident));
+        self.dcx()
+            .try_steal_modify_and_emit_err(ident.span, StashKey::LifetimeIsChar, |err| {
+                err.span_suggestion_verbose(
+                    ident.span.shrink_to_hi(),
+                    "add `'` to close the char literal",
+                    "'",
+                    Applicability::MaybeIncorrect,
+                );
+            })
+            .unwrap_or_else(|| {
+                err(self)
+                    .with_span_suggestion_verbose(
+                        ident.span.shrink_to_hi(),
+                        "add `'` to close the char literal",
+                        "'",
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit()
+            });
+        let name = ident.without_first_quote().name;
+        mk_lit_char(name, ident.span)
+    }
+
+    /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
+    fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+
+        self.bump(); // `do`
+        self.bump(); // `catch`
+
+        let span = lo.to(self.prev_token.span);
+        self.dcx().emit_err(errors::DoCatchSyntaxRemoved { span });
+
+        self.parse_try_block(lo)
+    }
+
+    /// Parse an expression if the token can begin one.
+    fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
+        Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
+    }
+
+    /// Parse `"return" expr?`.
+    fn parse_expr_return(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_token.span;
+        let kind = ExprKind::Ret(self.parse_expr_opt()?);
+        let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `"do" "yeet" expr?`.
+    fn parse_expr_yeet(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+
+        self.bump(); // `do`
+        self.bump(); // `yeet`
+
+        let kind = ExprKind::Yeet(self.parse_expr_opt()?);
+
+        let span = lo.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::yeet_expr, span);
+        let expr = self.mk_expr(span, kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `"become" expr`, with `"become"` token already eaten.
+    fn parse_expr_become(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_token.span;
+        let kind = ExprKind::Become(self.parse_expr()?);
+        let span = lo.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::explicit_tail_calls, span);
+        let expr = self.mk_expr(span, kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
+    /// If the label is followed immediately by a `:` token, the label and `:` are
+    /// parsed as part of the expression (i.e. a labeled loop). The language team has
+    /// decided in #87026 to require parentheses as a visual aid to avoid confusion if
+    /// the break expression of an unlabeled break is a labeled loop (as in
+    /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
+    /// expression only gets a warning for compatibility reasons; and a labeled break
+    /// with a labeled loop does not even get a warning because there is no ambiguity.
+    fn parse_expr_break(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_token.span;
+        let mut label = self.eat_label();
+        let kind = if self.token == token::Colon
+            && let Some(label) = label.take()
+        {
+            // The value expression can be a labeled loop, see issue #86948, e.g.:
+            // `loop { break 'label: loop { break 'label 42; }; }`
+            let lexpr = self.parse_expr_labeled(label, true)?;
+            self.dcx().emit_err(errors::LabeledLoopInBreak {
+                span: lexpr.span,
+                sub: errors::WrapInParentheses::Expression {
+                    left: lexpr.span.shrink_to_lo(),
+                    right: lexpr.span.shrink_to_hi(),
+                },
+            });
+            Some(lexpr)
+        } else if self.token != token::OpenDelim(Delimiter::Brace)
+            || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+        {
+            let mut expr = self.parse_expr_opt()?;
+            if let Some(expr) = &mut expr {
+                if label.is_some()
+                    && matches!(
+                        expr.kind,
+                        ExprKind::While(_, _, None)
+                            | ExprKind::ForLoop { label: None, .. }
+                            | ExprKind::Loop(_, None, _)
+                            | ExprKind::Block(_, None)
+                    )
+                {
+                    self.psess.buffer_lint_with_diagnostic(
+                        BREAK_WITH_LABEL_AND_LOOP,
+                        lo.to(expr.span),
+                        ast::CRATE_NODE_ID,
+                        "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
+                        BuiltinLintDiag::BreakWithLabelAndLoop(expr.span),
+                    );
+                }
+
+                // Recover `break label aaaaa`
+                if self.may_recover()
+                    && let ExprKind::Path(None, p) = &expr.kind
+                    && let [segment] = &*p.segments
+                    && let &ast::PathSegment { ident, args: None, .. } = segment
+                    && let Some(next) = self.parse_expr_opt()?
+                {
+                    label = Some(self.recover_ident_into_label(ident));
+                    *expr = next;
+                }
+            }
+
+            expr
+        } else {
+            None
+        };
+        let expr = self.mk_expr(lo.to(self.prev_token.span), ExprKind::Break(label, kind));
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `"continue" label?`.
+    fn parse_expr_continue(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+        let mut label = self.eat_label();
+
+        // Recover `continue label` -> `continue 'label`
+        if self.may_recover()
+            && label.is_none()
+            && let Some((ident, _)) = self.token.ident()
+        {
+            self.bump();
+            label = Some(self.recover_ident_into_label(ident));
+        }
+
+        let kind = ExprKind::Continue(label);
+        Ok(self.mk_expr(lo.to(self.prev_token.span), kind))
+    }
+
+    /// Parse `"yield" expr?`.
+    fn parse_expr_yield(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_token.span;
+        let kind = ExprKind::Yield(self.parse_expr_opt()?);
+        let span = lo.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::yield_expr, span);
+        let expr = self.mk_expr(span, kind);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    /// Parse `builtin # ident(args,*)`.
+    fn parse_expr_builtin(&mut self) -> PResult<'a, P<Expr>> {
+        self.parse_builtin(|this, lo, ident| {
+            Ok(match ident.name {
+                sym::offset_of => Some(this.parse_expr_offset_of(lo)?),
+                sym::type_ascribe => Some(this.parse_expr_type_ascribe(lo)?),
+                _ => None,
+            })
+        })
+    }
+
+    pub(crate) fn parse_builtin<T>(
+        &mut self,
+        parse: impl FnOnce(&mut Parser<'a>, Span, Ident) -> PResult<'a, Option<T>>,
+    ) -> PResult<'a, T> {
+        let lo = self.token.span;
+
+        self.bump(); // `builtin`
+        self.bump(); // `#`
+
+        let Some((ident, IdentIsRaw::No)) = self.token.ident() else {
+            let err = self.dcx().create_err(errors::ExpectedBuiltinIdent { span: self.token.span });
+            return Err(err);
+        };
+        self.psess.gated_spans.gate(sym::builtin_syntax, ident.span);
+        self.bump();
+
+        self.expect(&TokenKind::OpenDelim(Delimiter::Parenthesis))?;
+        let ret = if let Some(res) = parse(self, lo, ident)? {
+            Ok(res)
+        } else {
+            let err = self.dcx().create_err(errors::UnknownBuiltinConstruct {
+                span: lo.to(ident.span),
+                name: ident.name,
+            });
+            return Err(err);
+        };
+        self.expect(&TokenKind::CloseDelim(Delimiter::Parenthesis))?;
+
+        ret
+    }
+
+    /// Built-in macro for `offset_of!` expressions.
+    pub(crate) fn parse_expr_offset_of(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+        let container = self.parse_ty()?;
+        self.expect(&TokenKind::Comma)?;
+
+        let fields = self.parse_floating_field_access()?;
+        let trailing_comma = self.eat_noexpect(&TokenKind::Comma);
+
+        if let Err(mut e) =
+            self.expect_one_of(&[], &[TokenKind::CloseDelim(Delimiter::Parenthesis)])
+        {
+            if trailing_comma {
+                e.note("unexpected third argument to offset_of");
+            } else {
+                e.note("offset_of expects dot-separated field and variant names");
+            }
+            e.emit();
+        }
+
+        // Eat tokens until the macro call ends.
+        if self.may_recover() {
+            while !matches!(self.token.kind, token::CloseDelim(..) | token::Eof) {
+                self.bump();
+            }
+        }
+
+        let span = lo.to(self.token.span);
+        Ok(self.mk_expr(span, ExprKind::OffsetOf(container, fields)))
+    }
+
+    /// Built-in macro for type ascription expressions.
+    pub(crate) fn parse_expr_type_ascribe(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+        let expr = self.parse_expr()?;
+        self.expect(&token::Comma)?;
+        let ty = self.parse_ty()?;
+        let span = lo.to(self.token.span);
+        Ok(self.mk_expr(span, ExprKind::Type(expr, ty)))
+    }
+
+    /// Returns a string literal if the next token is a string literal.
+    /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
+    /// and returns `None` if the next token is not literal at all.
+    pub fn parse_str_lit(&mut self) -> Result<ast::StrLit, Option<MetaItemLit>> {
+        match self.parse_opt_meta_item_lit() {
+            Some(lit) => match lit.kind {
+                ast::LitKind::Str(symbol_unescaped, style) => Ok(ast::StrLit {
+                    style,
+                    symbol: lit.symbol,
+                    suffix: lit.suffix,
+                    span: lit.span,
+                    symbol_unescaped,
+                }),
+                _ => Err(Some(lit)),
+            },
+            None => Err(None),
+        }
+    }
+
+    pub(crate) fn mk_token_lit_char(name: Symbol, span: Span) -> (token::Lit, Span) {
+        (token::Lit { symbol: name, suffix: None, kind: token::Char }, span)
+    }
+
+    fn mk_meta_item_lit_char(name: Symbol, span: Span) -> MetaItemLit {
+        ast::MetaItemLit {
+            symbol: name,
+            suffix: None,
+            kind: ast::LitKind::Char(name.as_str().chars().next().unwrap_or('_')),
+            span,
+        }
+    }
+
+    fn handle_missing_lit<L>(
+        &mut self,
+        mk_lit_char: impl FnOnce(Symbol, Span) -> L,
+    ) -> PResult<'a, L> {
+        let token = self.token.clone();
+        let err = |self_: &Self| {
+            let msg = format!("unexpected token: {}", super::token_descr(&token));
+            self_.dcx().struct_span_err(token.span, msg)
+        };
+        // On an error path, eagerly consider a lifetime to be an unclosed character lit, if that
+        // makes sense.
+        if let Some(ident) = self.token.lifetime()
+            && could_be_unclosed_char_literal(ident)
+        {
+            let lt = self.expect_lifetime();
+            Ok(self.recover_unclosed_char(lt.ident, mk_lit_char, err))
+        } else {
+            Err(err(self))
+        }
+    }
+
+    pub(super) fn parse_token_lit(&mut self) -> PResult<'a, (token::Lit, Span)> {
+        self.parse_opt_token_lit()
+            .ok_or(())
+            .or_else(|()| self.handle_missing_lit(Parser::mk_token_lit_char))
+    }
+
+    pub(super) fn parse_meta_item_lit(&mut self) -> PResult<'a, MetaItemLit> {
+        self.parse_opt_meta_item_lit()
+            .ok_or(())
+            .or_else(|()| self.handle_missing_lit(Parser::mk_meta_item_lit_char))
+    }
+
+    fn recover_after_dot(&mut self) -> Option<Token> {
+        let mut recovered = None;
+        if self.token == token::Dot {
+            // Attempt to recover `.4` as `0.4`. We don't currently have any syntax where
+            // dot would follow an optional literal, so we do this unconditionally.
+            recovered = self.look_ahead(1, |next_token| {
+                if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
+                    next_token.kind
+                {
+                    // If this integer looks like a float, then recover as such.
+                    //
+                    // We will never encounter the exponent part of a floating
+                    // point literal here, since there's no use of the exponent
+                    // syntax that also constitutes a valid integer, so we need
+                    // not check for that.
+                    if suffix.map_or(true, |s| s == sym::f32 || s == sym::f64)
+                        && symbol.as_str().chars().all(|c| c.is_numeric() || c == '_')
+                        && self.token.span.hi() == next_token.span.lo()
+                    {
+                        let s = String::from("0.") + symbol.as_str();
+                        let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
+                        return Some(Token::new(kind, self.token.span.to(next_token.span)));
+                    }
+                }
+                None
+            });
+            if let Some(token) = &recovered {
+                self.bump();
+                self.dcx().emit_err(errors::FloatLiteralRequiresIntegerPart {
+                    span: token.span,
+                    correct: pprust::token_to_string(token).into_owned(),
+                });
+            }
+        }
+
+        recovered
+    }
+
+    /// Matches `lit = true | false | token_lit`.
+    /// Returns `None` if the next token is not a literal.
+    pub(super) fn parse_opt_token_lit(&mut self) -> Option<(token::Lit, Span)> {
+        let recovered = self.recover_after_dot();
+        let token = recovered.as_ref().unwrap_or(&self.token);
+        let span = token.span;
+
+        token::Lit::from_token(token).map(|token_lit| {
+            self.bump();
+            (token_lit, span)
+        })
+    }
+
+    /// Matches `lit = true | false | token_lit`.
+    /// Returns `None` if the next token is not a literal.
+    pub(super) fn parse_opt_meta_item_lit(&mut self) -> Option<MetaItemLit> {
+        let recovered = self.recover_after_dot();
+        let token = recovered.as_ref().unwrap_or(&self.token);
+        match token::Lit::from_token(token) {
+            Some(lit) => {
+                match MetaItemLit::from_token_lit(lit, token.span) {
+                    Ok(lit) => {
+                        self.bump();
+                        Some(lit)
+                    }
+                    Err(err) => {
+                        let span = token.uninterpolated_span();
+                        self.bump();
+                        let guar = report_lit_error(self.psess, err, lit, span);
+                        // Pack possible quotes and prefixes from the original literal into
+                        // the error literal's symbol so they can be pretty-printed faithfully.
+                        let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
+                        let symbol = Symbol::intern(&suffixless_lit.to_string());
+                        let lit = token::Lit::new(token::Err(guar), symbol, lit.suffix);
+                        Some(
+                            MetaItemLit::from_token_lit(lit, span)
+                                .unwrap_or_else(|_| unreachable!()),
+                        )
+                    }
+                }
+            }
+            None => None,
+        }
+    }
+
+    pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
+        if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
+            // #59553: warn instead of reject out of hand to allow the fix to percolate
+            // through the ecosystem when people fix their macros
+            self.dcx().emit_warn(errors::InvalidLiteralSuffixOnTupleIndex {
+                span,
+                suffix,
+                exception: Some(()),
+            });
+        } else {
+            self.dcx().emit_err(errors::InvalidLiteralSuffixOnTupleIndex {
+                span,
+                suffix,
+                exception: None,
+            });
+        }
+    }
+
+    /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
+    /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
+    pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
+        maybe_whole_expr!(self);
+
+        let lo = self.token.span;
+        let minus_present = self.eat(&token::BinOp(token::Minus));
+        let (token_lit, span) = self.parse_token_lit()?;
+        let expr = self.mk_expr(span, ExprKind::Lit(token_lit));
+
+        if minus_present {
+            Ok(self.mk_expr(lo.to(self.prev_token.span), self.mk_unary(UnOp::Neg, expr)))
+        } else {
+            Ok(expr)
+        }
+    }
+
+    fn is_array_like_block(&mut self) -> bool {
+        self.look_ahead(1, |t| matches!(t.kind, TokenKind::Ident(..) | TokenKind::Literal(_)))
+            && self.look_ahead(2, |t| t == &token::Comma)
+            && self.look_ahead(3, |t| t.can_begin_expr())
+    }
+
+    /// Emits a suggestion if it looks like the user meant an array but
+    /// accidentally used braces, causing the code to be interpreted as a block
+    /// expression.
+    fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
+        let mut snapshot = self.create_snapshot_for_diagnostic();
+        match snapshot.parse_expr_array_or_repeat(Delimiter::Brace) {
+            Ok(arr) => {
+                let guar = self.dcx().emit_err(errors::ArrayBracketsInsteadOfSpaces {
+                    span: arr.span,
+                    sub: errors::ArrayBracketsInsteadOfSpacesSugg {
+                        left: lo,
+                        right: snapshot.prev_token.span,
+                    },
+                });
+
+                self.restore_snapshot(snapshot);
+                Some(self.mk_expr_err(arr.span, guar))
+            }
+            Err(e) => {
+                e.cancel();
+                None
+            }
+        }
+    }
+
+    fn suggest_missing_semicolon_before_array(
+        &self,
+        prev_span: Span,
+        open_delim_span: Span,
+    ) -> PResult<'a, ()> {
+        if !self.may_recover() {
+            return Ok(());
+        }
+
+        if self.token.kind == token::Comma {
+            if !self.psess.source_map().is_multiline(prev_span.until(self.token.span)) {
+                return Ok(());
+            }
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            snapshot.bump();
+            match snapshot.parse_seq_to_before_end(
+                &token::CloseDelim(Delimiter::Bracket),
+                SeqSep::trailing_allowed(token::Comma),
+                |p| p.parse_expr(),
+            ) {
+                Ok(_)
+                    // When the close delim is `)`, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
+                    // but the actual `token.kind` is `token::CloseDelim(Delimiter::Bracket)`.
+                    // This is because the `token.kind` of the close delim is treated as the same as
+                    // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
+                    // Therefore, `token.kind` should not be compared here.
+                    if snapshot
+                        .span_to_snippet(snapshot.token.span)
+                        .is_ok_and(|snippet| snippet == "]") =>
+                {
+                    return Err(self.dcx().create_err(errors::MissingSemicolonBeforeArray {
+                        open_delim: open_delim_span,
+                        semicolon: prev_span.shrink_to_hi(),
+                    }));
+                }
+                Ok(_) => (),
+                Err(err) => err.cancel(),
+            }
+        }
+        Ok(())
+    }
+
+    /// Parses a block or unsafe block.
+    pub(super) fn parse_expr_block(
+        &mut self,
+        opt_label: Option<Label>,
+        lo: Span,
+        blk_mode: BlockCheckMode,
+    ) -> PResult<'a, P<Expr>> {
+        if self.may_recover() && self.is_array_like_block() {
+            if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
+                return Ok(arr);
+            }
+        }
+
+        if self.token.is_whole_block() {
+            self.dcx().emit_err(errors::InvalidBlockMacroSegment {
+                span: self.token.span,
+                context: lo.to(self.token.span),
+                wrap: errors::WrapInExplicitBlock {
+                    lo: self.token.span.shrink_to_lo(),
+                    hi: self.token.span.shrink_to_hi(),
+                },
+            });
+        }
+
+        let (attrs, blk) = self.parse_block_common(lo, blk_mode, true)?;
+        Ok(self.mk_expr_with_attrs(blk.span, ExprKind::Block(blk, opt_label), attrs))
+    }
+
+    /// Parse a block which takes no attributes and has no label
+    fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
+        let blk = self.parse_block()?;
+        Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
+    }
+
+    /// Parses a closure expression (e.g., `move |args| expr`).
+    fn parse_expr_closure(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+
+        let before = self.prev_token.clone();
+        let binder = if self.check_keyword(kw::For) {
+            let lo = self.token.span;
+            let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+            let span = lo.to(self.prev_token.span);
+
+            self.psess.gated_spans.gate(sym::closure_lifetime_binder, span);
+
+            ClosureBinder::For { span, generic_params: lifetime_defs }
+        } else {
+            ClosureBinder::NotPresent
+        };
+
+        let constness = self.parse_closure_constness();
+
+        let movability =
+            if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
+
+        let coroutine_kind = if self.token.uninterpolated_span().at_least_rust_2018() {
+            self.parse_coroutine_kind(Case::Sensitive)
+        } else {
+            None
+        };
+
+        let capture_clause = self.parse_capture_clause()?;
+        let (fn_decl, fn_arg_span) = self.parse_fn_block_decl()?;
+        let decl_hi = self.prev_token.span;
+        let mut body = match fn_decl.output {
+            FnRetTy::Default(_) => {
+                let restrictions =
+                    self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET;
+                let prev = self.prev_token.clone();
+                let token = self.token.clone();
+                match self.parse_expr_res(restrictions, None) {
+                    Ok(expr) => expr,
+                    Err(err) => self.recover_closure_body(err, before, prev, token, lo, decl_hi)?,
+                }
+            }
+            _ => {
+                // If an explicit return type is given, require a block to appear (RFC 968).
+                let body_lo = self.token.span;
+                self.parse_expr_block(None, body_lo, BlockCheckMode::Default)?
+            }
+        };
+
+        match coroutine_kind {
+            Some(CoroutineKind::Async { span, .. }) => {
+                // Feature-gate `async ||` closures.
+                self.psess.gated_spans.gate(sym::async_closure, span);
+            }
+            Some(CoroutineKind::Gen { span, .. }) | Some(CoroutineKind::AsyncGen { span, .. }) => {
+                // Feature-gate `gen ||` and `async gen ||` closures.
+                // FIXME(gen_blocks): This perhaps should be a different gate.
+                self.psess.gated_spans.gate(sym::gen_blocks, span);
+            }
+            None => {}
+        }
+
+        if self.token.kind == TokenKind::Semi
+            && matches!(self.token_cursor.stack.last(), Some((.., Delimiter::Parenthesis)))
+            && self.may_recover()
+        {
+            // It is likely that the closure body is a block but where the
+            // braces have been removed. We will recover and eat the next
+            // statements later in the parsing process.
+            body = self.mk_expr_err(
+                body.span,
+                self.dcx().span_delayed_bug(body.span, "recovered a closure body as a block"),
+            );
+        }
+
+        let body_span = body.span;
+
+        let closure = self.mk_expr(
+            lo.to(body.span),
+            ExprKind::Closure(Box::new(ast::Closure {
+                binder,
+                capture_clause,
+                constness,
+                coroutine_kind,
+                movability,
+                fn_decl,
+                body,
+                fn_decl_span: lo.to(decl_hi),
+                fn_arg_span,
+            })),
+        );
+
+        // Disable recovery for closure body
+        let spans =
+            ClosureSpans { whole_closure: closure.span, closing_pipe: decl_hi, body: body_span };
+        self.current_closure = Some(spans);
+
+        Ok(closure)
+    }
+
+    /// Parses an optional `move` prefix to a closure-like construct.
+    fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
+        if self.eat_keyword(kw::Move) {
+            let move_kw_span = self.prev_token.span;
+            // Check for `move async` and recover
+            if self.check_keyword(kw::Async) {
+                let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
+                Err(self
+                    .dcx()
+                    .create_err(errors::AsyncMoveOrderIncorrect { span: move_async_span }))
+            } else {
+                Ok(CaptureBy::Value { move_kw: move_kw_span })
+            }
+        } else {
+            Ok(CaptureBy::Ref)
+        }
+    }
+
+    /// Parses the `|arg, arg|` header of a closure.
+    fn parse_fn_block_decl(&mut self) -> PResult<'a, (P<FnDecl>, Span)> {
+        let arg_start = self.token.span.lo();
+
+        let inputs = if self.eat(&token::OrOr) {
+            ThinVec::new()
+        } else {
+            self.expect(&token::BinOp(token::Or))?;
+            let args = self
+                .parse_seq_to_before_tokens(
+                    &[&token::BinOp(token::Or), &token::OrOr],
+                    SeqSep::trailing_allowed(token::Comma),
+                    TokenExpectType::NoExpect,
+                    |p| p.parse_fn_block_param(),
+                )?
+                .0;
+            self.expect_or()?;
+            args
+        };
+        let arg_span = self.prev_token.span.with_lo(arg_start);
+        let output =
+            self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
+
+        Ok((P(FnDecl { inputs, output }), arg_span))
+    }
+
+    /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
+    fn parse_fn_block_param(&mut self) -> PResult<'a, Param> {
+        let lo = self.token.span;
+        let attrs = self.parse_outer_attributes()?;
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let pat = this.parse_pat_no_top_alt(Some(Expected::ParameterName), None)?;
+            let ty = if this.eat(&token::Colon) {
+                this.parse_ty()?
+            } else {
+                this.mk_ty(pat.span, TyKind::Infer)
+            };
+
+            Ok((
+                Param {
+                    attrs,
+                    ty,
+                    pat,
+                    span: lo.to(this.prev_token.span),
+                    id: DUMMY_NODE_ID,
+                    is_placeholder: false,
+                },
+                TrailingToken::MaybeComma,
+            ))
+        })
+    }
+
+    /// Parses an `if` expression (`if` token already eaten).
+    fn parse_expr_if(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_token.span;
+        let cond = self.parse_expr_cond()?;
+        self.parse_if_after_cond(lo, cond)
+    }
+
+    fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
+        let cond_span = cond.span;
+        // Tries to interpret `cond` as either a missing expression if it's a block,
+        // or as an unfinished expression if it's a binop and the RHS is a block.
+        // We could probably add more recoveries here too...
+        let mut recover_block_from_condition = |this: &mut Self| {
+            let block = match &mut cond.kind {
+                ExprKind::Binary(Spanned { span: binop_span, .. }, _, right)
+                    if let ExprKind::Block(_, None) = right.kind =>
+                {
+                    let guar = this.dcx().emit_err(errors::IfExpressionMissingThenBlock {
+                        if_span: lo,
+                        missing_then_block_sub:
+                            errors::IfExpressionMissingThenBlockSub::UnfinishedCondition(
+                                cond_span.shrink_to_lo().to(*binop_span),
+                            ),
+                        let_else_sub: None,
+                    });
+                    std::mem::replace(right, this.mk_expr_err(binop_span.shrink_to_hi(), guar))
+                }
+                ExprKind::Block(_, None) => {
+                    let guar = this.dcx().emit_err(errors::IfExpressionMissingCondition {
+                        if_span: lo.with_neighbor(cond.span).shrink_to_hi(),
+                        block_span: self.psess.source_map().start_point(cond_span),
+                    });
+                    std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi(), guar))
+                }
+                _ => {
+                    return None;
+                }
+            };
+            if let ExprKind::Block(block, _) = &block.kind {
+                Some(block.clone())
+            } else {
+                unreachable!()
+            }
+        };
+        // Parse then block
+        let thn = if self.token.is_keyword(kw::Else) {
+            if let Some(block) = recover_block_from_condition(self) {
+                block
+            } else {
+                let let_else_sub = matches!(cond.kind, ExprKind::Let(..))
+                    .then(|| errors::IfExpressionLetSomeSub { if_span: lo.until(cond_span) });
+
+                let guar = self.dcx().emit_err(errors::IfExpressionMissingThenBlock {
+                    if_span: lo,
+                    missing_then_block_sub: errors::IfExpressionMissingThenBlockSub::AddThenBlock(
+                        cond_span.shrink_to_hi(),
+                    ),
+                    let_else_sub,
+                });
+                self.mk_block_err(cond_span.shrink_to_hi(), guar)
+            }
+        } else {
+            let attrs = self.parse_outer_attributes()?; // For recovery.
+            let maybe_fatarrow = self.token.clone();
+            let block = if self.check(&token::OpenDelim(Delimiter::Brace)) {
+                self.parse_block()?
+            } else {
+                if let Some(block) = recover_block_from_condition(self) {
+                    block
+                } else {
+                    self.error_on_extra_if(&cond)?;
+                    // Parse block, which will always fail, but we can add a nice note to the error
+                    self.parse_block().map_err(|mut err| {
+                        if self.prev_token == token::Semi
+                            && self.token == token::AndAnd
+                            && let maybe_let = self.look_ahead(1, |t| t.clone())
+                            && maybe_let.is_keyword(kw::Let)
+                        {
+                            err.span_suggestion(
+                                self.prev_token.span,
+                                "consider removing this semicolon to parse the `let` as part of the same chain",
+                                "",
+                                Applicability::MachineApplicable,
+                            ).span_note(
+                                self.token.span.to(maybe_let.span),
+                                "you likely meant to continue parsing the let-chain starting here",
+                            );
+                        } else {
+                            // Look for usages of '=>' where '>=' might be intended
+                            if maybe_fatarrow.kind == token::FatArrow {
+                                err.span_suggestion(
+                                    maybe_fatarrow.span,
+                                    "you might have meant to write a \"greater than or equal to\" comparison",
+                                    ">=",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                            err.span_note(
+                                cond_span,
+                                "the `if` expression is missing a block after this condition",
+                            );
+                        }
+                        err
+                    })?
+                }
+            };
+            self.error_on_if_block_attrs(lo, false, block.span, attrs);
+            block
+        };
+        let els = if self.eat_keyword(kw::Else) { Some(self.parse_expr_else()?) } else { None };
+        Ok(self.mk_expr(lo.to(self.prev_token.span), ExprKind::If(cond, thn, els)))
+    }
+
+    /// Parses the condition of a `if` or `while` expression.
+    fn parse_expr_cond(&mut self) -> PResult<'a, P<Expr>> {
+        let mut cond =
+            self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
+
+        CondChecker::new(self).visit_expr(&mut cond);
+
+        if let ExprKind::Let(_, _, _, Recovered::No) = cond.kind {
+            // Remove the last feature gating of a `let` expression since it's stable.
+            self.psess.gated_spans.ungate_last(sym::let_chains, cond.span);
+        }
+
+        Ok(cond)
+    }
+
+    /// Parses a `let $pat = $expr` pseudo-expression.
+    fn parse_expr_let(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+        let recovered = if !restrictions.contains(Restrictions::ALLOW_LET) {
+            let err = errors::ExpectedExpressionFoundLet {
+                span: self.token.span,
+                reason: ForbiddenLetReason::OtherForbidden,
+                missing_let: None,
+                comparison: None,
+            };
+            if self.prev_token.kind == token::BinOp(token::Or) {
+                // This was part of a closure, the that part of the parser recover.
+                return Err(self.dcx().create_err(err));
+            } else {
+                Recovered::Yes(self.dcx().emit_err(err))
+            }
+        } else {
+            Recovered::No
+        };
+        self.bump(); // Eat `let` token
+        let lo = self.prev_token.span;
+        let pat = self.parse_pat_allow_top_alt(
+            None,
+            RecoverComma::Yes,
+            RecoverColon::Yes,
+            CommaRecoveryMode::LikelyTuple,
+        )?;
+        if self.token == token::EqEq {
+            self.dcx().emit_err(errors::ExpectedEqForLetExpr {
+                span: self.token.span,
+                sugg_span: self.token.span,
+            });
+            self.bump();
+        } else {
+            self.expect(&token::Eq)?;
+        }
+        let expr = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), None.into())?;
+        let span = lo.to(expr.span);
+        Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span, recovered)))
+    }
+
+    /// Parses an `else { ... }` expression (`else` token already eaten).
+    fn parse_expr_else(&mut self) -> PResult<'a, P<Expr>> {
+        let else_span = self.prev_token.span; // `else`
+        let attrs = self.parse_outer_attributes()?; // For recovery.
+        let expr = if self.eat_keyword(kw::If) {
+            ensure_sufficient_stack(|| self.parse_expr_if())?
+        } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
+            self.parse_simple_block()?
+        } else {
+            let snapshot = self.create_snapshot_for_diagnostic();
+            let first_tok = super::token_descr(&self.token);
+            let first_tok_span = self.token.span;
+            match self.parse_expr() {
+                Ok(cond)
+                // Try to guess the difference between a "condition-like" vs
+                // "statement-like" expression.
+                //
+                // We are seeing the following code, in which $cond is neither
+                // ExprKind::Block nor ExprKind::If (the 2 cases wherein this
+                // would be valid syntax).
+                //
+                //     if ... {
+                //     } else $cond
+                //
+                // If $cond is "condition-like" such as ExprKind::Binary, we
+                // want to suggest inserting `if`.
+                //
+                //     if ... {
+                //     } else if a == b {
+                //            ^^
+                //     }
+                //
+                // If $cond is "statement-like" such as ExprKind::While then we
+                // want to suggest wrapping in braces.
+                //
+                //     if ... {
+                //     } else {
+                //            ^
+                //         while true {}
+                //     }
+                //     ^
+                    if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
+                        && classify::expr_requires_semi_to_be_stmt(&cond) =>
+                {
+                    self.dcx().emit_err(errors::ExpectedElseBlock {
+                        first_tok_span,
+                        first_tok,
+                        else_span,
+                        condition_start: cond.span.shrink_to_lo(),
+                    });
+                    self.parse_if_after_cond(cond.span.shrink_to_lo(), cond)?
+                }
+                Err(e) => {
+                    e.cancel();
+                    self.restore_snapshot(snapshot);
+                    self.parse_simple_block()?
+                },
+                Ok(_) => {
+                    self.restore_snapshot(snapshot);
+                    self.parse_simple_block()?
+                },
+            }
+        };
+        self.error_on_if_block_attrs(else_span, true, expr.span, attrs);
+        Ok(expr)
+    }
+
+    fn error_on_if_block_attrs(
+        &self,
+        ctx_span: Span,
+        is_ctx_else: bool,
+        branch_span: Span,
+        attrs: AttrWrapper,
+    ) {
+        if !attrs.is_empty()
+            && let [x0 @ xn] | [x0, .., xn] = &*attrs.take_for_recovery(self.psess)
+        {
+            let attributes = x0.span.to(xn.span);
+            let last = xn.span;
+            let ctx = if is_ctx_else { "else" } else { "if" };
+            self.dcx().emit_err(errors::OuterAttributeNotAllowedOnIfElse {
+                last,
+                branch_span,
+                ctx_span,
+                ctx: ctx.to_string(),
+                attributes,
+            });
+        }
+    }
+
+    fn error_on_extra_if(&mut self, cond: &P<Expr>) -> PResult<'a, ()> {
+        if let ExprKind::Binary(Spanned { span: binop_span, node: binop }, _, right) = &cond.kind
+            && let BinOpKind::And = binop
+            && let ExprKind::If(cond, ..) = &right.kind
+        {
+            Err(self.dcx().create_err(errors::UnexpectedIfWithIf(
+                binop_span.shrink_to_hi().to(cond.span.shrink_to_lo()),
+            )))
+        } else {
+            Ok(())
+        }
+    }
+
+    fn parse_for_head(&mut self) -> PResult<'a, (P<Pat>, P<Expr>)> {
+        let begin_paren = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
+            // Record whether we are about to parse `for (`.
+            // This is used below for recovery in case of `for ( $stuff ) $block`
+            // in which case we will suggest `for $stuff $block`.
+            let start_span = self.token.span;
+            let left = self.prev_token.span.between(self.look_ahead(1, |t| t.span));
+            Some((start_span, left))
+        } else {
+            None
+        };
+        // Try to parse the pattern `for ($PAT) in $EXPR`.
+        let pat = match (
+            self.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::Yes,
+                RecoverColon::Yes,
+                CommaRecoveryMode::LikelyTuple,
+            ),
+            begin_paren,
+        ) {
+            (Ok(pat), _) => pat, // Happy path.
+            (Err(err), Some((start_span, left))) if self.eat_keyword(kw::In) => {
+                // We know for sure we have seen `for ($SOMETHING in`. In the happy path this would
+                // happen right before the return of this method.
+                let expr = match self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None) {
+                    Ok(expr) => expr,
+                    Err(expr_err) => {
+                        // We don't know what followed the `in`, so cancel and bubble up the
+                        // original error.
+                        expr_err.cancel();
+                        return Err(err);
+                    }
+                };
+                return if self.token.kind == token::CloseDelim(Delimiter::Parenthesis) {
+                    // We know for sure we have seen `for ($SOMETHING in $EXPR)`, so we recover the
+                    // parser state and emit a targeted suggestion.
+                    let span = vec![start_span, self.token.span];
+                    let right = self.prev_token.span.between(self.look_ahead(1, |t| t.span));
+                    self.bump(); // )
+                    err.cancel();
+                    self.dcx().emit_err(errors::ParenthesesInForHead {
+                        span,
+                        // With e.g. `for (x) in y)` this would replace `(x) in y)`
+                        // with `x) in y)` which is syntactically invalid.
+                        // However, this is prevented before we get here.
+                        sugg: errors::ParenthesesInForHeadSugg { left, right },
+                    });
+                    Ok((self.mk_pat(start_span.to(right), ast::PatKind::Wild), expr))
+                } else {
+                    Err(err) // Some other error, bubble up.
+                };
+            }
+            (Err(err), _) => return Err(err), // Some other error, bubble up.
+        };
+        if !self.eat_keyword(kw::In) {
+            self.error_missing_in_for_loop();
+        }
+        self.check_for_for_in_in_typo(self.prev_token.span);
+        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+        Ok((pat, expr))
+    }
+
+    /// Parses `for await? <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
+    fn parse_expr_for(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+        let is_await =
+            self.token.uninterpolated_span().at_least_rust_2018() && self.eat_keyword(kw::Await);
+
+        if is_await {
+            self.psess.gated_spans.gate(sym::async_for_loop, self.prev_token.span);
+        }
+
+        let kind = if is_await { ForLoopKind::ForAwait } else { ForLoopKind::For };
+
+        let (pat, expr) = self.parse_for_head()?;
+        // Recover from missing expression in `for` loop
+        if matches!(expr.kind, ExprKind::Block(..))
+            && !matches!(self.token.kind, token::OpenDelim(Delimiter::Brace))
+            && self.may_recover()
+        {
+            let guar = self
+                .dcx()
+                .emit_err(errors::MissingExpressionInForLoop { span: expr.span.shrink_to_lo() });
+            let err_expr = self.mk_expr(expr.span, ExprKind::Err(guar));
+            let block = self.mk_block(thin_vec![], BlockCheckMode::Default, self.prev_token.span);
+            return Ok(self.mk_expr(
+                lo.to(self.prev_token.span),
+                ExprKind::ForLoop { pat, iter: err_expr, body: block, label: opt_label, kind },
+            ));
+        }
+
+        let (attrs, loop_block) = self.parse_inner_attrs_and_block()?;
+
+        let kind = ExprKind::ForLoop { pat, iter: expr, body: loop_block, label: opt_label, kind };
+
+        self.recover_loop_else("for", lo)?;
+
+        Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
+    }
+
+    /// Recovers from an `else` clause after a loop (`for...else`, `while...else`)
+    fn recover_loop_else(&mut self, loop_kind: &'static str, loop_kw: Span) -> PResult<'a, ()> {
+        if self.token.is_keyword(kw::Else) && self.may_recover() {
+            let else_span = self.token.span;
+            self.bump();
+            let else_clause = self.parse_expr_else()?;
+            self.dcx().emit_err(errors::LoopElseNotSupported {
+                span: else_span.to(else_clause.span),
+                loop_kind,
+                loop_kw,
+            });
+        }
+        Ok(())
+    }
+
+    fn error_missing_in_for_loop(&mut self) {
+        let (span, sub): (_, fn(_) -> _) = if self.token.is_ident_named(sym::of) {
+            // Possibly using JS syntax (#75311).
+            let span = self.token.span;
+            self.bump();
+            (span, errors::MissingInInForLoopSub::InNotOf)
+        } else {
+            (self.prev_token.span.between(self.token.span), errors::MissingInInForLoopSub::AddIn)
+        };
+
+        self.dcx().emit_err(errors::MissingInInForLoop { span, sub: sub(span) });
+    }
+
+    /// Parses a `while` or `while let` expression (`while` token already eaten).
+    fn parse_expr_while(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+        let cond = self.parse_expr_cond().map_err(|mut err| {
+            err.span_label(lo, "while parsing the condition of this `while` expression");
+            err
+        })?;
+        let (attrs, body) = self.parse_inner_attrs_and_block().map_err(|mut err| {
+            err.span_label(lo, "while parsing the body of this `while` expression");
+            err.span_label(cond.span, "this `while` condition successfully parsed");
+            err
+        })?;
+
+        self.recover_loop_else("while", lo)?;
+
+        Ok(self.mk_expr_with_attrs(
+            lo.to(self.prev_token.span),
+            ExprKind::While(cond, body, opt_label),
+            attrs,
+        ))
+    }
+
+    /// Parses `loop { ... }` (`loop` token already eaten).
+    fn parse_expr_loop(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+        let loop_span = self.prev_token.span;
+        let (attrs, body) = self.parse_inner_attrs_and_block()?;
+        self.recover_loop_else("loop", lo)?;
+        Ok(self.mk_expr_with_attrs(
+            lo.to(self.prev_token.span),
+            ExprKind::Loop(body, opt_label, loop_span),
+            attrs,
+        ))
+    }
+
+    pub(crate) fn eat_label(&mut self) -> Option<Label> {
+        self.token.lifetime().map(|ident| {
+            self.bump();
+            Label { ident }
+        })
+    }
+
+    /// Parses a `match ... { ... }` expression (`match` token already eaten).
+    fn parse_expr_match(&mut self) -> PResult<'a, P<Expr>> {
+        let match_span = self.prev_token.span;
+        let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+
+        self.parse_match_block(match_span, match_span, scrutinee, MatchKind::Prefix)
+    }
+
+    /// Parses the block of a `match expr { ... }` or a `expr.match { ... }`
+    /// expression. This is after the match token and scrutinee are eaten
+    fn parse_match_block(
+        &mut self,
+        lo: Span,
+        match_span: Span,
+        scrutinee: P<Expr>,
+        match_kind: MatchKind,
+    ) -> PResult<'a, P<Expr>> {
+        if let Err(mut e) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
+            if self.token == token::Semi {
+                e.span_suggestion_short(
+                    match_span,
+                    "try removing this `match`",
+                    "",
+                    Applicability::MaybeIncorrect, // speculative
+                );
+            }
+            if self.maybe_recover_unexpected_block_label() {
+                e.cancel();
+                self.bump();
+            } else {
+                return Err(e);
+            }
+        }
+        let attrs = self.parse_inner_attributes()?;
+
+        let mut arms = ThinVec::new();
+        while self.token != token::CloseDelim(Delimiter::Brace) {
+            match self.parse_arm() {
+                Ok(arm) => arms.push(arm),
+                Err(e) => {
+                    // Recover by skipping to the end of the block.
+                    let guar = e.emit();
+                    self.recover_stmt();
+                    let span = lo.to(self.token.span);
+                    if self.token == token::CloseDelim(Delimiter::Brace) {
+                        self.bump();
+                    }
+                    // Always push at least one arm to make the match non-empty
+                    arms.push(Arm {
+                        attrs: Default::default(),
+                        pat: self.mk_pat(span, ast::PatKind::Err(guar)),
+                        guard: None,
+                        body: Some(self.mk_expr_err(span, guar)),
+                        span,
+                        id: DUMMY_NODE_ID,
+                        is_placeholder: false,
+                    });
+                    return Ok(self.mk_expr_with_attrs(
+                        span,
+                        ExprKind::Match(scrutinee, arms, match_kind),
+                        attrs,
+                    ));
+                }
+            }
+        }
+        let hi = self.token.span;
+        self.bump();
+        Ok(self.mk_expr_with_attrs(lo.to(hi), ExprKind::Match(scrutinee, arms, match_kind), attrs))
+    }
+
+    /// Attempt to recover from match arm body with statements and no surrounding braces.
+    fn parse_arm_body_missing_braces(
+        &mut self,
+        first_expr: &P<Expr>,
+        arrow_span: Span,
+    ) -> Option<(Span, ErrorGuaranteed)> {
+        if self.token.kind != token::Semi {
+            return None;
+        }
+        let start_snapshot = self.create_snapshot_for_diagnostic();
+        let semi_sp = self.token.span;
+        self.bump(); // `;`
+        let mut stmts =
+            vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
+        let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
+            let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
+
+            let guar = this.dcx().emit_err(errors::MatchArmBodyWithoutBraces {
+                statements: span,
+                arrow: arrow_span,
+                num_statements: stmts.len(),
+                sub: if stmts.len() > 1 {
+                    errors::MatchArmBodyWithoutBracesSugg::AddBraces {
+                        left: span.shrink_to_lo(),
+                        right: span.shrink_to_hi(),
+                    }
+                } else {
+                    errors::MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
+                },
+            });
+            (span, guar)
+        };
+        // We might have either a `,` -> `;` typo, or a block without braces. We need
+        // a more subtle parsing strategy.
+        loop {
+            if self.token.kind == token::CloseDelim(Delimiter::Brace) {
+                // We have reached the closing brace of the `match` expression.
+                return Some(err(self, stmts));
+            }
+            if self.token.kind == token::Comma {
+                self.restore_snapshot(start_snapshot);
+                return None;
+            }
+            let pre_pat_snapshot = self.create_snapshot_for_diagnostic();
+            match self.parse_pat_no_top_alt(None, None) {
+                Ok(_pat) => {
+                    if self.token.kind == token::FatArrow {
+                        // Reached arm end.
+                        self.restore_snapshot(pre_pat_snapshot);
+                        return Some(err(self, stmts));
+                    }
+                }
+                Err(err) => {
+                    err.cancel();
+                }
+            }
+
+            self.restore_snapshot(pre_pat_snapshot);
+            match self.parse_stmt_without_recovery(true, ForceCollect::No) {
+                // Consume statements for as long as possible.
+                Ok(Some(stmt)) => {
+                    stmts.push(stmt);
+                }
+                Ok(None) => {
+                    self.restore_snapshot(start_snapshot);
+                    break;
+                }
+                // We couldn't parse either yet another statement missing it's
+                // enclosing block nor the next arm's pattern or closing brace.
+                Err(stmt_err) => {
+                    stmt_err.cancel();
+                    self.restore_snapshot(start_snapshot);
+                    break;
+                }
+            }
+        }
+        None
+    }
+
+    pub(super) fn parse_arm(&mut self) -> PResult<'a, Arm> {
+        let attrs = self.parse_outer_attributes()?;
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let lo = this.token.span;
+            let (pat, guard) = this.parse_match_arm_pat_and_guard()?;
+
+            let span_before_body = this.prev_token.span;
+            let arm_body;
+            let is_fat_arrow = this.check(&token::FatArrow);
+            let is_almost_fat_arrow = TokenKind::FatArrow
+                .similar_tokens()
+                .is_some_and(|similar_tokens| similar_tokens.contains(&this.token.kind));
+
+            // this avoids the compiler saying that a `,` or `}` was expected even though
+            // the pattern isn't a never pattern (and thus an arm body is required)
+            let armless = (!is_fat_arrow && !is_almost_fat_arrow && pat.could_be_never_pattern())
+                || matches!(this.token.kind, token::Comma | token::CloseDelim(Delimiter::Brace));
+
+            let mut result = if armless {
+                // A pattern without a body, allowed for never patterns.
+                arm_body = None;
+                this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)]).map(
+                    |x| {
+                        // Don't gate twice
+                        if !pat.contains_never_pattern() {
+                            this.psess.gated_spans.gate(sym::never_patterns, pat.span);
+                        }
+                        x
+                    },
+                )
+            } else {
+                if let Err(mut err) = this.expect(&token::FatArrow) {
+                    // We might have a `=>` -> `=` or `->` typo (issue #89396).
+                    if is_almost_fat_arrow {
+                        err.span_suggestion(
+                            this.token.span,
+                            "use a fat arrow to start a match arm",
+                            "=>",
+                            Applicability::MachineApplicable,
+                        );
+                        if matches!(
+                            (&this.prev_token.kind, &this.token.kind),
+                            (token::DotDotEq, token::Gt)
+                        ) {
+                            // `error_inclusive_range_match_arrow` handles cases like `0..=> {}`,
+                            // so we suppress the error here
+                            err.delay_as_bug();
+                        } else {
+                            err.emit();
+                        }
+                        this.bump();
+                    } else {
+                        return Err(err);
+                    }
+                }
+                let arrow_span = this.prev_token.span;
+                let arm_start_span = this.token.span;
+
+                let expr =
+                    this.parse_expr_res(Restrictions::STMT_EXPR, None).map_err(|mut err| {
+                        err.span_label(arrow_span, "while parsing the `match` arm starting here");
+                        err
+                    })?;
+
+                let require_comma = !classify::expr_is_complete(&expr)
+                    && this.token != token::CloseDelim(Delimiter::Brace);
+
+                if !require_comma {
+                    arm_body = Some(expr);
+                    this.eat(&token::Comma);
+                    Ok(Recovered::No)
+                } else if let Some((span, guar)) =
+                    this.parse_arm_body_missing_braces(&expr, arrow_span)
+                {
+                    let body = this.mk_expr_err(span, guar);
+                    arm_body = Some(body);
+                    Ok(Recovered::Yes(guar))
+                } else {
+                    let expr_span = expr.span;
+                    arm_body = Some(expr);
+                    this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
+                        .map_err(|mut err| {
+                            if this.token == token::FatArrow {
+                                let sm = this.psess.source_map();
+                                if let Ok(expr_lines) = sm.span_to_lines(expr_span)
+                                    && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
+                                    && arm_start_lines.lines[0].end_col
+                                        == expr_lines.lines[0].end_col
+                                    && expr_lines.lines.len() == 2
+                                {
+                                    // We check whether there's any trailing code in the parse span,
+                                    // if there isn't, we very likely have the following:
+                                    //
+                                    // X |     &Y => "y"
+                                    //   |        --    - missing comma
+                                    //   |        |
+                                    //   |        arrow_span
+                                    // X |     &X => "x"
+                                    //   |      - ^^ self.token.span
+                                    //   |      |
+                                    //   |      parsed until here as `"y" & X`
+                                    err.span_suggestion_short(
+                                        arm_start_span.shrink_to_hi(),
+                                        "missing a comma here to end this `match` arm",
+                                        ",",
+                                        Applicability::MachineApplicable,
+                                    );
+                                }
+                            } else {
+                                err.span_label(
+                                    arrow_span,
+                                    "while parsing the `match` arm starting here",
+                                );
+                            }
+                            err
+                        })
+                }
+            };
+
+            let hi_span = arm_body.as_ref().map_or(span_before_body, |body| body.span);
+            let arm_span = lo.to(hi_span);
+
+            // We want to recover:
+            // X |     Some(_) => foo()
+            //   |                     - missing comma
+            // X |     None => "x"
+            //   |     ^^^^ self.token.span
+            // as well as:
+            // X |     Some(!)
+            //   |            - missing comma
+            // X |     None => "x"
+            //   |     ^^^^ self.token.span
+            // But we musn't recover
+            // X |     pat[0] => {}
+            //   |        ^ self.token.span
+            let recover_missing_comma = arm_body.is_some() || pat.could_be_never_pattern();
+            if recover_missing_comma {
+                result = result.or_else(|err| {
+                    // FIXME(compiler-errors): We could also recover `; PAT =>` here
+
+                    // Try to parse a following `PAT =>`, if successful
+                    // then we should recover.
+                    let mut snapshot = this.create_snapshot_for_diagnostic();
+                    let pattern_follows = snapshot
+                        .parse_pat_allow_top_alt(
+                            None,
+                            RecoverComma::Yes,
+                            RecoverColon::Yes,
+                            CommaRecoveryMode::EitherTupleOrPipe,
+                        )
+                        .map_err(|err| err.cancel())
+                        .is_ok();
+                    if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
+                        err.cancel();
+                        let guar = this.dcx().emit_err(errors::MissingCommaAfterMatchArm {
+                            span: arm_span.shrink_to_hi(),
+                        });
+                        return Ok(Recovered::Yes(guar));
+                    }
+                    Err(err)
+                });
+            }
+            result?;
+
+            Ok((
+                ast::Arm {
+                    attrs,
+                    pat,
+                    guard,
+                    body: arm_body,
+                    span: arm_span,
+                    id: DUMMY_NODE_ID,
+                    is_placeholder: false,
+                },
+                TrailingToken::None,
+            ))
+        })
+    }
+
+    fn parse_match_arm_guard(&mut self) -> PResult<'a, Option<P<Expr>>> {
+        // Used to check the `let_chains` and `if_let_guard` features mostly by scanning
+        // `&&` tokens.
+        fn check_let_expr(expr: &Expr) -> (bool, bool) {
+            match &expr.kind {
+                ExprKind::Binary(BinOp { node: BinOpKind::And, .. }, lhs, rhs) => {
+                    let lhs_rslt = check_let_expr(lhs);
+                    let rhs_rslt = check_let_expr(rhs);
+                    (lhs_rslt.0 || rhs_rslt.0, false)
+                }
+                ExprKind::Let(..) => (true, true),
+                _ => (false, true),
+            }
+        }
+        if !self.eat_keyword(kw::If) {
+            // No match arm guard present.
+            return Ok(None);
+        }
+
+        let if_span = self.prev_token.span;
+        let mut cond = self.parse_match_guard_condition()?;
+
+        CondChecker::new(self).visit_expr(&mut cond);
+
+        let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
+        if has_let_expr {
+            if does_not_have_bin_op {
+                // Remove the last feature gating of a `let` expression since it's stable.
+                self.psess.gated_spans.ungate_last(sym::let_chains, cond.span);
+            }
+            let span = if_span.to(cond.span);
+            self.psess.gated_spans.gate(sym::if_let_guard, span);
+        }
+        Ok(Some(cond))
+    }
+
+    fn parse_match_arm_pat_and_guard(&mut self) -> PResult<'a, (P<Pat>, Option<P<Expr>>)> {
+        if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
+            // Detect and recover from `($pat if $cond) => $arm`.
+            let left = self.token.span;
+            match self.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::Yes,
+                RecoverColon::Yes,
+                CommaRecoveryMode::EitherTupleOrPipe,
+            ) {
+                Ok(pat) => Ok((pat, self.parse_match_arm_guard()?)),
+                Err(err)
+                    if let prev_sp = self.prev_token.span
+                        && let true = self.eat_keyword(kw::If) =>
+                {
+                    // We know for certain we've found `($pat if` so far.
+                    let mut cond = match self.parse_match_guard_condition() {
+                        Ok(cond) => cond,
+                        Err(cond_err) => {
+                            cond_err.cancel();
+                            return Err(err);
+                        }
+                    };
+                    err.cancel();
+                    CondChecker::new(self).visit_expr(&mut cond);
+                    self.eat_to_tokens(&[&token::CloseDelim(Delimiter::Parenthesis)]);
+                    self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+                    let right = self.prev_token.span;
+                    self.dcx().emit_err(errors::ParenthesesInMatchPat {
+                        span: vec![left, right],
+                        sugg: errors::ParenthesesInMatchPatSugg { left, right },
+                    });
+                    Ok((self.mk_pat(left.to(prev_sp), ast::PatKind::Wild), Some(cond)))
+                }
+                Err(err) => Err(err),
+            }
+        } else {
+            // Regular parser flow:
+            let pat = self.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::Yes,
+                RecoverColon::Yes,
+                CommaRecoveryMode::EitherTupleOrPipe,
+            )?;
+            Ok((pat, self.parse_match_arm_guard()?))
+        }
+    }
+
+    fn parse_match_guard_condition(&mut self) -> PResult<'a, P<Expr>> {
+        self.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, None).map_err(
+            |mut err| {
+                if self.prev_token == token::OpenDelim(Delimiter::Brace) {
+                    let sugg_sp = self.prev_token.span.shrink_to_lo();
+                    // Consume everything within the braces, let's avoid further parse
+                    // errors.
+                    self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
+                    let msg = "you might have meant to start a match arm after the match guard";
+                    if self.eat(&token::CloseDelim(Delimiter::Brace)) {
+                        let applicability = if self.token.kind != token::FatArrow {
+                            // We have high confidence that we indeed didn't have a struct
+                            // literal in the match guard, but rather we had some operation
+                            // that ended in a path, immediately followed by a block that was
+                            // meant to be the match arm.
+                            Applicability::MachineApplicable
+                        } else {
+                            Applicability::MaybeIncorrect
+                        };
+                        err.span_suggestion_verbose(sugg_sp, msg, "=> ", applicability);
+                    }
+                }
+                err
+            },
+        )
+    }
+
+    pub(crate) fn is_builtin(&self) -> bool {
+        self.token.is_keyword(kw::Builtin) && self.look_ahead(1, |t| *t == token::Pound)
+    }
+
+    /// Parses a `try {...}` expression (`try` token already eaten).
+    fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
+        let (attrs, body) = self.parse_inner_attrs_and_block()?;
+        if self.eat_keyword(kw::Catch) {
+            Err(self.dcx().create_err(errors::CatchAfterTry { span: self.prev_token.span }))
+        } else {
+            let span = span_lo.to(body.span);
+            self.psess.gated_spans.gate(sym::try_blocks, span);
+            Ok(self.mk_expr_with_attrs(span, ExprKind::TryBlock(body), attrs))
+        }
+    }
+
+    fn is_do_catch_block(&self) -> bool {
+        self.token.is_keyword(kw::Do)
+            && self.is_keyword_ahead(1, &[kw::Catch])
+            && self
+                .look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+            && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+    }
+
+    fn is_do_yeet(&self) -> bool {
+        self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
+    }
+
+    fn is_try_block(&self) -> bool {
+        self.token.is_keyword(kw::Try)
+            && self
+                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+            && self.token.uninterpolated_span().at_least_rust_2018()
+    }
+
+    /// Parses an `async move? {...}` or `gen move? {...}` expression.
+    fn parse_gen_block(&mut self) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+        let kind = if self.eat_keyword(kw::Async) {
+            if self.eat_keyword(kw::Gen) { GenBlockKind::AsyncGen } else { GenBlockKind::Async }
+        } else {
+            assert!(self.eat_keyword(kw::Gen));
+            GenBlockKind::Gen
+        };
+        match kind {
+            GenBlockKind::Async => {
+                // `async` blocks are stable
+            }
+            GenBlockKind::Gen | GenBlockKind::AsyncGen => {
+                self.psess.gated_spans.gate(sym::gen_blocks, lo.to(self.prev_token.span));
+            }
+        }
+        let capture_clause = self.parse_capture_clause()?;
+        let (attrs, body) = self.parse_inner_attrs_and_block()?;
+        let kind = ExprKind::Gen(capture_clause, body, kind);
+        Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
+    }
+
+    fn is_gen_block(&self, kw: Symbol, lookahead: usize) -> bool {
+        self.is_keyword_ahead(lookahead, &[kw])
+            && ((
+                // `async move {`
+                self.is_keyword_ahead(lookahead + 1, &[kw::Move])
+                    && self.look_ahead(lookahead + 2, |t| {
+                        *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                    })
+            ) || (
+                // `async {`
+                self.look_ahead(lookahead + 1, |t| {
+                    *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                })
+            ))
+    }
+
+    pub(super) fn is_async_gen_block(&self) -> bool {
+        self.token.is_keyword(kw::Async) && self.is_gen_block(kw::Gen, 1)
+    }
+
+    fn is_certainly_not_a_block(&self) -> bool {
+        self.look_ahead(1, |t| t.is_ident())
+            && (
+                // `{ ident, ` cannot start a block.
+                self.look_ahead(2, |t| t == &token::Comma)
+                    || self.look_ahead(2, |t| t == &token::Colon)
+                        && (
+                            // `{ ident: token, ` cannot start a block.
+                            self.look_ahead(4, |t| t == &token::Comma)
+                                // `{ ident: ` cannot start a block unless it's a type ascription
+                                // `ident: Type`.
+                                || self.look_ahead(3, |t| !t.can_begin_type())
+                        )
+            )
+    }
+
+    fn maybe_parse_struct_expr(
+        &mut self,
+        qself: &Option<P<ast::QSelf>>,
+        path: &ast::Path,
+    ) -> Option<PResult<'a, P<Expr>>> {
+        let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
+        if struct_allowed || self.is_certainly_not_a_block() {
+            if let Err(err) = self.expect(&token::OpenDelim(Delimiter::Brace)) {
+                return Some(Err(err));
+            }
+            let expr = self.parse_expr_struct(qself.clone(), path.clone(), true);
+            if let (Ok(expr), false) = (&expr, struct_allowed) {
+                // This is a struct literal, but we don't can't accept them here.
+                self.dcx().emit_err(errors::StructLiteralNotAllowedHere {
+                    span: expr.span,
+                    sub: errors::StructLiteralNotAllowedHereSugg {
+                        left: path.span.shrink_to_lo(),
+                        right: expr.span.shrink_to_hi(),
+                    },
+                });
+            }
+            return Some(expr);
+        }
+        None
+    }
+
+    pub(super) fn parse_struct_fields(
+        &mut self,
+        pth: ast::Path,
+        recover: bool,
+        close_delim: Delimiter,
+    ) -> PResult<
+        'a,
+        (
+            ThinVec<ExprField>,
+            ast::StructRest,
+            Option<ErrorGuaranteed>, /* async blocks are forbidden in Rust 2015 */
+        ),
+    > {
+        let mut fields = ThinVec::new();
+        let mut base = ast::StructRest::None;
+        let mut recovered_async = None;
+        let in_if_guard = self.restrictions.contains(Restrictions::IN_IF_GUARD);
+
+        let async_block_err = |e: &mut Diag<'_>, span: Span| {
+            errors::AsyncBlockIn2015 { span }.add_to_diag(e);
+            errors::HelpUseLatestEdition::new().add_to_diag(e);
+        };
+
+        while self.token != token::CloseDelim(close_delim) {
+            if self.eat(&token::DotDot) || self.recover_struct_field_dots(close_delim) {
+                let exp_span = self.prev_token.span;
+                // We permit `.. }` on the left-hand side of a destructuring assignment.
+                if self.check(&token::CloseDelim(close_delim)) {
+                    base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi());
+                    break;
+                }
+                match self.parse_expr() {
+                    Ok(e) => base = ast::StructRest::Base(e),
+                    Err(e) if recover => {
+                        e.emit();
+                        self.recover_stmt();
+                    }
+                    Err(e) => return Err(e),
+                }
+                self.recover_struct_comma_after_dotdot(exp_span);
+                break;
+            }
+
+            // Peek the field's ident before parsing its expr in order to emit better diagnostics.
+            let peek = self
+                .token
+                .ident()
+                .filter(|(ident, is_raw)| {
+                    (!ident.is_reserved() || matches!(is_raw, IdentIsRaw::Yes))
+                        && self.look_ahead(1, |tok| *tok == token::Colon)
+                })
+                .map(|(ident, _)| ident);
+
+            // We still want a field even if its expr didn't parse.
+            let field_ident = |this: &Self, guar: ErrorGuaranteed| {
+                peek.map(|ident| {
+                    let span = ident.span;
+                    ExprField {
+                        ident,
+                        span,
+                        expr: this.mk_expr_err(span, guar),
+                        is_shorthand: false,
+                        attrs: AttrVec::new(),
+                        id: DUMMY_NODE_ID,
+                        is_placeholder: false,
+                    }
+                })
+            };
+
+            let parsed_field = match self.parse_expr_field() {
+                Ok(f) => Ok(f),
+                Err(mut e) => {
+                    if pth == kw::Async {
+                        async_block_err(&mut e, pth.span);
+                    } else {
+                        e.span_label(pth.span, "while parsing this struct");
+                    }
+
+                    if let Some((ident, _)) = self.token.ident()
+                        && !self.token.is_reserved_ident()
+                        && self.look_ahead(1, |t| {
+                            AssocOp::from_token(t).is_some()
+                                || matches!(t.kind, token::OpenDelim(_))
+                                || t.kind == token::Dot
+                        })
+                    {
+                        // Looks like they tried to write a shorthand, complex expression.
+                        e.span_suggestion_verbose(
+                            self.token.span.shrink_to_lo(),
+                            "try naming a field",
+                            &format!("{ident}: ",),
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    if in_if_guard && close_delim == Delimiter::Brace {
+                        return Err(e);
+                    }
+
+                    if !recover {
+                        return Err(e);
+                    }
+
+                    let guar = e.emit();
+                    if pth == kw::Async {
+                        recovered_async = Some(guar);
+                    }
+
+                    // If the next token is a comma, then try to parse
+                    // what comes next as additional fields, rather than
+                    // bailing out until next `}`.
+                    if self.token != token::Comma {
+                        self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
+                        if self.token != token::Comma {
+                            break;
+                        }
+                    }
+
+                    Err(guar)
+                }
+            };
+
+            let is_shorthand = parsed_field.as_ref().is_ok_and(|f| f.is_shorthand);
+            // A shorthand field can be turned into a full field with `:`.
+            // We should point this out.
+            self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
+
+            match self.expect_one_of(&[token::Comma], &[token::CloseDelim(close_delim)]) {
+                Ok(_) => {
+                    if let Ok(f) = parsed_field.or_else(|guar| field_ident(self, guar).ok_or(guar))
+                    {
+                        // Only include the field if there's no parse error for the field name.
+                        fields.push(f);
+                    }
+                }
+                Err(mut e) => {
+                    if pth == kw::Async {
+                        async_block_err(&mut e, pth.span);
+                    } else {
+                        e.span_label(pth.span, "while parsing this struct");
+                        if peek.is_some() {
+                            e.span_suggestion(
+                                self.prev_token.span.shrink_to_hi(),
+                                "try adding a comma",
+                                ",",
+                                Applicability::MachineApplicable,
+                            );
+                        }
+                    }
+                    if !recover {
+                        return Err(e);
+                    }
+                    let guar = e.emit();
+                    if pth == kw::Async {
+                        recovered_async = Some(guar);
+                    } else if let Some(f) = field_ident(self, guar) {
+                        fields.push(f);
+                    }
+                    self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
+                    self.eat(&token::Comma);
+                }
+            }
+        }
+        Ok((fields, base, recovered_async))
+    }
+
+    /// Precondition: already parsed the '{'.
+    pub(super) fn parse_expr_struct(
+        &mut self,
+        qself: Option<P<ast::QSelf>>,
+        pth: ast::Path,
+        recover: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let lo = pth.span;
+        let (fields, base, recovered_async) =
+            self.parse_struct_fields(pth.clone(), recover, Delimiter::Brace)?;
+        let span = lo.to(self.token.span);
+        self.expect(&token::CloseDelim(Delimiter::Brace))?;
+        let expr = if let Some(guar) = recovered_async {
+            ExprKind::Err(guar)
+        } else {
+            ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
+        };
+        Ok(self.mk_expr(span, expr))
+    }
+
+    fn recover_struct_comma_after_dotdot(&mut self, span: Span) {
+        if self.token != token::Comma {
+            return;
+        }
+        self.dcx().emit_err(errors::CommaAfterBaseStruct {
+            span: span.to(self.prev_token.span),
+            comma: self.token.span,
+        });
+        self.recover_stmt();
+    }
+
+    fn recover_struct_field_dots(&mut self, close_delim: Delimiter) -> bool {
+        if !self.look_ahead(1, |t| *t == token::CloseDelim(close_delim))
+            && self.eat(&token::DotDotDot)
+        {
+            // recover from typo of `...`, suggest `..`
+            let span = self.prev_token.span;
+            self.dcx().emit_err(errors::MissingDotDot { token_span: span, sugg_span: span });
+            return true;
+        }
+        false
+    }
+
+    /// Converts an ident into 'label and emits an "expected a label, found an identifier" error.
+    fn recover_ident_into_label(&mut self, ident: Ident) -> Label {
+        // Convert `label` -> `'label`,
+        // so that nameres doesn't complain about non-existing label
+        let label = format!("'{}", ident.name);
+        let ident = Ident { name: Symbol::intern(&label), span: ident.span };
+
+        self.dcx().emit_err(errors::ExpectedLabelFoundIdent {
+            span: ident.span,
+            start: ident.span.shrink_to_lo(),
+        });
+
+        Label { ident }
+    }
+
+    /// Parses `ident (COLON expr)?`.
+    fn parse_expr_field(&mut self) -> PResult<'a, ExprField> {
+        let attrs = self.parse_outer_attributes()?;
+        self.recover_vcs_conflict_marker();
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let lo = this.token.span;
+
+            // Check if a colon exists one ahead. This means we're parsing a fieldname.
+            let is_shorthand = !this.look_ahead(1, |t| t == &token::Colon || t == &token::Eq);
+            // Proactively check whether parsing the field will be incorrect.
+            let is_wrong = this.token.is_ident()
+                && !this.token.is_reserved_ident()
+                && !this.look_ahead(1, |t| {
+                    t == &token::Colon
+                        || t == &token::Eq
+                        || t == &token::Comma
+                        || t == &token::CloseDelim(Delimiter::Brace)
+                        || t == &token::CloseDelim(Delimiter::Parenthesis)
+                });
+            if is_wrong {
+                return Err(this.dcx().create_err(errors::ExpectedStructField {
+                    span: this.look_ahead(1, |t| t.span),
+                    ident_span: this.token.span,
+                    token: this.look_ahead(1, |t| t.clone()),
+                }));
+            }
+            let (ident, expr) = if is_shorthand {
+                // Mimic `x: x` for the `x` field shorthand.
+                let ident = this.parse_ident_common(false)?;
+                let path = ast::Path::from_ident(ident);
+                (ident, this.mk_expr(ident.span, ExprKind::Path(None, path)))
+            } else {
+                let ident = this.parse_field_name()?;
+                this.error_on_eq_field_init(ident);
+                this.bump(); // `:`
+                (ident, this.parse_expr()?)
+            };
+
+            Ok((
+                ast::ExprField {
+                    ident,
+                    span: lo.to(expr.span),
+                    expr,
+                    is_shorthand,
+                    attrs,
+                    id: DUMMY_NODE_ID,
+                    is_placeholder: false,
+                },
+                TrailingToken::MaybeComma,
+            ))
+        })
+    }
+
+    /// Check for `=`. This means the source incorrectly attempts to
+    /// initialize a field with an eq rather than a colon.
+    fn error_on_eq_field_init(&self, field_name: Ident) {
+        if self.token != token::Eq {
+            return;
+        }
+
+        self.dcx().emit_err(errors::EqFieldInit {
+            span: self.token.span,
+            eq: field_name.span.shrink_to_hi().to(self.token.span),
+        });
+    }
+
+    fn err_dotdotdot_syntax(&self, span: Span) {
+        self.dcx().emit_err(errors::DotDotDot { span });
+    }
+
+    fn err_larrow_operator(&self, span: Span) {
+        self.dcx().emit_err(errors::LeftArrowOperator { span });
+    }
+
+    fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+        ExprKind::AssignOp(binop, lhs, rhs)
+    }
+
+    fn mk_range(
+        &mut self,
+        start: Option<P<Expr>>,
+        end: Option<P<Expr>>,
+        limits: RangeLimits,
+    ) -> ExprKind {
+        if end.is_none() && limits == RangeLimits::Closed {
+            let guar = self.inclusive_range_with_incorrect_end();
+            ExprKind::Err(guar)
+        } else {
+            ExprKind::Range(start, end, limits)
+        }
+    }
+
+    fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
+        ExprKind::Unary(unop, expr)
+    }
+
+    fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+        ExprKind::Binary(binop, lhs, rhs)
+    }
+
+    fn mk_index(&self, expr: P<Expr>, idx: P<Expr>, brackets_span: Span) -> ExprKind {
+        ExprKind::Index(expr, idx, brackets_span)
+    }
+
+    fn mk_call(&self, f: P<Expr>, args: ThinVec<P<Expr>>) -> ExprKind {
+        ExprKind::Call(f, args)
+    }
+
+    fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
+        let span = lo.to(self.prev_token.span);
+        let await_expr = self.mk_expr(span, ExprKind::Await(self_arg, self.prev_token.span));
+        self.recover_from_await_method_call();
+        await_expr
+    }
+
+    pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
+        P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
+    }
+
+    pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
+        self.mk_expr_with_attrs(span, kind, AttrVec::new())
+    }
+
+    pub(super) fn mk_expr_err(&self, span: Span, guar: ErrorGuaranteed) -> P<Expr> {
+        self.mk_expr(span, ExprKind::Err(guar))
+    }
+
+    fn collect_tokens_for_expr(
+        &mut self,
+        attrs: AttrWrapper,
+        f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
+    ) -> PResult<'a, P<Expr>> {
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let res = f(this, attrs)?;
+            let trailing = if this.restrictions.contains(Restrictions::STMT_EXPR)
+                && this.token.kind == token::Semi
+            {
+                TrailingToken::Semi
+            } else if this.token.kind == token::Gt {
+                TrailingToken::Gt
+            } else {
+                // FIXME - pass this through from the place where we know
+                // we need a comma, rather than assuming that `#[attr] expr,`
+                // always captures a trailing comma
+                TrailingToken::MaybeComma
+            };
+            Ok((res, trailing))
+        })
+    }
+}
+
+/// Could this lifetime/label be an unclosed char literal? For example, `'a`
+/// could be, but `'abc` could not.
+pub(crate) fn could_be_unclosed_char_literal(ident: Ident) -> bool {
+    ident.name.as_str().starts_with('\'')
+        && unescape_char(ident.without_first_quote().name.as_str()).is_ok()
+}
+
+/// Used to forbid `let` expressions in certain syntactic locations.
+#[derive(Clone, Copy, Subdiagnostic)]
+pub(crate) enum ForbiddenLetReason {
+    /// `let` is not valid and the source environment is not important
+    OtherForbidden,
+    /// A let chain with the `||` operator
+    #[note(parse_not_supported_or)]
+    NotSupportedOr(#[primary_span] Span),
+    /// A let chain with invalid parentheses
+    ///
+    /// For example, `let 1 = 1 && (expr && expr)` is allowed
+    /// but `(let 1 = 1 && (let 1 = 1 && (let 1 = 1))) && let a = 1` is not
+    #[note(parse_not_supported_parentheses)]
+    NotSupportedParentheses(#[primary_span] Span),
+}
+
+/// Visitor to check for invalid/unstable use of `ExprKind::Let` that can't
+/// easily be caught in parsing. For example:
+///
+/// ```rust,ignore (example)
+/// // Only know that the let isn't allowed once the `||` token is reached
+/// if let Some(x) = y || true {}
+/// // Only know that the let isn't allowed once the second `=` token is reached.
+/// if let Some(x) = y && z = 1 {}
+/// ```
+struct CondChecker<'a> {
+    parser: &'a Parser<'a>,
+    forbid_let_reason: Option<ForbiddenLetReason>,
+    missing_let: Option<errors::MaybeMissingLet>,
+    comparison: Option<errors::MaybeComparison>,
+}
+
+impl<'a> CondChecker<'a> {
+    fn new(parser: &'a Parser<'a>) -> Self {
+        CondChecker { parser, forbid_let_reason: None, missing_let: None, comparison: None }
+    }
+}
+
+impl MutVisitor for CondChecker<'_> {
+    fn visit_expr(&mut self, e: &mut P<Expr>) {
+        use ForbiddenLetReason::*;
+
+        let span = e.span;
+        match e.kind {
+            ExprKind::Let(_, _, _, ref mut recovered @ Recovered::No) => {
+                if let Some(reason) = self.forbid_let_reason {
+                    *recovered = Recovered::Yes(self.parser.dcx().emit_err(
+                        errors::ExpectedExpressionFoundLet {
+                            span,
+                            reason,
+                            missing_let: self.missing_let,
+                            comparison: self.comparison,
+                        },
+                    ));
+                } else {
+                    self.parser.psess.gated_spans.gate(sym::let_chains, span);
+                }
+            }
+            ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, _, _) => {
+                noop_visit_expr(e, self);
+            }
+            ExprKind::Binary(Spanned { node: BinOpKind::Or, span: or_span }, _, _)
+                if let None | Some(NotSupportedOr(_)) = self.forbid_let_reason =>
+            {
+                let forbid_let_reason = self.forbid_let_reason;
+                self.forbid_let_reason = Some(NotSupportedOr(or_span));
+                noop_visit_expr(e, self);
+                self.forbid_let_reason = forbid_let_reason;
+            }
+            ExprKind::Paren(ref inner)
+                if let None | Some(NotSupportedParentheses(_)) = self.forbid_let_reason =>
+            {
+                let forbid_let_reason = self.forbid_let_reason;
+                self.forbid_let_reason = Some(NotSupportedParentheses(inner.span));
+                noop_visit_expr(e, self);
+                self.forbid_let_reason = forbid_let_reason;
+            }
+            ExprKind::Assign(ref lhs, _, span) => {
+                let forbid_let_reason = self.forbid_let_reason;
+                self.forbid_let_reason = Some(OtherForbidden);
+                let missing_let = self.missing_let;
+                if let ExprKind::Binary(_, _, rhs) = &lhs.kind
+                    && let ExprKind::Path(_, _)
+                    | ExprKind::Struct(_)
+                    | ExprKind::Call(_, _)
+                    | ExprKind::Array(_) = rhs.kind
+                {
+                    self.missing_let =
+                        Some(errors::MaybeMissingLet { span: rhs.span.shrink_to_lo() });
+                }
+                let comparison = self.comparison;
+                self.comparison = Some(errors::MaybeComparison { span: span.shrink_to_hi() });
+                noop_visit_expr(e, self);
+                self.forbid_let_reason = forbid_let_reason;
+                self.missing_let = missing_let;
+                self.comparison = comparison;
+            }
+            ExprKind::Unary(_, _)
+            | ExprKind::Await(_, _)
+            | ExprKind::AssignOp(_, _, _)
+            | ExprKind::Range(_, _, _)
+            | ExprKind::Try(_)
+            | ExprKind::AddrOf(_, _, _)
+            | ExprKind::Binary(_, _, _)
+            | ExprKind::Field(_, _)
+            | ExprKind::Index(_, _, _)
+            | ExprKind::Call(_, _)
+            | ExprKind::MethodCall(_)
+            | ExprKind::Tup(_)
+            | ExprKind::Paren(_) => {
+                let forbid_let_reason = self.forbid_let_reason;
+                self.forbid_let_reason = Some(OtherForbidden);
+                noop_visit_expr(e, self);
+                self.forbid_let_reason = forbid_let_reason;
+            }
+            ExprKind::Cast(ref mut op, _) | ExprKind::Type(ref mut op, _) => {
+                let forbid_let_reason = self.forbid_let_reason;
+                self.forbid_let_reason = Some(OtherForbidden);
+                self.visit_expr(op);
+                self.forbid_let_reason = forbid_let_reason;
+            }
+            ExprKind::Let(_, _, _, Recovered::Yes(_))
+            | ExprKind::Array(_)
+            | ExprKind::ConstBlock(_)
+            | ExprKind::Lit(_)
+            | ExprKind::If(_, _, _)
+            | ExprKind::While(_, _, _)
+            | ExprKind::ForLoop { .. }
+            | ExprKind::Loop(_, _, _)
+            | ExprKind::Match(_, _, _)
+            | ExprKind::Closure(_)
+            | ExprKind::Block(_, _)
+            | ExprKind::Gen(_, _, _)
+            | ExprKind::TryBlock(_)
+            | ExprKind::Underscore
+            | ExprKind::Path(_, _)
+            | ExprKind::Break(_, _)
+            | ExprKind::Continue(_)
+            | ExprKind::Ret(_)
+            | ExprKind::InlineAsm(_)
+            | ExprKind::OffsetOf(_, _)
+            | ExprKind::MacCall(_)
+            | ExprKind::Struct(_)
+            | ExprKind::Repeat(_, _)
+            | ExprKind::Yield(_)
+            | ExprKind::Yeet(_)
+            | ExprKind::Become(_)
+            | ExprKind::IncludedBytes(_)
+            | ExprKind::FormatArgs(_)
+            | ExprKind::Err(_)
+            | ExprKind::Dummy => {
+                // These would forbid any let expressions they contain already.
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
new file mode 100644
index 00000000000..93a15c938ec
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -0,0 +1,518 @@
+use crate::errors::{
+    self, MultipleWhereClauses, UnexpectedDefaultValueForLifetimeInGenericParameters,
+    UnexpectedSelfInGenericParameters, WhereClauseBeforeTupleStructBody,
+    WhereClauseBeforeTupleStructBodySugg,
+};
+
+use super::{ForceCollect, Parser, TrailingToken};
+
+use ast::token::Delimiter;
+use rustc_ast::token;
+use rustc_ast::{
+    self as ast, AttrVec, GenericBounds, GenericParam, GenericParamKind, TyKind, WhereClause,
+};
+use rustc_errors::{Applicability, PResult};
+use rustc_span::symbol::{kw, Ident};
+use rustc_span::Span;
+use thin_vec::ThinVec;
+
+enum PredicateOrStructBody {
+    Predicate(ast::WherePredicate),
+    StructBody(ThinVec<ast::FieldDef>),
+}
+
+impl<'a> Parser<'a> {
+    /// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
+    ///
+    /// ```text
+    /// BOUND = LT_BOUND (e.g., `'a`)
+    /// ```
+    fn parse_lt_param_bounds(&mut self) -> GenericBounds {
+        let mut lifetimes = Vec::new();
+        while self.check_lifetime() {
+            lifetimes.push(ast::GenericBound::Outlives(self.expect_lifetime()));
+
+            if !self.eat_plus() {
+                break;
+            }
+        }
+        lifetimes
+    }
+
+    /// Matches `typaram = IDENT (`?` unbound)? optbounds ( EQ ty )?`.
+    fn parse_ty_param(&mut self, preceding_attrs: AttrVec) -> PResult<'a, GenericParam> {
+        let ident = self.parse_ident()?;
+
+        // We might have a typo'd `Const` that was parsed as a type parameter.
+        if self.may_recover()
+            && ident.name.as_str().to_ascii_lowercase() == kw::Const.as_str()
+            && self.check_ident()
+        // `Const` followed by IDENT
+        {
+            return self.recover_const_param_with_mistyped_const(preceding_attrs, ident);
+        }
+
+        // Parse optional colon and param bounds.
+        let mut colon_span = None;
+        let bounds = if self.eat(&token::Colon) {
+            colon_span = Some(self.prev_token.span);
+            // recover from `impl Trait` in type param bound
+            if self.token.is_keyword(kw::Impl) {
+                let impl_span = self.token.span;
+                let snapshot = self.create_snapshot_for_diagnostic();
+                match self.parse_ty() {
+                    Ok(p) => {
+                        if let TyKind::ImplTrait(_, bounds, None) = &p.kind {
+                            let span = impl_span.to(self.token.span.shrink_to_lo());
+                            let mut err = self.dcx().struct_span_err(
+                                span,
+                                "expected trait bound, found `impl Trait` type",
+                            );
+                            err.span_label(span, "not a trait");
+                            if let [bound, ..] = &bounds[..] {
+                                err.span_suggestion_verbose(
+                                    impl_span.until(bound.span()),
+                                    "use the trait bounds directly",
+                                    String::new(),
+                                    Applicability::MachineApplicable,
+                                );
+                            }
+                            return Err(err);
+                        }
+                    }
+                    Err(err) => {
+                        err.cancel();
+                    }
+                }
+                self.restore_snapshot(snapshot);
+            }
+            self.parse_generic_bounds()?
+        } else {
+            Vec::new()
+        };
+
+        let default = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
+        Ok(GenericParam {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            attrs: preceding_attrs,
+            bounds,
+            kind: GenericParamKind::Type { default },
+            is_placeholder: false,
+            colon_span,
+        })
+    }
+
+    pub(crate) fn parse_const_param(
+        &mut self,
+        preceding_attrs: AttrVec,
+    ) -> PResult<'a, GenericParam> {
+        let const_span = self.token.span;
+
+        self.expect_keyword(kw::Const)?;
+        let ident = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        // Parse optional const generics default value.
+        let default = if self.eat(&token::Eq) { Some(self.parse_const_arg()?) } else { None };
+
+        Ok(GenericParam {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            attrs: preceding_attrs,
+            bounds: Vec::new(),
+            kind: GenericParamKind::Const { ty, kw_span: const_span, default },
+            is_placeholder: false,
+            colon_span: None,
+        })
+    }
+
+    pub(crate) fn recover_const_param_with_mistyped_const(
+        &mut self,
+        preceding_attrs: AttrVec,
+        mistyped_const_ident: Ident,
+    ) -> PResult<'a, GenericParam> {
+        let ident = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        // Parse optional const generics default value.
+        let default = if self.eat(&token::Eq) { Some(self.parse_const_arg()?) } else { None };
+
+        self.dcx()
+            .struct_span_err(
+                mistyped_const_ident.span,
+                format!("`const` keyword was mistyped as `{}`", mistyped_const_ident.as_str()),
+            )
+            .with_span_suggestion_verbose(
+                mistyped_const_ident.span,
+                "use the `const` keyword",
+                kw::Const,
+                Applicability::MachineApplicable,
+            )
+            .emit();
+
+        Ok(GenericParam {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            attrs: preceding_attrs,
+            bounds: Vec::new(),
+            kind: GenericParamKind::Const { ty, kw_span: mistyped_const_ident.span, default },
+            is_placeholder: false,
+            colon_span: None,
+        })
+    }
+
+    /// Parses a (possibly empty) list of lifetime and type parameters, possibly including
+    /// a trailing comma and erroneous trailing attributes.
+    pub(super) fn parse_generic_params(&mut self) -> PResult<'a, ThinVec<ast::GenericParam>> {
+        let mut params = ThinVec::new();
+        let mut done = false;
+        while !done {
+            let attrs = self.parse_outer_attributes()?;
+            let param =
+                self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+                    if this.eat_keyword_noexpect(kw::SelfUpper) {
+                        // `Self` as a generic param is invalid. Here we emit the diagnostic and continue parsing
+                        // as if `Self` never existed.
+                        this.dcx().emit_err(UnexpectedSelfInGenericParameters {
+                            span: this.prev_token.span,
+                        });
+
+                        this.eat(&token::Comma);
+                    }
+
+                    let param = if this.check_lifetime() {
+                        let lifetime = this.expect_lifetime();
+                        // Parse lifetime parameter.
+                        let (colon_span, bounds) = if this.eat(&token::Colon) {
+                            (Some(this.prev_token.span), this.parse_lt_param_bounds())
+                        } else {
+                            (None, Vec::new())
+                        };
+
+                        if this.check_noexpect(&token::Eq)
+                            && this.look_ahead(1, |t| t.is_lifetime())
+                        {
+                            let lo = this.token.span;
+                            // Parse `= 'lifetime`.
+                            this.bump(); // `=`
+                            this.bump(); // `'lifetime`
+                            let span = lo.to(this.prev_token.span);
+                            this.dcx().emit_err(
+                                UnexpectedDefaultValueForLifetimeInGenericParameters { span },
+                            );
+                        }
+
+                        Some(ast::GenericParam {
+                            ident: lifetime.ident,
+                            id: lifetime.id,
+                            attrs,
+                            bounds,
+                            kind: ast::GenericParamKind::Lifetime,
+                            is_placeholder: false,
+                            colon_span,
+                        })
+                    } else if this.check_keyword(kw::Const) {
+                        // Parse const parameter.
+                        Some(this.parse_const_param(attrs)?)
+                    } else if this.check_ident() {
+                        // Parse type parameter.
+                        Some(this.parse_ty_param(attrs)?)
+                    } else if this.token.can_begin_type() {
+                        // Trying to write an associated type bound? (#26271)
+                        let snapshot = this.create_snapshot_for_diagnostic();
+                        match this.parse_ty_where_predicate() {
+                            Ok(where_predicate) => {
+                                this.dcx().emit_err(errors::BadAssocTypeBounds {
+                                    span: where_predicate.span(),
+                                });
+                                // FIXME - try to continue parsing other generics?
+                                return Ok((None, TrailingToken::None));
+                            }
+                            Err(err) => {
+                                err.cancel();
+                                // FIXME - maybe we should overwrite 'self' outside of `collect_tokens`?
+                                this.restore_snapshot(snapshot);
+                                return Ok((None, TrailingToken::None));
+                            }
+                        }
+                    } else {
+                        // Check for trailing attributes and stop parsing.
+                        if !attrs.is_empty() {
+                            if !params.is_empty() {
+                                this.dcx()
+                                    .emit_err(errors::AttrAfterGeneric { span: attrs[0].span });
+                            } else {
+                                this.dcx()
+                                    .emit_err(errors::AttrWithoutGenerics { span: attrs[0].span });
+                            }
+                        }
+                        return Ok((None, TrailingToken::None));
+                    };
+
+                    if !this.eat(&token::Comma) {
+                        done = true;
+                    }
+                    // We just ate the comma, so no need to use `TrailingToken`
+                    Ok((param, TrailingToken::None))
+                })?;
+
+            if let Some(param) = param {
+                params.push(param);
+            } else {
+                break;
+            }
+        }
+        Ok(params)
+    }
+
+    /// Parses a set of optional generic type parameter declarations. Where
+    /// clauses are not parsed here, and must be added later via
+    /// `parse_where_clause()`.
+    ///
+    /// matches generics = ( ) | ( < > ) | ( < typaramseq ( , )? > ) | ( < lifetimes ( , )? > )
+    ///                  | ( < lifetimes , typaramseq ( , )? > )
+    /// where   typaramseq = ( typaram ) | ( typaram , typaramseq )
+    pub(super) fn parse_generics(&mut self) -> PResult<'a, ast::Generics> {
+        let span_lo = self.token.span;
+        let (params, span) = if self.eat_lt() {
+            let params = self.parse_generic_params()?;
+            self.expect_gt_or_maybe_suggest_closing_generics(&params)?;
+            (params, span_lo.to(self.prev_token.span))
+        } else {
+            (ThinVec::new(), self.prev_token.span.shrink_to_hi())
+        };
+        Ok(ast::Generics {
+            params,
+            where_clause: WhereClause {
+                has_where_token: false,
+                predicates: ThinVec::new(),
+                span: self.prev_token.span.shrink_to_hi(),
+            },
+            span,
+        })
+    }
+
+    /// Parses an optional where-clause.
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// where T : Trait<U, V> + 'b, 'a : 'b
+    /// ```
+    pub(super) fn parse_where_clause(&mut self) -> PResult<'a, WhereClause> {
+        self.parse_where_clause_common(None).map(|(clause, _)| clause)
+    }
+
+    pub(super) fn parse_struct_where_clause(
+        &mut self,
+        struct_name: Ident,
+        body_insertion_point: Span,
+    ) -> PResult<'a, (WhereClause, Option<ThinVec<ast::FieldDef>>)> {
+        self.parse_where_clause_common(Some((struct_name, body_insertion_point)))
+    }
+
+    fn parse_where_clause_common(
+        &mut self,
+        struct_: Option<(Ident, Span)>,
+    ) -> PResult<'a, (WhereClause, Option<ThinVec<ast::FieldDef>>)> {
+        let mut where_clause = WhereClause {
+            has_where_token: false,
+            predicates: ThinVec::new(),
+            span: self.prev_token.span.shrink_to_hi(),
+        };
+        let mut tuple_struct_body = None;
+
+        if !self.eat_keyword(kw::Where) {
+            return Ok((where_clause, None));
+        }
+        where_clause.has_where_token = true;
+        let where_lo = self.prev_token.span;
+
+        // We are considering adding generics to the `where` keyword as an alternative higher-rank
+        // parameter syntax (as in `where<'a>` or `where<T>`. To avoid that being a breaking
+        // change we parse those generics now, but report an error.
+        if self.choose_generics_over_qpath(0) {
+            let generics = self.parse_generics()?;
+            self.dcx().emit_err(errors::WhereOnGenerics { span: generics.span });
+        }
+
+        loop {
+            let where_sp = where_lo.to(self.prev_token.span);
+            let pred_lo = self.token.span;
+            if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
+                let lifetime = self.expect_lifetime();
+                // Bounds starting with a colon are mandatory, but possibly empty.
+                self.expect(&token::Colon)?;
+                let bounds = self.parse_lt_param_bounds();
+                where_clause.predicates.push(ast::WherePredicate::RegionPredicate(
+                    ast::WhereRegionPredicate {
+                        span: pred_lo.to(self.prev_token.span),
+                        lifetime,
+                        bounds,
+                    },
+                ));
+            } else if self.check_type() {
+                match self.parse_ty_where_predicate_or_recover_tuple_struct_body(
+                    struct_, pred_lo, where_sp,
+                )? {
+                    PredicateOrStructBody::Predicate(pred) => where_clause.predicates.push(pred),
+                    PredicateOrStructBody::StructBody(body) => {
+                        tuple_struct_body = Some(body);
+                        break;
+                    }
+                }
+            } else {
+                break;
+            }
+
+            let prev_token = self.prev_token.span;
+            let ate_comma = self.eat(&token::Comma);
+
+            if self.eat_keyword_noexpect(kw::Where) {
+                self.dcx().emit_err(MultipleWhereClauses {
+                    span: self.token.span,
+                    previous: pred_lo,
+                    between: prev_token.shrink_to_hi().to(self.prev_token.span),
+                });
+            } else if !ate_comma {
+                break;
+            }
+        }
+
+        where_clause.span = where_lo.to(self.prev_token.span);
+        Ok((where_clause, tuple_struct_body))
+    }
+
+    fn parse_ty_where_predicate_or_recover_tuple_struct_body(
+        &mut self,
+        struct_: Option<(Ident, Span)>,
+        pred_lo: Span,
+        where_sp: Span,
+    ) -> PResult<'a, PredicateOrStructBody> {
+        let mut snapshot = None;
+
+        if let Some(struct_) = struct_
+            && self.may_recover()
+            && self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
+        {
+            snapshot = Some((struct_, self.create_snapshot_for_diagnostic()));
+        };
+
+        match self.parse_ty_where_predicate() {
+            Ok(pred) => Ok(PredicateOrStructBody::Predicate(pred)),
+            Err(type_err) => {
+                let Some(((struct_name, body_insertion_point), mut snapshot)) = snapshot else {
+                    return Err(type_err);
+                };
+
+                // Check if we might have encountered an out of place tuple struct body.
+                match snapshot.parse_tuple_struct_body() {
+                    // Since we don't know the exact reason why we failed to parse the
+                    // predicate (we might have stumbled upon something bogus like `(T): ?`),
+                    // employ a simple heuristic to weed out some pathological cases:
+                    // Look for a semicolon (strong indicator) or anything that might mark
+                    // the end of the item (weak indicator) following the body.
+                    Ok(body)
+                        if matches!(snapshot.token.kind, token::Semi | token::Eof)
+                            || snapshot.token.can_begin_item() =>
+                    {
+                        type_err.cancel();
+
+                        let body_sp = pred_lo.to(snapshot.prev_token.span);
+                        let map = self.psess.source_map();
+
+                        self.dcx().emit_err(WhereClauseBeforeTupleStructBody {
+                            span: where_sp,
+                            name: struct_name.span,
+                            body: body_sp,
+                            sugg: map.span_to_snippet(body_sp).ok().map(|body| {
+                                WhereClauseBeforeTupleStructBodySugg {
+                                    left: body_insertion_point.shrink_to_hi(),
+                                    snippet: body,
+                                    right: map.end_point(where_sp).to(body_sp),
+                                }
+                            }),
+                        });
+
+                        self.restore_snapshot(snapshot);
+                        Ok(PredicateOrStructBody::StructBody(body))
+                    }
+                    Ok(_) => Err(type_err),
+                    Err(body_err) => {
+                        body_err.cancel();
+                        Err(type_err)
+                    }
+                }
+            }
+        }
+    }
+
+    fn parse_ty_where_predicate(&mut self) -> PResult<'a, ast::WherePredicate> {
+        let lo = self.token.span;
+        // Parse optional `for<'a, 'b>`.
+        // This `for` is parsed greedily and applies to the whole predicate,
+        // the bounded type can have its own `for` applying only to it.
+        // Examples:
+        // * `for<'a> Trait1<'a>: Trait2<'a /* ok */>`
+        // * `(for<'a> Trait1<'a>): Trait2<'a /* not ok */>`
+        // * `for<'a> for<'b> Trait1<'a, 'b>: Trait2<'a /* ok */, 'b /* not ok */>`
+        let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+
+        // Parse type with mandatory colon and (possibly empty) bounds,
+        // or with mandatory equality sign and the second type.
+        let ty = self.parse_ty_for_where_clause()?;
+        if self.eat(&token::Colon) {
+            let bounds = self.parse_generic_bounds()?;
+            Ok(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
+                span: lo.to(self.prev_token.span),
+                bound_generic_params: lifetime_defs,
+                bounded_ty: ty,
+                bounds,
+            }))
+        // FIXME: Decide what should be used here, `=` or `==`.
+        // FIXME: We are just dropping the binders in lifetime_defs on the floor here.
+        } else if self.eat(&token::Eq) || self.eat(&token::EqEq) {
+            let rhs_ty = self.parse_ty()?;
+            Ok(ast::WherePredicate::EqPredicate(ast::WhereEqPredicate {
+                span: lo.to(self.prev_token.span),
+                lhs_ty: ty,
+                rhs_ty,
+            }))
+        } else {
+            self.maybe_recover_bounds_doubled_colon(&ty)?;
+            self.unexpected_any()
+        }
+    }
+
+    pub(super) fn choose_generics_over_qpath(&self, start: usize) -> bool {
+        // There's an ambiguity between generic parameters and qualified paths in impls.
+        // If we see `<` it may start both, so we have to inspect some following tokens.
+        // The following combinations can only start generics,
+        // but not qualified paths (with one exception):
+        //     `<` `>` - empty generic parameters
+        //     `<` `#` - generic parameters with attributes
+        //     `<` (LIFETIME|IDENT) `>` - single generic parameter
+        //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
+        //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
+        //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
+        //     `<` const                - generic const parameter
+        //     `<` IDENT `?`            - RECOVERY for `impl<T ?Bound` missing a `:`, meant to
+        //                                avoid the `T?` to `Option<T>` recovery for types.
+        // The only truly ambiguous case is
+        //     `<` IDENT `>` `::` IDENT ...
+        // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
+        // because this is what almost always expected in practice, qualified paths in impls
+        // (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
+        self.look_ahead(start, |t| t == &token::Lt)
+            && (self.look_ahead(start + 1, |t| t == &token::Pound || t == &token::Gt)
+                || self.look_ahead(start + 1, |t| t.is_lifetime() || t.is_ident())
+                    && self.look_ahead(start + 2, |t| {
+                        matches!(t.kind, token::Gt | token::Comma | token::Colon | token::Eq)
+                        // Recovery-only branch -- this could be removed,
+                        // since it only affects diagnostics currently.
+                            || matches!(t.kind, token::Question)
+                    })
+                || self.is_keyword_ahead(start + 1, &[kw::Const]))
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
new file mode 100644
index 00000000000..a46c104b6d9
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -0,0 +1,2881 @@
+use super::diagnostics::{dummy_arg, ConsumeClosingDelim};
+use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
+use super::{
+    AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, Trailing, TrailingToken,
+};
+use crate::errors::{self, MacroExpandsToAdtField};
+use crate::fluent_generated as fluent;
+use crate::maybe_whole;
+use ast::token::IdentIsRaw;
+use rustc_ast::ast::*;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, TokenKind};
+use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
+use rustc_ast::util::case::Case;
+use rustc_ast::{self as ast};
+use rustc_ast_pretty::pprust;
+use rustc_errors::{codes::*, struct_span_code_err, Applicability, PResult, StashKey};
+use rustc_span::edit_distance::edit_distance;
+use rustc_span::edition::Edition;
+use rustc_span::source_map;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+use std::fmt::Write;
+use std::mem;
+use thin_vec::{thin_vec, ThinVec};
+
+impl<'a> Parser<'a> {
+    /// Parses a source module as a crate. This is the main entry point for the parser.
+    pub fn parse_crate_mod(&mut self) -> PResult<'a, ast::Crate> {
+        let (attrs, items, spans) = self.parse_mod(&token::Eof)?;
+        Ok(ast::Crate { attrs, items, spans, id: DUMMY_NODE_ID, is_placeholder: false })
+    }
+
+    /// Parses a `mod <foo> { ... }` or `mod <foo>;` item.
+    fn parse_item_mod(&mut self, attrs: &mut AttrVec) -> PResult<'a, ItemInfo> {
+        let safety = self.parse_safety(Case::Sensitive);
+        self.expect_keyword(kw::Mod)?;
+        let id = self.parse_ident()?;
+        let mod_kind = if self.eat(&token::Semi) {
+            ModKind::Unloaded
+        } else {
+            self.expect(&token::OpenDelim(Delimiter::Brace))?;
+            let (inner_attrs, items, inner_span) =
+                self.parse_mod(&token::CloseDelim(Delimiter::Brace))?;
+            attrs.extend(inner_attrs);
+            ModKind::Loaded(items, Inline::Yes, inner_span)
+        };
+        Ok((id, ItemKind::Mod(safety, mod_kind)))
+    }
+
+    /// Parses the contents of a module (inner attributes followed by module items).
+    /// We exit once we hit `term`
+    pub fn parse_mod(
+        &mut self,
+        term: &TokenKind,
+    ) -> PResult<'a, (AttrVec, ThinVec<P<Item>>, ModSpans)> {
+        let lo = self.token.span;
+        let attrs = self.parse_inner_attributes()?;
+
+        let post_attr_lo = self.token.span;
+        let mut items = ThinVec::new();
+        while let Some(item) = self.parse_item(ForceCollect::No)? {
+            self.maybe_consume_incorrect_semicolon(Some(&item));
+            items.push(item);
+        }
+
+        if !self.eat(term) {
+            let token_str = super::token_descr(&self.token);
+            if !self.maybe_consume_incorrect_semicolon(items.last().map(|x| &**x)) {
+                let msg = format!("expected item, found {token_str}");
+                let mut err = self.dcx().struct_span_err(self.token.span, msg);
+                let span = self.token.span;
+                if self.is_kw_followed_by_ident(kw::Let) {
+                    err.span_label(
+                        span,
+                        "consider using `const` or `static` instead of `let` for global variables",
+                    );
+                } else {
+                    err.span_label(span, "expected item")
+                        .note("for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>");
+                };
+                return Err(err);
+            }
+        }
+
+        let inject_use_span = post_attr_lo.data().with_hi(post_attr_lo.lo());
+        let mod_spans = ModSpans { inner_span: lo.to(self.prev_token.span), inject_use_span };
+        Ok((attrs, items, mod_spans))
+    }
+}
+
+pub(super) type ItemInfo = (Ident, ItemKind);
+
+impl<'a> Parser<'a> {
+    pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<P<Item>>> {
+        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+        self.parse_item_(fn_parse_mode, force_collect).map(|i| i.map(P))
+    }
+
+    fn parse_item_(
+        &mut self,
+        fn_parse_mode: FnParseMode,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Item>> {
+        self.recover_vcs_conflict_marker();
+        let attrs = self.parse_outer_attributes()?;
+        self.recover_vcs_conflict_marker();
+        self.parse_item_common(attrs, true, false, fn_parse_mode, force_collect)
+    }
+
+    pub(super) fn parse_item_common(
+        &mut self,
+        attrs: AttrWrapper,
+        mac_allowed: bool,
+        attrs_allowed: bool,
+        fn_parse_mode: FnParseMode,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Item>> {
+        maybe_whole!(self, NtItem, |item| {
+            attrs.prepend_to_nt_inner(&mut item.attrs);
+            Some(item.into_inner())
+        });
+
+        let item =
+            self.collect_tokens_trailing_token(attrs, force_collect, |this: &mut Self, attrs| {
+                let item =
+                    this.parse_item_common_(attrs, mac_allowed, attrs_allowed, fn_parse_mode);
+                Ok((item?, TrailingToken::None))
+            })?;
+
+        Ok(item)
+    }
+
+    fn parse_item_common_(
+        &mut self,
+        mut attrs: AttrVec,
+        mac_allowed: bool,
+        attrs_allowed: bool,
+        fn_parse_mode: FnParseMode,
+    ) -> PResult<'a, Option<Item>> {
+        let lo = self.token.span;
+        let vis = self.parse_visibility(FollowedByType::No)?;
+        let mut def = self.parse_defaultness();
+        let kind = self.parse_item_kind(
+            &mut attrs,
+            mac_allowed,
+            lo,
+            &vis,
+            &mut def,
+            fn_parse_mode,
+            Case::Sensitive,
+        )?;
+        if let Some((ident, kind)) = kind {
+            self.error_on_unconsumed_default(def, &kind);
+            let span = lo.to(self.prev_token.span);
+            let id = DUMMY_NODE_ID;
+            let item = Item { ident, attrs, id, kind, vis, span, tokens: None };
+            return Ok(Some(item));
+        }
+
+        // At this point, we have failed to parse an item.
+        if !matches!(vis.kind, VisibilityKind::Inherited) {
+            self.dcx().emit_err(errors::VisibilityNotFollowedByItem { span: vis.span, vis });
+        }
+
+        if let Defaultness::Default(span) = def {
+            self.dcx().emit_err(errors::DefaultNotFollowedByItem { span });
+        }
+
+        if !attrs_allowed {
+            self.recover_attrs_no_item(&attrs)?;
+        }
+        Ok(None)
+    }
+
+    /// Error in-case `default` was parsed in an in-appropriate context.
+    fn error_on_unconsumed_default(&self, def: Defaultness, kind: &ItemKind) {
+        if let Defaultness::Default(span) = def {
+            self.dcx().emit_err(errors::InappropriateDefault {
+                span,
+                article: kind.article(),
+                descr: kind.descr(),
+            });
+        }
+    }
+
+    /// Parses one of the items allowed by the flags.
+    fn parse_item_kind(
+        &mut self,
+        attrs: &mut AttrVec,
+        macros_allowed: bool,
+        lo: Span,
+        vis: &Visibility,
+        def: &mut Defaultness,
+        fn_parse_mode: FnParseMode,
+        case: Case,
+    ) -> PResult<'a, Option<ItemInfo>> {
+        let check_pub = def == &Defaultness::Final;
+        let mut def_ = || mem::replace(def, Defaultness::Final);
+
+        let info = if self.eat_keyword_case(kw::Use, case) {
+            self.parse_use_item()?
+        } else if self.check_fn_front_matter(check_pub, case) {
+            // FUNCTION ITEM
+            let (ident, sig, generics, body) =
+                self.parse_fn(attrs, fn_parse_mode, lo, vis, case)?;
+            (ident, ItemKind::Fn(Box::new(Fn { defaultness: def_(), sig, generics, body })))
+        } else if self.eat_keyword(kw::Extern) {
+            if self.eat_keyword(kw::Crate) {
+                // EXTERN CRATE
+                self.parse_item_extern_crate()?
+            } else {
+                // EXTERN BLOCK
+                self.parse_item_foreign_mod(attrs, Safety::Default)?
+            }
+        } else if self.is_unsafe_foreign_mod() {
+            // EXTERN BLOCK
+            let safety = self.parse_safety(Case::Sensitive);
+            self.expect_keyword(kw::Extern)?;
+            self.parse_item_foreign_mod(attrs, safety)?
+        } else if self.is_static_global() {
+            // STATIC ITEM
+            self.bump(); // `static`
+            let mutability = self.parse_mutability();
+            let (ident, item) = self.parse_static_item(mutability)?;
+            (ident, ItemKind::Static(Box::new(item)))
+        } else if let Const::Yes(const_span) = self.parse_constness(Case::Sensitive) {
+            // CONST ITEM
+            if self.token.is_keyword(kw::Impl) {
+                // recover from `const impl`, suggest `impl const`
+                self.recover_const_impl(const_span, attrs, def_())?
+            } else {
+                self.recover_const_mut(const_span);
+                let (ident, generics, ty, expr) = self.parse_const_item()?;
+                (
+                    ident,
+                    ItemKind::Const(Box::new(ConstItem {
+                        defaultness: def_(),
+                        generics,
+                        ty,
+                        expr,
+                    })),
+                )
+            }
+        } else if self.check_keyword(kw::Trait) || self.check_auto_or_unsafe_trait_item() {
+            // TRAIT ITEM
+            self.parse_item_trait(attrs, lo)?
+        } else if self.check_keyword(kw::Impl)
+            || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Impl])
+        {
+            // IMPL ITEM
+            self.parse_item_impl(attrs, def_())?
+        } else if self.is_reuse_path_item() {
+            self.parse_item_delegation()?
+        } else if self.check_keyword(kw::Mod)
+            || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Mod])
+        {
+            // MODULE ITEM
+            self.parse_item_mod(attrs)?
+        } else if self.eat_keyword(kw::Type) {
+            // TYPE ITEM
+            self.parse_type_alias(def_())?
+        } else if self.eat_keyword(kw::Enum) {
+            // ENUM ITEM
+            self.parse_item_enum()?
+        } else if self.eat_keyword(kw::Struct) {
+            // STRUCT ITEM
+            self.parse_item_struct()?
+        } else if self.is_kw_followed_by_ident(kw::Union) {
+            // UNION ITEM
+            self.bump(); // `union`
+            self.parse_item_union()?
+        } else if self.is_builtin() {
+            // BUILTIN# ITEM
+            return self.parse_item_builtin();
+        } else if self.eat_keyword(kw::Macro) {
+            // MACROS 2.0 ITEM
+            self.parse_item_decl_macro(lo)?
+        } else if let IsMacroRulesItem::Yes { has_bang } = self.is_macro_rules_item() {
+            // MACRO_RULES ITEM
+            self.parse_item_macro_rules(vis, has_bang)?
+        } else if self.isnt_macro_invocation()
+            && (self.token.is_ident_named(sym::import)
+                || self.token.is_ident_named(sym::using)
+                || self.token.is_ident_named(sym::include)
+                || self.token.is_ident_named(sym::require))
+        {
+            return self.recover_import_as_use();
+        } else if self.isnt_macro_invocation() && vis.kind.is_pub() {
+            self.recover_missing_kw_before_item()?;
+            return Ok(None);
+        } else if self.isnt_macro_invocation() && case == Case::Sensitive {
+            _ = def_;
+
+            // Recover wrong cased keywords
+            return self.parse_item_kind(
+                attrs,
+                macros_allowed,
+                lo,
+                vis,
+                def,
+                fn_parse_mode,
+                Case::Insensitive,
+            );
+        } else if macros_allowed && self.check_path() {
+            // MACRO INVOCATION ITEM
+            (Ident::empty(), ItemKind::MacCall(P(self.parse_item_macro(vis)?)))
+        } else {
+            return Ok(None);
+        };
+        Ok(Some(info))
+    }
+
+    fn recover_import_as_use(&mut self) -> PResult<'a, Option<ItemInfo>> {
+        let span = self.token.span;
+        let token_name = super::token_descr(&self.token);
+        let snapshot = self.create_snapshot_for_diagnostic();
+        self.bump();
+        match self.parse_use_item() {
+            Ok(u) => {
+                self.dcx().emit_err(errors::RecoverImportAsUse { span, token_name });
+                Ok(Some(u))
+            }
+            Err(e) => {
+                e.cancel();
+                self.restore_snapshot(snapshot);
+                Ok(None)
+            }
+        }
+    }
+
+    fn parse_use_item(&mut self) -> PResult<'a, ItemInfo> {
+        let tree = self.parse_use_tree()?;
+        if let Err(mut e) = self.expect_semi() {
+            match tree.kind {
+                UseTreeKind::Glob => {
+                    e.note("the wildcard token must be last on the path");
+                }
+                UseTreeKind::Nested { .. } => {
+                    e.note("glob-like brace syntax must be last on the path");
+                }
+                _ => (),
+            }
+            return Err(e);
+        }
+        Ok((Ident::empty(), ItemKind::Use(tree)))
+    }
+
+    /// When parsing a statement, would the start of a path be an item?
+    pub(super) fn is_path_start_item(&mut self) -> bool {
+        self.is_kw_followed_by_ident(kw::Union) // no: `union::b`, yes: `union U { .. }`
+        || self.is_reuse_path_item()
+        || self.check_auto_or_unsafe_trait_item() // no: `auto::b`, yes: `auto trait X { .. }`
+        || self.is_async_fn() // no(2015): `async::b`, yes: `async fn`
+        || matches!(self.is_macro_rules_item(), IsMacroRulesItem::Yes{..}) // no: `macro_rules::b`, yes: `macro_rules! mac`
+    }
+
+    fn is_reuse_path_item(&mut self) -> bool {
+        // no: `reuse ::path` for compatibility reasons with macro invocations
+        self.token.is_keyword(kw::Reuse)
+            && self.look_ahead(1, |t| t.is_path_start() && t.kind != token::PathSep)
+    }
+
+    /// Are we sure this could not possibly be a macro invocation?
+    fn isnt_macro_invocation(&mut self) -> bool {
+        self.check_ident() && self.look_ahead(1, |t| *t != token::Not && *t != token::PathSep)
+    }
+
+    /// Recover on encountering a struct or method definition where the user
+    /// forgot to add the `struct` or `fn` keyword after writing `pub`: `pub S {}`.
+    fn recover_missing_kw_before_item(&mut self) -> PResult<'a, ()> {
+        // Space between `pub` keyword and the identifier
+        //
+        //     pub   S {}
+        //        ^^^ `sp` points here
+        let sp = self.prev_token.span.between(self.token.span);
+        let full_sp = self.prev_token.span.to(self.token.span);
+        let ident_sp = self.token.span;
+
+        let ident = if self.look_ahead(1, |t| {
+            [
+                token::Lt,
+                token::OpenDelim(Delimiter::Brace),
+                token::OpenDelim(Delimiter::Parenthesis),
+            ]
+            .contains(&t.kind)
+        }) {
+            self.parse_ident().unwrap()
+        } else {
+            return Ok(());
+        };
+
+        let mut found_generics = false;
+        if self.check(&token::Lt) {
+            found_generics = true;
+            self.eat_to_tokens(&[&token::Gt]);
+            self.bump(); // `>`
+        }
+
+        let err = if self.check(&token::OpenDelim(Delimiter::Brace)) {
+            // possible public struct definition where `struct` was forgotten
+            Some(errors::MissingKeywordForItemDefinition::Struct { span: sp, ident })
+        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            // possible public function or tuple struct definition where `fn`/`struct` was
+            // forgotten
+            self.bump(); // `(`
+            let is_method = self.recover_self_param();
+
+            self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::Yes);
+
+            let err =
+                if self.check(&token::RArrow) || self.check(&token::OpenDelim(Delimiter::Brace)) {
+                    self.eat_to_tokens(&[&token::OpenDelim(Delimiter::Brace)]);
+                    self.bump(); // `{`
+                    self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
+                    if is_method {
+                        errors::MissingKeywordForItemDefinition::Method { span: sp, ident }
+                    } else {
+                        errors::MissingKeywordForItemDefinition::Function { span: sp, ident }
+                    }
+                } else if self.check(&token::Semi) {
+                    errors::MissingKeywordForItemDefinition::Struct { span: sp, ident }
+                } else {
+                    errors::MissingKeywordForItemDefinition::Ambiguous {
+                        span: sp,
+                        subdiag: if found_generics {
+                            None
+                        } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
+                            Some(errors::AmbiguousMissingKwForItemSub::SuggestMacro {
+                                span: full_sp,
+                                snippet,
+                            })
+                        } else {
+                            Some(errors::AmbiguousMissingKwForItemSub::HelpMacro)
+                        },
+                    }
+                };
+            Some(err)
+        } else if found_generics {
+            Some(errors::MissingKeywordForItemDefinition::Ambiguous { span: sp, subdiag: None })
+        } else {
+            None
+        };
+
+        if let Some(err) = err { Err(self.dcx().create_err(err)) } else { Ok(()) }
+    }
+
+    fn parse_item_builtin(&mut self) -> PResult<'a, Option<ItemInfo>> {
+        // To be expanded
+        return Ok(None);
+    }
+
+    /// Parses an item macro, e.g., `item!();`.
+    fn parse_item_macro(&mut self, vis: &Visibility) -> PResult<'a, MacCall> {
+        let path = self.parse_path(PathStyle::Mod)?; // `foo::bar`
+        self.expect(&token::Not)?; // `!`
+        match self.parse_delim_args() {
+            // `( .. )` or `[ .. ]` (followed by `;`), or `{ .. }`.
+            Ok(args) => {
+                self.eat_semi_for_macro_if_needed(&args);
+                self.complain_if_pub_macro(vis, false);
+                Ok(MacCall { path, args })
+            }
+
+            Err(mut err) => {
+                // Maybe the user misspelled `macro_rules` (issue #91227)
+                if self.token.is_ident()
+                    && path.segments.len() == 1
+                    && edit_distance("macro_rules", &path.segments[0].ident.to_string(), 2)
+                        .is_some()
+                {
+                    err.span_suggestion(
+                        path.span,
+                        "perhaps you meant to define a macro",
+                        "macro_rules",
+                        Applicability::MachineApplicable,
+                    );
+                }
+                Err(err)
+            }
+        }
+    }
+
+    /// Recover if we parsed attributes and expected an item but there was none.
+    fn recover_attrs_no_item(&mut self, attrs: &[Attribute]) -> PResult<'a, ()> {
+        let ([start @ end] | [start, .., end]) = attrs else {
+            return Ok(());
+        };
+        let msg = if end.is_doc_comment() {
+            "expected item after doc comment"
+        } else {
+            "expected item after attributes"
+        };
+        let mut err = self.dcx().struct_span_err(end.span, msg);
+        if end.is_doc_comment() {
+            err.span_label(end.span, "this doc comment doesn't document anything");
+        } else if self.token.kind == TokenKind::Semi {
+            err.span_suggestion_verbose(
+                self.token.span,
+                "consider removing this semicolon",
+                "",
+                Applicability::MaybeIncorrect,
+            );
+        }
+        if let [.., penultimate, _] = attrs {
+            err.span_label(start.span.to(penultimate.span), "other attributes here");
+        }
+        Err(err)
+    }
+
+    fn is_async_fn(&self) -> bool {
+        self.token.is_keyword(kw::Async) && self.is_keyword_ahead(1, &[kw::Fn])
+    }
+
+    fn parse_polarity(&mut self) -> ast::ImplPolarity {
+        // Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
+        if self.check(&token::Not) && self.look_ahead(1, |t| t.can_begin_type()) {
+            self.bump(); // `!`
+            ast::ImplPolarity::Negative(self.prev_token.span)
+        } else {
+            ast::ImplPolarity::Positive
+        }
+    }
+
+    /// Parses an implementation item.
+    ///
+    /// ```ignore (illustrative)
+    /// impl<'a, T> TYPE { /* impl items */ }
+    /// impl<'a, T> TRAIT for TYPE { /* impl items */ }
+    /// impl<'a, T> !TRAIT for TYPE { /* impl items */ }
+    /// impl<'a, T> const TRAIT for TYPE { /* impl items */ }
+    /// ```
+    ///
+    /// We actually parse slightly more relaxed grammar for better error reporting and recovery.
+    /// ```ebnf
+    /// "impl" GENERICS "const"? "!"? TYPE "for"? (TYPE | "..") ("where" PREDICATES)? "{" BODY "}"
+    /// "impl" GENERICS "const"? "!"? TYPE ("where" PREDICATES)? "{" BODY "}"
+    /// ```
+    fn parse_item_impl(
+        &mut self,
+        attrs: &mut AttrVec,
+        defaultness: Defaultness,
+    ) -> PResult<'a, ItemInfo> {
+        let safety = self.parse_safety(Case::Sensitive);
+        self.expect_keyword(kw::Impl)?;
+
+        // First, parse generic parameters if necessary.
+        let mut generics = if self.choose_generics_over_qpath(0) {
+            self.parse_generics()?
+        } else {
+            let mut generics = Generics::default();
+            // impl A for B {}
+            //    /\ this is where `generics.span` should point when there are no type params.
+            generics.span = self.prev_token.span.shrink_to_hi();
+            generics
+        };
+
+        let constness = self.parse_constness(Case::Sensitive);
+        if let Const::Yes(span) = constness {
+            self.psess.gated_spans.gate(sym::const_trait_impl, span);
+        }
+
+        // Parse stray `impl async Trait`
+        if (self.token.uninterpolated_span().at_least_rust_2018()
+            && self.token.is_keyword(kw::Async))
+            || self.is_kw_followed_by_ident(kw::Async)
+        {
+            self.bump();
+            self.dcx().emit_err(errors::AsyncImpl { span: self.prev_token.span });
+        }
+
+        let polarity = self.parse_polarity();
+
+        // Parse both types and traits as a type, then reinterpret if necessary.
+        let err_path = |span| ast::Path::from_ident(Ident::new(kw::Empty, span));
+        let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
+        {
+            let span = self.prev_token.span.between(self.token.span);
+            self.dcx().emit_err(errors::MissingTraitInTraitImpl {
+                span,
+                for_span: span.to(self.token.span),
+            });
+
+            P(Ty {
+                kind: TyKind::Path(None, err_path(span)),
+                span,
+                id: DUMMY_NODE_ID,
+                tokens: None,
+            })
+        } else {
+            self.parse_ty_with_generics_recovery(&generics)?
+        };
+
+        // If `for` is missing we try to recover.
+        let has_for = self.eat_keyword(kw::For);
+        let missing_for_span = self.prev_token.span.between(self.token.span);
+
+        let ty_second = if self.token == token::DotDot {
+            // We need to report this error after `cfg` expansion for compatibility reasons
+            self.bump(); // `..`, do not add it to expected tokens
+
+            // AST validation later detects this `TyKind::Dummy` and emits an
+            // error. (#121072 will hopefully remove all this special handling
+            // of the obsolete `impl Trait for ..` and then this can go away.)
+            Some(self.mk_ty(self.prev_token.span, TyKind::Dummy))
+        } else if has_for || self.token.can_begin_type() {
+            Some(self.parse_ty()?)
+        } else {
+            None
+        };
+
+        generics.where_clause = self.parse_where_clause()?;
+
+        let impl_items = self.parse_item_list(attrs, |p| p.parse_impl_item(ForceCollect::No))?;
+
+        let item_kind = match ty_second {
+            Some(ty_second) => {
+                // impl Trait for Type
+                if !has_for {
+                    self.dcx().emit_err(errors::MissingForInTraitImpl { span: missing_for_span });
+                }
+
+                let ty_first = ty_first.into_inner();
+                let path = match ty_first.kind {
+                    // This notably includes paths passed through `ty` macro fragments (#46438).
+                    TyKind::Path(None, path) => path,
+                    other => {
+                        if let TyKind::ImplTrait(_, bounds, None) = other
+                            && let [bound] = bounds.as_slice()
+                        {
+                            // Suggest removing extra `impl` keyword:
+                            // `impl<T: Default> impl Default for Wrapper<T>`
+                            //                   ^^^^^
+                            let extra_impl_kw = ty_first.span.until(bound.span());
+                            self.dcx().emit_err(errors::ExtraImplKeywordInTraitImpl {
+                                extra_impl_kw,
+                                impl_trait_span: ty_first.span,
+                            });
+                        } else {
+                            self.dcx().emit_err(errors::ExpectedTraitInTraitImplFoundType {
+                                span: ty_first.span,
+                            });
+                        }
+                        err_path(ty_first.span)
+                    }
+                };
+                let trait_ref = TraitRef { path, ref_id: ty_first.id };
+
+                ItemKind::Impl(Box::new(Impl {
+                    safety,
+                    polarity,
+                    defaultness,
+                    constness,
+                    generics,
+                    of_trait: Some(trait_ref),
+                    self_ty: ty_second,
+                    items: impl_items,
+                }))
+            }
+            None => {
+                // impl Type
+                ItemKind::Impl(Box::new(Impl {
+                    safety,
+                    polarity,
+                    defaultness,
+                    constness,
+                    generics,
+                    of_trait: None,
+                    self_ty: ty_first,
+                    items: impl_items,
+                }))
+            }
+        };
+
+        Ok((Ident::empty(), item_kind))
+    }
+
+    fn parse_item_delegation(&mut self) -> PResult<'a, ItemInfo> {
+        let span = self.token.span;
+        self.expect_keyword(kw::Reuse)?;
+
+        let (qself, path) = if self.eat_lt() {
+            let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+            (Some(qself), path)
+        } else {
+            (None, self.parse_path(PathStyle::Expr)?)
+        };
+
+        let rename = |this: &mut Self| {
+            Ok(if this.eat_keyword(kw::As) { Some(this.parse_ident()?) } else { None })
+        };
+        let body = |this: &mut Self| {
+            Ok(if this.check(&token::OpenDelim(Delimiter::Brace)) {
+                Some(this.parse_block()?)
+            } else {
+                this.expect(&token::Semi)?;
+                None
+            })
+        };
+
+        let (ident, item_kind) = if self.eat(&token::PathSep) {
+            let (suffixes, _) = self.parse_delim_comma_seq(Delimiter::Brace, |p| {
+                Ok((p.parse_path_segment_ident()?, rename(p)?))
+            })?;
+            let deleg = DelegationMac { qself, prefix: path, suffixes, body: body(self)? };
+            (Ident::empty(), ItemKind::DelegationMac(Box::new(deleg)))
+        } else {
+            let rename = rename(self)?;
+            let ident = rename.unwrap_or_else(|| path.segments.last().unwrap().ident);
+            let deleg = Delegation { id: DUMMY_NODE_ID, qself, path, rename, body: body(self)? };
+            (ident, ItemKind::Delegation(Box::new(deleg)))
+        };
+
+        let span = span.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::fn_delegation, span);
+
+        Ok((ident, item_kind))
+    }
+
+    fn parse_item_list<T>(
+        &mut self,
+        attrs: &mut AttrVec,
+        mut parse_item: impl FnMut(&mut Parser<'a>) -> PResult<'a, Option<Option<T>>>,
+    ) -> PResult<'a, ThinVec<T>> {
+        let open_brace_span = self.token.span;
+
+        // Recover `impl Ty;` instead of `impl Ty {}`
+        if self.token == TokenKind::Semi {
+            self.dcx().emit_err(errors::UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            return Ok(ThinVec::new());
+        }
+
+        self.expect(&token::OpenDelim(Delimiter::Brace))?;
+        attrs.extend(self.parse_inner_attributes()?);
+
+        let mut items = ThinVec::new();
+        while !self.eat(&token::CloseDelim(Delimiter::Brace)) {
+            if self.recover_doc_comment_before_brace() {
+                continue;
+            }
+            self.recover_vcs_conflict_marker();
+            match parse_item(self) {
+                Ok(None) => {
+                    let mut is_unnecessary_semicolon = !items.is_empty()
+                        // When the close delim is `)` in a case like the following, `token.kind` is expected to be `token::CloseDelim(Delimiter::Parenthesis)`,
+                        // but the actual `token.kind` is `token::CloseDelim(Delimiter::Brace)`.
+                        // This is because the `token.kind` of the close delim is treated as the same as
+                        // that of the open delim in `TokenTreesReader::parse_token_tree`, even if the delimiters of them are different.
+                        // Therefore, `token.kind` should not be compared here.
+                        //
+                        // issue-60075.rs
+                        // ```
+                        // trait T {
+                        //     fn qux() -> Option<usize> {
+                        //         let _ = if true {
+                        //         });
+                        //          ^ this close delim
+                        //         Some(4)
+                        //     }
+                        // ```
+                        && self
+                            .span_to_snippet(self.prev_token.span)
+                            .is_ok_and(|snippet| snippet == "}")
+                        && self.token.kind == token::Semi;
+                    let mut semicolon_span = self.token.span;
+                    if !is_unnecessary_semicolon {
+                        // #105369, Detect spurious `;` before assoc fn body
+                        is_unnecessary_semicolon = self.token == token::OpenDelim(Delimiter::Brace)
+                            && self.prev_token.kind == token::Semi;
+                        semicolon_span = self.prev_token.span;
+                    }
+                    // We have to bail or we'll potentially never make progress.
+                    let non_item_span = self.token.span;
+                    let is_let = self.token.is_keyword(kw::Let);
+
+                    let mut err =
+                        self.dcx().struct_span_err(non_item_span, "non-item in item list");
+                    self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
+                    if is_let {
+                        err.span_suggestion(
+                            non_item_span,
+                            "consider using `const` instead of `let` for associated const",
+                            "const",
+                            Applicability::MachineApplicable,
+                        );
+                    } else {
+                        err.span_label(open_brace_span, "item list starts here")
+                            .span_label(non_item_span, "non-item starts here")
+                            .span_label(self.prev_token.span, "item list ends here");
+                    }
+                    if is_unnecessary_semicolon {
+                        err.span_suggestion(
+                            semicolon_span,
+                            "consider removing this semicolon",
+                            "",
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                    err.emit();
+                    break;
+                }
+                Ok(Some(item)) => items.extend(item),
+                Err(err) => {
+                    self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
+                    err.with_span_label(
+                        open_brace_span,
+                        "while parsing this item list starting here",
+                    )
+                    .with_span_label(self.prev_token.span, "the item list ends here")
+                    .emit();
+                    break;
+                }
+            }
+        }
+        Ok(items)
+    }
+
+    /// Recover on a doc comment before `}`.
+    fn recover_doc_comment_before_brace(&mut self) -> bool {
+        if let token::DocComment(..) = self.token.kind {
+            if self.look_ahead(1, |tok| tok == &token::CloseDelim(Delimiter::Brace)) {
+                // FIXME: merge with `DocCommentDoesNotDocumentAnything` (E0585)
+                struct_span_code_err!(
+                    self.dcx(),
+                    self.token.span,
+                    E0584,
+                    "found a documentation comment that doesn't document anything",
+                )
+                .with_span_label(self.token.span, "this doc comment doesn't document anything")
+                .with_help(
+                    "doc comments must come before what they document, if a comment was \
+                    intended use `//`",
+                )
+                .emit();
+                self.bump();
+                return true;
+            }
+        }
+        false
+    }
+
+    /// Parses defaultness (i.e., `default` or nothing).
+    fn parse_defaultness(&mut self) -> Defaultness {
+        // We are interested in `default` followed by another identifier.
+        // However, we must avoid keywords that occur as binary operators.
+        // Currently, the only applicable keyword is `as` (`default as Ty`).
+        if self.check_keyword(kw::Default)
+            && self.look_ahead(1, |t| t.is_non_raw_ident_where(|i| i.name != kw::As))
+        {
+            self.bump(); // `default`
+            Defaultness::Default(self.prev_token.uninterpolated_span())
+        } else {
+            Defaultness::Final
+        }
+    }
+
+    /// Is this an `(unsafe auto? | auto) trait` item?
+    fn check_auto_or_unsafe_trait_item(&mut self) -> bool {
+        // auto trait
+        self.check_keyword(kw::Auto) && self.is_keyword_ahead(1, &[kw::Trait])
+            // unsafe auto trait
+            || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
+    }
+
+    /// Parses `unsafe? auto? trait Foo { ... }` or `trait Foo = Bar;`.
+    fn parse_item_trait(&mut self, attrs: &mut AttrVec, lo: Span) -> PResult<'a, ItemInfo> {
+        let safety = self.parse_safety(Case::Sensitive);
+        // Parse optional `auto` prefix.
+        let is_auto = if self.eat_keyword(kw::Auto) {
+            self.psess.gated_spans.gate(sym::auto_traits, self.prev_token.span);
+            IsAuto::Yes
+        } else {
+            IsAuto::No
+        };
+
+        self.expect_keyword(kw::Trait)?;
+        let ident = self.parse_ident()?;
+        let mut generics = self.parse_generics()?;
+
+        // Parse optional colon and supertrait bounds.
+        let had_colon = self.eat(&token::Colon);
+        let span_at_colon = self.prev_token.span;
+        let bounds = if had_colon { self.parse_generic_bounds()? } else { Vec::new() };
+
+        let span_before_eq = self.prev_token.span;
+        if self.eat(&token::Eq) {
+            // It's a trait alias.
+            if had_colon {
+                let span = span_at_colon.to(span_before_eq);
+                self.dcx().emit_err(errors::BoundsNotAllowedOnTraitAliases { span });
+            }
+
+            let bounds = self.parse_generic_bounds()?;
+            generics.where_clause = self.parse_where_clause()?;
+            self.expect_semi()?;
+
+            let whole_span = lo.to(self.prev_token.span);
+            if is_auto == IsAuto::Yes {
+                self.dcx().emit_err(errors::TraitAliasCannotBeAuto { span: whole_span });
+            }
+            if let Safety::Unsafe(_) = safety {
+                self.dcx().emit_err(errors::TraitAliasCannotBeUnsafe { span: whole_span });
+            }
+
+            self.psess.gated_spans.gate(sym::trait_alias, whole_span);
+
+            Ok((ident, ItemKind::TraitAlias(generics, bounds)))
+        } else {
+            // It's a normal trait.
+            generics.where_clause = self.parse_where_clause()?;
+            let items = self.parse_item_list(attrs, |p| p.parse_trait_item(ForceCollect::No))?;
+            Ok((
+                ident,
+                ItemKind::Trait(Box::new(Trait { is_auto, safety, generics, bounds, items })),
+            ))
+        }
+    }
+
+    pub fn parse_impl_item(
+        &mut self,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
+        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+        self.parse_assoc_item(fn_parse_mode, force_collect)
+    }
+
+    pub fn parse_trait_item(
+        &mut self,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
+        let fn_parse_mode =
+            FnParseMode { req_name: |edition| edition >= Edition::Edition2018, req_body: false };
+        self.parse_assoc_item(fn_parse_mode, force_collect)
+    }
+
+    /// Parses associated items.
+    fn parse_assoc_item(
+        &mut self,
+        fn_parse_mode: FnParseMode,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
+        Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
+            |Item { attrs, id, span, vis, ident, kind, tokens }| {
+                let kind = match AssocItemKind::try_from(kind) {
+                    Ok(kind) => kind,
+                    Err(kind) => match kind {
+                        ItemKind::Static(box StaticItem { ty, mutability: _, expr }) => {
+                            self.dcx().emit_err(errors::AssociatedStaticItemNotAllowed { span });
+                            AssocItemKind::Const(Box::new(ConstItem {
+                                defaultness: Defaultness::Final,
+                                generics: Generics::default(),
+                                ty,
+                                expr,
+                            }))
+                        }
+                        _ => return self.error_bad_item_kind(span, &kind, "`trait`s or `impl`s"),
+                    },
+                };
+                Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
+            },
+        ))
+    }
+
+    /// Parses a `type` alias with the following grammar:
+    /// ```ebnf
+    /// TypeAlias = "type" Ident Generics (":" GenericBounds)? WhereClause ("=" Ty)? WhereClause ";" ;
+    /// ```
+    /// The `"type"` has already been eaten.
+    fn parse_type_alias(&mut self, defaultness: Defaultness) -> PResult<'a, ItemInfo> {
+        let ident = self.parse_ident()?;
+        let mut generics = self.parse_generics()?;
+
+        // Parse optional colon and param bounds.
+        let bounds =
+            if self.eat(&token::Colon) { self.parse_generic_bounds()? } else { Vec::new() };
+        let before_where_clause = self.parse_where_clause()?;
+
+        let ty = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
+
+        let after_where_clause = self.parse_where_clause()?;
+
+        let where_clauses = TyAliasWhereClauses {
+            before: TyAliasWhereClause {
+                has_where_token: before_where_clause.has_where_token,
+                span: before_where_clause.span,
+            },
+            after: TyAliasWhereClause {
+                has_where_token: after_where_clause.has_where_token,
+                span: after_where_clause.span,
+            },
+            split: before_where_clause.predicates.len(),
+        };
+        let mut predicates = before_where_clause.predicates;
+        predicates.extend(after_where_clause.predicates);
+        let where_clause = WhereClause {
+            has_where_token: before_where_clause.has_where_token
+                || after_where_clause.has_where_token,
+            predicates,
+            span: DUMMY_SP,
+        };
+        generics.where_clause = where_clause;
+
+        self.expect_semi()?;
+
+        Ok((
+            ident,
+            ItemKind::TyAlias(Box::new(TyAlias {
+                defaultness,
+                generics,
+                where_clauses,
+                bounds,
+                ty,
+            })),
+        ))
+    }
+
+    /// Parses a `UseTree`.
+    ///
+    /// ```text
+    /// USE_TREE = [`::`] `*` |
+    ///            [`::`] `{` USE_TREE_LIST `}` |
+    ///            PATH `::` `*` |
+    ///            PATH `::` `{` USE_TREE_LIST `}` |
+    ///            PATH [`as` IDENT]
+    /// ```
+    fn parse_use_tree(&mut self) -> PResult<'a, UseTree> {
+        let lo = self.token.span;
+
+        let mut prefix =
+            ast::Path { segments: ThinVec::new(), span: lo.shrink_to_lo(), tokens: None };
+        let kind = if self.check(&token::OpenDelim(Delimiter::Brace))
+            || self.check(&token::BinOp(token::Star))
+            || self.is_import_coupler()
+        {
+            // `use *;` or `use ::*;` or `use {...};` or `use ::{...};`
+            let mod_sep_ctxt = self.token.span.ctxt();
+            if self.eat(&token::PathSep) {
+                prefix
+                    .segments
+                    .push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
+            }
+
+            self.parse_use_tree_glob_or_nested()?
+        } else {
+            // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
+            prefix = self.parse_path(PathStyle::Mod)?;
+
+            if self.eat(&token::PathSep) {
+                self.parse_use_tree_glob_or_nested()?
+            } else {
+                // Recover from using a colon as path separator.
+                while self.eat_noexpect(&token::Colon) {
+                    self.dcx()
+                        .emit_err(errors::SingleColonImportPath { span: self.prev_token.span });
+
+                    // We parse the rest of the path and append it to the original prefix.
+                    self.parse_path_segments(&mut prefix.segments, PathStyle::Mod, None)?;
+                    prefix.span = lo.to(self.prev_token.span);
+                }
+
+                UseTreeKind::Simple(self.parse_rename()?)
+            }
+        };
+
+        Ok(UseTree { prefix, kind, span: lo.to(self.prev_token.span) })
+    }
+
+    /// Parses `*` or `{...}`.
+    fn parse_use_tree_glob_or_nested(&mut self) -> PResult<'a, UseTreeKind> {
+        Ok(if self.eat(&token::BinOp(token::Star)) {
+            UseTreeKind::Glob
+        } else {
+            let lo = self.token.span;
+            UseTreeKind::Nested {
+                items: self.parse_use_tree_list()?,
+                span: lo.to(self.prev_token.span),
+            }
+        })
+    }
+
+    /// Parses a `UseTreeKind::Nested(list)`.
+    ///
+    /// ```text
+    /// USE_TREE_LIST = ∅ | (USE_TREE `,`)* USE_TREE [`,`]
+    /// ```
+    fn parse_use_tree_list(&mut self) -> PResult<'a, ThinVec<(UseTree, ast::NodeId)>> {
+        self.parse_delim_comma_seq(Delimiter::Brace, |p| {
+            p.recover_vcs_conflict_marker();
+            Ok((p.parse_use_tree()?, DUMMY_NODE_ID))
+        })
+        .map(|(r, _)| r)
+    }
+
+    fn parse_rename(&mut self) -> PResult<'a, Option<Ident>> {
+        if self.eat_keyword(kw::As) { self.parse_ident_or_underscore().map(Some) } else { Ok(None) }
+    }
+
+    fn parse_ident_or_underscore(&mut self) -> PResult<'a, Ident> {
+        match self.token.ident() {
+            Some((ident @ Ident { name: kw::Underscore, .. }, IdentIsRaw::No)) => {
+                self.bump();
+                Ok(ident)
+            }
+            _ => self.parse_ident(),
+        }
+    }
+
+    /// Parses `extern crate` links.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore (illustrative)
+    /// extern crate foo;
+    /// extern crate bar as foo;
+    /// ```
+    fn parse_item_extern_crate(&mut self) -> PResult<'a, ItemInfo> {
+        // Accept `extern crate name-like-this` for better diagnostics
+        let orig_name = self.parse_crate_name_with_dashes()?;
+        let (item_name, orig_name) = if let Some(rename) = self.parse_rename()? {
+            (rename, Some(orig_name.name))
+        } else {
+            (orig_name, None)
+        };
+        self.expect_semi()?;
+        Ok((item_name, ItemKind::ExternCrate(orig_name)))
+    }
+
+    fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, Ident> {
+        let ident = if self.token.is_keyword(kw::SelfLower) {
+            self.parse_path_segment_ident()
+        } else {
+            self.parse_ident()
+        }?;
+
+        let dash = token::BinOp(token::BinOpToken::Minus);
+        if self.token != dash {
+            return Ok(ident);
+        }
+
+        // Accept `extern crate name-like-this` for better diagnostics.
+        let mut dashes = vec![];
+        let mut idents = vec![];
+        while self.eat(&dash) {
+            dashes.push(self.prev_token.span);
+            idents.push(self.parse_ident()?);
+        }
+
+        let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
+        let mut fixed_name = ident.name.to_string();
+        for part in idents {
+            write!(fixed_name, "_{}", part.name).unwrap();
+        }
+
+        self.dcx().emit_err(errors::ExternCrateNameWithDashes {
+            span: fixed_name_sp,
+            sugg: errors::ExternCrateNameWithDashesSugg { dashes },
+        });
+
+        Ok(Ident::from_str_and_span(&fixed_name, fixed_name_sp))
+    }
+
+    /// Parses `extern` for foreign ABIs modules.
+    ///
+    /// `extern` is expected to have been consumed before calling this method.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// extern "C" {}
+    /// extern {}
+    /// ```
+    fn parse_item_foreign_mod(
+        &mut self,
+        attrs: &mut AttrVec,
+        mut safety: Safety,
+    ) -> PResult<'a, ItemInfo> {
+        let abi = self.parse_abi(); // ABI?
+        if safety == Safety::Default
+            && self.token.is_keyword(kw::Unsafe)
+            && self.look_ahead(1, |t| t.kind == token::OpenDelim(Delimiter::Brace))
+        {
+            self.expect(&token::OpenDelim(Delimiter::Brace)).unwrap_err().emit();
+            safety = Safety::Unsafe(self.token.span);
+            self.eat_keyword(kw::Unsafe);
+        }
+        let module = ast::ForeignMod {
+            safety,
+            abi,
+            items: self.parse_item_list(attrs, |p| p.parse_foreign_item(ForceCollect::No))?,
+        };
+        Ok((Ident::empty(), ItemKind::ForeignMod(module)))
+    }
+
+    /// Parses a foreign item (one in an `extern { ... }` block).
+    pub fn parse_foreign_item(
+        &mut self,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Option<P<ForeignItem>>>> {
+        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: false };
+        Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
+            |Item { attrs, id, span, vis, ident, kind, tokens }| {
+                let kind = match ForeignItemKind::try_from(kind) {
+                    Ok(kind) => kind,
+                    Err(kind) => match kind {
+                        ItemKind::Const(box ConstItem { ty, expr, .. }) => {
+                            let const_span = Some(span.with_hi(ident.span.lo()))
+                                .filter(|span| span.can_be_used_for_suggestions());
+                            self.dcx().emit_err(errors::ExternItemCannotBeConst {
+                                ident_span: ident.span,
+                                const_span,
+                            });
+                            ForeignItemKind::Static(Box::new(StaticForeignItem {
+                                ty,
+                                mutability: Mutability::Not,
+                                expr,
+                            }))
+                        }
+                        _ => return self.error_bad_item_kind(span, &kind, "`extern` blocks"),
+                    },
+                };
+                Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
+            },
+        ))
+    }
+
+    fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &'static str) -> Option<T> {
+        // FIXME(#100717): needs variant for each `ItemKind` (instead of using `ItemKind::descr()`)
+        let span = self.psess.source_map().guess_head_span(span);
+        let descr = kind.descr();
+        self.dcx().emit_err(errors::BadItemKind { span, descr, ctx });
+        None
+    }
+
+    fn is_unsafe_foreign_mod(&self) -> bool {
+        self.token.is_keyword(kw::Unsafe)
+            && self.is_keyword_ahead(1, &[kw::Extern])
+            && self.look_ahead(
+                2 + self.look_ahead(2, |t| t.can_begin_literal_maybe_minus() as usize),
+                |t| t.kind == token::OpenDelim(Delimiter::Brace),
+            )
+    }
+
+    fn is_static_global(&mut self) -> bool {
+        if self.check_keyword(kw::Static) {
+            // Check if this could be a closure.
+            !self.look_ahead(1, |token| {
+                if token.is_keyword(kw::Move) {
+                    return true;
+                }
+                matches!(token.kind, token::BinOp(token::Or) | token::OrOr)
+            })
+        } else {
+            false
+        }
+    }
+
+    /// Recover on `const mut` with `const` already eaten.
+    fn recover_const_mut(&mut self, const_span: Span) {
+        if self.eat_keyword(kw::Mut) {
+            let span = self.prev_token.span;
+            self.dcx()
+                .emit_err(errors::ConstGlobalCannotBeMutable { ident_span: span, const_span });
+        } else if self.eat_keyword(kw::Let) {
+            let span = self.prev_token.span;
+            self.dcx().emit_err(errors::ConstLetMutuallyExclusive { span: const_span.to(span) });
+        }
+    }
+
+    /// Recover on `const impl` with `const` already eaten.
+    fn recover_const_impl(
+        &mut self,
+        const_span: Span,
+        attrs: &mut AttrVec,
+        defaultness: Defaultness,
+    ) -> PResult<'a, ItemInfo> {
+        let impl_span = self.token.span;
+        let err = self.expected_ident_found_err();
+
+        // Only try to recover if this is implementing a trait for a type
+        let mut impl_info = match self.parse_item_impl(attrs, defaultness) {
+            Ok(impl_info) => impl_info,
+            Err(recovery_error) => {
+                // Recovery failed, raise the "expected identifier" error
+                recovery_error.cancel();
+                return Err(err);
+            }
+        };
+
+        match &mut impl_info.1 {
+            ItemKind::Impl(box Impl { of_trait: Some(trai), constness, .. }) => {
+                *constness = Const::Yes(const_span);
+
+                let before_trait = trai.path.span.shrink_to_lo();
+                let const_up_to_impl = const_span.with_hi(impl_span.lo());
+                err.with_multipart_suggestion(
+                    "you might have meant to write a const trait impl",
+                    vec![(const_up_to_impl, "".to_owned()), (before_trait, "const ".to_owned())],
+                    Applicability::MaybeIncorrect,
+                )
+                .emit();
+            }
+            ItemKind::Impl { .. } => return Err(err),
+            _ => unreachable!(),
+        }
+
+        Ok(impl_info)
+    }
+
+    /// Parse a static item with the prefix `"static" "mut"?` already parsed and stored in `mutability`.
+    ///
+    /// ```ebnf
+    /// Static = "static" "mut"? $ident ":" $ty (= $expr)? ";" ;
+    /// ```
+    fn parse_static_item(&mut self, mutability: Mutability) -> PResult<'a, (Ident, StaticItem)> {
+        let ident = self.parse_ident()?;
+
+        if self.token.kind == TokenKind::Lt && self.may_recover() {
+            let generics = self.parse_generics()?;
+            self.dcx().emit_err(errors::StaticWithGenerics { span: generics.span });
+        }
+
+        // Parse the type of a static item. That is, the `":" $ty` fragment.
+        // FIXME: This could maybe benefit from `.may_recover()`?
+        let ty = match (self.eat(&token::Colon), self.check(&token::Eq) | self.check(&token::Semi))
+        {
+            (true, false) => self.parse_ty()?,
+            // If there wasn't a `:` or the colon was followed by a `=` or `;`, recover a missing type.
+            (colon, _) => self.recover_missing_global_item_type(colon, Some(mutability)),
+        };
+
+        let expr = if self.eat(&token::Eq) { Some(self.parse_expr()?) } else { None };
+
+        self.expect_semi()?;
+
+        Ok((ident, StaticItem { ty, mutability, expr }))
+    }
+
+    /// Parse a constant item with the prefix `"const"` already parsed.
+    ///
+    /// ```ebnf
+    /// Const = "const" ($ident | "_") Generics ":" $ty (= $expr)? WhereClause ";" ;
+    /// ```
+    fn parse_const_item(&mut self) -> PResult<'a, (Ident, Generics, P<Ty>, Option<P<ast::Expr>>)> {
+        let ident = self.parse_ident_or_underscore()?;
+
+        let mut generics = self.parse_generics()?;
+
+        // Check the span for emptiness instead of the list of parameters in order to correctly
+        // recognize and subsequently flag empty parameter lists (`<>`) as unstable.
+        if !generics.span.is_empty() {
+            self.psess.gated_spans.gate(sym::generic_const_items, generics.span);
+        }
+
+        // Parse the type of a constant item. That is, the `":" $ty` fragment.
+        // FIXME: This could maybe benefit from `.may_recover()`?
+        let ty = match (
+            self.eat(&token::Colon),
+            self.check(&token::Eq) | self.check(&token::Semi) | self.check_keyword(kw::Where),
+        ) {
+            (true, false) => self.parse_ty()?,
+            // If there wasn't a `:` or the colon was followed by a `=`, `;` or `where`, recover a missing type.
+            (colon, _) => self.recover_missing_global_item_type(colon, None),
+        };
+
+        // Proactively parse a where-clause to be able to provide a good error message in case we
+        // encounter the item body following it.
+        let before_where_clause =
+            if self.may_recover() { self.parse_where_clause()? } else { WhereClause::default() };
+
+        let expr = if self.eat(&token::Eq) { Some(self.parse_expr()?) } else { None };
+
+        let after_where_clause = self.parse_where_clause()?;
+
+        // Provide a nice error message if the user placed a where-clause before the item body.
+        // Users may be tempted to write such code if they are still used to the deprecated
+        // where-clause location on type aliases and associated types. See also #89122.
+        if before_where_clause.has_where_token
+            && let Some(expr) = &expr
+        {
+            self.dcx().emit_err(errors::WhereClauseBeforeConstBody {
+                span: before_where_clause.span,
+                name: ident.span,
+                body: expr.span,
+                sugg: if !after_where_clause.has_where_token {
+                    self.psess.source_map().span_to_snippet(expr.span).ok().map(|body| {
+                        errors::WhereClauseBeforeConstBodySugg {
+                            left: before_where_clause.span.shrink_to_lo(),
+                            snippet: body,
+                            right: before_where_clause.span.shrink_to_hi().to(expr.span),
+                        }
+                    })
+                } else {
+                    // FIXME(generic_const_items): Provide a structured suggestion to merge the first
+                    // where-clause into the second one.
+                    None
+                },
+            });
+        }
+
+        // Merge the predicates of both where-clauses since either one can be relevant.
+        // If we didn't parse a body (which is valid for associated consts in traits) and we were
+        // allowed to recover, `before_where_clause` contains the predicates, otherwise they are
+        // in `after_where_clause`. Further, both of them might contain predicates iff two
+        // where-clauses were provided which is syntactically ill-formed but we want to recover from
+        // it and treat them as one large where-clause.
+        let mut predicates = before_where_clause.predicates;
+        predicates.extend(after_where_clause.predicates);
+        let where_clause = WhereClause {
+            has_where_token: before_where_clause.has_where_token
+                || after_where_clause.has_where_token,
+            predicates,
+            span: if after_where_clause.has_where_token {
+                after_where_clause.span
+            } else {
+                before_where_clause.span
+            },
+        };
+
+        if where_clause.has_where_token {
+            self.psess.gated_spans.gate(sym::generic_const_items, where_clause.span);
+        }
+
+        generics.where_clause = where_clause;
+
+        self.expect_semi()?;
+
+        Ok((ident, generics, ty, expr))
+    }
+
+    /// We were supposed to parse `":" $ty` but the `:` or the type was missing.
+    /// This means that the type is missing.
+    fn recover_missing_global_item_type(
+        &mut self,
+        colon_present: bool,
+        m: Option<Mutability>,
+    ) -> P<Ty> {
+        // Construct the error and stash it away with the hope
+        // that typeck will later enrich the error with a type.
+        let kind = match m {
+            Some(Mutability::Mut) => "static mut",
+            Some(Mutability::Not) => "static",
+            None => "const",
+        };
+
+        let colon = match colon_present {
+            true => "",
+            false => ":",
+        };
+
+        let span = self.prev_token.span.shrink_to_hi();
+        let err = self.dcx().create_err(errors::MissingConstType { span, colon, kind });
+        err.stash(span, StashKey::ItemNoType);
+
+        // The user intended that the type be inferred,
+        // so treat this as if the user wrote e.g. `const A: _ = expr;`.
+        P(Ty { kind: TyKind::Infer, span, id: ast::DUMMY_NODE_ID, tokens: None })
+    }
+
+    /// Parses an enum declaration.
+    fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
+        if self.token.is_keyword(kw::Struct) {
+            let span = self.prev_token.span.to(self.token.span);
+            let err = errors::EnumStructMutuallyExclusive { span };
+            if self.look_ahead(1, |t| t.is_ident()) {
+                self.bump();
+                self.dcx().emit_err(err);
+            } else {
+                return Err(self.dcx().create_err(err));
+            }
+        }
+
+        let prev_span = self.prev_token.span;
+        let id = self.parse_ident()?;
+        let mut generics = self.parse_generics()?;
+        generics.where_clause = self.parse_where_clause()?;
+
+        // Possibly recover `enum Foo;` instead of `enum Foo {}`
+        let (variants, _) = if self.token == TokenKind::Semi {
+            self.dcx().emit_err(errors::UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            (thin_vec![], Trailing::No)
+        } else {
+            self.parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant(id.span))
+                .map_err(|mut err| {
+                    err.span_label(id.span, "while parsing this enum");
+                    if self.token == token::Colon {
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump();
+                        match self.parse_ty() {
+                            Ok(_) => {
+                                err.span_suggestion_verbose(
+                                    prev_span,
+                                    "perhaps you meant to use `struct` here",
+                                    "struct",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                            Err(e) => {
+                                e.cancel();
+                            }
+                        }
+                        self.restore_snapshot(snapshot);
+                    }
+                    self.eat_to_tokens(&[&token::CloseDelim(Delimiter::Brace)]);
+                    self.bump(); // }
+                    err
+                })?
+        };
+
+        let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
+        Ok((id, ItemKind::Enum(enum_definition, generics)))
+    }
+
+    fn parse_enum_variant(&mut self, span: Span) -> PResult<'a, Option<Variant>> {
+        self.recover_vcs_conflict_marker();
+        let variant_attrs = self.parse_outer_attributes()?;
+        self.recover_vcs_conflict_marker();
+        let help = "enum variants can be `Variant`, `Variant = <integer>`, \
+                    `Variant(Type, ..., TypeN)` or `Variant { fields: Types }`";
+        self.collect_tokens_trailing_token(
+            variant_attrs,
+            ForceCollect::No,
+            |this, variant_attrs| {
+                let vlo = this.token.span;
+
+                let vis = this.parse_visibility(FollowedByType::No)?;
+                if !this.recover_nested_adt_item(kw::Enum)? {
+                    return Ok((None, TrailingToken::None));
+                }
+                let ident = this.parse_field_ident("enum", vlo)?;
+
+                if this.token == token::Not {
+                    if let Err(err) = this.unexpected() {
+                        err.with_note(fluent::parse_macro_expands_to_enum_variant).emit();
+                    }
+
+                    this.bump();
+                    this.parse_delim_args()?;
+
+                    return Ok((None, TrailingToken::MaybeComma));
+                }
+
+                let struct_def = if this.check(&token::OpenDelim(Delimiter::Brace)) {
+                    // Parse a struct variant.
+                    let (fields, recovered) =
+                        match this.parse_record_struct_body("struct", ident.span, false) {
+                            Ok((fields, recovered)) => (fields, recovered),
+                            Err(mut err) => {
+                                if this.token == token::Colon {
+                                    // We handle `enum` to `struct` suggestion in the caller.
+                                    return Err(err);
+                                }
+                                this.eat_to_tokens(&[&token::CloseDelim(Delimiter::Brace)]);
+                                this.bump(); // }
+                                err.span_label(span, "while parsing this enum");
+                                err.help(help);
+                                let guar = err.emit();
+                                (thin_vec![], Recovered::Yes(guar))
+                            }
+                        };
+                    VariantData::Struct { fields, recovered: recovered.into() }
+                } else if this.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+                    let body = match this.parse_tuple_struct_body() {
+                        Ok(body) => body,
+                        Err(mut err) => {
+                            if this.token == token::Colon {
+                                // We handle `enum` to `struct` suggestion in the caller.
+                                return Err(err);
+                            }
+                            this.eat_to_tokens(&[&token::CloseDelim(Delimiter::Parenthesis)]);
+                            this.bump(); // )
+                            err.span_label(span, "while parsing this enum");
+                            err.help(help);
+                            err.emit();
+                            thin_vec![]
+                        }
+                    };
+                    VariantData::Tuple(body, DUMMY_NODE_ID)
+                } else {
+                    VariantData::Unit(DUMMY_NODE_ID)
+                };
+
+                let disr_expr =
+                    if this.eat(&token::Eq) { Some(this.parse_expr_anon_const()?) } else { None };
+
+                let vr = ast::Variant {
+                    ident,
+                    vis,
+                    id: DUMMY_NODE_ID,
+                    attrs: variant_attrs,
+                    data: struct_def,
+                    disr_expr,
+                    span: vlo.to(this.prev_token.span),
+                    is_placeholder: false,
+                };
+
+                Ok((Some(vr), TrailingToken::MaybeComma))
+            },
+        )
+        .map_err(|mut err| {
+            err.help(help);
+            err
+        })
+    }
+
+    /// Parses `struct Foo { ... }`.
+    fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
+        let class_name = self.parse_ident()?;
+
+        let mut generics = self.parse_generics()?;
+
+        // There is a special case worth noting here, as reported in issue #17904.
+        // If we are parsing a tuple struct it is the case that the where clause
+        // should follow the field list. Like so:
+        //
+        // struct Foo<T>(T) where T: Copy;
+        //
+        // If we are parsing a normal record-style struct it is the case
+        // that the where clause comes before the body, and after the generics.
+        // So if we look ahead and see a brace or a where-clause we begin
+        // parsing a record style struct.
+        //
+        // Otherwise if we look ahead and see a paren we parse a tuple-style
+        // struct.
+
+        let vdata = if self.token.is_keyword(kw::Where) {
+            let tuple_struct_body;
+            (generics.where_clause, tuple_struct_body) =
+                self.parse_struct_where_clause(class_name, generics.span)?;
+
+            if let Some(body) = tuple_struct_body {
+                // If we see a misplaced tuple struct body: `struct Foo<T> where T: Copy, (T);`
+                let body = VariantData::Tuple(body, DUMMY_NODE_ID);
+                self.expect_semi()?;
+                body
+            } else if self.eat(&token::Semi) {
+                // If we see a: `struct Foo<T> where T: Copy;` style decl.
+                VariantData::Unit(DUMMY_NODE_ID)
+            } else {
+                // If we see: `struct Foo<T> where T: Copy { ... }`
+                let (fields, recovered) = self.parse_record_struct_body(
+                    "struct",
+                    class_name.span,
+                    generics.where_clause.has_where_token,
+                )?;
+                VariantData::Struct { fields, recovered: recovered.into() }
+            }
+        // No `where` so: `struct Foo<T>;`
+        } else if self.eat(&token::Semi) {
+            VariantData::Unit(DUMMY_NODE_ID)
+        // Record-style struct definition
+        } else if self.token == token::OpenDelim(Delimiter::Brace) {
+            let (fields, recovered) = self.parse_record_struct_body(
+                "struct",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
+            VariantData::Struct { fields, recovered: recovered.into() }
+        // Tuple-style struct definition with optional where-clause.
+        } else if self.token == token::OpenDelim(Delimiter::Parenthesis) {
+            let body = VariantData::Tuple(self.parse_tuple_struct_body()?, DUMMY_NODE_ID);
+            generics.where_clause = self.parse_where_clause()?;
+            self.expect_semi()?;
+            body
+        } else {
+            let err =
+                errors::UnexpectedTokenAfterStructName::new(self.token.span, self.token.clone());
+            return Err(self.dcx().create_err(err));
+        };
+
+        Ok((class_name, ItemKind::Struct(vdata, generics)))
+    }
+
+    /// Parses `union Foo { ... }`.
+    fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
+        let class_name = self.parse_ident()?;
+
+        let mut generics = self.parse_generics()?;
+
+        let vdata = if self.token.is_keyword(kw::Where) {
+            generics.where_clause = self.parse_where_clause()?;
+            let (fields, recovered) = self.parse_record_struct_body(
+                "union",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
+            VariantData::Struct { fields, recovered: recovered.into() }
+        } else if self.token == token::OpenDelim(Delimiter::Brace) {
+            let (fields, recovered) = self.parse_record_struct_body(
+                "union",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
+            VariantData::Struct { fields, recovered: recovered.into() }
+        } else {
+            let token_str = super::token_descr(&self.token);
+            let msg = format!("expected `where` or `{{` after union name, found {token_str}");
+            let mut err = self.dcx().struct_span_err(self.token.span, msg);
+            err.span_label(self.token.span, "expected `where` or `{` after union name");
+            return Err(err);
+        };
+
+        Ok((class_name, ItemKind::Union(vdata, generics)))
+    }
+
+    /// This function parses the fields of record structs:
+    ///
+    ///   - `struct S { ... }`
+    ///   - `enum E { Variant { ... } }`
+    pub(crate) fn parse_record_struct_body(
+        &mut self,
+        adt_ty: &str,
+        ident_span: Span,
+        parsed_where: bool,
+    ) -> PResult<'a, (ThinVec<FieldDef>, Recovered)> {
+        let mut fields = ThinVec::new();
+        let mut recovered = Recovered::No;
+        if self.eat(&token::OpenDelim(Delimiter::Brace)) {
+            while self.token != token::CloseDelim(Delimiter::Brace) {
+                match self.parse_field_def(adt_ty) {
+                    Ok(field) => {
+                        fields.push(field);
+                    }
+                    Err(mut err) => {
+                        self.consume_block(Delimiter::Brace, ConsumeClosingDelim::No);
+                        err.span_label(ident_span, format!("while parsing this {adt_ty}"));
+                        let guar = err.emit();
+                        recovered = Recovered::Yes(guar);
+                        break;
+                    }
+                }
+            }
+            self.eat(&token::CloseDelim(Delimiter::Brace));
+        } else {
+            let token_str = super::token_descr(&self.token);
+            let where_str = if parsed_where { "" } else { "`where`, or " };
+            let msg = format!("expected {where_str}`{{` after struct name, found {token_str}");
+            let mut err = self.dcx().struct_span_err(self.token.span, msg);
+            err.span_label(self.token.span, format!("expected {where_str}`{{` after struct name",));
+            return Err(err);
+        }
+
+        Ok((fields, recovered))
+    }
+
+    pub(super) fn parse_tuple_struct_body(&mut self) -> PResult<'a, ThinVec<FieldDef>> {
+        // This is the case where we find `struct Foo<T>(T) where T: Copy;`
+        // Unit like structs are handled in parse_item_struct function
+        self.parse_paren_comma_seq(|p| {
+            let attrs = p.parse_outer_attributes()?;
+            p.collect_tokens_trailing_token(attrs, ForceCollect::No, |p, attrs| {
+                let mut snapshot = None;
+                if p.is_vcs_conflict_marker(&TokenKind::BinOp(token::Shl), &TokenKind::Lt) {
+                    // Account for `<<<<<<<` diff markers. We can't proactively error here because
+                    // that can be a valid type start, so we snapshot and reparse only we've
+                    // encountered another parse error.
+                    snapshot = Some(p.create_snapshot_for_diagnostic());
+                }
+                let lo = p.token.span;
+                let vis = match p.parse_visibility(FollowedByType::Yes) {
+                    Ok(vis) => vis,
+                    Err(err) => {
+                        if let Some(ref mut snapshot) = snapshot {
+                            snapshot.recover_vcs_conflict_marker();
+                        }
+                        return Err(err);
+                    }
+                };
+                let ty = match p.parse_ty() {
+                    Ok(ty) => ty,
+                    Err(err) => {
+                        if let Some(ref mut snapshot) = snapshot {
+                            snapshot.recover_vcs_conflict_marker();
+                        }
+                        return Err(err);
+                    }
+                };
+
+                Ok((
+                    FieldDef {
+                        span: lo.to(ty.span),
+                        vis,
+                        ident: None,
+                        id: DUMMY_NODE_ID,
+                        ty,
+                        attrs,
+                        is_placeholder: false,
+                    },
+                    TrailingToken::MaybeComma,
+                ))
+            })
+        })
+        .map(|(r, _)| r)
+    }
+
+    /// Parses an element of a struct declaration.
+    fn parse_field_def(&mut self, adt_ty: &str) -> PResult<'a, FieldDef> {
+        self.recover_vcs_conflict_marker();
+        let attrs = self.parse_outer_attributes()?;
+        self.recover_vcs_conflict_marker();
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let lo = this.token.span;
+            let vis = this.parse_visibility(FollowedByType::No)?;
+            this.parse_single_struct_field(adt_ty, lo, vis, attrs)
+                .map(|field| (field, TrailingToken::None))
+        })
+    }
+
+    /// Parses a structure field declaration.
+    fn parse_single_struct_field(
+        &mut self,
+        adt_ty: &str,
+        lo: Span,
+        vis: Visibility,
+        attrs: AttrVec,
+    ) -> PResult<'a, FieldDef> {
+        let mut seen_comma: bool = false;
+        let a_var = self.parse_name_and_ty(adt_ty, lo, vis, attrs)?;
+        if self.token == token::Comma {
+            seen_comma = true;
+        }
+        if self.eat(&token::Semi) {
+            let sp = self.prev_token.span;
+            let mut err =
+                self.dcx().struct_span_err(sp, format!("{adt_ty} fields are separated by `,`"));
+            err.span_suggestion_short(
+                sp,
+                "replace `;` with `,`",
+                ",",
+                Applicability::MachineApplicable,
+            );
+            return Err(err);
+        }
+        match self.token.kind {
+            token::Comma => {
+                self.bump();
+            }
+            token::CloseDelim(Delimiter::Brace) => {}
+            token::DocComment(..) => {
+                let previous_span = self.prev_token.span;
+                let mut err = errors::DocCommentDoesNotDocumentAnything {
+                    span: self.token.span,
+                    missing_comma: None,
+                };
+                self.bump(); // consume the doc comment
+                let comma_after_doc_seen = self.eat(&token::Comma);
+                // `seen_comma` is always false, because we are inside doc block
+                // condition is here to make code more readable
+                if !seen_comma && comma_after_doc_seen {
+                    seen_comma = true;
+                }
+                if comma_after_doc_seen || self.token == token::CloseDelim(Delimiter::Brace) {
+                    self.dcx().emit_err(err);
+                } else {
+                    if !seen_comma {
+                        let sp = previous_span.shrink_to_hi();
+                        err.missing_comma = Some(sp);
+                    }
+                    return Err(self.dcx().create_err(err));
+                }
+            }
+            _ => {
+                let sp = self.prev_token.span.shrink_to_hi();
+                let msg =
+                    format!("expected `,`, or `}}`, found {}", super::token_descr(&self.token));
+
+                // Try to recover extra trailing angle brackets
+                if let TyKind::Path(_, Path { segments, .. }) = &a_var.ty.kind {
+                    if let Some(last_segment) = segments.last() {
+                        let guar = self.check_trailing_angle_brackets(
+                            last_segment,
+                            &[&token::Comma, &token::CloseDelim(Delimiter::Brace)],
+                        );
+                        if let Some(_guar) = guar {
+                            // Handle a case like `Vec<u8>>,` where we can continue parsing fields
+                            // after the comma
+                            self.eat(&token::Comma);
+
+                            // `check_trailing_angle_brackets` already emitted a nicer error, as
+                            // proven by the presence of `_guar`. We can continue parsing.
+                            return Ok(a_var);
+                        }
+                    }
+                }
+
+                let mut err = self.dcx().struct_span_err(sp, msg);
+
+                if self.token.is_ident()
+                    || (self.token.kind == TokenKind::Pound
+                        && (self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Bracket))))
+                {
+                    // This is likely another field, TokenKind::Pound is used for `#[..]`
+                    // attribute for next field. Emit the diagnostic and continue parsing.
+                    err.span_suggestion(
+                        sp,
+                        "try adding a comma",
+                        ",",
+                        Applicability::MachineApplicable,
+                    );
+                    err.emit();
+                } else {
+                    return Err(err);
+                }
+            }
+        }
+        Ok(a_var)
+    }
+
+    fn expect_field_ty_separator(&mut self) -> PResult<'a, ()> {
+        if let Err(err) = self.expect(&token::Colon) {
+            let sm = self.psess.source_map();
+            let eq_typo = self.token.kind == token::Eq && self.look_ahead(1, |t| t.is_path_start());
+            let semi_typo = self.token.kind == token::Semi
+                && self.look_ahead(1, |t| {
+                    t.is_path_start()
+                    // We check that we are in a situation like `foo; bar` to avoid bad suggestions
+                    // when there's no type and `;` was used instead of a comma.
+                    && match (sm.lookup_line(self.token.span.hi()), sm.lookup_line(t.span.lo())) {
+                        (Ok(l), Ok(r)) => l.line == r.line,
+                        _ => true,
+                    }
+                });
+            if eq_typo || semi_typo {
+                self.bump();
+                // Gracefully handle small typos.
+                err.with_span_suggestion_short(
+                    self.prev_token.span,
+                    "field names and their types are separated with `:`",
+                    ":",
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+            } else {
+                return Err(err);
+            }
+        }
+        Ok(())
+    }
+
+    /// Parses a structure field.
+    fn parse_name_and_ty(
+        &mut self,
+        adt_ty: &str,
+        lo: Span,
+        vis: Visibility,
+        attrs: AttrVec,
+    ) -> PResult<'a, FieldDef> {
+        let name = self.parse_field_ident(adt_ty, lo)?;
+        if self.token.kind == token::Not {
+            if let Err(mut err) = self.unexpected() {
+                // Encounter the macro invocation
+                err.subdiagnostic(self.dcx(), MacroExpandsToAdtField { adt_ty });
+                return Err(err);
+            }
+        }
+        self.expect_field_ty_separator()?;
+        let ty = self.parse_ty_for_field_def()?;
+        if self.token.kind == token::Colon && self.look_ahead(1, |tok| tok.kind != token::Colon) {
+            self.dcx().emit_err(errors::SingleColonStructType { span: self.token.span });
+        }
+        if self.token.kind == token::Eq {
+            self.bump();
+            let const_expr = self.parse_expr_anon_const()?;
+            let sp = ty.span.shrink_to_hi().to(const_expr.value.span);
+            self.dcx().emit_err(errors::EqualsStructDefault { span: sp });
+        }
+        Ok(FieldDef {
+            span: lo.to(self.prev_token.span),
+            ident: Some(name),
+            vis,
+            id: DUMMY_NODE_ID,
+            ty,
+            attrs,
+            is_placeholder: false,
+        })
+    }
+
+    /// Parses a field identifier. Specialized version of `parse_ident_common`
+    /// for better diagnostics and suggestions.
+    fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
+        let (ident, is_raw) = self.ident_or_err(true)?;
+        if ident.name == kw::Underscore {
+            self.psess.gated_spans.gate(sym::unnamed_fields, lo);
+        } else if matches!(is_raw, IdentIsRaw::No) && ident.is_reserved() {
+            let snapshot = self.create_snapshot_for_diagnostic();
+            let err = if self.check_fn_front_matter(false, Case::Sensitive) {
+                let inherited_vis =
+                    Visibility { span: DUMMY_SP, kind: VisibilityKind::Inherited, tokens: None };
+                // We use `parse_fn` to get a span for the function
+                let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+                match self.parse_fn(
+                    &mut AttrVec::new(),
+                    fn_parse_mode,
+                    lo,
+                    &inherited_vis,
+                    Case::Insensitive,
+                ) {
+                    Ok(_) => {
+                        self.dcx().struct_span_err(
+                            lo.to(self.prev_token.span),
+                            format!("functions are not allowed in {adt_ty} definitions"),
+                        )
+                        .with_help(
+                            "unlike in C++, Java, and C#, functions are declared in `impl` blocks",
+                        )
+                        .with_help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information")
+                    }
+                    Err(err) => {
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                        self.expected_ident_found_err()
+                    }
+                }
+            } else if self.eat_keyword(kw::Struct) {
+                match self.parse_item_struct() {
+                    Ok((ident, _)) => self
+                        .dcx()
+                        .struct_span_err(
+                            lo.with_hi(ident.span.hi()),
+                            format!("structs are not allowed in {adt_ty} definitions"),
+                        )
+                        .with_help(
+                            "consider creating a new `struct` definition instead of nesting",
+                        ),
+                    Err(err) => {
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                        self.expected_ident_found_err()
+                    }
+                }
+            } else {
+                let mut err = self.expected_ident_found_err();
+                if self.eat_keyword_noexpect(kw::Let)
+                    && let removal_span = self.prev_token.span.until(self.token.span)
+                    && let Ok(ident) = self
+                        .parse_ident_common(false)
+                        // Cancel this error, we don't need it.
+                        .map_err(|err| err.cancel())
+                    && self.token.kind == TokenKind::Colon
+                {
+                    err.span_suggestion(
+                        removal_span,
+                        "remove this `let` keyword",
+                        String::new(),
+                        Applicability::MachineApplicable,
+                    );
+                    err.note("the `let` keyword is not allowed in `struct` fields");
+                    err.note("see <https://doc.rust-lang.org/book/ch05-01-defining-structs.html> for more information");
+                    err.emit();
+                    return Ok(ident);
+                } else {
+                    self.restore_snapshot(snapshot);
+                }
+                err
+            };
+            return Err(err);
+        }
+        self.bump();
+        Ok(ident)
+    }
+
+    /// Parses a declarative macro 2.0 definition.
+    /// The `macro` keyword has already been parsed.
+    /// ```ebnf
+    /// MacBody = "{" TOKEN_STREAM "}" ;
+    /// MacParams = "(" TOKEN_STREAM ")" ;
+    /// DeclMac = "macro" Ident MacParams? MacBody ;
+    /// ```
+    fn parse_item_decl_macro(&mut self, lo: Span) -> PResult<'a, ItemInfo> {
+        let ident = self.parse_ident()?;
+        let body = if self.check(&token::OpenDelim(Delimiter::Brace)) {
+            self.parse_delim_args()? // `MacBody`
+        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            let params = self.parse_token_tree(); // `MacParams`
+            let pspan = params.span();
+            if !self.check(&token::OpenDelim(Delimiter::Brace)) {
+                self.unexpected()?;
+            }
+            let body = self.parse_token_tree(); // `MacBody`
+            // Convert `MacParams MacBody` into `{ MacParams => MacBody }`.
+            let bspan = body.span();
+            let arrow = TokenTree::token_alone(token::FatArrow, pspan.between(bspan)); // `=>`
+            let tokens = TokenStream::new(vec![params, arrow, body]);
+            let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());
+            P(DelimArgs { dspan, delim: Delimiter::Brace, tokens })
+        } else {
+            self.unexpected_any()?
+        };
+
+        self.psess.gated_spans.gate(sym::decl_macro, lo.to(self.prev_token.span));
+        Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: false })))
+    }
+
+    /// Is this a possibly malformed start of a `macro_rules! foo` item definition?
+    fn is_macro_rules_item(&mut self) -> IsMacroRulesItem {
+        if self.check_keyword(kw::MacroRules) {
+            let macro_rules_span = self.token.span;
+
+            if self.look_ahead(1, |t| *t == token::Not) && self.look_ahead(2, |t| t.is_ident()) {
+                return IsMacroRulesItem::Yes { has_bang: true };
+            } else if self.look_ahead(1, |t| (t.is_ident())) {
+                // macro_rules foo
+                self.dcx().emit_err(errors::MacroRulesMissingBang {
+                    span: macro_rules_span,
+                    hi: macro_rules_span.shrink_to_hi(),
+                });
+
+                return IsMacroRulesItem::Yes { has_bang: false };
+            }
+        }
+
+        IsMacroRulesItem::No
+    }
+
+    /// Parses a `macro_rules! foo { ... }` declarative macro.
+    fn parse_item_macro_rules(
+        &mut self,
+        vis: &Visibility,
+        has_bang: bool,
+    ) -> PResult<'a, ItemInfo> {
+        self.expect_keyword(kw::MacroRules)?; // `macro_rules`
+
+        if has_bang {
+            self.expect(&token::Not)?; // `!`
+        }
+        let ident = self.parse_ident()?;
+
+        if self.eat(&token::Not) {
+            // Handle macro_rules! foo!
+            let span = self.prev_token.span;
+            self.dcx().emit_err(errors::MacroNameRemoveBang { span });
+        }
+
+        let body = self.parse_delim_args()?;
+        self.eat_semi_for_macro_if_needed(&body);
+        self.complain_if_pub_macro(vis, true);
+
+        Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: true })))
+    }
+
+    /// Item macro invocations or `macro_rules!` definitions need inherited visibility.
+    /// If that's not the case, emit an error.
+    fn complain_if_pub_macro(&self, vis: &Visibility, macro_rules: bool) {
+        if let VisibilityKind::Inherited = vis.kind {
+            return;
+        }
+
+        let vstr = pprust::vis_to_string(vis);
+        let vstr = vstr.trim_end();
+        if macro_rules {
+            self.dcx().emit_err(errors::MacroRulesVisibility { span: vis.span, vis: vstr });
+        } else {
+            self.dcx().emit_err(errors::MacroInvocationVisibility { span: vis.span, vis: vstr });
+        }
+    }
+
+    fn eat_semi_for_macro_if_needed(&mut self, args: &DelimArgs) {
+        if args.need_semicolon() && !self.eat(&token::Semi) {
+            self.report_invalid_macro_expansion_item(args);
+        }
+    }
+
+    fn report_invalid_macro_expansion_item(&self, args: &DelimArgs) {
+        let span = args.dspan.entire();
+        let mut err = self.dcx().struct_span_err(
+            span,
+            "macros that expand to items must be delimited with braces or followed by a semicolon",
+        );
+        // FIXME: This will make us not emit the help even for declarative
+        // macros within the same crate (that we can fix), which is sad.
+        if !span.from_expansion() {
+            let DelimSpan { open, close } = args.dspan;
+            err.multipart_suggestion(
+                "change the delimiters to curly braces",
+                vec![(open, "{".to_string()), (close, '}'.to_string())],
+                Applicability::MaybeIncorrect,
+            );
+            err.span_suggestion(
+                span.with_neighbor(self.token.span).shrink_to_hi(),
+                "add a semicolon",
+                ';',
+                Applicability::MaybeIncorrect,
+            );
+        }
+        err.emit();
+    }
+
+    /// Checks if current token is one of tokens which cannot be nested like `kw::Enum`. In case
+    /// it is, we try to parse the item and report error about nested types.
+    fn recover_nested_adt_item(&mut self, keyword: Symbol) -> PResult<'a, bool> {
+        if (self.token.is_keyword(kw::Enum)
+            || self.token.is_keyword(kw::Struct)
+            || self.token.is_keyword(kw::Union))
+            && self.look_ahead(1, |t| t.is_ident())
+        {
+            let kw_token = self.token.clone();
+            let kw_str = pprust::token_to_string(&kw_token);
+            let item = self.parse_item(ForceCollect::No)?;
+            self.dcx().emit_err(errors::NestedAdt {
+                span: kw_token.span,
+                item: item.unwrap().span,
+                kw_str,
+                keyword: keyword.as_str(),
+            });
+            // We successfully parsed the item but we must inform the caller about nested problem.
+            return Ok(false);
+        }
+        Ok(true)
+    }
+}
+
+/// The parsing configuration used to parse a parameter list (see `parse_fn_params`).
+///
+/// The function decides if, per-parameter `p`, `p` must have a pattern or just a type.
+///
+/// This function pointer accepts an edition, because in edition 2015, trait declarations
+/// were allowed to omit parameter names. In 2018, they became required.
+type ReqName = fn(Edition) -> bool;
+
+/// Parsing configuration for functions.
+///
+/// The syntax of function items is slightly different within trait definitions,
+/// impl blocks, and modules. It is still parsed using the same code, just with
+/// different flags set, so that even when the input is wrong and produces a parse
+/// error, it still gets into the AST and the rest of the parser and
+/// type checker can run.
+#[derive(Clone, Copy)]
+pub(crate) struct FnParseMode {
+    /// A function pointer that decides if, per-parameter `p`, `p` must have a
+    /// pattern or just a type. This field affects parsing of the parameters list.
+    ///
+    /// ```text
+    /// fn foo(alef: A) -> X { X::new() }
+    ///        -----^^ affects parsing this part of the function signature
+    ///        |
+    ///        if req_name returns false, then this name is optional
+    ///
+    /// fn bar(A) -> X;
+    ///        ^
+    ///        |
+    ///        if req_name returns true, this is an error
+    /// ```
+    ///
+    /// Calling this function pointer should only return false if:
+    ///
+    ///   * The item is being parsed inside of a trait definition.
+    ///     Within an impl block or a module, it should always evaluate
+    ///     to true.
+    ///   * The span is from Edition 2015. In particular, you can get a
+    ///     2015 span inside a 2021 crate using macros.
+    pub req_name: ReqName,
+    /// If this flag is set to `true`, then plain, semicolon-terminated function
+    /// prototypes are not allowed here.
+    ///
+    /// ```text
+    /// fn foo(alef: A) -> X { X::new() }
+    ///                      ^^^^^^^^^^^^
+    ///                      |
+    ///                      this is always allowed
+    ///
+    /// fn bar(alef: A, bet: B) -> X;
+    ///                             ^
+    ///                             |
+    ///                             if req_body is set to true, this is an error
+    /// ```
+    ///
+    /// This field should only be set to false if the item is inside of a trait
+    /// definition or extern block. Within an impl block or a module, it should
+    /// always be set to true.
+    pub req_body: bool,
+}
+
+/// Parsing of functions and methods.
+impl<'a> Parser<'a> {
+    /// Parse a function starting from the front matter (`const ...`) to the body `{ ... }` or `;`.
+    fn parse_fn(
+        &mut self,
+        attrs: &mut AttrVec,
+        fn_parse_mode: FnParseMode,
+        sig_lo: Span,
+        vis: &Visibility,
+        case: Case,
+    ) -> PResult<'a, (Ident, FnSig, Generics, Option<P<Block>>)> {
+        let fn_span = self.token.span;
+        let header = self.parse_fn_front_matter(vis, case)?; // `const ... fn`
+        let ident = self.parse_ident()?; // `foo`
+        let mut generics = self.parse_generics()?; // `<'a, T, ...>`
+        let decl = match self.parse_fn_decl(
+            fn_parse_mode.req_name,
+            AllowPlus::Yes,
+            RecoverReturnSign::Yes,
+        ) {
+            Ok(decl) => decl,
+            Err(old_err) => {
+                // If we see `for Ty ...` then user probably meant `impl` item.
+                if self.token.is_keyword(kw::For) {
+                    old_err.cancel();
+                    return Err(self.dcx().create_err(errors::FnTypoWithImpl { fn_span }));
+                } else {
+                    return Err(old_err);
+                }
+            }
+        };
+        generics.where_clause = self.parse_where_clause()?; // `where T: Ord`
+
+        let mut sig_hi = self.prev_token.span;
+        let body = self.parse_fn_body(attrs, &ident, &mut sig_hi, fn_parse_mode.req_body)?; // `;` or `{ ... }`.
+        let fn_sig_span = sig_lo.to(sig_hi);
+        Ok((ident, FnSig { header, decl, span: fn_sig_span }, generics, body))
+    }
+
+    /// Parse the "body" of a function.
+    /// This can either be `;` when there's no body,
+    /// or e.g. a block when the function is a provided one.
+    fn parse_fn_body(
+        &mut self,
+        attrs: &mut AttrVec,
+        ident: &Ident,
+        sig_hi: &mut Span,
+        req_body: bool,
+    ) -> PResult<'a, Option<P<Block>>> {
+        let has_semi = if req_body {
+            self.token.kind == TokenKind::Semi
+        } else {
+            // Only include `;` in list of expected tokens if body is not required
+            self.check(&TokenKind::Semi)
+        };
+        let (inner_attrs, body) = if has_semi {
+            // Include the trailing semicolon in the span of the signature
+            self.expect_semi()?;
+            *sig_hi = self.prev_token.span;
+            (AttrVec::new(), None)
+        } else if self.check(&token::OpenDelim(Delimiter::Brace)) || self.token.is_whole_block() {
+            self.parse_block_common(self.token.span, BlockCheckMode::Default, false)
+                .map(|(attrs, body)| (attrs, Some(body)))?
+        } else if self.token.kind == token::Eq {
+            // Recover `fn foo() = $expr;`.
+            self.bump(); // `=`
+            let eq_sp = self.prev_token.span;
+            let _ = self.parse_expr()?;
+            self.expect_semi()?; // `;`
+            let span = eq_sp.to(self.prev_token.span);
+            let guar = self.dcx().emit_err(errors::FunctionBodyEqualsExpr {
+                span,
+                sugg: errors::FunctionBodyEqualsExprSugg { eq: eq_sp, semi: self.prev_token.span },
+            });
+            (AttrVec::new(), Some(self.mk_block_err(span, guar)))
+        } else {
+            let expected = if req_body {
+                &[token::OpenDelim(Delimiter::Brace)][..]
+            } else {
+                &[token::Semi, token::OpenDelim(Delimiter::Brace)]
+            };
+            if let Err(mut err) = self.expected_one_of_not_found(&[], expected) {
+                if self.token.kind == token::CloseDelim(Delimiter::Brace) {
+                    // The enclosing `mod`, `trait` or `impl` is being closed, so keep the `fn` in
+                    // the AST for typechecking.
+                    err.span_label(ident.span, "while parsing this `fn`");
+                    err.emit();
+                } else {
+                    // check for typo'd Fn* trait bounds such as
+                    // fn foo<F>() where F: FnOnce -> () {}
+                    if self.token.kind == token::RArrow {
+                        let machine_applicable = [sym::FnOnce, sym::FnMut, sym::Fn]
+                            .into_iter()
+                            .any(|s| self.prev_token.is_ident_named(s));
+
+                        err.subdiagnostic(
+                            self.dcx(),
+                            errors::FnTraitMissingParen {
+                                span: self.prev_token.span,
+                                machine_applicable,
+                            },
+                        );
+                    }
+                    return Err(err);
+                }
+            }
+            (AttrVec::new(), None)
+        };
+        attrs.extend(inner_attrs);
+        Ok(body)
+    }
+
+    /// Is the current token the start of an `FnHeader` / not a valid parse?
+    ///
+    /// `check_pub` adds additional `pub` to the checks in case users place it
+    /// wrongly, can be used to ensure `pub` never comes after `default`.
+    pub(super) fn check_fn_front_matter(&mut self, check_pub: bool, case: Case) -> bool {
+        // We use an over-approximation here.
+        // `const const`, `fn const` won't parse, but we're not stepping over other syntax either.
+        // `pub` is added in case users got confused with the ordering like `async pub fn`,
+        // only if it wasn't preceded by `default` as `default pub` is invalid.
+        let quals: &[Symbol] = if check_pub {
+            &[kw::Pub, kw::Gen, kw::Const, kw::Async, kw::Unsafe, kw::Extern]
+        } else {
+            &[kw::Gen, kw::Const, kw::Async, kw::Unsafe, kw::Extern]
+        };
+        self.check_keyword_case(kw::Fn, case) // Definitely an `fn`.
+            // `$qual fn` or `$qual $qual`:
+            || quals.iter().any(|&kw| self.check_keyword_case(kw, case))
+                && self.look_ahead(1, |t| {
+                    // `$qual fn`, e.g. `const fn` or `async fn`.
+                    t.is_keyword_case(kw::Fn, case)
+                    // Two qualifiers `$qual $qual` is enough, e.g. `async unsafe`.
+                    || (
+                        (
+                            t.is_non_raw_ident_where(|i|
+                                quals.contains(&i.name)
+                                    // Rule out 2015 `const async: T = val`.
+                                    && i.is_reserved()
+                            )
+                            || case == Case::Insensitive
+                                && t.is_non_raw_ident_where(|i| quals.iter().any(|qual| qual.as_str() == i.name.as_str().to_lowercase()))
+                        )
+                        // Rule out `unsafe extern {`.
+                        && !self.is_unsafe_foreign_mod()
+                        // Rule out `async gen {` and `async gen move {`
+                        && !self.is_async_gen_block())
+                })
+            // `extern ABI fn`
+            || self.check_keyword_case(kw::Extern, case)
+                && self.look_ahead(1, |t| t.can_begin_literal_maybe_minus())
+                && (self.look_ahead(2, |t| t.is_keyword_case(kw::Fn, case)) ||
+                    // this branch is only for better diagnostic in later, `pub` is not allowed here
+                    (self.may_recover()
+                        && self.look_ahead(2, |t| t.is_keyword(kw::Pub))
+                        && self.look_ahead(3, |t| t.is_keyword_case(kw::Fn, case))))
+    }
+
+    /// Parses all the "front matter" (or "qualifiers") for a `fn` declaration,
+    /// up to and including the `fn` keyword. The formal grammar is:
+    ///
+    /// ```text
+    /// Extern = "extern" StringLit? ;
+    /// FnQual = "const"? "async"? "unsafe"? Extern? ;
+    /// FnFrontMatter = FnQual "fn" ;
+    /// ```
+    ///
+    /// `vis` represents the visibility that was already parsed, if any. Use
+    /// `Visibility::Inherited` when no visibility is known.
+    pub(super) fn parse_fn_front_matter(
+        &mut self,
+        orig_vis: &Visibility,
+        case: Case,
+    ) -> PResult<'a, FnHeader> {
+        let sp_start = self.token.span;
+        let constness = self.parse_constness(case);
+
+        let async_start_sp = self.token.span;
+        let coroutine_kind = self.parse_coroutine_kind(case);
+
+        let unsafe_start_sp = self.token.span;
+        let safety = self.parse_safety(case);
+
+        let ext_start_sp = self.token.span;
+        let ext = self.parse_extern(case);
+
+        if let Some(CoroutineKind::Async { span, .. }) = coroutine_kind {
+            if span.is_rust_2015() {
+                self.dcx().emit_err(errors::AsyncFnIn2015 {
+                    span,
+                    help: errors::HelpUseLatestEdition::new(),
+                });
+            }
+        }
+
+        match coroutine_kind {
+            Some(CoroutineKind::Gen { span, .. }) | Some(CoroutineKind::AsyncGen { span, .. }) => {
+                self.psess.gated_spans.gate(sym::gen_blocks, span);
+            }
+            Some(CoroutineKind::Async { .. }) | None => {}
+        }
+
+        if !self.eat_keyword_case(kw::Fn, case) {
+            // It is possible for `expect_one_of` to recover given the contents of
+            // `self.expected_tokens`, therefore, do not use `self.unexpected()` which doesn't
+            // account for this.
+            match self.expect_one_of(&[], &[]) {
+                Ok(Recovered::Yes(_)) => {}
+                Ok(Recovered::No) => unreachable!(),
+                Err(mut err) => {
+                    // Qualifier keywords ordering check
+                    enum WrongKw {
+                        Duplicated(Span),
+                        Misplaced(Span),
+                    }
+
+                    // We may be able to recover
+                    let mut recover_constness = constness;
+                    let mut recover_coroutine_kind = coroutine_kind;
+                    let mut recover_safety = safety;
+                    // This will allow the machine fix to directly place the keyword in the correct place or to indicate
+                    // that the keyword is already present and the second instance should be removed.
+                    let wrong_kw = if self.check_keyword(kw::Const) {
+                        match constness {
+                            Const::Yes(sp) => Some(WrongKw::Duplicated(sp)),
+                            Const::No => {
+                                recover_constness = Const::Yes(self.token.span);
+                                Some(WrongKw::Misplaced(async_start_sp))
+                            }
+                        }
+                    } else if self.check_keyword(kw::Async) {
+                        match coroutine_kind {
+                            Some(CoroutineKind::Async { span, .. }) => {
+                                Some(WrongKw::Duplicated(span))
+                            }
+                            Some(CoroutineKind::AsyncGen { span, .. }) => {
+                                Some(WrongKw::Duplicated(span))
+                            }
+                            Some(CoroutineKind::Gen { .. }) => {
+                                recover_coroutine_kind = Some(CoroutineKind::AsyncGen {
+                                    span: self.token.span,
+                                    closure_id: DUMMY_NODE_ID,
+                                    return_impl_trait_id: DUMMY_NODE_ID,
+                                });
+                                // FIXME(gen_blocks): This span is wrong, didn't want to think about it.
+                                Some(WrongKw::Misplaced(unsafe_start_sp))
+                            }
+                            None => {
+                                recover_coroutine_kind = Some(CoroutineKind::Async {
+                                    span: self.token.span,
+                                    closure_id: DUMMY_NODE_ID,
+                                    return_impl_trait_id: DUMMY_NODE_ID,
+                                });
+                                Some(WrongKw::Misplaced(unsafe_start_sp))
+                            }
+                        }
+                    } else if self.check_keyword(kw::Unsafe) {
+                        match safety {
+                            Safety::Unsafe(sp) => Some(WrongKw::Duplicated(sp)),
+                            Safety::Default => {
+                                recover_safety = Safety::Unsafe(self.token.span);
+                                Some(WrongKw::Misplaced(ext_start_sp))
+                            }
+                        }
+                    } else {
+                        None
+                    };
+
+                    // The keyword is already present, suggest removal of the second instance
+                    if let Some(WrongKw::Duplicated(original_sp)) = wrong_kw {
+                        let original_kw = self
+                            .span_to_snippet(original_sp)
+                            .expect("Span extracted directly from keyword should always work");
+
+                        err.span_suggestion(
+                            self.token.uninterpolated_span(),
+                            format!("`{original_kw}` already used earlier, remove this one"),
+                            "",
+                            Applicability::MachineApplicable,
+                        )
+                        .span_note(original_sp, format!("`{original_kw}` first seen here"));
+                    }
+                    // The keyword has not been seen yet, suggest correct placement in the function front matter
+                    else if let Some(WrongKw::Misplaced(correct_pos_sp)) = wrong_kw {
+                        let correct_pos_sp = correct_pos_sp.to(self.prev_token.span);
+                        if let Ok(current_qual) = self.span_to_snippet(correct_pos_sp) {
+                            let misplaced_qual_sp = self.token.uninterpolated_span();
+                            let misplaced_qual = self.span_to_snippet(misplaced_qual_sp).unwrap();
+
+                            err.span_suggestion(
+                                    correct_pos_sp.to(misplaced_qual_sp),
+                                    format!("`{misplaced_qual}` must come before `{current_qual}`"),
+                                    format!("{misplaced_qual} {current_qual}"),
+                                    Applicability::MachineApplicable,
+                                ).note("keyword order for functions declaration is `pub`, `default`, `const`, `async`, `unsafe`, `extern`");
+                        }
+                    }
+                    // Recover incorrect visibility order such as `async pub`
+                    else if self.check_keyword(kw::Pub) {
+                        let sp = sp_start.to(self.prev_token.span);
+                        if let Ok(snippet) = self.span_to_snippet(sp) {
+                            let current_vis = match self.parse_visibility(FollowedByType::No) {
+                                Ok(v) => v,
+                                Err(d) => {
+                                    d.cancel();
+                                    return Err(err);
+                                }
+                            };
+                            let vs = pprust::vis_to_string(&current_vis);
+                            let vs = vs.trim_end();
+
+                            // There was no explicit visibility
+                            if matches!(orig_vis.kind, VisibilityKind::Inherited) {
+                                err.span_suggestion(
+                                    sp_start.to(self.prev_token.span),
+                                    format!("visibility `{vs}` must come before `{snippet}`"),
+                                    format!("{vs} {snippet}"),
+                                    Applicability::MachineApplicable,
+                                );
+                            }
+                            // There was an explicit visibility
+                            else {
+                                err.span_suggestion(
+                                    current_vis.span,
+                                    "there is already a visibility modifier, remove one",
+                                    "",
+                                    Applicability::MachineApplicable,
+                                )
+                                .span_note(orig_vis.span, "explicit visibility first seen here");
+                            }
+                        }
+                    }
+
+                    // FIXME(gen_blocks): add keyword recovery logic for genness
+
+                    if wrong_kw.is_some()
+                        && self.may_recover()
+                        && self.look_ahead(1, |tok| tok.is_keyword_case(kw::Fn, case))
+                    {
+                        // Advance past the misplaced keyword and `fn`
+                        self.bump();
+                        self.bump();
+                        err.emit();
+                        return Ok(FnHeader {
+                            constness: recover_constness,
+                            safety: recover_safety,
+                            coroutine_kind: recover_coroutine_kind,
+                            ext,
+                        });
+                    }
+
+                    return Err(err);
+                }
+            }
+        }
+
+        Ok(FnHeader { constness, safety, coroutine_kind, ext })
+    }
+
+    /// Parses the parameter list and result type of a function declaration.
+    pub(super) fn parse_fn_decl(
+        &mut self,
+        req_name: ReqName,
+        ret_allow_plus: AllowPlus,
+        recover_return_sign: RecoverReturnSign,
+    ) -> PResult<'a, P<FnDecl>> {
+        Ok(P(FnDecl {
+            inputs: self.parse_fn_params(req_name)?,
+            output: self.parse_ret_ty(ret_allow_plus, RecoverQPath::Yes, recover_return_sign)?,
+        }))
+    }
+
+    /// Parses the parameter list of a function, including the `(` and `)` delimiters.
+    pub(super) fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, ThinVec<Param>> {
+        let mut first_param = true;
+        // Parse the arguments, starting out with `self` being allowed...
+        if self.token.kind != TokenKind::OpenDelim(Delimiter::Parenthesis)
+        // might be typo'd trait impl, handled elsewhere
+        && !self.token.is_keyword(kw::For)
+        {
+            // recover from missing argument list, e.g. `fn main -> () {}`
+            self.dcx()
+                .emit_err(errors::MissingFnParams { span: self.prev_token.span.shrink_to_hi() });
+            return Ok(ThinVec::new());
+        }
+
+        let (mut params, _) = self.parse_paren_comma_seq(|p| {
+            p.recover_vcs_conflict_marker();
+            let snapshot = p.create_snapshot_for_diagnostic();
+            let param = p.parse_param_general(req_name, first_param).or_else(|e| {
+                let guar = e.emit();
+                let lo = p.prev_token.span;
+                p.restore_snapshot(snapshot);
+                // Skip every token until next possible arg or end.
+                p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(Delimiter::Parenthesis)]);
+                // Create a placeholder argument for proper arg count (issue #34264).
+                Ok(dummy_arg(Ident::new(kw::Empty, lo.to(p.prev_token.span)), guar))
+            });
+            // ...now that we've parsed the first argument, `self` is no longer allowed.
+            first_param = false;
+            param
+        })?;
+        // Replace duplicated recovered params with `_` pattern to avoid unnecessary errors.
+        self.deduplicate_recovered_params_names(&mut params);
+        Ok(params)
+    }
+
+    /// Parses a single function parameter.
+    ///
+    /// - `self` is syntactically allowed when `first_param` holds.
+    fn parse_param_general(&mut self, req_name: ReqName, first_param: bool) -> PResult<'a, Param> {
+        let lo = self.token.span;
+        let attrs = self.parse_outer_attributes()?;
+        self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            // Possibly parse `self`. Recover if we parsed it and it wasn't allowed here.
+            if let Some(mut param) = this.parse_self_param()? {
+                param.attrs = attrs;
+                let res = if first_param { Ok(param) } else { this.recover_bad_self_param(param) };
+                return Ok((res?, TrailingToken::None));
+            }
+
+            let is_name_required = match this.token.kind {
+                token::DotDotDot => false,
+                _ => req_name(this.token.span.with_neighbor(this.prev_token.span).edition()),
+            };
+            let (pat, ty) = if is_name_required || this.is_named_param() {
+                debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
+                let (pat, colon) = this.parse_fn_param_pat_colon()?;
+                if !colon {
+                    let mut err = this.unexpected().unwrap_err();
+                    return if let Some(ident) =
+                        this.parameter_without_type(&mut err, pat, is_name_required, first_param)
+                    {
+                        let guar = err.emit();
+                        Ok((dummy_arg(ident, guar), TrailingToken::None))
+                    } else {
+                        Err(err)
+                    };
+                }
+
+                this.eat_incorrect_doc_comment_for_param_type();
+                (pat, this.parse_ty_for_param()?)
+            } else {
+                debug!("parse_param_general ident_to_pat");
+                let parser_snapshot_before_ty = this.create_snapshot_for_diagnostic();
+                this.eat_incorrect_doc_comment_for_param_type();
+                let mut ty = this.parse_ty_for_param();
+                if ty.is_ok()
+                    && this.token != token::Comma
+                    && this.token != token::CloseDelim(Delimiter::Parenthesis)
+                {
+                    // This wasn't actually a type, but a pattern looking like a type,
+                    // so we are going to rollback and re-parse for recovery.
+                    ty = this.unexpected_any();
+                }
+                match ty {
+                    Ok(ty) => {
+                        let ident = Ident::new(kw::Empty, this.prev_token.span);
+                        let bm = BindingMode::NONE;
+                        let pat = this.mk_pat_ident(ty.span, bm, ident);
+                        (pat, ty)
+                    }
+                    // If this is a C-variadic argument and we hit an error, return the error.
+                    Err(err) if this.token == token::DotDotDot => return Err(err),
+                    // Recover from attempting to parse the argument as a type without pattern.
+                    Err(err) => {
+                        err.cancel();
+                        this.restore_snapshot(parser_snapshot_before_ty);
+                        this.recover_arg_parse()?
+                    }
+                }
+            };
+
+            let span = lo.to(this.prev_token.span);
+
+            Ok((
+                Param { attrs, id: ast::DUMMY_NODE_ID, is_placeholder: false, pat, span, ty },
+                TrailingToken::None,
+            ))
+        })
+    }
+
+    /// Returns the parsed optional self parameter and whether a self shortcut was used.
+    fn parse_self_param(&mut self) -> PResult<'a, Option<Param>> {
+        // Extract an identifier *after* having confirmed that the token is one.
+        let expect_self_ident = |this: &mut Self| match this.token.ident() {
+            Some((ident, IdentIsRaw::No)) => {
+                this.bump();
+                ident
+            }
+            _ => unreachable!(),
+        };
+        // Is `self` `n` tokens ahead?
+        let is_isolated_self = |this: &Self, n| {
+            this.is_keyword_ahead(n, &[kw::SelfLower])
+                && this.look_ahead(n + 1, |t| t != &token::PathSep)
+        };
+        // Is `mut self` `n` tokens ahead?
+        let is_isolated_mut_self =
+            |this: &Self, n| this.is_keyword_ahead(n, &[kw::Mut]) && is_isolated_self(this, n + 1);
+        // Parse `self` or `self: TYPE`. We already know the current token is `self`.
+        let parse_self_possibly_typed = |this: &mut Self, m| {
+            let eself_ident = expect_self_ident(this);
+            let eself_hi = this.prev_token.span;
+            let eself = if this.eat(&token::Colon) {
+                SelfKind::Explicit(this.parse_ty()?, m)
+            } else {
+                SelfKind::Value(m)
+            };
+            Ok((eself, eself_ident, eself_hi))
+        };
+        // Recover for the grammar `*self`, `*const self`, and `*mut self`.
+        let recover_self_ptr = |this: &mut Self| {
+            this.dcx().emit_err(errors::SelfArgumentPointer { span: this.token.span });
+
+            Ok((SelfKind::Value(Mutability::Not), expect_self_ident(this), this.prev_token.span))
+        };
+
+        // Parse optional `self` parameter of a method.
+        // Only a limited set of initial token sequences is considered `self` parameters; anything
+        // else is parsed as a normal function parameter list, so some lookahead is required.
+        let eself_lo = self.token.span;
+        let (eself, eself_ident, eself_hi) = match self.token.uninterpolate().kind {
+            token::BinOp(token::And) => {
+                let eself = if is_isolated_self(self, 1) {
+                    // `&self`
+                    self.bump();
+                    SelfKind::Region(None, Mutability::Not)
+                } else if is_isolated_mut_self(self, 1) {
+                    // `&mut self`
+                    self.bump();
+                    self.bump();
+                    SelfKind::Region(None, Mutability::Mut)
+                } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_self(self, 2) {
+                    // `&'lt self`
+                    self.bump();
+                    let lt = self.expect_lifetime();
+                    SelfKind::Region(Some(lt), Mutability::Not)
+                } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_mut_self(self, 2) {
+                    // `&'lt mut self`
+                    self.bump();
+                    let lt = self.expect_lifetime();
+                    self.bump();
+                    SelfKind::Region(Some(lt), Mutability::Mut)
+                } else {
+                    // `&not_self`
+                    return Ok(None);
+                };
+                (eself, expect_self_ident(self), self.prev_token.span)
+            }
+            // `*self`
+            token::BinOp(token::Star) if is_isolated_self(self, 1) => {
+                self.bump();
+                recover_self_ptr(self)?
+            }
+            // `*mut self` and `*const self`
+            token::BinOp(token::Star)
+                if self.look_ahead(1, |t| t.is_mutability()) && is_isolated_self(self, 2) =>
+            {
+                self.bump();
+                self.bump();
+                recover_self_ptr(self)?
+            }
+            // `self` and `self: TYPE`
+            token::Ident(..) if is_isolated_self(self, 0) => {
+                parse_self_possibly_typed(self, Mutability::Not)?
+            }
+            // `mut self` and `mut self: TYPE`
+            token::Ident(..) if is_isolated_mut_self(self, 0) => {
+                self.bump();
+                parse_self_possibly_typed(self, Mutability::Mut)?
+            }
+            _ => return Ok(None),
+        };
+
+        let eself = source_map::respan(eself_lo.to(eself_hi), eself);
+        Ok(Some(Param::from_self(AttrVec::default(), eself, eself_ident)))
+    }
+
+    fn is_named_param(&self) -> bool {
+        let offset = match &self.token.kind {
+            token::Interpolated(nt) => match &**nt {
+                token::NtPat(..) => return self.look_ahead(1, |t| t == &token::Colon),
+                _ => 0,
+            },
+            token::BinOp(token::And) | token::AndAnd => 1,
+            _ if self.token.is_keyword(kw::Mut) => 1,
+            _ => 0,
+        };
+
+        self.look_ahead(offset, |t| t.is_ident())
+            && self.look_ahead(offset + 1, |t| t == &token::Colon)
+    }
+
+    fn recover_self_param(&mut self) -> bool {
+        matches!(
+            self.parse_outer_attributes()
+                .and_then(|_| self.parse_self_param())
+                .map_err(|e| e.cancel()),
+            Ok(Some(_))
+        )
+    }
+}
+
+enum IsMacroRulesItem {
+    Yes { has_bang: bool },
+    No,
+}
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
new file mode 100644
index 00000000000..c2183258eef
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -0,0 +1,1643 @@
+pub mod attr;
+mod attr_wrapper;
+mod diagnostics;
+mod expr;
+mod generics;
+mod item;
+mod nonterminal;
+mod pat;
+mod path;
+mod stmt;
+mod ty;
+
+use crate::lexer::UnmatchedDelim;
+pub use attr_wrapper::AttrWrapper;
+pub use diagnostics::AttemptLocalParseRecovery;
+pub(crate) use expr::ForbiddenLetReason;
+pub(crate) use item::FnParseMode;
+pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
+pub use path::PathStyle;
+
+use core::fmt;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, IdentIsRaw, Nonterminal, Token, TokenKind};
+use rustc_ast::tokenstream::{AttributesData, DelimSpacing, DelimSpan, Spacing};
+use rustc_ast::tokenstream::{TokenStream, TokenTree, TokenTreeCursor};
+use rustc_ast::util::case::Case;
+use rustc_ast::{
+    self as ast, AnonConst, AttrArgs, AttrArgsEq, AttrId, ByRef, Const, CoroutineKind, DelimArgs,
+    Expr, ExprKind, Extern, HasAttrs, HasTokens, Mutability, Recovered, Safety, StrLit, Visibility,
+    VisibilityKind, DUMMY_NODE_ID,
+};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::{Applicability, Diag, FatalError, MultiSpan, PResult};
+use rustc_session::parse::ParseSess;
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use rustc_span::{Span, DUMMY_SP};
+use std::ops::Range;
+use std::{mem, slice};
+use thin_vec::ThinVec;
+use tracing::debug;
+
+use crate::errors::{
+    self, IncorrectVisibilityRestriction, MismatchedClosingDelimiter, NonStringAbiLiteral,
+};
+
+#[cfg(test)]
+mod tests;
+
+// Ideally, these tests would be in `rustc_ast`. But they depend on having a
+// parser, so they are here.
+#[cfg(test)]
+mod tokenstream {
+    mod tests;
+}
+#[cfg(test)]
+mod mut_visit {
+    mod tests;
+}
+
+bitflags::bitflags! {
+    #[derive(Clone, Copy, Debug)]
+    struct Restrictions: u8 {
+        const STMT_EXPR         = 1 << 0;
+        const NO_STRUCT_LITERAL = 1 << 1;
+        const CONST_EXPR        = 1 << 2;
+        const ALLOW_LET         = 1 << 3;
+        const IN_IF_GUARD       = 1 << 4;
+        const IS_PAT            = 1 << 5;
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum SemiColonMode {
+    Break,
+    Ignore,
+    Comma,
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum BlockMode {
+    Break,
+    Ignore,
+}
+
+/// Whether or not we should force collection of tokens for an AST node,
+/// regardless of whether or not it has attributes
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum ForceCollect {
+    Yes,
+    No,
+}
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum TrailingToken {
+    None,
+    Semi,
+    Gt,
+    /// If the trailing token is a comma, then capture it
+    /// Otherwise, ignore the trailing token
+    MaybeComma,
+}
+
+/// Like `maybe_whole_expr`, but for things other than expressions.
+#[macro_export]
+macro_rules! maybe_whole {
+    ($p:expr, $constructor:ident, |$x:ident| $e:expr) => {
+        if let token::Interpolated(nt) = &$p.token.kind
+            && let token::$constructor(x) = &**nt
+        {
+            #[allow(unused_mut)]
+            let mut $x = x.clone();
+            $p.bump();
+            return Ok($e);
+        }
+    };
+}
+
+/// If the next tokens are ill-formed `$ty::` recover them as `<$ty>::`.
+#[macro_export]
+macro_rules! maybe_recover_from_interpolated_ty_qpath {
+    ($self: expr, $allow_qpath_recovery: expr) => {
+        if $allow_qpath_recovery
+            && $self.may_recover()
+            && $self.look_ahead(1, |t| t == &token::PathSep)
+            && let token::Interpolated(nt) = &$self.token.kind
+            && let token::NtTy(ty) = &**nt
+        {
+            let ty = ty.clone();
+            $self.bump();
+            return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
+        }
+    };
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum Recovery {
+    Allowed,
+    Forbidden,
+}
+
+#[derive(Clone)]
+pub struct Parser<'a> {
+    pub psess: &'a ParseSess,
+    /// The current token.
+    pub token: Token,
+    /// The spacing for the current token.
+    pub token_spacing: Spacing,
+    /// The previous token.
+    pub prev_token: Token,
+    pub capture_cfg: bool,
+    restrictions: Restrictions,
+    expected_tokens: Vec<TokenType>,
+    token_cursor: TokenCursor,
+    // The number of calls to `bump`, i.e. the position in the token stream.
+    num_bump_calls: usize,
+    // During parsing we may sometimes need to 'unglue' a glued token into two
+    // component tokens (e.g. '>>' into '>' and '>), so the parser can consume
+    // them one at a time. This process bypasses the normal capturing mechanism
+    // (e.g. `num_bump_calls` will not be incremented), since the 'unglued'
+    // tokens due not exist in the original `TokenStream`.
+    //
+    // If we end up consuming both unglued tokens, this is not an issue. We'll
+    // end up capturing the single 'glued' token.
+    //
+    // However, sometimes we may want to capture just the first 'unglued'
+    // token. For example, capturing the `Vec<u8>` in `Option<Vec<u8>>`
+    // requires us to unglue the trailing `>>` token. The `break_last_token`
+    // field is used to track this token. It gets appended to the captured
+    // stream when we evaluate a `LazyAttrTokenStream`.
+    break_last_token: bool,
+    /// This field is used to keep track of how many left angle brackets we have seen. This is
+    /// required in order to detect extra leading left angle brackets (`<` characters) and error
+    /// appropriately.
+    ///
+    /// See the comments in the `parse_path_segment` function for more details.
+    unmatched_angle_bracket_count: u16,
+    angle_bracket_nesting: u16,
+
+    last_unexpected_token_span: Option<Span>,
+    /// If present, this `Parser` is not parsing Rust code but rather a macro call.
+    subparser_name: Option<&'static str>,
+    capture_state: CaptureState,
+    /// This allows us to recover when the user forget to add braces around
+    /// multiple statements in the closure body.
+    current_closure: Option<ClosureSpans>,
+    /// Whether the parser is allowed to do recovery.
+    /// This is disabled when parsing macro arguments, see #103534
+    pub recovery: Recovery,
+}
+
+// This type is used a lot, e.g. it's cloned when matching many declarative macro rules with nonterminals. Make sure
+// it doesn't unintentionally get bigger.
+#[cfg(target_pointer_width = "64")]
+rustc_data_structures::static_assert_size!(Parser<'_>, 264);
+
+/// Stores span information about a closure.
+#[derive(Clone, Debug)]
+pub struct ClosureSpans {
+    pub whole_closure: Span,
+    pub closing_pipe: Span,
+    pub body: Span,
+}
+
+/// Indicates a range of tokens that should be replaced by
+/// the tokens in the provided vector. This is used in two
+/// places during token collection:
+///
+/// 1. During the parsing of an AST node that may have a `#[derive]`
+/// attribute, we parse a nested AST node that has `#[cfg]` or `#[cfg_attr]`
+/// In this case, we use a `ReplaceRange` to replace the entire inner AST node
+/// with `FlatToken::AttrTarget`, allowing us to perform eager cfg-expansion
+/// on an `AttrTokenStream`.
+///
+/// 2. When we parse an inner attribute while collecting tokens. We
+/// remove inner attributes from the token stream entirely, and
+/// instead track them through the `attrs` field on the AST node.
+/// This allows us to easily manipulate them (for example, removing
+/// the first macro inner attribute to invoke a proc-macro).
+/// When create a `TokenStream`, the inner attributes get inserted
+/// into the proper place in the token stream.
+pub type ReplaceRange = (Range<u32>, Vec<(FlatToken, Spacing)>);
+
+/// Controls how we capture tokens. Capturing can be expensive,
+/// so we try to avoid performing capturing in cases where
+/// we will never need an `AttrTokenStream`.
+#[derive(Copy, Clone, Debug)]
+pub enum Capturing {
+    /// We aren't performing any capturing - this is the default mode.
+    No,
+    /// We are capturing tokens
+    Yes,
+}
+
+#[derive(Clone, Debug)]
+struct CaptureState {
+    capturing: Capturing,
+    replace_ranges: Vec<ReplaceRange>,
+    inner_attr_ranges: FxHashMap<AttrId, ReplaceRange>,
+}
+
+/// Iterator over a `TokenStream` that produces `Token`s. It's a bit odd that
+/// we (a) lex tokens into a nice tree structure (`TokenStream`), and then (b)
+/// use this type to emit them as a linear sequence. But a linear sequence is
+/// what the parser expects, for the most part.
+#[derive(Clone, Debug)]
+struct TokenCursor {
+    // Cursor for the current (innermost) token stream. The delimiters for this
+    // token stream are found in `self.stack.last()`; when that is `None` then
+    // we are in the outermost token stream which never has delimiters.
+    tree_cursor: TokenTreeCursor,
+
+    // Token streams surrounding the current one. The delimiters for stack[n]'s
+    // tokens are in `stack[n-1]`. `stack[0]` (when present) has no delimiters
+    // because it's the outermost token stream which never has delimiters.
+    stack: Vec<(TokenTreeCursor, DelimSpan, DelimSpacing, Delimiter)>,
+}
+
+impl TokenCursor {
+    fn next(&mut self) -> (Token, Spacing) {
+        self.inlined_next()
+    }
+
+    /// This always-inlined version should only be used on hot code paths.
+    #[inline(always)]
+    fn inlined_next(&mut self) -> (Token, Spacing) {
+        loop {
+            // FIXME: we currently don't return `Delimiter::Invisible` open/close delims. To fix
+            // #67062 we will need to, whereupon the `delim != Delimiter::Invisible` conditions
+            // below can be removed.
+            if let Some(tree) = self.tree_cursor.next_ref() {
+                match tree {
+                    &TokenTree::Token(ref token, spacing) => {
+                        debug_assert!(!matches!(
+                            token.kind,
+                            token::OpenDelim(_) | token::CloseDelim(_)
+                        ));
+                        return (token.clone(), spacing);
+                    }
+                    &TokenTree::Delimited(sp, spacing, delim, ref tts) => {
+                        let trees = tts.clone().into_trees();
+                        self.stack.push((
+                            mem::replace(&mut self.tree_cursor, trees),
+                            sp,
+                            spacing,
+                            delim,
+                        ));
+                        if delim != Delimiter::Invisible {
+                            return (Token::new(token::OpenDelim(delim), sp.open), spacing.open);
+                        }
+                        // No open delimiter to return; continue on to the next iteration.
+                    }
+                };
+            } else if let Some((tree_cursor, span, spacing, delim)) = self.stack.pop() {
+                // We have exhausted this token stream. Move back to its parent token stream.
+                self.tree_cursor = tree_cursor;
+                if delim != Delimiter::Invisible {
+                    return (Token::new(token::CloseDelim(delim), span.close), spacing.close);
+                }
+                // No close delimiter to return; continue on to the next iteration.
+            } else {
+                // We have exhausted the outermost token stream. The use of
+                // `Spacing::Alone` is arbitrary and immaterial, because the
+                // `Eof` token's spacing is never used.
+                return (Token::new(token::Eof, DUMMY_SP), Spacing::Alone);
+            }
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+enum TokenType {
+    Token(TokenKind),
+    Keyword(Symbol),
+    Operator,
+    Lifetime,
+    Ident,
+    Path,
+    Type,
+    Const,
+}
+
+impl TokenType {
+    fn to_string(&self) -> String {
+        match self {
+            TokenType::Token(t) => format!("`{}`", pprust::token_kind_to_string(t)),
+            TokenType::Keyword(kw) => format!("`{kw}`"),
+            TokenType::Operator => "an operator".to_string(),
+            TokenType::Lifetime => "lifetime".to_string(),
+            TokenType::Ident => "identifier".to_string(),
+            TokenType::Path => "path".to_string(),
+            TokenType::Type => "type".to_string(),
+            TokenType::Const => "a const expression".to_string(),
+        }
+    }
+}
+
+/// Used by [`Parser::expect_any_with_type`].
+#[derive(Copy, Clone, Debug)]
+enum TokenExpectType {
+    /// Unencountered tokens are inserted into [`Parser::expected_tokens`].
+    /// See [`Parser::check`].
+    Expect,
+
+    /// Unencountered tokens are not inserted into [`Parser::expected_tokens`].
+    /// See [`Parser::check_noexpect`].
+    NoExpect,
+}
+
+/// A sequence separator.
+#[derive(Debug)]
+struct SeqSep {
+    /// The separator token.
+    sep: Option<TokenKind>,
+    /// `true` if a trailing separator is allowed.
+    trailing_sep_allowed: bool,
+}
+
+impl SeqSep {
+    fn trailing_allowed(t: TokenKind) -> SeqSep {
+        SeqSep { sep: Some(t), trailing_sep_allowed: true }
+    }
+
+    fn none() -> SeqSep {
+        SeqSep { sep: None, trailing_sep_allowed: false }
+    }
+}
+
+#[derive(Debug)]
+pub enum FollowedByType {
+    Yes,
+    No,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum Trailing {
+    No,
+    Yes,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum TokenDescription {
+    ReservedIdentifier,
+    Keyword,
+    ReservedKeyword,
+    DocComment,
+}
+
+impl TokenDescription {
+    pub fn from_token(token: &Token) -> Option<Self> {
+        match token.kind {
+            _ if token.is_special_ident() => Some(TokenDescription::ReservedIdentifier),
+            _ if token.is_used_keyword() => Some(TokenDescription::Keyword),
+            _ if token.is_unused_keyword() => Some(TokenDescription::ReservedKeyword),
+            token::DocComment(..) => Some(TokenDescription::DocComment),
+            _ => None,
+        }
+    }
+}
+
+pub(super) fn token_descr(token: &Token) -> String {
+    let name = pprust::token_to_string(token).to_string();
+
+    let kind = match (TokenDescription::from_token(token), &token.kind) {
+        (Some(TokenDescription::ReservedIdentifier), _) => Some("reserved identifier"),
+        (Some(TokenDescription::Keyword), _) => Some("keyword"),
+        (Some(TokenDescription::ReservedKeyword), _) => Some("reserved keyword"),
+        (Some(TokenDescription::DocComment), _) => Some("doc comment"),
+        (None, TokenKind::NtIdent(..)) => Some("identifier"),
+        (None, TokenKind::NtLifetime(..)) => Some("lifetime"),
+        (None, TokenKind::Interpolated(node)) => Some(node.descr()),
+        (None, _) => None,
+    };
+
+    if let Some(kind) = kind { format!("{kind} `{name}`") } else { format!("`{name}`") }
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(
+        psess: &'a ParseSess,
+        stream: TokenStream,
+        subparser_name: Option<&'static str>,
+    ) -> Self {
+        let mut parser = Parser {
+            psess,
+            token: Token::dummy(),
+            token_spacing: Spacing::Alone,
+            prev_token: Token::dummy(),
+            capture_cfg: false,
+            restrictions: Restrictions::empty(),
+            expected_tokens: Vec::new(),
+            token_cursor: TokenCursor { tree_cursor: stream.into_trees(), stack: Vec::new() },
+            num_bump_calls: 0,
+            break_last_token: false,
+            unmatched_angle_bracket_count: 0,
+            angle_bracket_nesting: 0,
+            last_unexpected_token_span: None,
+            subparser_name,
+            capture_state: CaptureState {
+                capturing: Capturing::No,
+                replace_ranges: Vec::new(),
+                inner_attr_ranges: Default::default(),
+            },
+            current_closure: None,
+            recovery: Recovery::Allowed,
+        };
+
+        // Make parser point to the first token.
+        parser.bump();
+
+        parser
+    }
+
+    #[inline]
+    pub fn recovery(mut self, recovery: Recovery) -> Self {
+        self.recovery = recovery;
+        self
+    }
+
+    /// Whether the parser is allowed to recover from broken code.
+    ///
+    /// If this returns false, recovering broken code into valid code (especially if this recovery does lookahead)
+    /// is not allowed. All recovery done by the parser must be gated behind this check.
+    ///
+    /// Technically, this only needs to restrict eager recovery by doing lookahead at more tokens.
+    /// But making the distinction is very subtle, and simply forbidding all recovery is a lot simpler to uphold.
+    #[inline]
+    fn may_recover(&self) -> bool {
+        matches!(self.recovery, Recovery::Allowed)
+    }
+
+    /// Version of [`unexpected`](Parser::unexpected) that "returns" any type in the `Ok`
+    /// (both those functions never return "Ok", and so can lie like that in the type).
+    pub fn unexpected_any<T>(&mut self) -> PResult<'a, T> {
+        match self.expect_one_of(&[], &[]) {
+            Err(e) => Err(e),
+            // We can get `Ok(true)` from `recover_closing_delimiter`
+            // which is called in `expected_one_of_not_found`.
+            Ok(_) => FatalError.raise(),
+        }
+    }
+
+    pub fn unexpected(&mut self) -> PResult<'a, ()> {
+        self.unexpected_any()
+    }
+
+    /// Expects and consumes the token `t`. Signals an error if the next token is not `t`.
+    pub fn expect(&mut self, t: &TokenKind) -> PResult<'a, Recovered> {
+        if self.expected_tokens.is_empty() {
+            if self.token == *t {
+                self.bump();
+                Ok(Recovered::No)
+            } else {
+                self.unexpected_try_recover(t)
+            }
+        } else {
+            self.expect_one_of(slice::from_ref(t), &[])
+        }
+    }
+
+    /// Expect next token to be edible or inedible token. If edible,
+    /// then consume it; if inedible, then return without consuming
+    /// anything. Signal a fatal error if next token is unexpected.
+    pub fn expect_one_of(
+        &mut self,
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
+    ) -> PResult<'a, Recovered> {
+        if edible.contains(&self.token.kind) {
+            self.bump();
+            Ok(Recovered::No)
+        } else if inedible.contains(&self.token.kind) {
+            // leave it in the input
+            Ok(Recovered::No)
+        } else if self.token.kind != token::Eof
+            && self.last_unexpected_token_span == Some(self.token.span)
+        {
+            FatalError.raise();
+        } else {
+            self.expected_one_of_not_found(edible, inedible)
+        }
+    }
+
+    // Public for rustfmt usage.
+    pub fn parse_ident(&mut self) -> PResult<'a, Ident> {
+        self.parse_ident_common(true)
+    }
+
+    fn parse_ident_common(&mut self, recover: bool) -> PResult<'a, Ident> {
+        let (ident, is_raw) = self.ident_or_err(recover)?;
+
+        if matches!(is_raw, IdentIsRaw::No) && ident.is_reserved() {
+            let err = self.expected_ident_found_err();
+            if recover {
+                err.emit();
+            } else {
+                return Err(err);
+            }
+        }
+        self.bump();
+        Ok(ident)
+    }
+
+    fn ident_or_err(&mut self, recover: bool) -> PResult<'a, (Ident, IdentIsRaw)> {
+        match self.token.ident() {
+            Some(ident) => Ok(ident),
+            None => self.expected_ident_found(recover),
+        }
+    }
+
+    /// Checks if the next token is `tok`, and returns `true` if so.
+    ///
+    /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
+    /// encountered.
+    #[inline]
+    fn check(&mut self, tok: &TokenKind) -> bool {
+        let is_present = self.token == *tok;
+        if !is_present {
+            self.expected_tokens.push(TokenType::Token(tok.clone()));
+        }
+        is_present
+    }
+
+    #[inline]
+    fn check_noexpect(&self, tok: &TokenKind) -> bool {
+        self.token == *tok
+    }
+
+    /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
+    ///
+    /// the main purpose of this function is to reduce the cluttering of the suggestions list
+    /// which using the normal eat method could introduce in some cases.
+    #[inline]
+    pub fn eat_noexpect(&mut self, tok: &TokenKind) -> bool {
+        let is_present = self.check_noexpect(tok);
+        if is_present {
+            self.bump()
+        }
+        is_present
+    }
+
+    /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
+    #[inline]
+    pub fn eat(&mut self, tok: &TokenKind) -> bool {
+        let is_present = self.check(tok);
+        if is_present {
+            self.bump()
+        }
+        is_present
+    }
+
+    /// If the next token is the given keyword, returns `true` without eating it.
+    /// An expectation is also added for diagnostics purposes.
+    #[inline]
+    fn check_keyword(&mut self, kw: Symbol) -> bool {
+        self.expected_tokens.push(TokenType::Keyword(kw));
+        self.token.is_keyword(kw)
+    }
+
+    #[inline]
+    fn check_keyword_case(&mut self, kw: Symbol, case: Case) -> bool {
+        if self.check_keyword(kw) {
+            return true;
+        }
+
+        if case == Case::Insensitive
+            && let Some((ident, IdentIsRaw::No)) = self.token.ident()
+            && ident.as_str().to_lowercase() == kw.as_str().to_lowercase()
+        {
+            true
+        } else {
+            false
+        }
+    }
+
+    /// If the next token is the given keyword, eats it and returns `true`.
+    /// Otherwise, returns `false`. An expectation is also added for diagnostics purposes.
+    // Public for rustfmt usage.
+    #[inline]
+    pub fn eat_keyword(&mut self, kw: Symbol) -> bool {
+        if self.check_keyword(kw) {
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Eats a keyword, optionally ignoring the case.
+    /// If the case differs (and is ignored) an error is issued.
+    /// This is useful for recovery.
+    #[inline]
+    fn eat_keyword_case(&mut self, kw: Symbol, case: Case) -> bool {
+        if self.eat_keyword(kw) {
+            return true;
+        }
+
+        if case == Case::Insensitive
+            && let Some((ident, IdentIsRaw::No)) = self.token.ident()
+            && ident.as_str().to_lowercase() == kw.as_str().to_lowercase()
+        {
+            self.dcx().emit_err(errors::KwBadCase { span: ident.span, kw: kw.as_str() });
+            self.bump();
+            return true;
+        }
+
+        false
+    }
+
+    #[inline]
+    fn eat_keyword_noexpect(&mut self, kw: Symbol) -> bool {
+        if self.token.is_keyword(kw) {
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// If the given word is not a keyword, signals an error.
+    /// If the next token is not the given word, signals an error.
+    /// Otherwise, eats it.
+    fn expect_keyword(&mut self, kw: Symbol) -> PResult<'a, ()> {
+        if !self.eat_keyword(kw) { self.unexpected() } else { Ok(()) }
+    }
+
+    /// Is the given keyword `kw` followed by a non-reserved identifier?
+    fn is_kw_followed_by_ident(&self, kw: Symbol) -> bool {
+        self.token.is_keyword(kw) && self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
+    }
+
+    #[inline]
+    fn check_or_expected(&mut self, ok: bool, typ: TokenType) -> bool {
+        if ok {
+            true
+        } else {
+            self.expected_tokens.push(typ);
+            false
+        }
+    }
+
+    fn check_ident(&mut self) -> bool {
+        self.check_or_expected(self.token.is_ident(), TokenType::Ident)
+    }
+
+    fn check_path(&mut self) -> bool {
+        self.check_or_expected(self.token.is_path_start(), TokenType::Path)
+    }
+
+    fn check_type(&mut self) -> bool {
+        self.check_or_expected(self.token.can_begin_type(), TokenType::Type)
+    }
+
+    fn check_const_arg(&mut self) -> bool {
+        self.check_or_expected(self.token.can_begin_const_arg(), TokenType::Const)
+    }
+
+    fn check_const_closure(&self) -> bool {
+        self.is_keyword_ahead(0, &[kw::Const])
+            && self.look_ahead(1, |t| match &t.kind {
+                // async closures do not work with const closures, so we do not parse that here.
+                token::Ident(kw::Move | kw::Static, _) | token::OrOr | token::BinOp(token::Or) => {
+                    true
+                }
+                _ => false,
+            })
+    }
+
+    fn check_inline_const(&self, dist: usize) -> bool {
+        self.is_keyword_ahead(dist, &[kw::Const])
+            && self.look_ahead(dist + 1, |t| match &t.kind {
+                token::Interpolated(nt) => matches!(&**nt, token::NtBlock(..)),
+                token::OpenDelim(Delimiter::Brace) => true,
+                _ => false,
+            })
+    }
+
+    /// Checks to see if the next token is either `+` or `+=`.
+    /// Otherwise returns `false`.
+    #[inline]
+    fn check_plus(&mut self) -> bool {
+        self.check_or_expected(
+            self.token.is_like_plus(),
+            TokenType::Token(token::BinOp(token::Plus)),
+        )
+    }
+
+    /// Eats the expected token if it's present possibly breaking
+    /// compound tokens like multi-character operators in process.
+    /// Returns `true` if the token was eaten.
+    fn break_and_eat(&mut self, expected: TokenKind) -> bool {
+        if self.token.kind == expected {
+            self.bump();
+            return true;
+        }
+        match self.token.kind.break_two_token_op() {
+            Some((first, second)) if first == expected => {
+                let first_span = self.psess.source_map().start_point(self.token.span);
+                let second_span = self.token.span.with_lo(first_span.hi());
+                self.token = Token::new(first, first_span);
+                // Keep track of this token - if we end token capturing now,
+                // we'll want to append this token to the captured stream.
+                //
+                // If we consume any additional tokens, then this token
+                // is not needed (we'll capture the entire 'glued' token),
+                // and `bump` will set this field to `None`
+                self.break_last_token = true;
+                // Use the spacing of the glued token as the spacing of the
+                // unglued second token.
+                self.bump_with((Token::new(second, second_span), self.token_spacing));
+                true
+            }
+            _ => {
+                self.expected_tokens.push(TokenType::Token(expected));
+                false
+            }
+        }
+    }
+
+    /// Eats `+` possibly breaking tokens like `+=` in process.
+    fn eat_plus(&mut self) -> bool {
+        self.break_and_eat(token::BinOp(token::Plus))
+    }
+
+    /// Eats `&` possibly breaking tokens like `&&` in process.
+    /// Signals an error if `&` is not eaten.
+    fn expect_and(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::BinOp(token::And)) { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `|` possibly breaking tokens like `||` in process.
+    /// Signals an error if `|` was not eaten.
+    fn expect_or(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::BinOp(token::Or)) { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `<` possibly breaking tokens like `<<` in process.
+    fn eat_lt(&mut self) -> bool {
+        let ate = self.break_and_eat(token::Lt);
+        if ate {
+            // See doc comment for `unmatched_angle_bracket_count`.
+            self.unmatched_angle_bracket_count += 1;
+            debug!("eat_lt: (increment) count={:?}", self.unmatched_angle_bracket_count);
+        }
+        ate
+    }
+
+    /// Eats `<` possibly breaking tokens like `<<` in process.
+    /// Signals an error if `<` was not eaten.
+    fn expect_lt(&mut self) -> PResult<'a, ()> {
+        if self.eat_lt() { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `>` possibly breaking tokens like `>>` in process.
+    /// Signals an error if `>` was not eaten.
+    fn expect_gt(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::Gt) {
+            // See doc comment for `unmatched_angle_bracket_count`.
+            if self.unmatched_angle_bracket_count > 0 {
+                self.unmatched_angle_bracket_count -= 1;
+                debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+            }
+            Ok(())
+        } else {
+            self.unexpected()
+        }
+    }
+
+    /// Checks if the next token is contained within `kets`, and returns `true` if so.
+    fn expect_any_with_type(&mut self, kets: &[&TokenKind], expect: TokenExpectType) -> bool {
+        kets.iter().any(|k| match expect {
+            TokenExpectType::Expect => self.check(k),
+            TokenExpectType::NoExpect => self.check_noexpect(k),
+        })
+    }
+
+    /// Parses a sequence until the specified delimiters. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_seq_to_before_tokens<T>(
+        &mut self,
+        kets: &[&TokenKind],
+        sep: SeqSep,
+        expect: TokenExpectType,
+        mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing, Recovered)> {
+        let mut first = true;
+        let mut recovered = Recovered::No;
+        let mut trailing = Trailing::No;
+        let mut v = ThinVec::new();
+
+        while !self.expect_any_with_type(kets, expect) {
+            if let token::CloseDelim(..) | token::Eof = self.token.kind {
+                break;
+            }
+            if let Some(t) = &sep.sep {
+                if first {
+                    // no separator for the first element
+                    first = false;
+                } else {
+                    // check for separator
+                    match self.expect(t) {
+                        Ok(Recovered::No) => {
+                            self.current_closure.take();
+                        }
+                        Ok(Recovered::Yes(guar)) => {
+                            self.current_closure.take();
+                            recovered = Recovered::Yes(guar);
+                            break;
+                        }
+                        Err(mut expect_err) => {
+                            let sp = self.prev_token.span.shrink_to_hi();
+                            let token_str = pprust::token_kind_to_string(t);
+
+                            match self.current_closure.take() {
+                                Some(closure_spans) if self.token.kind == TokenKind::Semi => {
+                                    // Finding a semicolon instead of a comma
+                                    // after a closure body indicates that the
+                                    // closure body may be a block but the user
+                                    // forgot to put braces around its
+                                    // statements.
+
+                                    self.recover_missing_braces_around_closure_body(
+                                        closure_spans,
+                                        expect_err,
+                                    )?;
+
+                                    continue;
+                                }
+
+                                _ => {
+                                    // Attempt to keep parsing if it was a similar separator.
+                                    if let Some(tokens) = t.similar_tokens() {
+                                        if tokens.contains(&self.token.kind) {
+                                            self.bump();
+                                        }
+                                    }
+                                }
+                            }
+
+                            // If this was a missing `@` in a binding pattern
+                            // bail with a suggestion
+                            // https://github.com/rust-lang/rust/issues/72373
+                            if self.prev_token.is_ident() && self.token.kind == token::DotDot {
+                                let msg = format!(
+                                    "if you meant to bind the contents of the rest of the array \
+                                     pattern into `{}`, use `@`",
+                                    pprust::token_to_string(&self.prev_token)
+                                );
+                                expect_err
+                                    .with_span_suggestion_verbose(
+                                        self.prev_token.span.shrink_to_hi().until(self.token.span),
+                                        msg,
+                                        " @ ",
+                                        Applicability::MaybeIncorrect,
+                                    )
+                                    .emit();
+                                break;
+                            }
+
+                            // Attempt to keep parsing if it was an omitted separator.
+                            self.last_unexpected_token_span = None;
+                            match f(self) {
+                                Ok(t) => {
+                                    // Parsed successfully, therefore most probably the code only
+                                    // misses a separator.
+                                    expect_err
+                                        .with_span_suggestion_short(
+                                            sp,
+                                            format!("missing `{token_str}`"),
+                                            token_str,
+                                            Applicability::MaybeIncorrect,
+                                        )
+                                        .emit();
+
+                                    v.push(t);
+                                    continue;
+                                }
+                                Err(e) => {
+                                    // Parsing failed, therefore it must be something more serious
+                                    // than just a missing separator.
+                                    for xx in &e.children {
+                                        // propagate the help message from sub error 'e' to main error 'expect_err;
+                                        expect_err.children.push(xx.clone());
+                                    }
+                                    e.cancel();
+                                    if self.token == token::Colon {
+                                        // we will try to recover in `maybe_recover_struct_lit_bad_delims`
+                                        return Err(expect_err);
+                                    } else if let [token::CloseDelim(Delimiter::Parenthesis)] = kets
+                                    {
+                                        return Err(expect_err);
+                                    } else {
+                                        expect_err.emit();
+                                        break;
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
+                trailing = Trailing::Yes;
+                break;
+            }
+
+            let t = f(self)?;
+            v.push(t);
+        }
+
+        Ok((v, trailing, recovered))
+    }
+
+    fn recover_missing_braces_around_closure_body(
+        &mut self,
+        closure_spans: ClosureSpans,
+        mut expect_err: Diag<'_>,
+    ) -> PResult<'a, ()> {
+        let initial_semicolon = self.token.span;
+
+        while self.eat(&TokenKind::Semi) {
+            let _ =
+                self.parse_stmt_without_recovery(false, ForceCollect::Yes).unwrap_or_else(|e| {
+                    e.cancel();
+                    None
+                });
+        }
+
+        expect_err
+            .primary_message("closure bodies that contain statements must be surrounded by braces");
+
+        let preceding_pipe_span = closure_spans.closing_pipe;
+        let following_token_span = self.token.span;
+
+        let mut first_note = MultiSpan::from(vec![initial_semicolon]);
+        first_note.push_span_label(
+            initial_semicolon,
+            "this `;` turns the preceding closure into a statement",
+        );
+        first_note.push_span_label(
+            closure_spans.body,
+            "this expression is a statement because of the trailing semicolon",
+        );
+        expect_err.span_note(first_note, "statement found outside of a block");
+
+        let mut second_note = MultiSpan::from(vec![closure_spans.whole_closure]);
+        second_note.push_span_label(closure_spans.whole_closure, "this is the parsed closure...");
+        second_note.push_span_label(
+            following_token_span,
+            "...but likely you meant the closure to end here",
+        );
+        expect_err.span_note(second_note, "the closure body may be incorrectly delimited");
+
+        expect_err.span(vec![preceding_pipe_span, following_token_span]);
+
+        let opening_suggestion_str = " {".to_string();
+        let closing_suggestion_str = "}".to_string();
+
+        expect_err.multipart_suggestion(
+            "try adding braces",
+            vec![
+                (preceding_pipe_span.shrink_to_hi(), opening_suggestion_str),
+                (following_token_span.shrink_to_lo(), closing_suggestion_str),
+            ],
+            Applicability::MaybeIncorrect,
+        );
+
+        expect_err.emit();
+
+        Ok(())
+    }
+
+    /// Parses a sequence, not including the delimiters. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_seq_to_before_end<T>(
+        &mut self,
+        ket: &TokenKind,
+        sep: SeqSep,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing, Recovered)> {
+        self.parse_seq_to_before_tokens(&[ket], sep, TokenExpectType::Expect, f)
+    }
+
+    /// Parses a sequence, including only the closing delimiter. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_seq_to_end<T>(
+        &mut self,
+        ket: &TokenKind,
+        sep: SeqSep,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
+        let (val, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
+        if matches!(recovered, Recovered::No) {
+            self.eat(ket);
+        }
+        Ok((val, trailing))
+    }
+
+    /// Parses a sequence, including both delimiters. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_unspanned_seq<T>(
+        &mut self,
+        bra: &TokenKind,
+        ket: &TokenKind,
+        sep: SeqSep,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
+        self.expect(bra)?;
+        self.parse_seq_to_end(ket, sep, f)
+    }
+
+    /// Parses a comma-separated sequence, including both delimiters.
+    /// The function `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_delim_comma_seq<T>(
+        &mut self,
+        delim: Delimiter,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
+        self.parse_unspanned_seq(
+            &token::OpenDelim(delim),
+            &token::CloseDelim(delim),
+            SeqSep::trailing_allowed(token::Comma),
+            f,
+        )
+    }
+
+    /// Parses a comma-separated sequence delimited by parentheses (e.g. `(x, y)`).
+    /// The function `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_paren_comma_seq<T>(
+        &mut self,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
+        self.parse_delim_comma_seq(Delimiter::Parenthesis, f)
+    }
+
+    /// Advance the parser by one token using provided token as the next one.
+    fn bump_with(&mut self, next: (Token, Spacing)) {
+        self.inlined_bump_with(next)
+    }
+
+    /// This always-inlined version should only be used on hot code paths.
+    #[inline(always)]
+    fn inlined_bump_with(&mut self, (next_token, next_spacing): (Token, Spacing)) {
+        // Update the current and previous tokens.
+        self.prev_token = mem::replace(&mut self.token, next_token);
+        self.token_spacing = next_spacing;
+
+        // Diagnostics.
+        self.expected_tokens.clear();
+    }
+
+    /// Advance the parser by one token.
+    pub fn bump(&mut self) {
+        // Note: destructuring here would give nicer code, but it was found in #96210 to be slower
+        // than `.0`/`.1` access.
+        let mut next = self.token_cursor.inlined_next();
+        self.num_bump_calls += 1;
+        // We've retrieved an token from the underlying
+        // cursor, so we no longer need to worry about
+        // an unglued token. See `break_and_eat` for more details
+        self.break_last_token = false;
+        if next.0.span.is_dummy() {
+            // Tweak the location for better diagnostics, but keep syntactic context intact.
+            let fallback_span = self.token.span;
+            next.0.span = fallback_span.with_ctxt(next.0.span.ctxt());
+        }
+        debug_assert!(!matches!(
+            next.0.kind,
+            token::OpenDelim(Delimiter::Invisible) | token::CloseDelim(Delimiter::Invisible)
+        ));
+        self.inlined_bump_with(next)
+    }
+
+    /// Look-ahead `dist` tokens of `self.token` and get access to that token there.
+    /// When `dist == 0` then the current token is looked at. `Eof` will be
+    /// returned if the look-ahead is any distance past the end of the tokens.
+    pub fn look_ahead<R>(&self, dist: usize, looker: impl FnOnce(&Token) -> R) -> R {
+        if dist == 0 {
+            return looker(&self.token);
+        }
+
+        if let Some(&(_, span, _, delim)) = self.token_cursor.stack.last()
+            && delim != Delimiter::Invisible
+        {
+            // We are not in the outermost token stream, and the token stream
+            // we are in has non-skipped delimiters. Look for skipped
+            // delimiters in the lookahead range.
+            let tree_cursor = &self.token_cursor.tree_cursor;
+            let all_normal = (0..dist).all(|i| {
+                let token = tree_cursor.look_ahead(i);
+                !matches!(token, Some(TokenTree::Delimited(.., Delimiter::Invisible, _)))
+            });
+            if all_normal {
+                // There were no skipped delimiters. Do lookahead by plain indexing.
+                return match tree_cursor.look_ahead(dist - 1) {
+                    Some(tree) => {
+                        // Indexing stayed within the current token stream.
+                        match tree {
+                            TokenTree::Token(token, _) => looker(token),
+                            TokenTree::Delimited(dspan, _, delim, _) => {
+                                looker(&Token::new(token::OpenDelim(*delim), dspan.open))
+                            }
+                        }
+                    }
+                    None => {
+                        // Indexing went past the end of the current token
+                        // stream. Use the close delimiter, no matter how far
+                        // ahead `dist` went.
+                        looker(&Token::new(token::CloseDelim(delim), span.close))
+                    }
+                };
+            }
+        }
+
+        // We are in a more complex case. Just clone the token cursor and use
+        // `next`, skipping delimiters as necessary. Slow but simple.
+        let mut cursor = self.token_cursor.clone();
+        let mut i = 0;
+        let mut token = Token::dummy();
+        while i < dist {
+            token = cursor.next().0;
+            if matches!(
+                token.kind,
+                token::OpenDelim(Delimiter::Invisible) | token::CloseDelim(Delimiter::Invisible)
+            ) {
+                continue;
+            }
+            i += 1;
+        }
+        looker(&token)
+    }
+
+    /// Returns whether any of the given keywords are `dist` tokens ahead of the current one.
+    pub(crate) fn is_keyword_ahead(&self, dist: usize, kws: &[Symbol]) -> bool {
+        self.look_ahead(dist, |t| kws.iter().any(|&kw| t.is_keyword(kw)))
+    }
+
+    /// Parses asyncness: `async` or nothing.
+    fn parse_coroutine_kind(&mut self, case: Case) -> Option<CoroutineKind> {
+        let span = self.token.uninterpolated_span();
+        if self.eat_keyword_case(kw::Async, case) {
+            // FIXME(gen_blocks): Do we want to unconditionally parse `gen` and then
+            // error if edition <= 2024, like we do with async and edition <= 2018?
+            if self.token.uninterpolated_span().at_least_rust_2024()
+                && self.eat_keyword_case(kw::Gen, case)
+            {
+                let gen_span = self.prev_token.uninterpolated_span();
+                Some(CoroutineKind::AsyncGen {
+                    span: span.to(gen_span),
+                    closure_id: DUMMY_NODE_ID,
+                    return_impl_trait_id: DUMMY_NODE_ID,
+                })
+            } else {
+                Some(CoroutineKind::Async {
+                    span,
+                    closure_id: DUMMY_NODE_ID,
+                    return_impl_trait_id: DUMMY_NODE_ID,
+                })
+            }
+        } else if self.token.uninterpolated_span().at_least_rust_2024()
+            && self.eat_keyword_case(kw::Gen, case)
+        {
+            Some(CoroutineKind::Gen {
+                span,
+                closure_id: DUMMY_NODE_ID,
+                return_impl_trait_id: DUMMY_NODE_ID,
+            })
+        } else {
+            None
+        }
+    }
+
+    /// Parses fn unsafety: `unsafe`, `safe` or nothing.
+    fn parse_safety(&mut self, case: Case) -> Safety {
+        if self.eat_keyword_case(kw::Unsafe, case) {
+            Safety::Unsafe(self.prev_token.uninterpolated_span())
+        } else {
+            Safety::Default
+        }
+    }
+
+    /// Parses constness: `const` or nothing.
+    fn parse_constness(&mut self, case: Case) -> Const {
+        self.parse_constness_(case, false)
+    }
+
+    /// Parses constness for closures (case sensitive, feature-gated)
+    fn parse_closure_constness(&mut self) -> Const {
+        let constness = self.parse_constness_(Case::Sensitive, true);
+        if let Const::Yes(span) = constness {
+            self.psess.gated_spans.gate(sym::const_closures, span);
+        }
+        constness
+    }
+
+    fn parse_constness_(&mut self, case: Case, is_closure: bool) -> Const {
+        // Avoid const blocks and const closures to be parsed as const items
+        if (self.check_const_closure() == is_closure)
+            && !self
+                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
+            && self.eat_keyword_case(kw::Const, case)
+        {
+            Const::Yes(self.prev_token.uninterpolated_span())
+        } else {
+            Const::No
+        }
+    }
+
+    /// Parses inline const expressions.
+    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, P<Expr>> {
+        if pat {
+            self.psess.gated_spans.gate(sym::inline_const_pat, span);
+        }
+        self.eat_keyword(kw::Const);
+        let (attrs, blk) = self.parse_inner_attrs_and_block()?;
+        let anon_const = AnonConst {
+            id: DUMMY_NODE_ID,
+            value: self.mk_expr(blk.span, ExprKind::Block(blk, None)),
+        };
+        let blk_span = anon_const.value.span;
+        Ok(self.mk_expr_with_attrs(span.to(blk_span), ExprKind::ConstBlock(anon_const), attrs))
+    }
+
+    /// Parses mutability (`mut` or nothing).
+    fn parse_mutability(&mut self) -> Mutability {
+        if self.eat_keyword(kw::Mut) { Mutability::Mut } else { Mutability::Not }
+    }
+
+    /// Parses reference binding mode (`ref`, `ref mut`, or nothing).
+    fn parse_byref(&mut self) -> ByRef {
+        if self.eat_keyword(kw::Ref) { ByRef::Yes(self.parse_mutability()) } else { ByRef::No }
+    }
+
+    /// Possibly parses mutability (`const` or `mut`).
+    fn parse_const_or_mut(&mut self) -> Option<Mutability> {
+        if self.eat_keyword(kw::Mut) {
+            Some(Mutability::Mut)
+        } else if self.eat_keyword(kw::Const) {
+            Some(Mutability::Not)
+        } else {
+            None
+        }
+    }
+
+    fn parse_field_name(&mut self) -> PResult<'a, Ident> {
+        if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = self.token.kind
+        {
+            if let Some(suffix) = suffix {
+                self.expect_no_tuple_index_suffix(self.token.span, suffix);
+            }
+            self.bump();
+            Ok(Ident::new(symbol, self.prev_token.span))
+        } else {
+            self.parse_ident_common(true)
+        }
+    }
+
+    fn parse_delim_args(&mut self) -> PResult<'a, P<DelimArgs>> {
+        if let Some(args) = self.parse_delim_args_inner() {
+            Ok(P(args))
+        } else {
+            self.unexpected_any()
+        }
+    }
+
+    fn parse_attr_args(&mut self) -> PResult<'a, AttrArgs> {
+        Ok(if let Some(args) = self.parse_delim_args_inner() {
+            AttrArgs::Delimited(args)
+        } else {
+            if self.eat(&token::Eq) {
+                let eq_span = self.prev_token.span;
+                AttrArgs::Eq(eq_span, AttrArgsEq::Ast(self.parse_expr_force_collect()?))
+            } else {
+                AttrArgs::Empty
+            }
+        })
+    }
+
+    fn parse_delim_args_inner(&mut self) -> Option<DelimArgs> {
+        let delimited = self.check(&token::OpenDelim(Delimiter::Parenthesis))
+            || self.check(&token::OpenDelim(Delimiter::Bracket))
+            || self.check(&token::OpenDelim(Delimiter::Brace));
+
+        delimited.then(|| {
+            let TokenTree::Delimited(dspan, _, delim, tokens) = self.parse_token_tree() else {
+                unreachable!()
+            };
+            DelimArgs { dspan, delim, tokens }
+        })
+    }
+
+    fn parse_or_use_outer_attributes(
+        &mut self,
+        already_parsed_attrs: Option<AttrWrapper>,
+    ) -> PResult<'a, AttrWrapper> {
+        if let Some(attrs) = already_parsed_attrs {
+            Ok(attrs)
+        } else {
+            self.parse_outer_attributes()
+        }
+    }
+
+    /// Parses a single token tree from the input.
+    pub fn parse_token_tree(&mut self) -> TokenTree {
+        match self.token.kind {
+            token::OpenDelim(..) => {
+                // Grab the tokens within the delimiters.
+                let stream = self.token_cursor.tree_cursor.stream.clone();
+                let (_, span, spacing, delim) = *self.token_cursor.stack.last().unwrap();
+
+                // Advance the token cursor through the entire delimited
+                // sequence. After getting the `OpenDelim` we are *within* the
+                // delimited sequence, i.e. at depth `d`. After getting the
+                // matching `CloseDelim` we are *after* the delimited sequence,
+                // i.e. at depth `d - 1`.
+                let target_depth = self.token_cursor.stack.len() - 1;
+                loop {
+                    // Advance one token at a time, so `TokenCursor::next()`
+                    // can capture these tokens if necessary.
+                    self.bump();
+                    if self.token_cursor.stack.len() == target_depth {
+                        debug_assert!(matches!(self.token.kind, token::CloseDelim(_)));
+                        break;
+                    }
+                }
+
+                // Consume close delimiter
+                self.bump();
+                TokenTree::Delimited(span, spacing, delim, stream)
+            }
+            token::CloseDelim(_) | token::Eof => unreachable!(),
+            _ => {
+                let prev_spacing = self.token_spacing;
+                self.bump();
+                TokenTree::Token(self.prev_token.clone(), prev_spacing)
+            }
+        }
+    }
+
+    pub fn parse_tokens(&mut self) -> TokenStream {
+        let mut result = Vec::new();
+        loop {
+            match self.token.kind {
+                token::Eof | token::CloseDelim(..) => break,
+                _ => result.push(self.parse_token_tree()),
+            }
+        }
+        TokenStream::new(result)
+    }
+
+    /// Evaluates the closure with restrictions in place.
+    ///
+    /// Afters the closure is evaluated, restrictions are reset.
+    fn with_res<T>(&mut self, res: Restrictions, f: impl FnOnce(&mut Self) -> T) -> T {
+        let old = self.restrictions;
+        self.restrictions = res;
+        let res = f(self);
+        self.restrictions = old;
+        res
+    }
+
+    /// Parses `pub` and `pub(in path)` plus shortcuts `pub(crate)` for `pub(in crate)`, `pub(self)`
+    /// for `pub(in self)` and `pub(super)` for `pub(in super)`.
+    /// If the following element can't be a tuple (i.e., it's a function definition), then
+    /// it's not a tuple struct field), and the contents within the parentheses aren't valid,
+    /// so emit a proper diagnostic.
+    // Public for rustfmt usage.
+    pub fn parse_visibility(&mut self, fbt: FollowedByType) -> PResult<'a, Visibility> {
+        maybe_whole!(self, NtVis, |vis| vis.into_inner());
+
+        if !self.eat_keyword(kw::Pub) {
+            // We need a span for our `Spanned<VisibilityKind>`, but there's inherently no
+            // keyword to grab a span from for inherited visibility; an empty span at the
+            // beginning of the current token would seem to be the "Schelling span".
+            return Ok(Visibility {
+                span: self.token.span.shrink_to_lo(),
+                kind: VisibilityKind::Inherited,
+                tokens: None,
+            });
+        }
+        let lo = self.prev_token.span;
+
+        if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            // We don't `self.bump()` the `(` yet because this might be a struct definition where
+            // `()` or a tuple might be allowed. For example, `struct Struct(pub (), pub (usize));`.
+            // Because of this, we only `bump` the `(` if we're assured it is appropriate to do so
+            // by the following tokens.
+            if self.is_keyword_ahead(1, &[kw::In]) {
+                // Parse `pub(in path)`.
+                self.bump(); // `(`
+                self.bump(); // `in`
+                let path = self.parse_path(PathStyle::Mod)?; // `path`
+                self.expect(&token::CloseDelim(Delimiter::Parenthesis))?; // `)`
+                let vis = VisibilityKind::Restricted {
+                    path: P(path),
+                    id: ast::DUMMY_NODE_ID,
+                    shorthand: false,
+                };
+                return Ok(Visibility {
+                    span: lo.to(self.prev_token.span),
+                    kind: vis,
+                    tokens: None,
+                });
+            } else if self.look_ahead(2, |t| t == &token::CloseDelim(Delimiter::Parenthesis))
+                && self.is_keyword_ahead(1, &[kw::Crate, kw::Super, kw::SelfLower])
+            {
+                // Parse `pub(crate)`, `pub(self)`, or `pub(super)`.
+                self.bump(); // `(`
+                let path = self.parse_path(PathStyle::Mod)?; // `crate`/`super`/`self`
+                self.expect(&token::CloseDelim(Delimiter::Parenthesis))?; // `)`
+                let vis = VisibilityKind::Restricted {
+                    path: P(path),
+                    id: ast::DUMMY_NODE_ID,
+                    shorthand: true,
+                };
+                return Ok(Visibility {
+                    span: lo.to(self.prev_token.span),
+                    kind: vis,
+                    tokens: None,
+                });
+            } else if let FollowedByType::No = fbt {
+                // Provide this diagnostic if a type cannot follow;
+                // in particular, if this is not a tuple struct.
+                self.recover_incorrect_vis_restriction()?;
+                // Emit diagnostic, but continue with public visibility.
+            }
+        }
+
+        Ok(Visibility { span: lo, kind: VisibilityKind::Public, tokens: None })
+    }
+
+    /// Recovery for e.g. `pub(something) fn ...` or `struct X { pub(something) y: Z }`
+    fn recover_incorrect_vis_restriction(&mut self) -> PResult<'a, ()> {
+        self.bump(); // `(`
+        let path = self.parse_path(PathStyle::Mod)?;
+        self.expect(&token::CloseDelim(Delimiter::Parenthesis))?; // `)`
+
+        let path_str = pprust::path_to_string(&path);
+        self.dcx()
+            .emit_err(IncorrectVisibilityRestriction { span: path.span, inner_str: path_str });
+
+        Ok(())
+    }
+
+    /// Parses `extern string_literal?`.
+    fn parse_extern(&mut self, case: Case) -> Extern {
+        if self.eat_keyword_case(kw::Extern, case) {
+            let mut extern_span = self.prev_token.span;
+            let abi = self.parse_abi();
+            if let Some(abi) = abi {
+                extern_span = extern_span.to(abi.span);
+            }
+            Extern::from_abi(abi, extern_span)
+        } else {
+            Extern::None
+        }
+    }
+
+    /// Parses a string literal as an ABI spec.
+    fn parse_abi(&mut self) -> Option<StrLit> {
+        match self.parse_str_lit() {
+            Ok(str_lit) => Some(str_lit),
+            Err(Some(lit)) => match lit.kind {
+                ast::LitKind::Err(_) => None,
+                _ => {
+                    self.dcx().emit_err(NonStringAbiLiteral { span: lit.span });
+                    None
+                }
+            },
+            Err(None) => None,
+        }
+    }
+
+    pub fn collect_tokens_no_attrs<R: HasAttrs + HasTokens>(
+        &mut self,
+        f: impl FnOnce(&mut Self) -> PResult<'a, R>,
+    ) -> PResult<'a, R> {
+        // The only reason to call `collect_tokens_no_attrs` is if you want tokens, so use
+        // `ForceCollect::Yes`
+        self.collect_tokens_trailing_token(
+            AttrWrapper::empty(),
+            ForceCollect::Yes,
+            |this, _attrs| Ok((f(this)?, TrailingToken::None)),
+        )
+    }
+
+    /// `::{` or `::*`
+    fn is_import_coupler(&mut self) -> bool {
+        self.check(&token::PathSep)
+            && self.look_ahead(1, |t| {
+                *t == token::OpenDelim(Delimiter::Brace) || *t == token::BinOp(token::Star)
+            })
+    }
+
+    // debug view of the parser's token stream, up to `{lookahead}` tokens
+    pub fn debug_lookahead(&self, lookahead: usize) -> impl fmt::Debug + '_ {
+        struct DebugParser<'dbg> {
+            parser: &'dbg Parser<'dbg>,
+            lookahead: usize,
+        }
+
+        impl fmt::Debug for DebugParser<'_> {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                let Self { parser, lookahead } = self;
+                let mut dbg_fmt = f.debug_struct("Parser"); // or at least, one view of
+
+                // we don't need N spans, but we want at least one, so print all of prev_token
+                dbg_fmt.field("prev_token", &parser.prev_token);
+                // make it easier to peek farther ahead by taking TokenKinds only until EOF
+                let tokens = (0..*lookahead)
+                    .map(|i| parser.look_ahead(i, |tok| tok.kind.clone()))
+                    .scan(parser.prev_token == TokenKind::Eof, |eof, tok| {
+                        let current = eof.then_some(tok.clone()); // include a trailing EOF token
+                        *eof |= &tok == &TokenKind::Eof;
+                        current
+                    });
+                dbg_fmt.field_with("tokens", |field| field.debug_list().entries(tokens).finish());
+                dbg_fmt.field("approx_token_stream_pos", &parser.num_bump_calls);
+
+                // some fields are interesting for certain values, as they relate to macro parsing
+                if let Some(subparser) = parser.subparser_name {
+                    dbg_fmt.field("subparser_name", &subparser);
+                }
+                if let Recovery::Forbidden = parser.recovery {
+                    dbg_fmt.field("recovery", &parser.recovery);
+                }
+
+                // imply there's "more to know" than this view
+                dbg_fmt.finish_non_exhaustive()
+            }
+        }
+
+        DebugParser { parser: self, lookahead }
+    }
+
+    pub fn clear_expected_tokens(&mut self) {
+        self.expected_tokens.clear();
+    }
+
+    pub fn approx_token_stream_pos(&self) -> usize {
+        self.num_bump_calls
+    }
+}
+
+pub(crate) fn make_unclosed_delims_error(
+    unmatched: UnmatchedDelim,
+    psess: &ParseSess,
+) -> Option<Diag<'_>> {
+    // `None` here means an `Eof` was found. We already emit those errors elsewhere, we add them to
+    // `unmatched_delims` only for error recovery in the `Parser`.
+    let found_delim = unmatched.found_delim?;
+    let mut spans = vec![unmatched.found_span];
+    if let Some(sp) = unmatched.unclosed_span {
+        spans.push(sp);
+    };
+    let err = psess.dcx.create_err(MismatchedClosingDelimiter {
+        spans,
+        delimiter: pprust::token_kind_to_string(&token::CloseDelim(found_delim)).to_string(),
+        unmatched: unmatched.found_span,
+        opening_candidate: unmatched.candidate_span,
+        unclosed: unmatched.unclosed_span,
+    });
+    Some(err)
+}
+
+/// A helper struct used when building an `AttrTokenStream` from
+/// a `LazyAttrTokenStream`. Both delimiter and non-delimited tokens
+/// are stored as `FlatToken::Token`. A vector of `FlatToken`s
+/// is then 'parsed' to build up an `AttrTokenStream` with nested
+/// `AttrTokenTree::Delimited` tokens.
+#[derive(Debug, Clone)]
+pub enum FlatToken {
+    /// A token - this holds both delimiter (e.g. '{' and '}')
+    /// and non-delimiter tokens
+    Token(Token),
+    /// Holds the `AttributesData` for an AST node. The
+    /// `AttributesData` is inserted directly into the
+    /// constructed `AttrTokenStream` as
+    /// an `AttrTokenTree::Attributes`.
+    AttrTarget(AttributesData),
+    /// A special 'empty' token that is ignored during the conversion
+    /// to an `AttrTokenStream`. This is used to simplify the
+    /// handling of replace ranges.
+    Empty,
+}
+
+// Metavar captures of various kinds.
+#[derive(Clone, Debug)]
+pub enum ParseNtResult {
+    Tt(TokenTree),
+    Ident(Ident, IdentIsRaw),
+    Lifetime(Ident),
+
+    /// This case will eventually be removed, along with `Token::Interpolate`.
+    Nt(Lrc<Nonterminal>),
+}
diff --git a/compiler/rustc_parse/src/parser/mut_visit/tests.rs b/compiler/rustc_parse/src/parser/mut_visit/tests.rs
new file mode 100644
index 00000000000..b3cb28af657
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/mut_visit/tests.rs
@@ -0,0 +1,71 @@
+use crate::parser::tests::{matches_codepattern, string_to_crate};
+use rustc_ast as ast;
+use rustc_ast::mut_visit::MutVisitor;
+use rustc_ast_pretty::pprust;
+use rustc_span::create_default_session_globals_then;
+use rustc_span::symbol::Ident;
+
+// This version doesn't care about getting comments or doc-strings in.
+fn print_crate_items(krate: &ast::Crate) -> String {
+    krate.items.iter().map(|i| pprust::item_to_string(i)).collect::<Vec<_>>().join(" ")
+}
+
+// Change every identifier to "zz".
+struct ToZzIdentMutVisitor;
+
+impl MutVisitor for ToZzIdentMutVisitor {
+    const VISIT_TOKENS: bool = true;
+
+    fn visit_ident(&mut self, ident: &mut Ident) {
+        *ident = Ident::from_str("zz");
+    }
+}
+
+// Maybe add to `expand.rs`.
+macro_rules! assert_pred {
+    ($pred:expr, $predname:expr, $a:expr , $b:expr) => {{
+        let pred_val = $pred;
+        let a_val = $a;
+        let b_val = $b;
+        if !(pred_val(&a_val, &b_val)) {
+            panic!("expected args satisfying {}, got {} and {}", $predname, a_val, b_val);
+        }
+    }};
+}
+
+// Make sure idents get transformed everywhere.
+#[test]
+fn ident_transformation() {
+    create_default_session_globals_then(|| {
+        let mut zz_visitor = ToZzIdentMutVisitor;
+        let mut krate =
+            string_to_crate("#[a] mod b {fn c (d : e, f : g) {h!(i,j,k);l;m}}".to_string());
+        zz_visitor.visit_crate(&mut krate);
+        assert_pred!(
+            matches_codepattern,
+            "matches_codepattern",
+            print_crate_items(&krate),
+            "#[zz]mod zz{fn zz(zz:zz,zz:zz){zz!(zz,zz,zz);zz;zz}}".to_string()
+        );
+    })
+}
+
+// Make sure idents get transformed even inside macro defs.
+#[test]
+fn ident_transformation_in_defs() {
+    create_default_session_globals_then(|| {
+        let mut zz_visitor = ToZzIdentMutVisitor;
+        let mut krate = string_to_crate(
+            "macro_rules! a {(b $c:expr $(d $e:token)f+ => \
+            (g $(d $d $e)+))} "
+                .to_string(),
+        );
+        zz_visitor.visit_crate(&mut krate);
+        assert_pred!(
+            matches_codepattern,
+            "matches_codepattern",
+            print_crate_items(&krate),
+            "macro_rules! zz{(zz$zz:zz$(zz $zz:zz)zz+=>(zz$(zz$zz$zz)+))}".to_string()
+        );
+    })
+}
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
new file mode 100644
index 00000000000..619c4c63e51
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -0,0 +1,214 @@
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Nonterminal::*, NonterminalKind, Token};
+use rustc_ast::HasTokens;
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::PResult;
+use rustc_span::symbol::{kw, Ident};
+
+use crate::errors::UnexpectedNonterminal;
+use crate::parser::pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
+use crate::parser::{FollowedByType, ForceCollect, ParseNtResult, Parser, PathStyle};
+
+impl<'a> Parser<'a> {
+    /// Checks whether a non-terminal may begin with a particular token.
+    ///
+    /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with
+    /// that token. Be conservative (return true) if not sure. Inlined because it has a single call
+    /// site.
+    #[inline]
+    pub fn nonterminal_may_begin_with(kind: NonterminalKind, token: &Token) -> bool {
+        /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
+        fn may_be_ident(nt: &token::Nonterminal) -> bool {
+            match nt {
+                NtStmt(_)
+                | NtPat(_)
+                | NtExpr(_)
+                | NtTy(_)
+                | NtLiteral(_) // `true`, `false`
+                | NtMeta(_)
+                | NtPath(_) => true,
+
+                NtItem(_)
+                | NtBlock(_)
+                | NtVis(_) => false,
+            }
+        }
+
+        match kind {
+            NonterminalKind::Expr2021 => {
+                token.can_begin_expr()
+                // This exception is here for backwards compatibility.
+                && !token.is_keyword(kw::Let)
+                // This exception is here for backwards compatibility.
+                && !token.is_keyword(kw::Const)
+            }
+            NonterminalKind::Expr => {
+                token.can_begin_expr()
+                // This exception is here for backwards compatibility.
+                && !token.is_keyword(kw::Let)
+                && (token.span.edition().at_least_rust_2024() || !token.is_keyword(kw::Const))
+            }
+            NonterminalKind::Ty => token.can_begin_type(),
+            NonterminalKind::Ident => get_macro_ident(token).is_some(),
+            NonterminalKind::Literal => token.can_begin_literal_maybe_minus(),
+            NonterminalKind::Vis => match token.kind {
+                // The follow-set of :vis + "priv" keyword + interpolated
+                token::Comma
+                | token::Ident(..)
+                | token::NtIdent(..)
+                | token::NtLifetime(..)
+                | token::Interpolated(_) => true,
+                _ => token.can_begin_type(),
+            },
+            NonterminalKind::Block => match &token.kind {
+                token::OpenDelim(Delimiter::Brace) => true,
+                token::NtLifetime(..) => true,
+                token::Interpolated(nt) => match &**nt {
+                    NtBlock(_) | NtStmt(_) | NtExpr(_) | NtLiteral(_) => true,
+                    NtItem(_) | NtPat(_) | NtTy(_) | NtMeta(_) | NtPath(_) | NtVis(_) => false,
+                },
+                _ => false,
+            },
+            NonterminalKind::Path | NonterminalKind::Meta => match &token.kind {
+                token::PathSep | token::Ident(..) | token::NtIdent(..) => true,
+                token::Interpolated(nt) => may_be_ident(nt),
+                _ => false,
+            },
+            NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr => match &token.kind {
+                // box, ref, mut, and other identifiers (can stricten)
+                token::Ident(..) | token::NtIdent(..) |
+                token::OpenDelim(Delimiter::Parenthesis) |  // tuple pattern
+                token::OpenDelim(Delimiter::Bracket) |      // slice pattern
+                token::BinOp(token::And) |                  // reference
+                token::BinOp(token::Minus) |                // negative literal
+                token::AndAnd |                             // double reference
+                token::Literal(_) |                         // literal
+                token::DotDot |                             // range pattern (future compat)
+                token::DotDotDot |                          // range pattern (future compat)
+                token::PathSep |                             // path
+                token::Lt |                                 // path (UFCS constant)
+                token::BinOp(token::Shl) => true,           // path (double UFCS)
+                // leading vert `|` or-pattern
+                token::BinOp(token::Or) => matches!(kind, NonterminalKind::PatWithOr),
+                token::Interpolated(nt) => may_be_ident(nt),
+                _ => false,
+            },
+            NonterminalKind::Lifetime => match &token.kind {
+                token::Lifetime(_) | token::NtLifetime(..) => true,
+                _ => false,
+            },
+            NonterminalKind::TT | NonterminalKind::Item | NonterminalKind::Stmt => {
+                !matches!(token.kind, token::CloseDelim(_))
+            }
+        }
+    }
+
+    /// Parse a non-terminal (e.g. MBE `:pat` or `:ident`). Inlined because there is only one call
+    /// site.
+    #[inline]
+    pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, ParseNtResult> {
+        // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
+        // which requires having captured tokens available. Since we cannot determine
+        // in advance whether or not a proc-macro will be (transitively) invoked,
+        // we always capture tokens for any `Nonterminal` which needs them.
+        let mut nt = match kind {
+            // Note that TT is treated differently to all the others.
+            NonterminalKind::TT => return Ok(ParseNtResult::Tt(self.parse_token_tree())),
+            NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
+                Some(item) => NtItem(item),
+                None => {
+                    return Err(self
+                        .dcx()
+                        .create_err(UnexpectedNonterminal::Item(self.token.span)));
+                }
+            },
+            NonterminalKind::Block => {
+                // While a block *expression* may have attributes (e.g. `#[my_attr] { ... }`),
+                // the ':block' matcher does not support them
+                NtBlock(self.collect_tokens_no_attrs(|this| this.parse_block())?)
+            }
+            NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
+                Some(s) => NtStmt(P(s)),
+                None => {
+                    return Err(self
+                        .dcx()
+                        .create_err(UnexpectedNonterminal::Statement(self.token.span)));
+                }
+            },
+            NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr => {
+                NtPat(self.collect_tokens_no_attrs(|this| match kind {
+                    NonterminalKind::PatParam { .. } => this.parse_pat_no_top_alt(None, None),
+                    NonterminalKind::PatWithOr => this.parse_pat_allow_top_alt(
+                        None,
+                        RecoverComma::No,
+                        RecoverColon::No,
+                        CommaRecoveryMode::EitherTupleOrPipe,
+                    ),
+                    _ => unreachable!(),
+                })?)
+            }
+
+            NonterminalKind::Expr | NonterminalKind::Expr2021 => {
+                NtExpr(self.parse_expr_force_collect()?)
+            }
+            NonterminalKind::Literal => {
+                // The `:literal` matcher does not support attributes
+                NtLiteral(self.collect_tokens_no_attrs(|this| this.parse_literal_maybe_minus())?)
+            }
+
+            NonterminalKind::Ty => {
+                NtTy(self.collect_tokens_no_attrs(|this| this.parse_ty_no_question_mark_recover())?)
+            }
+
+            // this could be handled like a token, since it is one
+            NonterminalKind::Ident => {
+                return if let Some((ident, is_raw)) = get_macro_ident(&self.token) {
+                    self.bump();
+                    Ok(ParseNtResult::Ident(ident, is_raw))
+                } else {
+                    Err(self.dcx().create_err(UnexpectedNonterminal::Ident {
+                        span: self.token.span,
+                        token: self.token.clone(),
+                    }))
+                };
+            }
+            NonterminalKind::Path => {
+                NtPath(P(self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?))
+            }
+            NonterminalKind::Meta => NtMeta(P(self.parse_attr_item(true)?)),
+            NonterminalKind::Vis => {
+                NtVis(P(self
+                    .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?))
+            }
+            NonterminalKind::Lifetime => {
+                return if self.check_lifetime() {
+                    Ok(ParseNtResult::Lifetime(self.expect_lifetime().ident))
+                } else {
+                    Err(self.dcx().create_err(UnexpectedNonterminal::Lifetime {
+                        span: self.token.span,
+                        token: self.token.clone(),
+                    }))
+                };
+            }
+        };
+
+        // If tokens are supported at all, they should be collected.
+        if matches!(nt.tokens_mut(), Some(None)) {
+            panic!(
+                "Missing tokens for nt {:?} at {:?}: {:?}",
+                nt,
+                nt.use_span(),
+                pprust::nonterminal_to_string(&nt)
+            );
+        }
+
+        Ok(ParseNtResult::Nt(Lrc::new(nt)))
+    }
+}
+
+/// The token is an identifier, but not `_`.
+/// We prohibit passing `_` to macros expecting `ident` for now.
+fn get_macro_ident(token: &Token) -> Option<(Ident, token::IdentIsRaw)> {
+    token.ident().filter(|(ident, _)| ident.name != kw::Underscore)
+}
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
new file mode 100644
index 00000000000..8af415f7c9d
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -0,0 +1,1426 @@
+use super::{ForceCollect, Parser, PathStyle, Restrictions, Trailing, TrailingToken};
+use crate::errors::{
+    self, AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
+    DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
+    ExpectedCommaAfterPatternField, GenericArgsInPatRequireTurbofishSyntax,
+    InclusiveRangeExtraEquals, InclusiveRangeMatchArrow, InclusiveRangeNoEnd, InvalidMutInPattern,
+    PatternOnWrongSideOfAt, RemoveLet, RepeatedMutInPattern, SwitchRefBoxOrder,
+    TopLevelOrPatternNotAllowed, TopLevelOrPatternNotAllowedSugg, TrailingVertNotAllowed,
+    UnexpectedExpressionInPattern, UnexpectedLifetimeInPattern, UnexpectedParenInRangePat,
+    UnexpectedParenInRangePatSugg, UnexpectedVertVertBeforeFunctionParam,
+    UnexpectedVertVertInPattern,
+};
+use crate::parser::expr::could_be_unclosed_char_literal;
+use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
+use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, BinOpToken, Delimiter, Token};
+use rustc_ast::{
+    self as ast, AttrVec, BindingMode, ByRef, Expr, ExprKind, MacCall, Mutability, Pat, PatField,
+    PatFieldsRest, PatKind, Path, QSelf, RangeEnd, RangeSyntax,
+};
+use rustc_ast_pretty::pprust;
+use rustc_errors::{Applicability, Diag, PResult};
+use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::source_map::{respan, Spanned};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{ErrorGuaranteed, Span};
+use thin_vec::{thin_vec, ThinVec};
+
+#[derive(PartialEq, Copy, Clone)]
+pub enum Expected {
+    ParameterName,
+    ArgumentName,
+    Identifier,
+    BindingPattern,
+}
+
+impl Expected {
+    // FIXME(#100717): migrate users of this to proper localization
+    fn to_string_or_fallback(expected: Option<Expected>) -> &'static str {
+        match expected {
+            Some(Expected::ParameterName) => "parameter name",
+            Some(Expected::ArgumentName) => "argument name",
+            Some(Expected::Identifier) => "identifier",
+            Some(Expected::BindingPattern) => "binding pattern",
+            None => "pattern",
+        }
+    }
+}
+
+const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here";
+
+/// Whether or not to recover a `,` when parsing or-patterns.
+#[derive(PartialEq, Copy, Clone)]
+pub enum RecoverComma {
+    Yes,
+    No,
+}
+
+/// Whether or not to recover a `:` when parsing patterns that were meant to be paths.
+#[derive(PartialEq, Copy, Clone)]
+pub enum RecoverColon {
+    Yes,
+    No,
+}
+
+/// Whether or not to recover a `a, b` when parsing patterns as `(a, b)` or that *and* `a | b`.
+#[derive(PartialEq, Copy, Clone)]
+pub enum CommaRecoveryMode {
+    LikelyTuple,
+    EitherTupleOrPipe,
+}
+
+/// The result of `eat_or_separator`. We want to distinguish which case we are in to avoid
+/// emitting duplicate diagnostics.
+#[derive(Debug, Clone, Copy)]
+enum EatOrResult {
+    /// We recovered from a trailing vert.
+    TrailingVert,
+    /// We ate an `|` (or `||` and recovered).
+    AteOr,
+    /// We did not eat anything (i.e. the current token is not `|` or `||`).
+    None,
+}
+
+/// The syntax location of a given pattern. Used for diagnostics.
+#[derive(Clone, Copy)]
+pub enum PatternLocation {
+    LetBinding,
+    FunctionParameter,
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a pattern.
+    ///
+    /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
+    /// at the top level. Used when parsing the parameters of lambda expressions,
+    /// functions, function pointers, and `pat` macro fragments.
+    pub fn parse_pat_no_top_alt(
+        &mut self,
+        expected: Option<Expected>,
+        syntax_loc: Option<PatternLocation>,
+    ) -> PResult<'a, P<Pat>> {
+        self.parse_pat_with_range_pat(true, expected, syntax_loc)
+    }
+
+    /// Parses a pattern.
+    ///
+    /// Corresponds to `top_pat` in RFC 2535 and allows or-pattern at the top level.
+    /// Used for parsing patterns in all cases when `pat<no_top_alt>` is not used.
+    ///
+    /// Note that after the FCP in <https://github.com/rust-lang/rust/issues/81415>,
+    /// a leading vert is allowed in nested or-patterns, too. This allows us to
+    /// simplify the grammar somewhat.
+    pub fn parse_pat_allow_top_alt(
+        &mut self,
+        expected: Option<Expected>,
+        rc: RecoverComma,
+        ra: RecoverColon,
+        rt: CommaRecoveryMode,
+    ) -> PResult<'a, P<Pat>> {
+        self.parse_pat_allow_top_alt_inner(expected, rc, ra, rt, None).map(|(pat, _)| pat)
+    }
+
+    /// Returns the pattern and a bool indicating whether we recovered from a trailing vert (true =
+    /// recovered).
+    fn parse_pat_allow_top_alt_inner(
+        &mut self,
+        expected: Option<Expected>,
+        rc: RecoverComma,
+        ra: RecoverColon,
+        rt: CommaRecoveryMode,
+        syntax_loc: Option<PatternLocation>,
+    ) -> PResult<'a, (P<Pat>, bool)> {
+        // Keep track of whether we recovered from a trailing vert so that we can avoid duplicated
+        // suggestions (which bothers rustfix).
+        //
+        // Allow a '|' before the pats (RFCs 1925, 2530, and 2535).
+        let (leading_vert_span, mut trailing_vert) = match self.eat_or_separator(None) {
+            EatOrResult::AteOr => (Some(self.prev_token.span), false),
+            EatOrResult::TrailingVert => (None, true),
+            EatOrResult::None => (None, false),
+        };
+
+        // Parse the first pattern (`p_0`).
+        let mut first_pat = match self.parse_pat_no_top_alt(expected, syntax_loc) {
+            Ok(pat) => pat,
+            Err(err)
+                if self.token.is_reserved_ident()
+                    && !self.token.is_keyword(kw::In)
+                    && !self.token.is_keyword(kw::If) =>
+            {
+                err.emit();
+                self.bump();
+                self.mk_pat(self.token.span, PatKind::Wild)
+            }
+            Err(err) => return Err(err),
+        };
+        if rc == RecoverComma::Yes && !first_pat.could_be_never_pattern() {
+            self.maybe_recover_unexpected_comma(first_pat.span, rt)?;
+        }
+
+        // If the next token is not a `|`,
+        // this is not an or-pattern and we should exit here.
+        if !self.check(&token::BinOp(token::Or)) && self.token != token::OrOr {
+            // If we parsed a leading `|` which should be gated,
+            // then we should really gate the leading `|`.
+            // This complicated procedure is done purely for diagnostics UX.
+
+            // Check if the user wrote `foo:bar` instead of `foo::bar`.
+            if ra == RecoverColon::Yes {
+                first_pat = self.maybe_recover_colon_colon_in_pat_typo(first_pat, expected);
+            }
+
+            if let Some(leading_vert_span) = leading_vert_span {
+                // If there was a leading vert, treat this as an or-pattern. This improves
+                // diagnostics.
+                let span = leading_vert_span.to(self.prev_token.span);
+                return Ok((self.mk_pat(span, PatKind::Or(thin_vec![first_pat])), trailing_vert));
+            }
+
+            return Ok((first_pat, trailing_vert));
+        }
+
+        // Parse the patterns `p_1 | ... | p_n` where `n > 0`.
+        let lo = leading_vert_span.unwrap_or(first_pat.span);
+        let mut pats = thin_vec![first_pat];
+        loop {
+            match self.eat_or_separator(Some(lo)) {
+                EatOrResult::AteOr => {}
+                EatOrResult::None => break,
+                EatOrResult::TrailingVert => {
+                    trailing_vert = true;
+                    break;
+                }
+            }
+            let pat = self.parse_pat_no_top_alt(expected, syntax_loc).map_err(|mut err| {
+                err.span_label(lo, WHILE_PARSING_OR_MSG);
+                err
+            })?;
+            if rc == RecoverComma::Yes && !pat.could_be_never_pattern() {
+                self.maybe_recover_unexpected_comma(pat.span, rt)?;
+            }
+            pats.push(pat);
+        }
+        let or_pattern_span = lo.to(self.prev_token.span);
+
+        Ok((self.mk_pat(or_pattern_span, PatKind::Or(pats)), trailing_vert))
+    }
+
+    /// Parse a pattern and (maybe) a `Colon` in positions where a pattern may be followed by a
+    /// type annotation (e.g. for `let` bindings or `fn` params).
+    ///
+    /// Generally, this corresponds to `pat_no_top_alt` followed by an optional `Colon`. It will
+    /// eat the `Colon` token if one is present.
+    ///
+    /// The return value represents the parsed pattern and `true` if a `Colon` was parsed (`false`
+    /// otherwise).
+    pub(super) fn parse_pat_before_ty(
+        &mut self,
+        expected: Option<Expected>,
+        rc: RecoverComma,
+        syntax_loc: PatternLocation,
+    ) -> PResult<'a, (P<Pat>, bool)> {
+        // We use `parse_pat_allow_top_alt` regardless of whether we actually want top-level
+        // or-patterns so that we can detect when a user tries to use it. This allows us to print a
+        // better error message.
+        let (pat, trailing_vert) = self.parse_pat_allow_top_alt_inner(
+            expected,
+            rc,
+            RecoverColon::No,
+            CommaRecoveryMode::LikelyTuple,
+            Some(syntax_loc),
+        )?;
+        let colon = self.eat(&token::Colon);
+
+        if let PatKind::Or(pats) = &pat.kind {
+            let span = pat.span;
+            let pat = pprust::pat_to_string(&pat);
+            let sub = if pats.len() == 1 {
+                Some(TopLevelOrPatternNotAllowedSugg::RemoveLeadingVert { span, pat })
+            } else {
+                Some(TopLevelOrPatternNotAllowedSugg::WrapInParens { span, pat })
+            };
+
+            let err = self.dcx().create_err(match syntax_loc {
+                PatternLocation::LetBinding => {
+                    TopLevelOrPatternNotAllowed::LetBinding { span, sub }
+                }
+                PatternLocation::FunctionParameter => {
+                    TopLevelOrPatternNotAllowed::FunctionParameter { span, sub }
+                }
+            });
+            if trailing_vert {
+                err.delay_as_bug();
+            } else {
+                err.emit();
+            }
+        }
+
+        Ok((pat, colon))
+    }
+
+    /// Parse the pattern for a function or function pointer parameter, followed by a colon.
+    ///
+    /// The return value represents the parsed pattern and `true` if a `Colon` was parsed (`false`
+    /// otherwise).
+    pub(super) fn parse_fn_param_pat_colon(&mut self) -> PResult<'a, (P<Pat>, bool)> {
+        // In order to get good UX, we first recover in the case of a leading vert for an illegal
+        // top-level or-pat. Normally, this means recovering both `|` and `||`, but in this case,
+        // a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
+        // separately.
+        if let token::OrOr = self.token.kind {
+            self.dcx().emit_err(UnexpectedVertVertBeforeFunctionParam { span: self.token.span });
+            self.bump();
+        }
+
+        self.parse_pat_before_ty(
+            Some(Expected::ParameterName),
+            RecoverComma::No,
+            PatternLocation::FunctionParameter,
+        )
+    }
+
+    /// Eat the or-pattern `|` separator.
+    /// If instead a `||` token is encountered, recover and pretend we parsed `|`.
+    fn eat_or_separator(&mut self, lo: Option<Span>) -> EatOrResult {
+        if self.recover_trailing_vert(lo) {
+            EatOrResult::TrailingVert
+        } else if matches!(self.token.kind, token::OrOr) {
+            // Found `||`; Recover and pretend we parsed `|`.
+            self.dcx().emit_err(UnexpectedVertVertInPattern { span: self.token.span, start: lo });
+            self.bump();
+            EatOrResult::AteOr
+        } else if self.eat(&token::BinOp(token::Or)) {
+            EatOrResult::AteOr
+        } else {
+            EatOrResult::None
+        }
+    }
+
+    /// Recover if `|` or `||` is the current token and we have one of the
+    /// tokens `=>`, `if`, `=`, `:`, `;`, `,`, `]`, `)`, or `}` ahead of us.
+    ///
+    /// These tokens all indicate that we reached the end of the or-pattern
+    /// list and can now reliably say that the `|` was an illegal trailing vert.
+    /// Note that there are more tokens such as `@` for which we know that the `|`
+    /// is an illegal parse. However, the user's intent is less clear in that case.
+    fn recover_trailing_vert(&mut self, lo: Option<Span>) -> bool {
+        let is_end_ahead = self.look_ahead(1, |token| {
+            matches!(
+                &token.uninterpolate().kind,
+                token::FatArrow // e.g. `a | => 0,`.
+                | token::Ident(kw::If, token::IdentIsRaw::No) // e.g. `a | if expr`.
+                | token::Eq // e.g. `let a | = 0`.
+                | token::Semi // e.g. `let a |;`.
+                | token::Colon // e.g. `let a | :`.
+                | token::Comma // e.g. `let (a |,)`.
+                | token::CloseDelim(Delimiter::Bracket) // e.g. `let [a | ]`.
+                | token::CloseDelim(Delimiter::Parenthesis) // e.g. `let (a | )`.
+                | token::CloseDelim(Delimiter::Brace) // e.g. `let A { f: a | }`.
+            )
+        });
+        match (is_end_ahead, &self.token.kind) {
+            (true, token::BinOp(token::Or) | token::OrOr) => {
+                // A `|` or possibly `||` token shouldn't be here. Ban it.
+                self.dcx().emit_err(TrailingVertNotAllowed {
+                    span: self.token.span,
+                    start: lo,
+                    token: self.token.clone(),
+                    note_double_vert: matches!(self.token.kind, token::OrOr).then_some(()),
+                });
+                self.bump();
+                true
+            }
+            _ => false,
+        }
+    }
+
+    /// Ensures that the last parsed pattern (or pattern range bound) is not followed by a method call or an operator.
+    ///
+    /// `is_end_bound` indicates whether the last parsed thing was the end bound of a range pattern (see [`parse_pat_range_end`](Self::parse_pat_range_end))
+    /// in order to say "expected a pattern range bound" instead of "expected a pattern";
+    /// ```text
+    /// 0..=1 + 2
+    ///     ^^^^^
+    /// ```
+    /// Only the end bound is spanned, and this function have no idea if there were a `..=` before `pat_span`, hence the parameter.
+    #[must_use = "the pattern must be discarded as `PatKind::Err` if this function returns Some"]
+    fn maybe_recover_trailing_expr(
+        &mut self,
+        pat_span: Span,
+        is_end_bound: bool,
+    ) -> Option<ErrorGuaranteed> {
+        if self.prev_token.is_keyword(kw::Underscore) || !self.may_recover() {
+            // Don't recover anything after an `_` or if recovery is disabled.
+            return None;
+        }
+
+        // Check for `.hello()`, but allow `.Hello()` to be recovered as `, Hello()` in `parse_seq_to_before_tokens()`.
+        let has_trailing_method = self.check_noexpect(&token::Dot)
+            && self.look_ahead(1, |tok| {
+                tok.ident()
+                    .and_then(|(ident, _)| ident.name.as_str().chars().next())
+                    .is_some_and(char::is_lowercase)
+            })
+            && self.look_ahead(2, |tok| tok.kind == token::OpenDelim(Delimiter::Parenthesis));
+
+        // Check for operators.
+        // `|` is excluded as it is used in pattern alternatives and lambdas,
+        // `?` is included for error propagation,
+        // `[` is included for indexing operations,
+        // `[]` is excluded as `a[]` isn't an expression and should be recovered as `a, []` (cf. `tests/ui/parser/pat-lt-bracket-7.rs`)
+        let has_trailing_operator = matches!(self.token.kind, token::BinOp(op) if op != BinOpToken::Or)
+            || self.token.kind == token::Question
+            || (self.token.kind == token::OpenDelim(Delimiter::Bracket)
+                && self.look_ahead(1, |tok| tok.kind != token::CloseDelim(Delimiter::Bracket)));
+
+        if !has_trailing_method && !has_trailing_operator {
+            // Nothing to recover here.
+            return None;
+        }
+
+        // Let's try to parse an expression to emit a better diagnostic.
+        let mut snapshot = self.create_snapshot_for_diagnostic();
+        snapshot.restrictions.insert(Restrictions::IS_PAT);
+
+        // Parse `?`, `.f`, `(arg0, arg1, ...)` or `[expr]` until they've all been eaten.
+        if let Ok(expr) = snapshot
+            .parse_expr_dot_or_call_with(
+                self.mk_expr(pat_span, ExprKind::Dummy), // equivalent to transforming the parsed pattern into an `Expr`
+                pat_span,
+                AttrVec::new(),
+            )
+            .map_err(|err| err.cancel())
+        {
+            let non_assoc_span = expr.span;
+
+            // Parse an associative expression such as `+ expr`, `% expr`, ...
+            // Assignements, ranges and `|` are disabled by [`Restrictions::IS_PAT`].
+            if let Ok(expr) =
+                snapshot.parse_expr_assoc_with(0, expr.into()).map_err(|err| err.cancel())
+            {
+                // We got a valid expression.
+                self.restore_snapshot(snapshot);
+                self.restrictions.remove(Restrictions::IS_PAT);
+
+                let is_bound = is_end_bound
+                    // is_start_bound: either `..` or `)..`
+                    || self.token.is_range_separator()
+                    || self.token.kind == token::CloseDelim(Delimiter::Parenthesis)
+                        && self.look_ahead(1, Token::is_range_separator);
+
+                // Check that `parse_expr_assoc_with` didn't eat a rhs.
+                let is_method_call = has_trailing_method && non_assoc_span == expr.span;
+
+                return Some(self.dcx().emit_err(UnexpectedExpressionInPattern {
+                    span: expr.span,
+                    is_bound,
+                    is_method_call,
+                }));
+            }
+        }
+
+        // We got a trailing method/operator, but we couldn't parse an expression.
+        None
+    }
+
+    /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
+    /// allowed).
+    fn parse_pat_with_range_pat(
+        &mut self,
+        allow_range_pat: bool,
+        expected: Option<Expected>,
+        syntax_loc: Option<PatternLocation>,
+    ) -> PResult<'a, P<Pat>> {
+        maybe_recover_from_interpolated_ty_qpath!(self, true);
+        maybe_whole!(self, NtPat, |pat| pat);
+
+        let mut lo = self.token.span;
+
+        if self.token.is_keyword(kw::Let) && self.look_ahead(1, |tok| tok.can_begin_pattern()) {
+            self.bump();
+            self.dcx().emit_err(RemoveLet { span: lo });
+            lo = self.token.span;
+        }
+
+        let pat = if self.check(&token::BinOp(token::And)) || self.token.kind == token::AndAnd {
+            self.parse_pat_deref(expected)?
+        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            self.parse_pat_tuple_or_parens()?
+        } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
+            // Parse `[pat, pat,...]` as a slice pattern.
+            let (pats, _) = self.parse_delim_comma_seq(Delimiter::Bracket, |p| {
+                p.parse_pat_allow_top_alt(
+                    None,
+                    RecoverComma::No,
+                    RecoverColon::No,
+                    CommaRecoveryMode::EitherTupleOrPipe,
+                )
+            })?;
+            PatKind::Slice(pats)
+        } else if self.check(&token::DotDot) && !self.is_pat_range_end_start(1) {
+            // A rest pattern `..`.
+            self.bump(); // `..`
+            PatKind::Rest
+        } else if self.check(&token::DotDotDot) && !self.is_pat_range_end_start(1) {
+            self.recover_dotdotdot_rest_pat(lo)
+        } else if let Some(form) = self.parse_range_end() {
+            self.parse_pat_range_to(form)? // `..=X`, `...X`, or `..X`.
+        } else if self.eat(&token::Not) {
+            // Parse `!`
+            self.psess.gated_spans.gate(sym::never_patterns, self.prev_token.span);
+            PatKind::Never
+        } else if self.eat_keyword(kw::Underscore) {
+            // Parse `_`
+            PatKind::Wild
+        } else if self.eat_keyword(kw::Mut) {
+            self.parse_pat_ident_mut()?
+        } else if self.eat_keyword(kw::Ref) {
+            if self.check_keyword(kw::Box) {
+                // Suggest `box ref`.
+                let span = self.prev_token.span.to(self.token.span);
+                self.bump();
+                self.dcx().emit_err(SwitchRefBoxOrder { span });
+            }
+            // Parse ref ident @ pat / ref mut ident @ pat
+            let mutbl = self.parse_mutability();
+            self.parse_pat_ident(BindingMode(ByRef::Yes(mutbl), Mutability::Not), syntax_loc)?
+        } else if self.eat_keyword(kw::Box) {
+            self.parse_pat_box()?
+        } else if self.check_inline_const(0) {
+            // Parse `const pat`
+            let const_expr = self.parse_const_block(lo.to(self.token.span), true)?;
+
+            if let Some(re) = self.parse_range_end() {
+                self.parse_pat_range_begin_with(const_expr, re)?
+            } else {
+                PatKind::Lit(const_expr)
+            }
+        } else if self.is_builtin() {
+            self.parse_pat_builtin()?
+        }
+        // Don't eagerly error on semantically invalid tokens when matching
+        // declarative macros, as the input to those doesn't have to be
+        // semantically valid. For attribute/derive proc macros this is not the
+        // case, so doing the recovery for them is fine.
+        else if self.can_be_ident_pat()
+            || (self.is_lit_bad_ident().is_some() && self.may_recover())
+        {
+            // Parse `ident @ pat`
+            // This can give false positives and parse nullary enums,
+            // they are dealt with later in resolve.
+            self.parse_pat_ident(BindingMode::NONE, syntax_loc)?
+        } else if self.is_start_of_pat_with_path() {
+            // Parse pattern starting with a path
+            let (qself, path) = if self.eat_lt() {
+                // Parse a qualified path
+                let (qself, path) = self.parse_qpath(PathStyle::Pat)?;
+                (Some(qself), path)
+            } else {
+                // Parse an unqualified path
+                (None, self.parse_path(PathStyle::Pat)?)
+            };
+            let span = lo.to(self.prev_token.span);
+
+            if qself.is_none() && self.check(&token::Not) {
+                self.parse_pat_mac_invoc(path)?
+            } else if let Some(form) = self.parse_range_end() {
+                let begin = self.mk_expr(span, ExprKind::Path(qself, path));
+                self.parse_pat_range_begin_with(begin, form)?
+            } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
+                self.parse_pat_struct(qself, path)?
+            } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+                self.parse_pat_tuple_struct(qself, path)?
+            } else {
+                match self.maybe_recover_trailing_expr(span, false) {
+                    Some(guar) => PatKind::Err(guar),
+                    None => PatKind::Path(qself, path),
+                }
+            }
+        } else if let token::Lifetime(lt) = self.token.kind
+            // In pattern position, we're totally fine with using "next token isn't colon"
+            // as a heuristic. We could probably just always try to recover if it's a lifetime,
+            // because we never have `'a: label {}` in a pattern position anyways, but it does
+            // keep us from suggesting something like `let 'a: Ty = ..` => `let 'a': Ty = ..`
+            && could_be_unclosed_char_literal(Ident::with_dummy_span(lt))
+            && !self.look_ahead(1, |token| matches!(token.kind, token::Colon))
+        {
+            // Recover a `'a` as a `'a'` literal
+            let lt = self.expect_lifetime();
+            let (lit, _) =
+                self.recover_unclosed_char(lt.ident, Parser::mk_token_lit_char, |self_| {
+                    let expected = Expected::to_string_or_fallback(expected);
+                    let msg = format!(
+                        "expected {}, found {}",
+                        expected,
+                        super::token_descr(&self_.token)
+                    );
+
+                    self_
+                        .dcx()
+                        .struct_span_err(self_.token.span, msg)
+                        .with_span_label(self_.token.span, format!("expected {expected}"))
+                });
+            PatKind::Lit(self.mk_expr(lo, ExprKind::Lit(lit)))
+        } else {
+            // Try to parse everything else as literal with optional minus
+            match self.parse_literal_maybe_minus() {
+                Ok(begin) => {
+                    let begin = match self.maybe_recover_trailing_expr(begin.span, false) {
+                        Some(guar) => self.mk_expr_err(begin.span, guar),
+                        None => begin,
+                    };
+
+                    match self.parse_range_end() {
+                        Some(form) => self.parse_pat_range_begin_with(begin, form)?,
+                        None => PatKind::Lit(begin),
+                    }
+                }
+                Err(err) => return self.fatal_unexpected_non_pat(err, expected),
+            }
+        };
+
+        let pat = self.mk_pat(lo.to(self.prev_token.span), pat);
+        let pat = self.maybe_recover_from_bad_qpath(pat)?;
+        let pat = self.recover_intersection_pat(pat)?;
+
+        if !allow_range_pat {
+            self.ban_pat_range_if_ambiguous(&pat)
+        }
+
+        Ok(pat)
+    }
+
+    /// Recover from a typoed `...` pattern that was encountered
+    /// Ref: Issue #70388
+    fn recover_dotdotdot_rest_pat(&mut self, lo: Span) -> PatKind {
+        // A typoed rest pattern `...`.
+        self.bump(); // `...`
+
+        // The user probably mistook `...` for a rest pattern `..`.
+        self.dcx().emit_err(DotDotDotRestPattern { span: lo });
+        PatKind::Rest
+    }
+
+    /// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
+    ///
+    /// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
+    /// should already have been parsed by now at this point,
+    /// if the next token is `@` then we can try to parse the more general form.
+    ///
+    /// Consult `parse_pat_ident` for the `binding` grammar.
+    ///
+    /// The notion of intersection patterns are found in
+    /// e.g. [F#][and] where they are called AND-patterns.
+    ///
+    /// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
+    fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
+        if self.token.kind != token::At {
+            // Next token is not `@` so it's not going to be an intersection pattern.
+            return Ok(lhs);
+        }
+
+        // At this point we attempt to parse `@ $pat_rhs` and emit an error.
+        self.bump(); // `@`
+        let mut rhs = self.parse_pat_no_top_alt(None, None)?;
+        let whole_span = lhs.span.to(rhs.span);
+
+        if let PatKind::Ident(_, _, sub @ None) = &mut rhs.kind {
+            // The user inverted the order, so help them fix that.
+            let lhs_span = lhs.span;
+            // Move the LHS into the RHS as a subpattern.
+            // The RHS is now the full pattern.
+            *sub = Some(lhs);
+
+            self.dcx().emit_err(PatternOnWrongSideOfAt {
+                whole_span,
+                whole_pat: pprust::pat_to_string(&rhs),
+                pattern: lhs_span,
+                binding: rhs.span,
+            });
+        } else {
+            // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
+            rhs.kind = PatKind::Wild;
+            self.dcx().emit_err(ExpectedBindingLeftOfAt {
+                whole_span,
+                lhs: lhs.span,
+                rhs: rhs.span,
+            });
+        }
+
+        rhs.span = whole_span;
+        Ok(rhs)
+    }
+
+    /// Ban a range pattern if it has an ambiguous interpretation.
+    fn ban_pat_range_if_ambiguous(&self, pat: &Pat) {
+        match pat.kind {
+            PatKind::Range(
+                ..,
+                Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. },
+            ) => return,
+            PatKind::Range(..) => {}
+            _ => return,
+        }
+
+        self.dcx()
+            .emit_err(AmbiguousRangePattern { span: pat.span, pat: pprust::pat_to_string(pat) });
+    }
+
+    /// Parse `&pat` / `&mut pat`.
+    fn parse_pat_deref(&mut self, expected: Option<Expected>) -> PResult<'a, PatKind> {
+        self.expect_and()?;
+        if let token::Lifetime(name) = self.token.kind {
+            self.bump(); // `'a`
+
+            self.dcx()
+                .emit_err(UnexpectedLifetimeInPattern { span: self.prev_token.span, symbol: name });
+        }
+
+        let mutbl = self.parse_mutability();
+        let subpat = self.parse_pat_with_range_pat(false, expected, None)?;
+        Ok(PatKind::Ref(subpat, mutbl))
+    }
+
+    /// Parse a tuple or parenthesis pattern.
+    fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
+        let open_paren = self.token.span;
+
+        let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
+            p.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::No,
+                RecoverColon::No,
+                CommaRecoveryMode::LikelyTuple,
+            )
+        })?;
+
+        // Here, `(pat,)` is a tuple pattern.
+        // For backward compatibility, `(..)` is a tuple pattern as well.
+        let paren_pattern =
+            fields.len() == 1 && !(matches!(trailing_comma, Trailing::Yes) || fields[0].is_rest());
+        if paren_pattern {
+            let pat = fields.into_iter().next().unwrap();
+            let close_paren = self.prev_token.span;
+
+            match &pat.kind {
+                // recover ranges with parentheses around the `(start)..`
+                PatKind::Lit(begin)
+                    if self.may_recover()
+                        && let Some(form) = self.parse_range_end() =>
+                {
+                    self.dcx().emit_err(UnexpectedParenInRangePat {
+                        span: vec![open_paren, close_paren],
+                        sugg: UnexpectedParenInRangePatSugg {
+                            start_span: open_paren,
+                            end_span: close_paren,
+                        },
+                    });
+
+                    self.parse_pat_range_begin_with(begin.clone(), form)
+                }
+                // recover ranges with parentheses around the `(start)..`
+                PatKind::Err(guar)
+                    if self.may_recover()
+                        && let Some(form) = self.parse_range_end() =>
+                {
+                    self.dcx().emit_err(UnexpectedParenInRangePat {
+                        span: vec![open_paren, close_paren],
+                        sugg: UnexpectedParenInRangePatSugg {
+                            start_span: open_paren,
+                            end_span: close_paren,
+                        },
+                    });
+
+                    self.parse_pat_range_begin_with(self.mk_expr_err(pat.span, *guar), form)
+                }
+
+                // (pat) with optional parentheses
+                _ => Ok(PatKind::Paren(pat)),
+            }
+        } else {
+            Ok(PatKind::Tuple(fields))
+        }
+    }
+
+    /// Parse a mutable binding with the `mut` token already eaten.
+    fn parse_pat_ident_mut(&mut self) -> PResult<'a, PatKind> {
+        let mut_span = self.prev_token.span;
+
+        self.recover_additional_muts();
+
+        let byref = self.parse_byref();
+
+        self.recover_additional_muts();
+
+        // Make sure we don't allow e.g. `let mut $p;` where `$p:pat`.
+        if let token::Interpolated(nt) = &self.token.kind {
+            if let token::NtPat(..) = &**nt {
+                self.expected_ident_found_err().emit();
+            }
+        }
+
+        // Parse the pattern we hope to be an identifier.
+        let mut pat = self.parse_pat_no_top_alt(Some(Expected::Identifier), None)?;
+
+        // If we don't have `mut $ident (@ pat)?`, error.
+        if let PatKind::Ident(BindingMode(br @ ByRef::No, m @ Mutability::Not), ..) = &mut pat.kind
+        {
+            // Don't recurse into the subpattern.
+            // `mut` on the outer binding doesn't affect the inner bindings.
+            *br = byref;
+            *m = Mutability::Mut;
+        } else {
+            // Add `mut` to any binding in the parsed pattern.
+            let changed_any_binding = Self::make_all_value_bindings_mutable(&mut pat);
+            self.ban_mut_general_pat(mut_span, &pat, changed_any_binding);
+        }
+
+        if matches!(pat.kind, PatKind::Ident(BindingMode(ByRef::Yes(_), Mutability::Mut), ..)) {
+            self.psess.gated_spans.gate(sym::mut_ref, pat.span);
+        }
+        Ok(pat.into_inner().kind)
+    }
+
+    /// Turn all by-value immutable bindings in a pattern into mutable bindings.
+    /// Returns `true` if any change was made.
+    fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
+        struct AddMut(bool);
+        impl MutVisitor for AddMut {
+            fn visit_pat(&mut self, pat: &mut P<Pat>) {
+                if let PatKind::Ident(BindingMode(ByRef::No, m @ Mutability::Not), ..) =
+                    &mut pat.kind
+                {
+                    self.0 = true;
+                    *m = Mutability::Mut;
+                }
+                noop_visit_pat(pat, self);
+            }
+        }
+
+        let mut add_mut = AddMut(false);
+        add_mut.visit_pat(pat);
+        add_mut.0
+    }
+
+    /// Error on `mut $pat` where `$pat` is not an ident.
+    fn ban_mut_general_pat(&self, lo: Span, pat: &Pat, changed_any_binding: bool) {
+        self.dcx().emit_err(if changed_any_binding {
+            InvalidMutInPattern::NestedIdent {
+                span: lo.to(pat.span),
+                pat: pprust::pat_to_string(pat),
+            }
+        } else {
+            InvalidMutInPattern::NonIdent { span: lo.until(pat.span) }
+        });
+    }
+
+    /// Eat any extraneous `mut`s and error + recover if we ate any.
+    fn recover_additional_muts(&mut self) {
+        let lo = self.token.span;
+        while self.eat_keyword(kw::Mut) {}
+        if lo == self.token.span {
+            return;
+        }
+
+        self.dcx().emit_err(RepeatedMutInPattern { span: lo.to(self.prev_token.span) });
+    }
+
+    /// Parse macro invocation
+    fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
+        self.bump();
+        let args = self.parse_delim_args()?;
+        let mac = P(MacCall { path, args });
+        Ok(PatKind::MacCall(mac))
+    }
+
+    fn fatal_unexpected_non_pat(
+        &mut self,
+        err: Diag<'a>,
+        expected: Option<Expected>,
+    ) -> PResult<'a, P<Pat>> {
+        err.cancel();
+
+        let expected = Expected::to_string_or_fallback(expected);
+        let msg = format!("expected {}, found {}", expected, super::token_descr(&self.token));
+
+        let mut err = self.dcx().struct_span_err(self.token.span, msg);
+        err.span_label(self.token.span, format!("expected {expected}"));
+
+        let sp = self.psess.source_map().start_point(self.token.span);
+        if let Some(sp) = self.psess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            err.subdiagnostic(self.dcx(), ExprParenthesesNeeded::surrounding(*sp));
+        }
+
+        Err(err)
+    }
+
+    /// Parses the range pattern end form `".." | "..." | "..=" ;`.
+    fn parse_range_end(&mut self) -> Option<Spanned<RangeEnd>> {
+        let re = if self.eat(&token::DotDotDot) {
+            RangeEnd::Included(RangeSyntax::DotDotDot)
+        } else if self.eat(&token::DotDotEq) {
+            RangeEnd::Included(RangeSyntax::DotDotEq)
+        } else if self.eat(&token::DotDot) {
+            RangeEnd::Excluded
+        } else {
+            return None;
+        };
+        Some(respan(self.prev_token.span, re))
+    }
+
+    /// Parse a range pattern `$begin $form $end?` where `$form = ".." | "..." | "..=" ;`.
+    /// `$begin $form` has already been parsed.
+    fn parse_pat_range_begin_with(
+        &mut self,
+        begin: P<Expr>,
+        re: Spanned<RangeEnd>,
+    ) -> PResult<'a, PatKind> {
+        let end = if self.is_pat_range_end_start(0) {
+            // Parsing e.g. `X..=Y`.
+            Some(self.parse_pat_range_end()?)
+        } else {
+            // Parsing e.g. `X..`.
+            if let RangeEnd::Included(_) = re.node {
+                // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
+                self.inclusive_range_with_incorrect_end();
+            }
+            None
+        };
+        Ok(PatKind::Range(Some(begin), end, re))
+    }
+
+    pub(super) fn inclusive_range_with_incorrect_end(&mut self) -> ErrorGuaranteed {
+        let tok = &self.token;
+        let span = self.prev_token.span;
+        // If the user typed "..==" instead of "..=", we want to give them
+        // a specific error message telling them to use "..=".
+        // If they typed "..=>", suggest they use ".. =>".
+        // Otherwise, we assume that they meant to type a half open exclusive
+        // range and give them an error telling them to do that instead.
+        let no_space = tok.span.lo() == span.hi();
+        match tok.kind {
+            token::Eq if no_space => {
+                let span_with_eq = span.to(tok.span);
+
+                // Ensure the user doesn't receive unhelpful unexpected token errors
+                self.bump();
+                if self.is_pat_range_end_start(0) {
+                    let _ = self.parse_pat_range_end().map_err(|e| e.cancel());
+                }
+
+                self.dcx().emit_err(InclusiveRangeExtraEquals { span: span_with_eq })
+            }
+            token::Gt if no_space => {
+                let after_pat = span.with_hi(span.hi() - rustc_span::BytePos(1)).shrink_to_hi();
+                self.dcx().emit_err(InclusiveRangeMatchArrow { span, arrow: tok.span, after_pat })
+            }
+            _ => self.dcx().emit_err(InclusiveRangeNoEnd { span }),
+        }
+    }
+
+    /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
+    ///
+    /// The form `...X` is prohibited to reduce confusion with the potential
+    /// expression syntax `...expr` for splatting in expressions.
+    fn parse_pat_range_to(&mut self, mut re: Spanned<RangeEnd>) -> PResult<'a, PatKind> {
+        let end = self.parse_pat_range_end()?;
+        if let RangeEnd::Included(syn @ RangeSyntax::DotDotDot) = &mut re.node {
+            *syn = RangeSyntax::DotDotEq;
+            self.dcx().emit_err(DotDotDotRangeToPatternNotAllowed { span: re.span });
+        }
+        Ok(PatKind::Range(None, Some(end), re))
+    }
+
+    /// Is the token `dist` away from the current suitable as the start of a range patterns end?
+    fn is_pat_range_end_start(&self, dist: usize) -> bool {
+        self.check_inline_const(dist)
+            || self.look_ahead(dist, |t| {
+                t.is_path_start() // e.g. `MY_CONST`;
+                || t.kind == token::Dot // e.g. `.5` for recovery;
+                || t.can_begin_literal_maybe_minus() // e.g. `42`.
+                || t.is_whole_expr()
+                || t.is_lifetime() // recover `'a` instead of `'a'`
+                || (self.may_recover() // recover leading `(`
+                    && t.kind == token::OpenDelim(Delimiter::Parenthesis)
+                    && self.look_ahead(dist + 1, |t| t.kind != token::OpenDelim(Delimiter::Parenthesis))
+                    && self.is_pat_range_end_start(dist + 1))
+            })
+    }
+
+    /// Parse a range pattern end bound
+    fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
+        // recover leading `(`
+        let open_paren = (self.may_recover()
+            && self.eat_noexpect(&token::OpenDelim(Delimiter::Parenthesis)))
+        .then_some(self.prev_token.span);
+
+        let bound = if self.check_inline_const(0) {
+            self.parse_const_block(self.token.span, true)
+        } else if self.check_path() {
+            let lo = self.token.span;
+            let (qself, path) = if self.eat_lt() {
+                // Parse a qualified path
+                let (qself, path) = self.parse_qpath(PathStyle::Pat)?;
+                (Some(qself), path)
+            } else {
+                // Parse an unqualified path
+                (None, self.parse_path(PathStyle::Pat)?)
+            };
+            let hi = self.prev_token.span;
+            Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path)))
+        } else {
+            self.parse_literal_maybe_minus()
+        }?;
+
+        let recovered = self.maybe_recover_trailing_expr(bound.span, true);
+
+        // recover trailing `)`
+        if let Some(open_paren) = open_paren {
+            self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+
+            self.dcx().emit_err(UnexpectedParenInRangePat {
+                span: vec![open_paren, self.prev_token.span],
+                sugg: UnexpectedParenInRangePatSugg {
+                    start_span: open_paren,
+                    end_span: self.prev_token.span,
+                },
+            });
+        }
+
+        Ok(match recovered {
+            Some(guar) => self.mk_expr_err(bound.span, guar),
+            None => bound,
+        })
+    }
+
+    /// Is this the start of a pattern beginning with a path?
+    fn is_start_of_pat_with_path(&mut self) -> bool {
+        self.check_path()
+        // Just for recovery (see `can_be_ident`).
+        || self.token.is_ident() && !self.token.is_bool_lit() && !self.token.is_keyword(kw::In)
+    }
+
+    /// Would `parse_pat_ident` be appropriate here?
+    fn can_be_ident_pat(&mut self) -> bool {
+        self.check_ident()
+        && !self.token.is_bool_lit() // Avoid `true` or `false` as a binding as it is a literal.
+        && !self.token.is_path_segment_keyword() // Avoid e.g. `Self` as it is a path.
+        // Avoid `in`. Due to recovery in the list parser this messes with `for ( $pat in $expr )`.
+        && !self.token.is_keyword(kw::In)
+        // Try to do something more complex?
+        && self.look_ahead(1, |t| !matches!(t.kind, token::OpenDelim(Delimiter::Parenthesis) // A tuple struct pattern.
+            | token::OpenDelim(Delimiter::Brace) // A struct pattern.
+            | token::DotDotDot | token::DotDotEq | token::DotDot // A range pattern.
+            | token::PathSep // A tuple / struct variant pattern.
+            | token::Not)) // A macro expanding to a pattern.
+    }
+
+    /// Parses `ident` or `ident @ pat`.
+    /// Used by the copy foo and ref foo patterns to give a good
+    /// error message when parsing mistakes like `ref foo(a, b)`.
+    fn parse_pat_ident(
+        &mut self,
+        binding_annotation: BindingMode,
+        syntax_loc: Option<PatternLocation>,
+    ) -> PResult<'a, PatKind> {
+        let ident = self.parse_ident_common(false)?;
+
+        if self.may_recover()
+            && !matches!(syntax_loc, Some(PatternLocation::FunctionParameter))
+            && self.check_noexpect(&token::Lt)
+            && self.look_ahead(1, |t| t.can_begin_type())
+        {
+            return Err(self.dcx().create_err(GenericArgsInPatRequireTurbofishSyntax {
+                span: self.token.span,
+                suggest_turbofish: self.token.span.shrink_to_lo(),
+            }));
+        }
+
+        let sub = if self.eat(&token::At) {
+            Some(self.parse_pat_no_top_alt(Some(Expected::BindingPattern), None)?)
+        } else {
+            None
+        };
+
+        // Just to be friendly, if they write something like `ref Some(i)`,
+        // we end up here with `(` as the current token.
+        // This shortly leads to a parse error. Note that if there is no explicit
+        // binding mode then we do not end up here, because the lookahead
+        // will direct us over to `parse_enum_variant()`.
+        if self.token == token::OpenDelim(Delimiter::Parenthesis) {
+            return Err(self
+                .dcx()
+                .create_err(EnumPatternInsteadOfIdentifier { span: self.prev_token.span }));
+        }
+
+        // Check for method calls after the `ident`,
+        // but not `ident @ subpat` as `subpat` was already checked and `ident` continues with `@`.
+
+        let pat = if sub.is_none()
+            && let Some(guar) = self.maybe_recover_trailing_expr(ident.span, false)
+        {
+            PatKind::Err(guar)
+        } else {
+            PatKind::Ident(binding_annotation, ident, sub)
+        };
+        Ok(pat)
+    }
+
+    /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
+    fn parse_pat_struct(&mut self, qself: Option<P<QSelf>>, path: Path) -> PResult<'a, PatKind> {
+        if qself.is_some() {
+            // Feature gate the use of qualified paths in patterns
+            self.psess.gated_spans.gate(sym::more_qualified_paths, path.span);
+        }
+        self.bump();
+        let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
+            e.span_label(path.span, "while parsing the fields for this pattern");
+            e.emit();
+            self.recover_stmt();
+            // When recovering, pretend we had `Foo { .. }`, to avoid cascading errors.
+            (ThinVec::new(), PatFieldsRest::Rest)
+        });
+        self.bump();
+        Ok(PatKind::Struct(qself, path, fields, etc))
+    }
+
+    /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
+    fn parse_pat_tuple_struct(
+        &mut self,
+        qself: Option<P<QSelf>>,
+        path: Path,
+    ) -> PResult<'a, PatKind> {
+        let (fields, _) = self.parse_paren_comma_seq(|p| {
+            p.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::No,
+                RecoverColon::No,
+                CommaRecoveryMode::EitherTupleOrPipe,
+            )
+        })?;
+        if qself.is_some() {
+            self.psess.gated_spans.gate(sym::more_qualified_paths, path.span);
+        }
+        Ok(PatKind::TupleStruct(qself, path, fields))
+    }
+
+    /// Are we sure this could not possibly be the start of a pattern?
+    ///
+    /// Currently, this only accounts for tokens that can follow identifiers
+    /// in patterns, but this can be extended as necessary.
+    fn isnt_pattern_start(&self) -> bool {
+        [
+            token::Eq,
+            token::Colon,
+            token::Comma,
+            token::Semi,
+            token::At,
+            token::OpenDelim(Delimiter::Brace),
+            token::CloseDelim(Delimiter::Brace),
+            token::CloseDelim(Delimiter::Parenthesis),
+        ]
+        .contains(&self.token.kind)
+    }
+
+    fn parse_pat_builtin(&mut self) -> PResult<'a, PatKind> {
+        self.parse_builtin(|self_, _lo, ident| {
+            Ok(match ident.name {
+                // builtin#deref(PAT)
+                sym::deref => Some(ast::PatKind::Deref(self_.parse_pat_allow_top_alt(
+                    None,
+                    RecoverComma::Yes,
+                    RecoverColon::Yes,
+                    CommaRecoveryMode::LikelyTuple,
+                )?)),
+                _ => None,
+            })
+        })
+    }
+
+    /// Parses `box pat`
+    fn parse_pat_box(&mut self) -> PResult<'a, PatKind> {
+        let box_span = self.prev_token.span;
+
+        if self.isnt_pattern_start() {
+            let descr = super::token_descr(&self.token);
+            self.dcx().emit_err(errors::BoxNotPat {
+                span: self.token.span,
+                kw: box_span,
+                lo: box_span.shrink_to_lo(),
+                descr,
+            });
+
+            // We cannot use `parse_pat_ident()` since it will complain `box`
+            // is not an identifier.
+            let sub = if self.eat(&token::At) {
+                Some(self.parse_pat_no_top_alt(Some(Expected::BindingPattern), None)?)
+            } else {
+                None
+            };
+
+            Ok(PatKind::Ident(BindingMode::NONE, Ident::new(kw::Box, box_span), sub))
+        } else {
+            let pat = self.parse_pat_with_range_pat(false, None, None)?;
+            self.psess.gated_spans.gate(sym::box_patterns, box_span.to(self.prev_token.span));
+            Ok(PatKind::Box(pat))
+        }
+    }
+
+    /// Parses the fields of a struct-like pattern.
+    fn parse_pat_fields(&mut self) -> PResult<'a, (ThinVec<PatField>, PatFieldsRest)> {
+        let mut fields = ThinVec::new();
+        let mut etc = PatFieldsRest::None;
+        let mut ate_comma = true;
+        let mut delayed_err: Option<Diag<'a>> = None;
+        let mut first_etc_and_maybe_comma_span = None;
+        let mut last_non_comma_dotdot_span = None;
+
+        while self.token != token::CloseDelim(Delimiter::Brace) {
+            let attrs = match self.parse_outer_attributes() {
+                Ok(attrs) => attrs,
+                Err(err) => {
+                    if let Some(delayed) = delayed_err {
+                        delayed.emit();
+                    }
+                    return Err(err);
+                }
+            };
+            let lo = self.token.span;
+
+            // check that a comma comes after every field
+            if !ate_comma {
+                let mut err =
+                    self.dcx().create_err(ExpectedCommaAfterPatternField { span: self.token.span });
+                if let Some(delayed) = delayed_err {
+                    delayed.emit();
+                }
+                self.recover_misplaced_pattern_modifiers(&fields, &mut err);
+                return Err(err);
+            }
+            ate_comma = false;
+
+            if self.check(&token::DotDot)
+                || self.check_noexpect(&token::DotDotDot)
+                || self.check_keyword(kw::Underscore)
+            {
+                etc = PatFieldsRest::Rest;
+                let mut etc_sp = self.token.span;
+                if first_etc_and_maybe_comma_span.is_none() {
+                    if let Some(comma_tok) = self
+                        .look_ahead(1, |t| if *t == token::Comma { Some(t.clone()) } else { None })
+                    {
+                        let nw_span = self
+                            .psess
+                            .source_map()
+                            .span_extend_to_line(comma_tok.span)
+                            .trim_start(comma_tok.span.shrink_to_lo())
+                            .map(|s| self.psess.source_map().span_until_non_whitespace(s));
+                        first_etc_and_maybe_comma_span = nw_span.map(|s| etc_sp.to(s));
+                    } else {
+                        first_etc_and_maybe_comma_span =
+                            Some(self.psess.source_map().span_until_non_whitespace(etc_sp));
+                    }
+                }
+
+                self.recover_bad_dot_dot();
+                self.bump(); // `..` || `...` || `_`
+
+                if self.token == token::CloseDelim(Delimiter::Brace) {
+                    break;
+                }
+                let token_str = super::token_descr(&self.token);
+                let msg = format!("expected `}}`, found {token_str}");
+                let mut err = self.dcx().struct_span_err(self.token.span, msg);
+
+                err.span_label(self.token.span, "expected `}`");
+                let mut comma_sp = None;
+                if self.token == token::Comma {
+                    // Issue #49257
+                    let nw_span =
+                        self.psess.source_map().span_until_non_whitespace(self.token.span);
+                    etc_sp = etc_sp.to(nw_span);
+                    err.span_label(
+                        etc_sp,
+                        "`..` must be at the end and cannot have a trailing comma",
+                    );
+                    comma_sp = Some(self.token.span);
+                    self.bump();
+                    ate_comma = true;
+                }
+
+                if self.token == token::CloseDelim(Delimiter::Brace) {
+                    // If the struct looks otherwise well formed, recover and continue.
+                    if let Some(sp) = comma_sp {
+                        err.span_suggestion_short(
+                            sp,
+                            "remove this comma",
+                            "",
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                    err.emit();
+                    break;
+                } else if self.token.is_ident() && ate_comma {
+                    // Accept fields coming after `..,`.
+                    // This way we avoid "pattern missing fields" errors afterwards.
+                    // We delay this error until the end in order to have a span for a
+                    // suggested fix.
+                    if let Some(delayed_err) = delayed_err {
+                        delayed_err.emit();
+                        return Err(err);
+                    } else {
+                        delayed_err = Some(err);
+                    }
+                } else {
+                    if let Some(err) = delayed_err {
+                        err.emit();
+                    }
+                    return Err(err);
+                }
+            }
+
+            let field =
+                self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+                    let field = match this.parse_pat_field(lo, attrs) {
+                        Ok(field) => Ok(field),
+                        Err(err) => {
+                            if let Some(delayed_err) = delayed_err.take() {
+                                delayed_err.emit();
+                            }
+                            return Err(err);
+                        }
+                    }?;
+                    ate_comma = this.eat(&token::Comma);
+
+                    last_non_comma_dotdot_span = Some(this.prev_token.span);
+
+                    // We just ate a comma, so there's no need to use
+                    // `TrailingToken::Comma`
+                    Ok((field, TrailingToken::None))
+                })?;
+
+            fields.push(field)
+        }
+
+        if let Some(mut err) = delayed_err {
+            if let Some(first_etc_span) = first_etc_and_maybe_comma_span {
+                if self.prev_token == token::DotDot {
+                    // We have `.., x, ..`.
+                    err.multipart_suggestion(
+                        "remove the starting `..`",
+                        vec![(first_etc_span, String::new())],
+                        Applicability::MachineApplicable,
+                    );
+                } else {
+                    if let Some(last_non_comma_dotdot_span) = last_non_comma_dotdot_span {
+                        // We have `.., x`.
+                        err.multipart_suggestion(
+                            "move the `..` to the end of the field list",
+                            vec![
+                                (first_etc_span, String::new()),
+                                (
+                                    self.token.span.to(last_non_comma_dotdot_span.shrink_to_hi()),
+                                    format!("{} .. }}", if ate_comma { "" } else { "," }),
+                                ),
+                            ],
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                }
+            }
+            err.emit();
+        }
+        Ok((fields, etc))
+    }
+
+    /// If the user writes `S { ref field: name }` instead of `S { field: ref name }`, we suggest
+    /// the correct code.
+    fn recover_misplaced_pattern_modifiers(&self, fields: &ThinVec<PatField>, err: &mut Diag<'a>) {
+        if let Some(last) = fields.iter().last()
+            && last.is_shorthand
+            && let PatKind::Ident(binding, ident, None) = last.pat.kind
+            && binding != BindingMode::NONE
+            && self.token == token::Colon
+            // We found `ref mut? ident:`, try to parse a `name,` or `name }`.
+            && let Some(name_span) = self.look_ahead(1, |t| t.is_ident().then(|| t.span))
+            && self.look_ahead(2, |t| {
+                t == &token::Comma || t == &token::CloseDelim(Delimiter::Brace)
+            })
+        {
+            let span = last.pat.span.with_hi(ident.span.lo());
+            // We have `S { ref field: name }` instead of `S { field: ref name }`
+            err.multipart_suggestion(
+                "the pattern modifiers belong after the `:`",
+                vec![
+                    (span, String::new()),
+                    (name_span.shrink_to_lo(), binding.prefix_str().to_string()),
+                ],
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
+    /// Recover on `...` or `_` as if it were `..` to avoid further errors.
+    /// See issue #46718.
+    fn recover_bad_dot_dot(&self) {
+        if self.token == token::DotDot {
+            return;
+        }
+
+        let token_str = pprust::token_to_string(&self.token);
+        self.dcx().emit_err(DotDotDotForRemainingFields { span: self.token.span, token_str });
+    }
+
+    fn parse_pat_field(&mut self, lo: Span, attrs: AttrVec) -> PResult<'a, PatField> {
+        // Check if a colon exists one ahead. This means we're parsing a fieldname.
+        let hi;
+        let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
+            // Parsing a pattern of the form `fieldname: pat`.
+            let fieldname = self.parse_field_name()?;
+            self.bump();
+            let pat = self.parse_pat_allow_top_alt(
+                None,
+                RecoverComma::No,
+                RecoverColon::No,
+                CommaRecoveryMode::EitherTupleOrPipe,
+            )?;
+            hi = pat.span;
+            (pat, fieldname, false)
+        } else {
+            // Parsing a pattern of the form `(box) (ref) (mut) fieldname`.
+            let is_box = self.eat_keyword(kw::Box);
+            let boxed_span = self.token.span;
+            let mutability = self.parse_mutability();
+            let by_ref = self.parse_byref();
+
+            let fieldname = self.parse_field_name()?;
+            hi = self.prev_token.span;
+            let ann = BindingMode(by_ref, mutability);
+            let fieldpat = self.mk_pat_ident(boxed_span.to(hi), ann, fieldname);
+            let subpat =
+                if is_box { self.mk_pat(lo.to(hi), PatKind::Box(fieldpat)) } else { fieldpat };
+            (subpat, fieldname, true)
+        };
+
+        Ok(PatField {
+            ident: fieldname,
+            pat: subpat,
+            is_shorthand,
+            attrs,
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            is_placeholder: false,
+        })
+    }
+
+    pub(super) fn mk_pat_ident(&self, span: Span, ann: BindingMode, ident: Ident) -> P<Pat> {
+        self.mk_pat(span, PatKind::Ident(ann, ident, None))
+    }
+
+    pub(super) fn mk_pat(&self, span: Span, kind: PatKind) -> P<Pat> {
+        P(Pat { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
new file mode 100644
index 00000000000..d845e8ab90d
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -0,0 +1,967 @@
+use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
+use super::{Parser, Restrictions, TokenType};
+use crate::errors::PathSingleColon;
+use crate::parser::{CommaRecoveryMode, RecoverColon, RecoverComma};
+use crate::{errors, maybe_whole};
+use ast::token::IdentIsRaw;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Token, TokenKind};
+use rustc_ast::{
+    self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AssocConstraint,
+    AssocConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs,
+    Path, PathSegment, QSelf,
+};
+use rustc_errors::{Applicability, Diag, PResult};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{BytePos, Span};
+use std::mem;
+use thin_vec::ThinVec;
+use tracing::debug;
+
+/// Specifies how to parse a path.
+#[derive(Copy, Clone, PartialEq)]
+pub enum PathStyle {
+    /// In some contexts, notably in expressions, paths with generic arguments are ambiguous
+    /// with something else. For example, in expressions `segment < ....` can be interpreted
+    /// as a comparison and `segment ( ....` can be interpreted as a function call.
+    /// In all such contexts the non-path interpretation is preferred by default for practical
+    /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g.
+    /// `x<y>` - comparisons, `x::<y>` - unambiguously a path.
+    ///
+    /// Also, a path may never be followed by a `:`. This means that we can eagerly recover if
+    /// we encounter it.
+    Expr,
+    /// The same as `Expr`, but may be followed by a `:`.
+    /// For example, this code:
+    /// ```rust
+    /// struct S;
+    ///
+    /// let S: S;
+    /// //  ^ Followed by a `:`
+    /// ```
+    Pat,
+    /// In other contexts, notably in types, no ambiguity exists and paths can be written
+    /// without the disambiguator, e.g., `x<y>` - unambiguously a path.
+    /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too.
+    Type,
+    /// A path with generic arguments disallowed, e.g., `foo::bar::Baz`, used in imports,
+    /// visibilities or attributes.
+    /// Technically, this variant is unnecessary and e.g., `Expr` can be used instead
+    /// (paths in "mod" contexts have to be checked later for absence of generic arguments
+    /// anyway, due to macros), but it is used to avoid weird suggestions about expected
+    /// tokens when something goes wrong.
+    Mod,
+}
+
+impl PathStyle {
+    fn has_generic_ambiguity(&self) -> bool {
+        matches!(self, Self::Expr | Self::Pat)
+    }
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a qualified path.
+    /// Assumes that the leading `<` has been parsed already.
+    ///
+    /// `qualified_path = <type [as trait_ref]>::path`
+    ///
+    /// # Examples
+    /// `<T>::default`
+    /// `<T as U>::a`
+    /// `<T as U>::F::a<S>` (without disambiguator)
+    /// `<T as U>::F::a::<S>` (with disambiguator)
+    pub(super) fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (P<QSelf>, Path)> {
+        let lo = self.prev_token.span;
+        let ty = self.parse_ty()?;
+
+        // `path` will contain the prefix of the path up to the `>`,
+        // if any (e.g., `U` in the `<T as U>::*` examples
+        // above). `path_span` has the span of that path, or an empty
+        // span in the case of something like `<T>::Bar`.
+        let (mut path, path_span);
+        if self.eat_keyword(kw::As) {
+            let path_lo = self.token.span;
+            path = self.parse_path(PathStyle::Type)?;
+            path_span = path_lo.to(self.prev_token.span);
+        } else {
+            path_span = self.token.span.to(self.token.span);
+            path = ast::Path { segments: ThinVec::new(), span: path_span, tokens: None };
+        }
+
+        // See doc comment for `unmatched_angle_bracket_count`.
+        self.expect(&token::Gt)?;
+        if self.unmatched_angle_bracket_count > 0 {
+            self.unmatched_angle_bracket_count -= 1;
+            debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+        }
+
+        let is_import_coupler = self.is_import_coupler();
+        if !is_import_coupler && !self.recover_colon_before_qpath_proj() {
+            self.expect(&token::PathSep)?;
+        }
+
+        let qself = P(QSelf { ty, path_span, position: path.segments.len() });
+        if !is_import_coupler {
+            self.parse_path_segments(&mut path.segments, style, None)?;
+        }
+
+        Ok((
+            qself,
+            Path { segments: path.segments, span: lo.to(self.prev_token.span), tokens: None },
+        ))
+    }
+
+    /// Recover from an invalid single colon, when the user likely meant a qualified path.
+    /// We avoid emitting this if not followed by an identifier, as our assumption that the user
+    /// intended this to be a qualified path may not be correct.
+    ///
+    /// ```ignore (diagnostics)
+    /// <Bar as Baz<T>>:Qux
+    ///                ^ help: use double colon
+    /// ```
+    fn recover_colon_before_qpath_proj(&mut self) -> bool {
+        if !self.check_noexpect(&TokenKind::Colon)
+            || self.look_ahead(1, |t| !t.is_ident() || t.is_reserved_ident())
+        {
+            return false;
+        }
+
+        self.bump(); // colon
+
+        self.dcx()
+            .struct_span_err(
+                self.prev_token.span,
+                "found single colon before projection in qualified path",
+            )
+            .with_span_suggestion(
+                self.prev_token.span,
+                "use double colon",
+                "::",
+                Applicability::MachineApplicable,
+            )
+            .emit();
+
+        true
+    }
+
+    pub(super) fn parse_path(&mut self, style: PathStyle) -> PResult<'a, Path> {
+        self.parse_path_inner(style, None)
+    }
+
+    /// Parses simple paths.
+    ///
+    /// `path = [::] segment+`
+    /// `segment = ident | ident[::]<args> | ident[::](args) [-> type]`
+    ///
+    /// # Examples
+    /// `a::b::C<D>` (without disambiguator)
+    /// `a::b::C::<D>` (with disambiguator)
+    /// `Fn(Args)` (without disambiguator)
+    /// `Fn::(Args)` (with disambiguator)
+    pub(super) fn parse_path_inner(
+        &mut self,
+        style: PathStyle,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, Path> {
+        let reject_generics_if_mod_style = |parser: &Parser<'_>, path: Path| {
+            // Ensure generic arguments don't end up in attribute paths, such as:
+            //
+            //     macro_rules! m {
+            //         ($p:path) => { #[$p] struct S; }
+            //     }
+            //
+            //     m!(inline<u8>); //~ ERROR: unexpected generic arguments in path
+            //
+            if style == PathStyle::Mod && path.segments.iter().any(|segment| segment.args.is_some())
+            {
+                let span = path
+                    .segments
+                    .iter()
+                    .filter_map(|segment| segment.args.as_ref())
+                    .map(|arg| arg.span())
+                    .collect::<Vec<_>>();
+                parser.dcx().emit_err(errors::GenericsInPath { span });
+                // Ignore these arguments to prevent unexpected behaviors.
+                let segments = path
+                    .segments
+                    .iter()
+                    .map(|segment| PathSegment { ident: segment.ident, id: segment.id, args: None })
+                    .collect();
+                Path { segments, ..path }
+            } else {
+                path
+            }
+        };
+
+        maybe_whole!(self, NtPath, |path| reject_generics_if_mod_style(self, path.into_inner()));
+
+        if let token::Interpolated(nt) = &self.token.kind {
+            if let token::NtTy(ty) = &**nt {
+                if let ast::TyKind::Path(None, path) = &ty.kind {
+                    let path = path.clone();
+                    self.bump();
+                    return Ok(reject_generics_if_mod_style(self, path));
+                }
+            }
+        }
+
+        let lo = self.token.span;
+        let mut segments = ThinVec::new();
+        let mod_sep_ctxt = self.token.span.ctxt();
+        if self.eat(&token::PathSep) {
+            segments.push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
+        }
+        self.parse_path_segments(&mut segments, style, ty_generics)?;
+        Ok(Path { segments, span: lo.to(self.prev_token.span), tokens: None })
+    }
+
+    pub(super) fn parse_path_segments(
+        &mut self,
+        segments: &mut ThinVec<PathSegment>,
+        style: PathStyle,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, ()> {
+        loop {
+            let segment = self.parse_path_segment(style, ty_generics)?;
+            if style.has_generic_ambiguity() {
+                // In order to check for trailing angle brackets, we must have finished
+                // recursing (`parse_path_segment` can indirectly call this function),
+                // that is, the next token must be the highlighted part of the below example:
+                //
+                // `Foo::<Bar as Baz<T>>::Qux`
+                //                      ^ here
+                //
+                // As opposed to the below highlight (if we had only finished the first
+                // recursion):
+                //
+                // `Foo::<Bar as Baz<T>>::Qux`
+                //                     ^ here
+                //
+                // `PathStyle::Expr` is only provided at the root invocation and never in
+                // `parse_path_segment` to recurse and therefore can be checked to maintain
+                // this invariant.
+                self.check_trailing_angle_brackets(&segment, &[&token::PathSep]);
+            }
+            segments.push(segment);
+
+            if self.is_import_coupler() || !self.eat(&token::PathSep) {
+                if style == PathStyle::Expr
+                    && self.may_recover()
+                    && self.token == token::Colon
+                    && self.look_ahead(1, |token| token.is_ident() && !token.is_reserved_ident())
+                {
+                    // Emit a special error message for `a::b:c` to help users
+                    // otherwise, `a: c` might have meant to introduce a new binding
+                    if self.token.span.lo() == self.prev_token.span.hi()
+                        && self.look_ahead(1, |token| self.token.span.hi() == token.span.lo())
+                    {
+                        self.bump(); // bump past the colon
+                        self.dcx().emit_err(PathSingleColon {
+                            span: self.prev_token.span,
+                            type_ascription: self
+                                .psess
+                                .unstable_features
+                                .is_nightly_build()
+                                .then_some(()),
+                        });
+                    }
+                    continue;
+                }
+
+                return Ok(());
+            }
+        }
+    }
+
+    pub(super) fn parse_path_segment(
+        &mut self,
+        style: PathStyle,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, PathSegment> {
+        let ident = self.parse_path_segment_ident()?;
+        let is_args_start = |token: &Token| {
+            matches!(
+                token.kind,
+                token::Lt
+                    | token::BinOp(token::Shl)
+                    | token::OpenDelim(Delimiter::Parenthesis)
+                    | token::LArrow
+            )
+        };
+        let check_args_start = |this: &mut Self| {
+            this.expected_tokens.extend_from_slice(&[
+                TokenType::Token(token::Lt),
+                TokenType::Token(token::OpenDelim(Delimiter::Parenthesis)),
+            ]);
+            is_args_start(&this.token)
+        };
+
+        Ok(
+            if style == PathStyle::Type && check_args_start(self)
+                || style != PathStyle::Mod
+                    && self.check(&token::PathSep)
+                    && self.look_ahead(1, |t| is_args_start(t))
+            {
+                // We use `style == PathStyle::Expr` to check if this is in a recursion or not. If
+                // it isn't, then we reset the unmatched angle bracket count as we're about to start
+                // parsing a new path.
+                if style == PathStyle::Expr {
+                    self.unmatched_angle_bracket_count = 0;
+                }
+
+                // Generic arguments are found - `<`, `(`, `::<` or `::(`.
+                self.eat(&token::PathSep);
+                let lo = self.token.span;
+                let args = if self.eat_lt() {
+                    // `<'a, T, A = U>`
+                    let args = self.parse_angle_args_with_leading_angle_bracket_recovery(
+                        style,
+                        lo,
+                        ty_generics,
+                    )?;
+                    self.expect_gt().map_err(|mut err| {
+                        // Try to recover a `:` into a `::`
+                        if self.token == token::Colon
+                            && self.look_ahead(1, |token| {
+                                token.is_ident() && !token.is_reserved_ident()
+                            })
+                        {
+                            err.cancel();
+                            err = self.dcx().create_err(PathSingleColon {
+                                span: self.token.span,
+                                type_ascription: self
+                                    .psess
+                                    .unstable_features
+                                    .is_nightly_build()
+                                    .then_some(()),
+                            });
+                        }
+                        // Attempt to find places where a missing `>` might belong.
+                        else if let Some(arg) = args
+                            .iter()
+                            .rev()
+                            .find(|arg| !matches!(arg, AngleBracketedArg::Constraint(_)))
+                        {
+                            err.span_suggestion_verbose(
+                                arg.span().shrink_to_hi(),
+                                "you might have meant to end the type parameters here",
+                                ">",
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
+                        err
+                    })?;
+                    let span = lo.to(self.prev_token.span);
+                    AngleBracketedArgs { args, span }.into()
+                } else if self.may_recover()
+                    && self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
+                    // FIXME(return_type_notation): Could also recover `...` here.
+                    && self.look_ahead(1, |tok| tok.kind == token::DotDot)
+                {
+                    self.bump();
+                    self.dcx()
+                        .emit_err(errors::BadReturnTypeNotationDotDot { span: self.token.span });
+                    self.bump();
+                    self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+                    let span = lo.to(self.prev_token.span);
+
+                    if self.eat_noexpect(&token::RArrow) {
+                        let lo = self.prev_token.span;
+                        let ty = self.parse_ty()?;
+                        self.dcx()
+                            .emit_err(errors::BadReturnTypeNotationOutput { span: lo.to(ty.span) });
+                    }
+
+                    ParenthesizedArgs {
+                        span,
+                        inputs: ThinVec::new(),
+                        inputs_span: span,
+                        output: ast::FnRetTy::Default(self.prev_token.span.shrink_to_hi()),
+                    }
+                    .into()
+                } else {
+                    // `(T, U) -> R`
+
+                    let prev_token_before_parsing = self.prev_token.clone();
+                    let token_before_parsing = self.token.clone();
+                    let mut snapshot = None;
+                    if self.may_recover()
+                        && prev_token_before_parsing.kind == token::PathSep
+                        && (style == PathStyle::Expr && self.token.can_begin_expr()
+                            || style == PathStyle::Pat && self.token.can_begin_pattern())
+                    {
+                        snapshot = Some(self.create_snapshot_for_diagnostic());
+                    }
+
+                    let (inputs, _) = match self.parse_paren_comma_seq(|p| p.parse_ty()) {
+                        Ok(output) => output,
+                        Err(mut error) if prev_token_before_parsing.kind == token::PathSep => {
+                            error.span_label(
+                                prev_token_before_parsing.span.to(token_before_parsing.span),
+                                "while parsing this parenthesized list of type arguments starting here",
+                            );
+
+                            if let Some(mut snapshot) = snapshot {
+                                snapshot.recover_fn_call_leading_path_sep(
+                                    style,
+                                    prev_token_before_parsing,
+                                    &mut error,
+                                )
+                            }
+
+                            return Err(error);
+                        }
+                        Err(error) => return Err(error),
+                    };
+                    let inputs_span = lo.to(self.prev_token.span);
+                    let output =
+                        self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
+                    let span = ident.span.to(self.prev_token.span);
+                    ParenthesizedArgs { span, inputs, inputs_span, output }.into()
+                };
+
+                PathSegment { ident, args: Some(args), id: ast::DUMMY_NODE_ID }
+            } else {
+                // Generic arguments are not found.
+                PathSegment::from_ident(ident)
+            },
+        )
+    }
+
+    pub(super) fn parse_path_segment_ident(&mut self) -> PResult<'a, Ident> {
+        match self.token.ident() {
+            Some((ident, IdentIsRaw::No)) if ident.is_path_segment_keyword() => {
+                self.bump();
+                Ok(ident)
+            }
+            _ => self.parse_ident(),
+        }
+    }
+
+    /// Recover `$path::(...)` as `$path(...)`.
+    ///
+    /// ```ignore (diagnostics)
+    /// foo::(420, "bar")
+    ///    ^^ remove extra separator to make the function call
+    /// // or
+    /// match x {
+    ///    Foo::(420, "bar") => { ... },
+    ///       ^^ remove extra separator to turn this into tuple struct pattern
+    ///    _ => { ... },
+    /// }
+    /// ```
+    fn recover_fn_call_leading_path_sep(
+        &mut self,
+        style: PathStyle,
+        prev_token_before_parsing: Token,
+        error: &mut Diag<'_>,
+    ) {
+        match style {
+            PathStyle::Expr
+                if let Ok(_) = self
+                    .parse_paren_comma_seq(|p| p.parse_expr())
+                    .map_err(|error| error.cancel()) => {}
+            PathStyle::Pat
+                if let Ok(_) = self
+                    .parse_paren_comma_seq(|p| {
+                        p.parse_pat_allow_top_alt(
+                            None,
+                            RecoverComma::No,
+                            RecoverColon::No,
+                            CommaRecoveryMode::LikelyTuple,
+                        )
+                    })
+                    .map_err(|error| error.cancel()) => {}
+            _ => {
+                return;
+            }
+        }
+
+        if let token::PathSep | token::RArrow = self.token.kind {
+            return;
+        }
+
+        error.span_suggestion_verbose(
+            prev_token_before_parsing.span,
+            format!(
+                "consider removing the `::` here to {}",
+                match style {
+                    PathStyle::Expr => "call the expression",
+                    PathStyle::Pat => "turn this into a tuple struct pattern",
+                    _ => {
+                        return;
+                    }
+                }
+            ),
+            "",
+            Applicability::MaybeIncorrect,
+        );
+    }
+
+    /// Parses generic args (within a path segment) with recovery for extra leading angle brackets.
+    /// For the purposes of understanding the parsing logic of generic arguments, this function
+    /// can be thought of being the same as just calling `self.parse_angle_args()` if the source
+    /// had the correct amount of leading angle brackets.
+    ///
+    /// ```ignore (diagnostics)
+    /// bar::<<<<T as Foo>::Output>();
+    ///      ^^ help: remove extra angle brackets
+    /// ```
+    fn parse_angle_args_with_leading_angle_bracket_recovery(
+        &mut self,
+        style: PathStyle,
+        lo: Span,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, ThinVec<AngleBracketedArg>> {
+        // We need to detect whether there are extra leading left angle brackets and produce an
+        // appropriate error and suggestion. This cannot be implemented by looking ahead at
+        // upcoming tokens for a matching `>` character - if there are unmatched `<` tokens
+        // then there won't be matching `>` tokens to find.
+        //
+        // To explain how this detection works, consider the following example:
+        //
+        // ```ignore (diagnostics)
+        // bar::<<<<T as Foo>::Output>();
+        //      ^^ help: remove extra angle brackets
+        // ```
+        //
+        // Parsing of the left angle brackets starts in this function. We start by parsing the
+        // `<` token (incrementing the counter of unmatched angle brackets on `Parser` via
+        // `eat_lt`):
+        //
+        // *Upcoming tokens:* `<<<<T as Foo>::Output>;`
+        // *Unmatched count:* 1
+        // *`parse_path_segment` calls deep:* 0
+        //
+        // This has the effect of recursing as this function is called if a `<` character
+        // is found within the expected generic arguments:
+        //
+        // *Upcoming tokens:* `<<<T as Foo>::Output>;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 1
+        //
+        // Eventually we will have recursed until having consumed all of the `<` tokens and
+        // this will be reflected in the count:
+        //
+        // *Upcoming tokens:* `T as Foo>::Output>;`
+        // *Unmatched count:* 4
+        // `parse_path_segment` calls deep:* 3
+        //
+        // The parser will continue until reaching the first `>` - this will decrement the
+        // unmatched angle bracket count and return to the parent invocation of this function
+        // having succeeded in parsing:
+        //
+        // *Upcoming tokens:* `::Output>;`
+        // *Unmatched count:* 3
+        // *`parse_path_segment` calls deep:* 2
+        //
+        // This will continue until the next `>` character which will also return successfully
+        // to the parent invocation of this function and decrement the count:
+        //
+        // *Upcoming tokens:* `;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 1
+        //
+        // At this point, this function will expect to find another matching `>` character but
+        // won't be able to and will return an error. This will continue all the way up the
+        // call stack until the first invocation:
+        //
+        // *Upcoming tokens:* `;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 0
+        //
+        // In doing this, we have managed to work out how many unmatched leading left angle
+        // brackets there are, but we cannot recover as the unmatched angle brackets have
+        // already been consumed. To remedy this, we keep a snapshot of the parser state
+        // before we do the above. We can then inspect whether we ended up with a parsing error
+        // and unmatched left angle brackets and if so, restore the parser state before we
+        // consumed any `<` characters to emit an error and consume the erroneous tokens to
+        // recover by attempting to parse again.
+        //
+        // In practice, the recursion of this function is indirect and there will be other
+        // locations that consume some `<` characters - as long as we update the count when
+        // this happens, it isn't an issue.
+
+        let is_first_invocation = style == PathStyle::Expr;
+        // Take a snapshot before attempting to parse - we can restore this later.
+        let snapshot = is_first_invocation.then(|| self.clone());
+
+        self.angle_bracket_nesting += 1;
+        debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
+        match self.parse_angle_args(ty_generics) {
+            Ok(args) => {
+                self.angle_bracket_nesting -= 1;
+                Ok(args)
+            }
+            Err(e) if self.angle_bracket_nesting > 10 => {
+                self.angle_bracket_nesting -= 1;
+                // When encountering severely malformed code where there are several levels of
+                // nested unclosed angle args (`f::<f::<f::<f::<...`), we avoid severe O(n^2)
+                // behavior by bailing out earlier (#117080).
+                e.emit();
+                rustc_errors::FatalError.raise();
+            }
+            Err(e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => {
+                self.angle_bracket_nesting -= 1;
+
+                // Swap `self` with our backup of the parser state before attempting to parse
+                // generic arguments.
+                let snapshot = mem::replace(self, snapshot.unwrap());
+
+                // Eat the unmatched angle brackets.
+                let all_angle_brackets = (0..snapshot.unmatched_angle_bracket_count)
+                    .fold(true, |a, _| a && self.eat_lt());
+
+                if !all_angle_brackets {
+                    // If there are other tokens in between the extraneous `<`s, we cannot simply
+                    // suggest to remove them. This check also prevents us from accidentally ending
+                    // up in the middle of a multibyte character (issue #84104).
+                    let _ = mem::replace(self, snapshot);
+                    Err(e)
+                } else {
+                    // Cancel error from being unable to find `>`. We know the error
+                    // must have been this due to a non-zero unmatched angle bracket
+                    // count.
+                    e.cancel();
+
+                    debug!(
+                        "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \
+                         snapshot.count={:?}",
+                        snapshot.unmatched_angle_bracket_count,
+                    );
+
+                    // Make a span over ${unmatched angle bracket count} characters.
+                    // This is safe because `all_angle_brackets` ensures that there are only `<`s,
+                    // i.e. no multibyte characters, in this range.
+                    let span = lo
+                        .with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count.into()));
+                    self.dcx().emit_err(errors::UnmatchedAngle {
+                        span,
+                        plural: snapshot.unmatched_angle_bracket_count > 1,
+                    });
+
+                    // Try again without unmatched angle bracket characters.
+                    self.parse_angle_args(ty_generics)
+                }
+            }
+            Err(e) => {
+                self.angle_bracket_nesting -= 1;
+                Err(e)
+            }
+        }
+    }
+
+    /// Parses (possibly empty) list of generic arguments / associated item constraints,
+    /// possibly including trailing comma.
+    pub(super) fn parse_angle_args(
+        &mut self,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, ThinVec<AngleBracketedArg>> {
+        let mut args = ThinVec::new();
+        while let Some(arg) = self.parse_angle_arg(ty_generics)? {
+            args.push(arg);
+            if !self.eat(&token::Comma) {
+                if self.check_noexpect(&TokenKind::Semi)
+                    && self.look_ahead(1, |t| t.is_ident() || t.is_lifetime())
+                {
+                    // Add `>` to the list of expected tokens.
+                    self.check(&token::Gt);
+                    // Handle `,` to `;` substitution
+                    let mut err = self.unexpected().unwrap_err();
+                    self.bump();
+                    err.span_suggestion_verbose(
+                        self.prev_token.span.until(self.token.span),
+                        "use a comma to separate type parameters",
+                        ", ",
+                        Applicability::MachineApplicable,
+                    );
+                    err.emit();
+                    continue;
+                }
+                if !self.token.kind.should_end_const_arg() {
+                    if self.handle_ambiguous_unbraced_const_arg(&mut args)? {
+                        // We've managed to (partially) recover, so continue trying to parse
+                        // arguments.
+                        continue;
+                    }
+                }
+                break;
+            }
+        }
+        Ok(args)
+    }
+
+    /// Parses a single argument in the angle arguments `<...>` of a path segment.
+    fn parse_angle_arg(
+        &mut self,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, Option<AngleBracketedArg>> {
+        let lo = self.token.span;
+        let arg = self.parse_generic_arg(ty_generics)?;
+        match arg {
+            Some(arg) => {
+                // we are using noexpect here because we first want to find out if either `=` or `:`
+                // is present and then use that info to push the other token onto the tokens list
+                let separated =
+                    self.check_noexpect(&token::Colon) || self.check_noexpect(&token::Eq);
+                if separated && (self.check(&token::Colon) | self.check(&token::Eq)) {
+                    let arg_span = arg.span();
+                    let (binder, ident, gen_args) = match self.get_ident_from_generic_arg(&arg) {
+                        Ok(ident_gen_args) => ident_gen_args,
+                        Err(()) => return Ok(Some(AngleBracketedArg::Arg(arg))),
+                    };
+                    if binder {
+                        // FIXME(compiler-errors): this could be improved by suggesting lifting
+                        // this up to the trait, at least before this becomes real syntax.
+                        // e.g. `Trait<for<'a> Assoc = Ty>` -> `for<'a> Trait<Assoc = Ty>`
+                        return Err(self.dcx().struct_span_err(
+                            arg_span,
+                            "`for<...>` is not allowed on associated type bounds",
+                        ));
+                    }
+                    let kind = if self.eat(&token::Colon) {
+                        // Parse associated type constraint bound.
+
+                        let bounds = self.parse_generic_bounds()?;
+                        AssocConstraintKind::Bound { bounds }
+                    } else if self.eat(&token::Eq) {
+                        self.parse_assoc_equality_term(
+                            ident,
+                            gen_args.as_ref(),
+                            self.prev_token.span,
+                        )?
+                    } else {
+                        unreachable!();
+                    };
+
+                    let span = lo.to(self.prev_token.span);
+                    // Gate associated type bounds, e.g., `Iterator<Item: Ord>`.
+                    if let AssocConstraintKind::Bound { .. } = kind {
+                        if let Some(ast::GenericArgs::Parenthesized(args)) = &gen_args
+                            && args.inputs.is_empty()
+                            && matches!(args.output, ast::FnRetTy::Default(..))
+                        {
+                            self.psess.gated_spans.gate(sym::return_type_notation, span);
+                        }
+                    }
+                    let constraint =
+                        AssocConstraint { id: ast::DUMMY_NODE_ID, ident, gen_args, kind, span };
+                    Ok(Some(AngleBracketedArg::Constraint(constraint)))
+                } else {
+                    // we only want to suggest `:` and `=` in contexts where the previous token
+                    // is an ident and the current token or the next token is an ident
+                    if self.prev_token.is_ident()
+                        && (self.token.is_ident() || self.look_ahead(1, |token| token.is_ident()))
+                    {
+                        self.check(&token::Colon);
+                        self.check(&token::Eq);
+                    }
+                    Ok(Some(AngleBracketedArg::Arg(arg)))
+                }
+            }
+            _ => Ok(None),
+        }
+    }
+
+    /// Parse the term to the right of an associated item equality constraint.
+    ///
+    /// That is, parse `$term` in `Item = $term` where `$term` is a type or
+    /// a const expression (wrapped in curly braces if complex).
+    fn parse_assoc_equality_term(
+        &mut self,
+        ident: Ident,
+        gen_args: Option<&GenericArgs>,
+        eq: Span,
+    ) -> PResult<'a, AssocConstraintKind> {
+        let arg = self.parse_generic_arg(None)?;
+        let span = ident.span.to(self.prev_token.span);
+        let term = match arg {
+            Some(GenericArg::Type(ty)) => ty.into(),
+            Some(GenericArg::Const(c)) => {
+                self.psess.gated_spans.gate(sym::associated_const_equality, span);
+                c.into()
+            }
+            Some(GenericArg::Lifetime(lt)) => {
+                let guar = self.dcx().emit_err(errors::LifetimeInEqConstraint {
+                    span: lt.ident.span,
+                    lifetime: lt.ident,
+                    binding_label: span,
+                    colon_sugg: gen_args
+                        .map_or(ident.span, |args| args.span())
+                        .between(lt.ident.span),
+                });
+                self.mk_ty(lt.ident.span, ast::TyKind::Err(guar)).into()
+            }
+            None => {
+                let after_eq = eq.shrink_to_hi();
+                let before_next = self.token.span.shrink_to_lo();
+                let mut err = self
+                    .dcx()
+                    .struct_span_err(after_eq.to(before_next), "missing type to the right of `=`");
+                if matches!(self.token.kind, token::Comma | token::Gt) {
+                    err.span_suggestion(
+                        self.psess.source_map().next_point(eq).to(before_next),
+                        "to constrain the associated type, add a type after `=`",
+                        " TheType",
+                        Applicability::HasPlaceholders,
+                    );
+                    err.span_suggestion(
+                        eq.to(before_next),
+                        format!("remove the `=` if `{ident}` is a type"),
+                        "",
+                        Applicability::MaybeIncorrect,
+                    )
+                } else {
+                    err.span_label(
+                        self.token.span,
+                        format!("expected type, found {}", super::token_descr(&self.token)),
+                    )
+                };
+                return Err(err);
+            }
+        };
+        Ok(AssocConstraintKind::Equality { term })
+    }
+
+    /// We do not permit arbitrary expressions as const arguments. They must be one of:
+    /// - An expression surrounded in `{}`.
+    /// - A literal.
+    /// - A numeric literal prefixed by `-`.
+    /// - A single-segment path.
+    pub(super) fn expr_is_valid_const_arg(&self, expr: &P<rustc_ast::Expr>) -> bool {
+        match &expr.kind {
+            ast::ExprKind::Block(_, _)
+            | ast::ExprKind::Lit(_)
+            | ast::ExprKind::IncludedBytes(..) => true,
+            ast::ExprKind::Unary(ast::UnOp::Neg, expr) => {
+                matches!(expr.kind, ast::ExprKind::Lit(_))
+            }
+            // We can only resolve single-segment paths at the moment, because multi-segment paths
+            // require type-checking: see `visit_generic_arg` in `src/librustc_resolve/late.rs`.
+            ast::ExprKind::Path(None, path)
+                if path.segments.len() == 1 && path.segments[0].args.is_none() =>
+            {
+                true
+            }
+            _ => false,
+        }
+    }
+
+    /// Parse a const argument, e.g. `<3>`. It is assumed the angle brackets will be parsed by
+    /// the caller.
+    pub(super) fn parse_const_arg(&mut self) -> PResult<'a, AnonConst> {
+        // Parse const argument.
+        let value = if let token::OpenDelim(Delimiter::Brace) = self.token.kind {
+            self.parse_expr_block(None, self.token.span, BlockCheckMode::Default)?
+        } else {
+            self.handle_unambiguous_unbraced_const_arg()?
+        };
+        Ok(AnonConst { id: ast::DUMMY_NODE_ID, value })
+    }
+
+    /// Parse a generic argument in a path segment.
+    /// This does not include constraints, e.g., `Item = u8`, which is handled in `parse_angle_arg`.
+    pub(super) fn parse_generic_arg(
+        &mut self,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, Option<GenericArg>> {
+        let start = self.token.span;
+        let arg = if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
+            // Parse lifetime argument.
+            GenericArg::Lifetime(self.expect_lifetime())
+        } else if self.check_const_arg() {
+            // Parse const argument.
+            GenericArg::Const(self.parse_const_arg()?)
+        } else if self.check_type() {
+            // Parse type argument.
+
+            // Proactively create a parser snapshot enabling us to rewind and try to reparse the
+            // input as a const expression in case we fail to parse a type. If we successfully
+            // do so, we will report an error that it needs to be wrapped in braces.
+            let mut snapshot = None;
+            if self.may_recover() && self.token.can_begin_expr() {
+                snapshot = Some(self.create_snapshot_for_diagnostic());
+            }
+
+            match self.parse_ty() {
+                Ok(ty) => {
+                    // Since the type parser recovers from some malformed slice and array types and
+                    // successfully returns a type, we need to look for `TyKind::Err`s in the
+                    // type to determine if error recovery has occurred and if the input is not a
+                    // syntactically valid type after all.
+                    if let ast::TyKind::Slice(inner_ty) | ast::TyKind::Array(inner_ty, _) = &ty.kind
+                        && let ast::TyKind::Err(_) = inner_ty.kind
+                        && let Some(snapshot) = snapshot
+                        && let Some(expr) =
+                            self.recover_unbraced_const_arg_that_can_begin_ty(snapshot)
+                    {
+                        return Ok(Some(
+                            self.dummy_const_arg_needs_braces(
+                                self.dcx()
+                                    .struct_span_err(expr.span, "invalid const generic expression"),
+                                expr.span,
+                            ),
+                        ));
+                    }
+
+                    GenericArg::Type(ty)
+                }
+                Err(err) => {
+                    if let Some(snapshot) = snapshot
+                        && let Some(expr) =
+                            self.recover_unbraced_const_arg_that_can_begin_ty(snapshot)
+                    {
+                        return Ok(Some(self.dummy_const_arg_needs_braces(err, expr.span)));
+                    }
+                    // Try to recover from possible `const` arg without braces.
+                    return self.recover_const_arg(start, err).map(Some);
+                }
+            }
+        } else if self.token.is_keyword(kw::Const) {
+            return self.recover_const_param_declaration(ty_generics);
+        } else {
+            // Fall back by trying to parse a const-expr expression. If we successfully do so,
+            // then we should report an error that it needs to be wrapped in braces.
+            let snapshot = self.create_snapshot_for_diagnostic();
+            match self.parse_expr_res(Restrictions::CONST_EXPR, None) {
+                Ok(expr) => {
+                    return Ok(Some(self.dummy_const_arg_needs_braces(
+                        self.dcx().struct_span_err(expr.span, "invalid const generic expression"),
+                        expr.span,
+                    )));
+                }
+                Err(err) => {
+                    self.restore_snapshot(snapshot);
+                    err.cancel();
+                    return Ok(None);
+                }
+            }
+        };
+        Ok(Some(arg))
+    }
+
+    /// Given a arg inside of generics, we try to destructure it as if it were the LHS in
+    /// `LHS = ...`, i.e. an associated type binding.
+    /// This returns a bool indicating if there are any `for<'a, 'b>` binder args, the
+    /// identifier, and any GAT arguments.
+    fn get_ident_from_generic_arg(
+        &self,
+        gen_arg: &GenericArg,
+    ) -> Result<(bool, Ident, Option<GenericArgs>), ()> {
+        if let GenericArg::Type(ty) = gen_arg {
+            if let ast::TyKind::Path(qself, path) = &ty.kind
+                && qself.is_none()
+                && let [seg] = path.segments.as_slice()
+            {
+                return Ok((false, seg.ident, seg.args.as_deref().cloned()));
+            } else if let ast::TyKind::TraitObject(bounds, ast::TraitObjectSyntax::None) = &ty.kind
+                && let [ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifiers::NONE)] =
+                    bounds.as_slice()
+                && let [seg] = trait_ref.trait_ref.path.segments.as_slice()
+            {
+                return Ok((true, seg.ident, seg.args.as_deref().cloned()));
+            }
+        }
+        Err(())
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
new file mode 100644
index 00000000000..7424fbea9b0
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -0,0 +1,853 @@
+use super::attr::InnerAttrForbiddenReason;
+use super::diagnostics::AttemptLocalParseRecovery;
+use super::expr::LhsExpr;
+use super::pat::{PatternLocation, RecoverComma};
+use super::path::PathStyle;
+use super::TrailingToken;
+use super::{
+    AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
+};
+use crate::errors;
+use crate::maybe_whole;
+
+use crate::errors::MalformedLoopLabel;
+use ast::Label;
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, TokenKind};
+use rustc_ast::util::classify;
+use rustc_ast::{AttrStyle, AttrVec, LocalKind, MacCall, MacCallStmt, MacStmtStyle};
+use rustc_ast::{Block, BlockCheckMode, Expr, ExprKind, HasAttrs, Local, Recovered, Stmt};
+use rustc_ast::{StmtKind, DUMMY_NODE_ID};
+use rustc_errors::{Applicability, Diag, PResult};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{BytePos, ErrorGuaranteed, Span};
+
+use std::borrow::Cow;
+use std::mem;
+use thin_vec::{thin_vec, ThinVec};
+
+impl<'a> Parser<'a> {
+    /// Parses a statement. This stops just before trailing semicolons on everything but items.
+    /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
+    // Public for rustfmt usage.
+    pub fn parse_stmt(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<Stmt>> {
+        Ok(self.parse_stmt_without_recovery(false, force_collect).unwrap_or_else(|e| {
+            e.emit();
+            self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
+            None
+        }))
+    }
+
+    /// If `force_collect` is [`ForceCollect::Yes`], forces collection of tokens regardless of
+    /// whether or not we have attributes.
+    // Public for `cfg_eval` macro expansion.
+    pub fn parse_stmt_without_recovery(
+        &mut self,
+        capture_semi: bool,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Option<Stmt>> {
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+
+        maybe_whole!(self, NtStmt, |stmt| {
+            stmt.visit_attrs(|stmt_attrs| {
+                attrs.prepend_to_nt_inner(stmt_attrs);
+            });
+            Some(stmt.into_inner())
+        });
+
+        if self.token.is_keyword(kw::Mut) && self.is_keyword_ahead(1, &[kw::Let]) {
+            self.bump();
+            let mut_let_span = lo.to(self.token.span);
+            self.dcx().emit_err(errors::InvalidVariableDeclaration {
+                span: mut_let_span,
+                sub: errors::InvalidVariableDeclarationSub::SwitchMutLetOrder(mut_let_span),
+            });
+        }
+
+        Ok(Some(if self.token.is_keyword(kw::Let) {
+            self.parse_local_mk(lo, attrs, capture_semi, force_collect)?
+        } else if self.is_kw_followed_by_ident(kw::Mut) && self.may_recover() {
+            self.recover_stmt_local_after_let(
+                lo,
+                attrs,
+                errors::InvalidVariableDeclarationSub::MissingLet,
+            )?
+        } else if self.is_kw_followed_by_ident(kw::Auto) && self.may_recover() {
+            self.bump(); // `auto`
+            self.recover_stmt_local_after_let(
+                lo,
+                attrs,
+                errors::InvalidVariableDeclarationSub::UseLetNotAuto,
+            )?
+        } else if self.is_kw_followed_by_ident(sym::var) && self.may_recover() {
+            self.bump(); // `var`
+            self.recover_stmt_local_after_let(
+                lo,
+                attrs,
+                errors::InvalidVariableDeclarationSub::UseLetNotVar,
+            )?
+        } else if self.check_path()
+            && !self.token.is_qpath_start()
+            && !self.is_path_start_item()
+            && !self.is_builtin()
+        {
+            // We have avoided contextual keywords like `union`, items with `crate` visibility,
+            // or `auto trait` items. We aim to parse an arbitrary path `a::b` but not something
+            // that starts like a path (1 token), but it fact not a path.
+            // Also, we avoid stealing syntax from `parse_item_`.
+            match force_collect {
+                ForceCollect::Yes => {
+                    self.collect_tokens_no_attrs(|this| this.parse_stmt_path_start(lo, attrs))?
+                }
+                ForceCollect::No => match self.parse_stmt_path_start(lo, attrs) {
+                    Ok(stmt) => stmt,
+                    Err(mut err) => {
+                        self.suggest_add_missing_let_for_stmt(&mut err);
+                        return Err(err);
+                    }
+                },
+            }
+        } else if let Some(item) = self.parse_item_common(
+            attrs.clone(),
+            false,
+            true,
+            FnParseMode { req_name: |_| true, req_body: true },
+            force_collect,
+        )? {
+            // FIXME: Bad copy of attrs
+            self.mk_stmt(lo.to(item.span), StmtKind::Item(P(item)))
+        } else if self.eat(&token::Semi) {
+            // Do not attempt to parse an expression if we're done here.
+            self.error_outer_attrs(attrs);
+            self.mk_stmt(lo, StmtKind::Empty)
+        } else if self.token != token::CloseDelim(Delimiter::Brace) {
+            // Remainder are line-expr stmts.
+            let e = match force_collect {
+                ForceCollect::Yes => self.collect_tokens_no_attrs(|this| {
+                    this.parse_expr_res(Restrictions::STMT_EXPR, Some(attrs))
+                })?,
+                ForceCollect::No => self.parse_expr_res(Restrictions::STMT_EXPR, Some(attrs))?,
+            };
+            if matches!(e.kind, ExprKind::Assign(..)) && self.eat_keyword(kw::Else) {
+                let bl = self.parse_block()?;
+                // Destructuring assignment ... else.
+                // This is not allowed, but point it out in a nice way.
+                self.dcx().emit_err(errors::AssignmentElseNotAllowed { span: e.span.to(bl.span) });
+            }
+            self.mk_stmt(lo.to(e.span), StmtKind::Expr(e))
+        } else {
+            self.error_outer_attrs(attrs);
+            return Ok(None);
+        }))
+    }
+
+    fn parse_stmt_path_start(&mut self, lo: Span, attrs: AttrWrapper) -> PResult<'a, Stmt> {
+        let stmt = self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
+            let path = this.parse_path(PathStyle::Expr)?;
+
+            if this.eat(&token::Not) {
+                let stmt_mac = this.parse_stmt_mac(lo, attrs, path)?;
+                if this.token == token::Semi {
+                    return Ok((stmt_mac, TrailingToken::Semi));
+                } else {
+                    return Ok((stmt_mac, TrailingToken::None));
+                }
+            }
+
+            let expr = if this.eat(&token::OpenDelim(Delimiter::Brace)) {
+                this.parse_expr_struct(None, path, true)?
+            } else {
+                let hi = this.prev_token.span;
+                this.mk_expr(lo.to(hi), ExprKind::Path(None, path))
+            };
+
+            let expr = this.with_res(Restrictions::STMT_EXPR, |this| {
+                this.parse_expr_dot_or_call_with(expr, lo, attrs)
+            })?;
+            // `DUMMY_SP` will get overwritten later in this function
+            Ok((this.mk_stmt(rustc_span::DUMMY_SP, StmtKind::Expr(expr)), TrailingToken::None))
+        })?;
+
+        if let StmtKind::Expr(expr) = stmt.kind {
+            // Perform this outside of the `collect_tokens_trailing_token` closure,
+            // since our outer attributes do not apply to this part of the expression
+            let expr = self.with_res(Restrictions::STMT_EXPR, |this| {
+                this.parse_expr_assoc_with(
+                    0,
+                    LhsExpr::AlreadyParsed { expr, starts_statement: true },
+                )
+            })?;
+            Ok(self.mk_stmt(lo.to(self.prev_token.span), StmtKind::Expr(expr)))
+        } else {
+            Ok(stmt)
+        }
+    }
+
+    /// Parses a statement macro `mac!(args)` provided a `path` representing `mac`.
+    /// At this point, the `!` token after the path has already been eaten.
+    fn parse_stmt_mac(&mut self, lo: Span, attrs: AttrVec, path: ast::Path) -> PResult<'a, Stmt> {
+        let args = self.parse_delim_args()?;
+        let hi = self.prev_token.span;
+
+        let style = match args.delim {
+            Delimiter::Brace => MacStmtStyle::Braces,
+            _ => MacStmtStyle::NoBraces,
+        };
+
+        let mac = P(MacCall { path, args });
+
+        let kind = if (style == MacStmtStyle::Braces
+            && self.token != token::Dot
+            && self.token != token::Question)
+            || self.token == token::Semi
+            || self.token == token::Eof
+        {
+            StmtKind::MacCall(P(MacCallStmt { mac, style, attrs, tokens: None }))
+        } else {
+            // Since none of the above applied, this is an expression statement macro.
+            let e = self.mk_expr(lo.to(hi), ExprKind::MacCall(mac));
+            let e = self.maybe_recover_from_bad_qpath(e)?;
+            let e = self.parse_expr_dot_or_call_with(e, lo, attrs)?;
+            let e = self.parse_expr_assoc_with(
+                0,
+                LhsExpr::AlreadyParsed { expr: e, starts_statement: false },
+            )?;
+            StmtKind::Expr(e)
+        };
+        Ok(self.mk_stmt(lo.to(hi), kind))
+    }
+
+    /// Error on outer attributes in this context.
+    /// Also error if the previous token was a doc comment.
+    fn error_outer_attrs(&self, attrs: AttrWrapper) {
+        if !attrs.is_empty()
+            && let attrs @ [.., last] = &*attrs.take_for_recovery(self.psess)
+        {
+            if last.is_doc_comment() {
+                self.dcx().emit_err(errors::DocCommentDoesNotDocumentAnything {
+                    span: last.span,
+                    missing_comma: None,
+                });
+            } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
+                self.dcx().emit_err(errors::ExpectedStatementAfterOuterAttr { span: last.span });
+            }
+        }
+    }
+
+    fn recover_stmt_local_after_let(
+        &mut self,
+        lo: Span,
+        attrs: AttrWrapper,
+        subdiagnostic: fn(Span) -> errors::InvalidVariableDeclarationSub,
+    ) -> PResult<'a, Stmt> {
+        let stmt =
+            self.collect_tokens_trailing_token(attrs, ForceCollect::Yes, |this, attrs| {
+                let local = this.parse_local(attrs)?;
+                // FIXME - maybe capture semicolon in recovery?
+                Ok((
+                    this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
+                    TrailingToken::None,
+                ))
+            })?;
+        self.dcx()
+            .emit_err(errors::InvalidVariableDeclaration { span: lo, sub: subdiagnostic(lo) });
+        Ok(stmt)
+    }
+
+    fn parse_local_mk(
+        &mut self,
+        lo: Span,
+        attrs: AttrWrapper,
+        capture_semi: bool,
+        force_collect: ForceCollect,
+    ) -> PResult<'a, Stmt> {
+        self.collect_tokens_trailing_token(attrs, force_collect, |this, attrs| {
+            this.expect_keyword(kw::Let)?;
+            let local = this.parse_local(attrs)?;
+            let trailing = if capture_semi && this.token.kind == token::Semi {
+                TrailingToken::Semi
+            } else {
+                TrailingToken::None
+            };
+            Ok((this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)), trailing))
+        })
+    }
+
+    /// Parses a local variable declaration.
+    fn parse_local(&mut self, attrs: AttrVec) -> PResult<'a, P<Local>> {
+        let lo = self.prev_token.span;
+
+        if self.token.is_keyword(kw::Const) && self.look_ahead(1, |t| t.is_ident()) {
+            self.dcx().emit_err(errors::ConstLetMutuallyExclusive { span: lo.to(self.token.span) });
+            self.bump();
+        }
+
+        let (pat, colon) =
+            self.parse_pat_before_ty(None, RecoverComma::Yes, PatternLocation::LetBinding)?;
+
+        let (err, ty, colon_sp) = if colon {
+            // Save the state of the parser before parsing type normally, in case there is a `:`
+            // instead of an `=` typo.
+            let parser_snapshot_before_type = self.clone();
+            let colon_sp = self.prev_token.span;
+            match self.parse_ty() {
+                Ok(ty) => (None, Some(ty), Some(colon_sp)),
+                Err(mut err) => {
+                    err.span_label(
+                        colon_sp,
+                        format!(
+                            "while parsing the type for {}",
+                            pat.descr()
+                                .map_or_else(|| "the binding".to_string(), |n| format!("`{n}`"))
+                        ),
+                    );
+                    // we use noexpect here because we don't actually expect Eq to be here
+                    // but we are still checking for it in order to be able to handle it if
+                    // it is there
+                    let err = if self.check_noexpect(&token::Eq) {
+                        err.emit();
+                        None
+                    } else {
+                        // Rewind to before attempting to parse the type and continue parsing.
+                        let parser_snapshot_after_type =
+                            mem::replace(self, parser_snapshot_before_type);
+                        Some((parser_snapshot_after_type, colon_sp, err))
+                    };
+                    (err, None, Some(colon_sp))
+                }
+            }
+        } else {
+            (None, None, None)
+        };
+        let init = match (self.parse_initializer(err.is_some()), err) {
+            (Ok(init), None) => {
+                // init parsed, ty parsed
+                init
+            }
+            (Ok(init), Some((_, colon_sp, mut err))) => {
+                // init parsed, ty error
+                // Could parse the type as if it were the initializer, it is likely there was a
+                // typo in the code: `:` instead of `=`. Add suggestion and emit the error.
+                err.span_suggestion_short(
+                    colon_sp,
+                    "use `=` if you meant to assign",
+                    " =",
+                    Applicability::MachineApplicable,
+                );
+                err.emit();
+                // As this was parsed successfully, continue as if the code has been fixed for the
+                // rest of the file. It will still fail due to the emitted error, but we avoid
+                // extra noise.
+                init
+            }
+            (Err(init_err), Some((snapshot, _, ty_err))) => {
+                // init error, ty error
+                init_err.cancel();
+                // Couldn't parse the type nor the initializer, only raise the type error and
+                // return to the parser state before parsing the type as the initializer.
+                // let x: <parse_error>;
+                *self = snapshot;
+                return Err(ty_err);
+            }
+            (Err(err), None) => {
+                // init error, ty parsed
+                // Couldn't parse the initializer and we're not attempting to recover a failed
+                // parse of the type, return the error.
+                return Err(err);
+            }
+        };
+        let kind = match init {
+            None => LocalKind::Decl,
+            Some(init) => {
+                if self.eat_keyword(kw::Else) {
+                    if self.token.is_keyword(kw::If) {
+                        // `let...else if`. Emit the same error that `parse_block()` would,
+                        // but explicitly point out that this pattern is not allowed.
+                        let msg = "conditional `else if` is not supported for `let...else`";
+                        return Err(self.error_block_no_opening_brace_msg(Cow::from(msg)));
+                    }
+                    let els = self.parse_block()?;
+                    self.check_let_else_init_bool_expr(&init);
+                    self.check_let_else_init_trailing_brace(&init);
+                    LocalKind::InitElse(init, els)
+                } else {
+                    LocalKind::Init(init)
+                }
+            }
+        };
+        let hi = if self.token == token::Semi { self.token.span } else { self.prev_token.span };
+        Ok(P(ast::Local {
+            ty,
+            pat,
+            kind,
+            id: DUMMY_NODE_ID,
+            span: lo.to(hi),
+            colon_sp,
+            attrs,
+            tokens: None,
+        }))
+    }
+
+    fn check_let_else_init_bool_expr(&self, init: &ast::Expr) {
+        if let ast::ExprKind::Binary(op, ..) = init.kind {
+            if op.node.is_lazy() {
+                self.dcx().emit_err(errors::InvalidExpressionInLetElse {
+                    span: init.span,
+                    operator: op.node.as_str(),
+                    sugg: errors::WrapInParentheses::Expression {
+                        left: init.span.shrink_to_lo(),
+                        right: init.span.shrink_to_hi(),
+                    },
+                });
+            }
+        }
+    }
+
+    fn check_let_else_init_trailing_brace(&self, init: &ast::Expr) {
+        if let Some(trailing) = classify::expr_trailing_brace(init) {
+            let sugg = match &trailing.kind {
+                ExprKind::MacCall(mac) => errors::WrapInParentheses::MacroArgs {
+                    left: mac.args.dspan.open,
+                    right: mac.args.dspan.close,
+                },
+                _ => errors::WrapInParentheses::Expression {
+                    left: trailing.span.shrink_to_lo(),
+                    right: trailing.span.shrink_to_hi(),
+                },
+            };
+            self.dcx().emit_err(errors::InvalidCurlyInLetElse {
+                span: trailing.span.with_lo(trailing.span.hi() - BytePos(1)),
+                sugg,
+            });
+        }
+    }
+
+    /// Parses the RHS of a local variable declaration (e.g., `= 14;`).
+    fn parse_initializer(&mut self, eq_optional: bool) -> PResult<'a, Option<P<Expr>>> {
+        let eq_consumed = match self.token.kind {
+            token::BinOpEq(..) => {
+                // Recover `let x <op>= 1` as `let x = 1`
+                self.dcx()
+                    .emit_err(errors::CompoundAssignmentExpressionInLet { span: self.token.span });
+                self.bump();
+                true
+            }
+            _ => self.eat(&token::Eq),
+        };
+
+        Ok(if eq_consumed || eq_optional { Some(self.parse_expr()?) } else { None })
+    }
+
+    /// Parses a block. No inner attributes are allowed.
+    pub fn parse_block(&mut self) -> PResult<'a, P<Block>> {
+        let (attrs, block) = self.parse_inner_attrs_and_block()?;
+        if let [.., last] = &*attrs {
+            self.error_on_forbidden_inner_attr(
+                last.span,
+                super::attr::InnerAttrPolicy::Forbidden(Some(
+                    InnerAttrForbiddenReason::InCodeBlock,
+                )),
+            );
+        }
+        Ok(block)
+    }
+
+    fn error_block_no_opening_brace_msg(&mut self, msg: Cow<'static, str>) -> Diag<'a> {
+        let sp = self.token.span;
+        let mut e = self.dcx().struct_span_err(sp, msg);
+        let do_not_suggest_help = self.token.is_keyword(kw::In) || self.token == token::Colon;
+
+        // Check to see if the user has written something like
+        //
+        //    if (cond)
+        //      bar;
+        //
+        // which is valid in other languages, but not Rust.
+        match self.parse_stmt_without_recovery(false, ForceCollect::No) {
+            // If the next token is an open brace, e.g., we have:
+            //
+            //     if expr other_expr {
+            //        ^    ^          ^- lookahead(1) is a brace
+            //        |    |- current token is not "else"
+            //        |- (statement we just parsed)
+            //
+            // the place-inside-a-block suggestion would be more likely wrong than right.
+            //
+            // FIXME(compiler-errors): this should probably parse an arbitrary expr and not
+            // just lookahead one token, so we can see if there's a brace after _that_,
+            // since we want to protect against:
+            //     `if 1 1 + 1 {` being suggested as  `if { 1 } 1 + 1 {`
+            //                                            +   +
+            Ok(Some(_))
+                if (!self.token.is_keyword(kw::Else)
+                    && self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Brace)))
+                    || do_not_suggest_help => {}
+            // Do not suggest `if foo println!("") {;}` (as would be seen in test for #46836).
+            Ok(Some(Stmt { kind: StmtKind::Empty, .. })) => {}
+            Ok(Some(stmt)) => {
+                let stmt_own_line = self.psess.source_map().is_line_before_span_empty(sp);
+                let stmt_span = if stmt_own_line && self.eat(&token::Semi) {
+                    // Expand the span to include the semicolon.
+                    stmt.span.with_hi(self.prev_token.span.hi())
+                } else {
+                    stmt.span
+                };
+                e.multipart_suggestion(
+                    "try placing this code inside a block",
+                    vec![
+                        (stmt_span.shrink_to_lo(), "{ ".to_string()),
+                        (stmt_span.shrink_to_hi(), " }".to_string()),
+                    ],
+                    // Speculative; has been misleading in the past (#46836).
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            Err(e) => {
+                self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
+                e.cancel();
+            }
+            _ => {}
+        }
+        e.span_label(sp, "expected `{`");
+        e
+    }
+
+    fn error_block_no_opening_brace<T>(&mut self) -> PResult<'a, T> {
+        let tok = super::token_descr(&self.token);
+        let msg = format!("expected `{{`, found {tok}");
+        Err(self.error_block_no_opening_brace_msg(Cow::from(msg)))
+    }
+
+    /// Parses a block. Inner attributes are allowed.
+    pub(super) fn parse_inner_attrs_and_block(&mut self) -> PResult<'a, (AttrVec, P<Block>)> {
+        self.parse_block_common(self.token.span, BlockCheckMode::Default, true)
+    }
+
+    /// Parses a block. Inner attributes are allowed.
+    pub(super) fn parse_block_common(
+        &mut self,
+        lo: Span,
+        blk_mode: BlockCheckMode,
+        can_be_struct_literal: bool,
+    ) -> PResult<'a, (AttrVec, P<Block>)> {
+        maybe_whole!(self, NtBlock, |block| (AttrVec::new(), block));
+
+        let maybe_ident = self.prev_token.clone();
+        self.maybe_recover_unexpected_block_label();
+        if !self.eat(&token::OpenDelim(Delimiter::Brace)) {
+            return self.error_block_no_opening_brace();
+        }
+
+        let attrs = self.parse_inner_attributes()?;
+        let tail = match self.maybe_suggest_struct_literal(
+            lo,
+            blk_mode,
+            maybe_ident,
+            can_be_struct_literal,
+        ) {
+            Some(tail) => tail?,
+            None => self.parse_block_tail(lo, blk_mode, AttemptLocalParseRecovery::Yes)?,
+        };
+        Ok((attrs, tail))
+    }
+
+    /// Parses the rest of a block expression or function body.
+    /// Precondition: already parsed the '{'.
+    pub(crate) fn parse_block_tail(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode,
+        recover: AttemptLocalParseRecovery,
+    ) -> PResult<'a, P<Block>> {
+        let mut stmts = ThinVec::new();
+        let mut snapshot = None;
+        while !self.eat(&token::CloseDelim(Delimiter::Brace)) {
+            if self.token == token::Eof {
+                break;
+            }
+            if self.is_vcs_conflict_marker(&TokenKind::BinOp(token::Shl), &TokenKind::Lt) {
+                // Account for `<<<<<<<` diff markers. We can't proactively error here because
+                // that can be a valid path start, so we snapshot and reparse only we've
+                // encountered another parse error.
+                snapshot = Some(self.create_snapshot_for_diagnostic());
+            }
+            let stmt = match self.parse_full_stmt(recover) {
+                Err(mut err) if recover.yes() => {
+                    if let Some(ref mut snapshot) = snapshot {
+                        snapshot.recover_vcs_conflict_marker();
+                    }
+                    if self.token == token::Colon {
+                        // if a previous and next token of the current one is
+                        // integer literal (e.g. `1:42`), it's likely a range
+                        // expression for Pythonistas and we can suggest so.
+                        if self.prev_token.is_integer_lit()
+                            && self.may_recover()
+                            && self.look_ahead(1, |token| token.is_integer_lit())
+                        {
+                            // FIXME(hkmatsumoto): Might be better to trigger
+                            // this only when parsing an index expression.
+                            err.span_suggestion_verbose(
+                                self.token.span,
+                                "you might have meant a range expression",
+                                "..",
+                                Applicability::MaybeIncorrect,
+                            );
+                        } else {
+                            // if next token is following a colon, it's likely a path
+                            // and we can suggest a path separator
+                            self.bump();
+                            if self.token.span.lo() == self.prev_token.span.hi() {
+                                err.span_suggestion_verbose(
+                                    self.prev_token.span,
+                                    "maybe write a path separator here",
+                                    "::",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                            if self.psess.unstable_features.is_nightly_build() {
+                                // FIXME(Nilstrieb): Remove this again after a few months.
+                                err.note("type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>");
+                            }
+                        }
+                    }
+
+                    let guar = err.emit();
+                    self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
+                    Some(self.mk_stmt_err(self.token.span, guar))
+                }
+                Ok(stmt) => stmt,
+                Err(err) => return Err(err),
+            };
+            if let Some(stmt) = stmt {
+                stmts.push(stmt);
+            } else {
+                // Found only `;` or `}`.
+                continue;
+            };
+        }
+        Ok(self.mk_block(stmts, s, lo.to(self.prev_token.span)))
+    }
+
+    /// Parses a statement, including the trailing semicolon.
+    pub fn parse_full_stmt(
+        &mut self,
+        recover: AttemptLocalParseRecovery,
+    ) -> PResult<'a, Option<Stmt>> {
+        // Skip looking for a trailing semicolon when we have an interpolated statement.
+        maybe_whole!(self, NtStmt, |stmt| Some(stmt.into_inner()));
+
+        let Some(mut stmt) = self.parse_stmt_without_recovery(true, ForceCollect::No)? else {
+            return Ok(None);
+        };
+
+        let mut eat_semi = true;
+        let mut add_semi_to_stmt = false;
+
+        match &mut stmt.kind {
+            // Expression without semicolon.
+            StmtKind::Expr(expr)
+                if classify::expr_requires_semi_to_be_stmt(expr)
+                    && !expr.attrs.is_empty()
+                    && ![token::Eof, token::Semi, token::CloseDelim(Delimiter::Brace)]
+                        .contains(&self.token.kind) =>
+            {
+                // The user has written `#[attr] expr` which is unsupported. (#106020)
+                let guar = self.attr_on_non_tail_expr(&expr);
+                // We already emitted an error, so don't emit another type error
+                let sp = expr.span.to(self.prev_token.span);
+                *expr = self.mk_expr_err(sp, guar);
+            }
+
+            // Expression without semicolon.
+            StmtKind::Expr(expr)
+                if self.token != token::Eof && classify::expr_requires_semi_to_be_stmt(expr) =>
+            {
+                // Just check for errors and recover; do not eat semicolon yet.
+
+                let expect_result =
+                    self.expect_one_of(&[], &[token::Semi, token::CloseDelim(Delimiter::Brace)]);
+
+                // Try to both emit a better diagnostic, and avoid further errors by replacing
+                // the `expr` with `ExprKind::Err`.
+                let replace_with_err = 'break_recover: {
+                    match expect_result {
+                        Ok(Recovered::No) => None,
+                        Ok(Recovered::Yes(guar)) => {
+                            // Skip type error to avoid extra errors.
+                            Some(guar)
+                        }
+                        Err(e) => {
+                            if self.recover_colon_as_semi() {
+                                // recover_colon_as_semi has already emitted a nicer error.
+                                e.delay_as_bug();
+                                add_semi_to_stmt = true;
+                                eat_semi = false;
+
+                                break 'break_recover None;
+                            }
+
+                            match &expr.kind {
+                                ExprKind::Path(None, ast::Path { segments, .. })
+                                    if segments.len() == 1 =>
+                                {
+                                    if self.token == token::Colon
+                                        && self.look_ahead(1, |token| {
+                                            token.is_whole_block()
+                                                || matches!(
+                                                    token.kind,
+                                                    token::Ident(
+                                                        kw::For | kw::Loop | kw::While,
+                                                        token::IdentIsRaw::No
+                                                    ) | token::OpenDelim(Delimiter::Brace)
+                                                )
+                                        })
+                                    {
+                                        let snapshot = self.create_snapshot_for_diagnostic();
+                                        let label = Label {
+                                            ident: Ident::from_str_and_span(
+                                                &format!("'{}", segments[0].ident),
+                                                segments[0].ident.span,
+                                            ),
+                                        };
+                                        match self.parse_expr_labeled(label, false) {
+                                            Ok(labeled_expr) => {
+                                                e.cancel();
+                                                self.dcx().emit_err(MalformedLoopLabel {
+                                                    span: label.ident.span,
+                                                    correct_label: label.ident,
+                                                });
+                                                *expr = labeled_expr;
+                                                break 'break_recover None;
+                                            }
+                                            Err(err) => {
+                                                err.cancel();
+                                                self.restore_snapshot(snapshot);
+                                            }
+                                        }
+                                    }
+                                }
+                                _ => {}
+                            }
+
+                            let res =
+                                self.check_mistyped_turbofish_with_multiple_type_params(e, expr);
+
+                            Some(if recover.no() {
+                                res?
+                            } else {
+                                res.unwrap_or_else(|e| {
+                                    let guar = e.emit();
+                                    self.recover_stmt();
+                                    guar
+                                })
+                            })
+                        }
+                    }
+                };
+
+                if let Some(guar) = replace_with_err {
+                    // We already emitted an error, so don't emit another type error
+                    let sp = expr.span.to(self.prev_token.span);
+                    *expr = self.mk_expr_err(sp, guar);
+                }
+            }
+            StmtKind::Expr(_) | StmtKind::MacCall(_) => {}
+            StmtKind::Let(local) if let Err(mut e) = self.expect_semi() => {
+                // We might be at the `,` in `let x = foo<bar, baz>;`. Try to recover.
+                match &mut local.kind {
+                    LocalKind::Init(expr) | LocalKind::InitElse(expr, _) => {
+                        self.check_mistyped_turbofish_with_multiple_type_params(e, expr)?;
+                        // We found `foo<bar, baz>`, have we fully recovered?
+                        self.expect_semi()?;
+                    }
+                    LocalKind::Decl => {
+                        if let Some(colon_sp) = local.colon_sp {
+                            e.span_label(
+                                colon_sp,
+                                format!(
+                                    "while parsing the type for {}",
+                                    local.pat.descr().map_or_else(
+                                        || "the binding".to_string(),
+                                        |n| format!("`{n}`")
+                                    )
+                                ),
+                            );
+                            let suggest_eq = if self.token.kind == token::Dot
+                                && let _ = self.bump()
+                                && let mut snapshot = self.create_snapshot_for_diagnostic()
+                                && let Ok(_) = snapshot
+                                    .parse_dot_suffix_expr(
+                                        colon_sp,
+                                        self.mk_expr_err(
+                                            colon_sp,
+                                            self.dcx()
+                                                .delayed_bug("error during `:` -> `=` recovery"),
+                                        ),
+                                    )
+                                    .map_err(Diag::cancel)
+                            {
+                                true
+                            } else if let Some(op) = self.check_assoc_op()
+                                && op.node.can_continue_expr_unambiguously()
+                            {
+                                true
+                            } else {
+                                false
+                            };
+                            if suggest_eq {
+                                e.span_suggestion_short(
+                                    colon_sp,
+                                    "use `=` if you meant to assign",
+                                    "=",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                        }
+                        return Err(e);
+                    }
+                }
+                eat_semi = false;
+            }
+            StmtKind::Empty | StmtKind::Item(_) | StmtKind::Let(_) | StmtKind::Semi(_) => {
+                eat_semi = false
+            }
+        }
+
+        if add_semi_to_stmt || (eat_semi && self.eat(&token::Semi)) {
+            stmt = stmt.add_trailing_semicolon();
+        }
+
+        stmt.span = stmt.span.to(self.prev_token.span);
+        Ok(Some(stmt))
+    }
+
+    pub(super) fn mk_block(
+        &self,
+        stmts: ThinVec<Stmt>,
+        rules: BlockCheckMode,
+        span: Span,
+    ) -> P<Block> {
+        P(Block {
+            stmts,
+            id: DUMMY_NODE_ID,
+            rules,
+            span,
+            tokens: None,
+            could_be_bare_literal: false,
+        })
+    }
+
+    pub(super) fn mk_stmt(&self, span: Span, kind: StmtKind) -> Stmt {
+        Stmt { id: DUMMY_NODE_ID, kind, span }
+    }
+
+    pub(super) fn mk_stmt_err(&self, span: Span, guar: ErrorGuaranteed) -> Stmt {
+        self.mk_stmt(span, StmtKind::Expr(self.mk_expr_err(span, guar)))
+    }
+
+    pub(super) fn mk_block_err(&self, span: Span, guar: ErrorGuaranteed) -> P<Block> {
+        self.mk_block(thin_vec![self.mk_stmt_err(span, guar)], BlockCheckMode::Default, span)
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/tests.rs b/compiler/rustc_parse/src/parser/tests.rs
new file mode 100644
index 00000000000..a31e350541a
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/tests.rs
@@ -0,0 +1,1422 @@
+use crate::parser::ForceCollect;
+use crate::{new_parser_from_source_str, parser::Parser, source_file_to_stream};
+use ast::token::IdentIsRaw;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Token};
+use rustc_ast::tokenstream::{DelimSpacing, DelimSpan, Spacing, TokenStream, TokenTree};
+use rustc_ast::visit;
+use rustc_ast::{self as ast, PatKind};
+use rustc_ast_pretty::pprust::item_to_string;
+use rustc_data_structures::sync::Lrc;
+use rustc_errors::emitter::HumanEmitter;
+use rustc_errors::{DiagCtxt, MultiSpan, PResult};
+use rustc_session::parse::ParseSess;
+use rustc_span::create_default_session_globals_then;
+use rustc_span::source_map::{FilePathMapping, SourceMap};
+use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::{BytePos, FileName, Pos, Span};
+use std::io;
+use std::io::prelude::*;
+use std::iter::Peekable;
+use std::path::{Path, PathBuf};
+use std::str;
+use std::sync::{Arc, Mutex};
+use termcolor::WriteColor;
+
+fn psess() -> ParseSess {
+    ParseSess::new(vec![crate::DEFAULT_LOCALE_RESOURCE, crate::DEFAULT_LOCALE_RESOURCE])
+}
+
+/// Map string to parser (via tts).
+fn string_to_parser(psess: &ParseSess, source_str: String) -> Parser<'_> {
+    new_parser_from_source_str(psess, PathBuf::from("bogofile").into(), source_str)
+}
+
+fn create_test_handler() -> (DiagCtxt, Lrc<SourceMap>, Arc<Mutex<Vec<u8>>>) {
+    let output = Arc::new(Mutex::new(Vec::new()));
+    let source_map = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+    let fallback_bundle = rustc_errors::fallback_fluent_bundle(
+        vec![crate::DEFAULT_LOCALE_RESOURCE, crate::DEFAULT_LOCALE_RESOURCE],
+        false,
+    );
+    let emitter = HumanEmitter::new(Box::new(Shared { data: output.clone() }), fallback_bundle)
+        .sm(Some(source_map.clone()))
+        .diagnostic_width(Some(140));
+    let dcx = DiagCtxt::new(Box::new(emitter));
+    (dcx, source_map, output)
+}
+
+/// Returns the result of parsing the given string via the given callback.
+///
+/// If there are any errors, this will panic.
+fn with_error_checking_parse<'a, T, F>(s: String, psess: &'a ParseSess, f: F) -> T
+where
+    F: FnOnce(&mut Parser<'a>) -> PResult<'a, T>,
+{
+    let mut p = string_to_parser(&psess, s);
+    let x = f(&mut p).unwrap();
+    p.psess.dcx.abort_if_errors();
+    x
+}
+
+/// Verifies that parsing the given string using the given callback will
+/// generate an error that contains the given text.
+fn with_expected_parse_error<T, F>(source_str: &str, expected_output: &str, f: F)
+where
+    F: for<'a> FnOnce(&mut Parser<'a>) -> PResult<'a, T>,
+{
+    let (handler, source_map, output) = create_test_handler();
+    let psess = ParseSess::with_dcx(handler, source_map);
+    let mut p = string_to_parser(&psess, source_str.to_string());
+    let result = f(&mut p);
+    assert!(result.is_ok());
+
+    let bytes = output.lock().unwrap();
+    let actual_output = str::from_utf8(&bytes).unwrap();
+    println!("expected output:\n------\n{}------", expected_output);
+    println!("actual output:\n------\n{}------", actual_output);
+
+    assert!(actual_output.contains(expected_output))
+}
+
+/// Maps a string to tts, using a made-up filename.
+pub(crate) fn string_to_stream(source_str: String) -> TokenStream {
+    let psess = psess();
+    source_file_to_stream(
+        &psess,
+        psess.source_map().new_source_file(PathBuf::from("bogofile").into(), source_str),
+        None,
+    )
+}
+
+/// Parses a string, returns a crate.
+pub(crate) fn string_to_crate(source_str: String) -> ast::Crate {
+    let psess = psess();
+    with_error_checking_parse(source_str, &psess, |p| p.parse_crate_mod())
+}
+
+/// Does the given string match the pattern? whitespace in the first string
+/// may be deleted or replaced with other whitespace to match the pattern.
+/// This function is relatively Unicode-ignorant; fortunately, the careful design
+/// of UTF-8 mitigates this ignorance. It doesn't do NKF-normalization(?).
+pub(crate) fn matches_codepattern(a: &str, b: &str) -> bool {
+    let mut a_iter = a.chars().peekable();
+    let mut b_iter = b.chars().peekable();
+
+    loop {
+        let (a, b) = match (a_iter.peek(), b_iter.peek()) {
+            (None, None) => return true,
+            (None, _) => return false,
+            (Some(&a), None) => {
+                if rustc_lexer::is_whitespace(a) {
+                    break; // Trailing whitespace check is out of loop for borrowck.
+                } else {
+                    return false;
+                }
+            }
+            (Some(&a), Some(&b)) => (a, b),
+        };
+
+        if rustc_lexer::is_whitespace(a) && rustc_lexer::is_whitespace(b) {
+            // Skip whitespace for `a` and `b`.
+            scan_for_non_ws_or_end(&mut a_iter);
+            scan_for_non_ws_or_end(&mut b_iter);
+        } else if rustc_lexer::is_whitespace(a) {
+            // Skip whitespace for `a`.
+            scan_for_non_ws_or_end(&mut a_iter);
+        } else if a == b {
+            a_iter.next();
+            b_iter.next();
+        } else {
+            return false;
+        }
+    }
+
+    // Check if a has *only* trailing whitespace.
+    a_iter.all(rustc_lexer::is_whitespace)
+}
+
+/// Advances the given peekable `Iterator` until it reaches a non-whitespace character.
+fn scan_for_non_ws_or_end<I: Iterator<Item = char>>(iter: &mut Peekable<I>) {
+    while iter.peek().copied().is_some_and(rustc_lexer::is_whitespace) {
+        iter.next();
+    }
+}
+
+/// Identifies a position in the text by the n'th occurrence of a string.
+struct Position {
+    string: &'static str,
+    count: usize,
+}
+
+struct SpanLabel {
+    start: Position,
+    end: Position,
+    label: &'static str,
+}
+
+struct Shared<T: Write> {
+    data: Arc<Mutex<T>>,
+}
+
+impl<T: Write> WriteColor for Shared<T> {
+    fn supports_color(&self) -> bool {
+        false
+    }
+
+    fn set_color(&mut self, _spec: &termcolor::ColorSpec) -> io::Result<()> {
+        Ok(())
+    }
+
+    fn reset(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl<T: Write> Write for Shared<T> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.data.lock().unwrap().write(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.data.lock().unwrap().flush()
+    }
+}
+
+#[allow(rustc::untranslatable_diagnostic)] // no translation needed for tests
+fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
+    create_default_session_globals_then(|| {
+        let (handler, source_map, output) = create_test_handler();
+        source_map.new_source_file(Path::new("test.rs").to_owned().into(), file_text.to_owned());
+
+        let primary_span = make_span(&file_text, &span_labels[0].start, &span_labels[0].end);
+        let mut msp = MultiSpan::from_span(primary_span);
+        for span_label in span_labels {
+            let span = make_span(&file_text, &span_label.start, &span_label.end);
+            msp.push_span_label(span, span_label.label);
+            println!("span: {:?} label: {:?}", span, span_label.label);
+            println!("text: {:?}", source_map.span_to_snippet(span));
+        }
+
+        handler.span_err(msp, "foo");
+
+        assert!(
+            expected_output.chars().next() == Some('\n'),
+            "expected output should begin with newline"
+        );
+        let expected_output = &expected_output[1..];
+
+        let bytes = output.lock().unwrap();
+        let actual_output = str::from_utf8(&bytes).unwrap();
+        println!("expected output:\n------\n{}------", expected_output);
+        println!("actual output:\n------\n{}------", actual_output);
+
+        assert!(expected_output == actual_output)
+    })
+}
+
+fn make_span(file_text: &str, start: &Position, end: &Position) -> Span {
+    let start = make_pos(file_text, start);
+    let end = make_pos(file_text, end) + end.string.len(); // just after matching thing ends
+    assert!(start <= end);
+    Span::with_root_ctxt(BytePos(start as u32), BytePos(end as u32))
+}
+
+fn make_pos(file_text: &str, pos: &Position) -> usize {
+    let mut remainder = file_text;
+    let mut offset = 0;
+    for _ in 0..pos.count {
+        if let Some(n) = remainder.find(&pos.string) {
+            offset += n;
+            remainder = &remainder[n + 1..];
+        } else {
+            panic!("failed to find {} instances of {:?} in {:?}", pos.count, pos.string, file_text);
+        }
+    }
+    offset
+}
+
+#[test]
+fn ends_on_col0() {
+    test_harness(
+        r#"
+fn foo() {
+}
+"#,
+        vec![SpanLabel {
+            start: Position { string: "{", count: 1 },
+            end: Position { string: "}", count: 1 },
+            label: "test",
+        }],
+        r#"
+error: foo
+ --> test.rs:2:10
+  |
+2 |   fn foo() {
+  |  __________^
+3 | | }
+  | |_^ test
+
+"#,
+    );
+}
+
+#[test]
+fn ends_on_col2() {
+    test_harness(
+        r#"
+fn foo() {
+
+
+  }
+"#,
+        vec![SpanLabel {
+            start: Position { string: "{", count: 1 },
+            end: Position { string: "}", count: 1 },
+            label: "test",
+        }],
+        r#"
+error: foo
+ --> test.rs:2:10
+  |
+2 |   fn foo() {
+  |  __________^
+... |
+5 | |   }
+  | |___^ test
+
+"#,
+    );
+}
+#[test]
+fn non_nested() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0
+  X1 Y1
+  X2 Y2
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "Y2", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |      X0 Y0
+  |   ___^__-
+  |  |___|
+  | ||
+4 | ||   X1 Y1
+5 | ||   X2 Y2
+  | ||____^__- `Y` is a good letter too
+  | |_____|
+  |       `X` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn nested() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0
+  Y1 X1
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X1", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "Y1", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |      X0 Y0
+  |   ___^__-
+  |  |___|
+  | ||
+4 | ||   Y1 X1
+  | ||____-__^ `X` is a good letter
+  |  |____|
+  |       `Y` is a good letter too
+
+"#,
+    );
+}
+
+#[test]
+fn different_overlap() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Z1", count: 1 },
+                end: Position { string: "X3", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:6
+  |
+3 |      X0 Y0 Z0
+  |  _______^
+4 | |    X1 Y1 Z1
+  | | _________-
+5 | ||   X2 Y2 Z2
+  | ||____^ `X` is a good letter
+6 |  |   X3 Y3 Z3
+  |  |____- `Y` is a good letter too
+
+"#,
+    );
+}
+
+#[test]
+fn triple_overlap() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "Y2", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+            SpanLabel {
+                start: Position { string: "Z0", count: 1 },
+                end: Position { string: "Z2", count: 1 },
+                label: "`Z` label",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |       X0 Y0 Z0
+  |    ___^__-__-
+  |   |___|__|
+  |  ||___|
+  | |||
+4 | |||   X1 Y1 Z1
+5 | |||   X2 Y2 Z2
+  | |||____^__-__- `Z` label
+  | ||_____|__|
+  | |______|  `Y` is a good letter too
+  |        `X` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn triple_exact_overlap() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X2", count: 1 },
+                label: "`Z` label",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 | /   X0 Y0 Z0
+4 | |   X1 Y1 Z1
+5 | |   X2 Y2 Z2
+  | |    ^
+  | |    |
+  | |    `X` is a good letter
+  | |____`Y` is a good letter too
+  |      `Z` label
+
+"#,
+    );
+}
+
+#[test]
+fn minimum_depth() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "X1", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Y1", count: 1 },
+                end: Position { string: "Z2", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+            SpanLabel {
+                start: Position { string: "X2", count: 1 },
+                end: Position { string: "Y3", count: 1 },
+                label: "`Z`",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:6
+  |
+3 |      X0 Y0 Z0
+  |  _______^
+4 | |    X1 Y1 Z1
+  | | ____^_-
+  | ||____|
+  |  |    `X` is a good letter
+5 |  |   X2 Y2 Z2
+  |  |___-______- `Y` is a good letter too
+  |   ___|
+  |  |
+6 |  |   X3 Y3 Z3
+  |  |_______- `Z`
+
+"#,
+    );
+}
+
+#[test]
+fn non_overlapping() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "X0", count: 1 },
+                end: Position { string: "X1", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Y2", count: 1 },
+                end: Position { string: "Z3", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 | /   X0 Y0 Z0
+4 | |   X1 Y1 Z1
+  | |____^ `X` is a good letter
+5 |     X2 Y2 Z2
+  |  ______-
+6 | |   X3 Y3 Z3
+  | |__________- `Y` is a good letter too
+
+"#,
+    );
+}
+
+#[test]
+fn overlapping_start_and_end() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+  X2 Y2 Z2
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "X1", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Z1", count: 1 },
+                end: Position { string: "Z3", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:6
+  |
+3 |      X0 Y0 Z0
+  |  _______^
+4 | |    X1 Y1 Z1
+  | | ____^____-
+  | ||____|
+  |  |    `X` is a good letter
+5 |  |   X2 Y2 Z2
+6 |  |   X3 Y3 Z3
+  |  |__________- `Y` is a good letter too
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_primary_without_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "`a` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "c", count: 1 },
+                end: Position { string: "c", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:7
+  |
+3 |   a { b { c } d }
+  |   ----^^^^-^^-- `a` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_secondary_without_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "`a` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^-------^^ `a` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_primary_without_message_2() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "`b` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "c", count: 1 },
+                end: Position { string: "c", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:7
+  |
+3 |   a { b { c } d }
+  |   ----^^^^-^^--
+  |       |
+  |       `b` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_secondary_without_message_2() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "`b` is a good letter",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^-------^^
+  |       |
+  |       `b` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_secondary_without_message_3() {
+    test_harness(
+        r#"
+fn foo() {
+  a  bc  d
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "b", count: 1 },
+                label: "`a` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "c", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a  bc  d
+  |   ^^^^----
+  |   |
+  |   `a` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_without_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^-------^^
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_without_message_2() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "",
+            },
+            SpanLabel {
+                start: Position { string: "c", count: 1 },
+                end: Position { string: "c", count: 1 },
+                label: "",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:7
+  |
+3 |   a { b { c } d }
+  |   ----^^^^-^^--
+
+"#,
+    );
+}
+
+#[test]
+fn multiple_labels_with_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "a", count: 1 },
+                end: Position { string: "d", count: 1 },
+                label: "`a` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "b", count: 1 },
+                end: Position { string: "}", count: 1 },
+                label: "`b` is a good letter",
+            },
+        ],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^-------^^
+  |   |   |
+  |   |   `b` is a good letter
+  |   `a` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn single_label_with_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![SpanLabel {
+            start: Position { string: "a", count: 1 },
+            end: Position { string: "d", count: 1 },
+            label: "`a` is a good letter",
+        }],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^^^^^^^^^^ `a` is a good letter
+
+"#,
+    );
+}
+
+#[test]
+fn single_label_without_message() {
+    test_harness(
+        r#"
+fn foo() {
+  a { b { c } d }
+}
+"#,
+        vec![SpanLabel {
+            start: Position { string: "a", count: 1 },
+            end: Position { string: "d", count: 1 },
+            label: "",
+        }],
+        r#"
+error: foo
+ --> test.rs:3:3
+  |
+3 |   a { b { c } d }
+  |   ^^^^^^^^^^^^^
+
+"#,
+    );
+}
+
+#[test]
+fn long_snippet() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+  X1 Y1 Z1
+1
+2
+3
+4
+5
+6
+7
+8
+9
+10
+  X2 Y2 Z2
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "X1", count: 1 },
+                label: "`X` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Z1", count: 1 },
+                end: Position { string: "Z3", count: 1 },
+                label: "`Y` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+  --> test.rs:3:6
+   |
+3  |      X0 Y0 Z0
+   |  _______^
+4  | |    X1 Y1 Z1
+   | | ____^____-
+   | ||____|
+   |  |    `X` is a good letter
+5  |  | 1
+6  |  | 2
+7  |  | 3
+...   |
+15 |  |   X2 Y2 Z2
+16 |  |   X3 Y3 Z3
+   |  |__________- `Y` is a good letter too
+
+"#,
+    );
+}
+
+#[test]
+fn long_snippet_multiple_spans() {
+    test_harness(
+        r#"
+fn foo() {
+  X0 Y0 Z0
+1
+2
+3
+  X1 Y1 Z1
+4
+5
+6
+  X2 Y2 Z2
+7
+8
+9
+10
+  X3 Y3 Z3
+}
+"#,
+        vec![
+            SpanLabel {
+                start: Position { string: "Y0", count: 1 },
+                end: Position { string: "Y3", count: 1 },
+                label: "`Y` is a good letter",
+            },
+            SpanLabel {
+                start: Position { string: "Z1", count: 1 },
+                end: Position { string: "Z2", count: 1 },
+                label: "`Z` is a good letter too",
+            },
+        ],
+        r#"
+error: foo
+  --> test.rs:3:6
+   |
+3  |      X0 Y0 Z0
+   |  _______^
+4  | |  1
+5  | |  2
+6  | |  3
+7  | |    X1 Y1 Z1
+   | | _________-
+8  | || 4
+9  | || 5
+10 | || 6
+11 | ||   X2 Y2 Z2
+   | ||__________- `Z` is a good letter too
+...  |
+15 | |  10
+16 | |    X3 Y3 Z3
+   | |________^ `Y` is a good letter
+
+"#,
+    );
+}
+
+/// Parses an item.
+///
+/// Returns `Ok(Some(item))` when successful, `Ok(None)` when no item was found, and `Err`
+/// when a syntax error occurred.
+fn parse_item_from_source_str(
+    name: FileName,
+    source: String,
+    psess: &ParseSess,
+) -> PResult<'_, Option<P<ast::Item>>> {
+    new_parser_from_source_str(psess, name, source).parse_item(ForceCollect::No)
+}
+
+// Produces a `rustc_span::span`.
+fn sp(a: u32, b: u32) -> Span {
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
+}
+
+/// Parses a string, return an expression.
+fn string_to_expr(source_str: String) -> P<ast::Expr> {
+    with_error_checking_parse(source_str, &psess(), |p| p.parse_expr())
+}
+
+/// Parses a string, returns an item.
+fn string_to_item(source_str: String) -> Option<P<ast::Item>> {
+    with_error_checking_parse(source_str, &psess(), |p| p.parse_item(ForceCollect::No))
+}
+
+#[test]
+fn bad_path_expr_1() {
+    // This should trigger error: expected identifier, found keyword `return`
+    create_default_session_globals_then(|| {
+        with_expected_parse_error(
+            "::abc::def::return",
+            "expected identifier, found keyword `return`",
+            |p| p.parse_expr(),
+        );
+    })
+}
+
+// Checks the token-tree-ization of macros.
+#[test]
+fn string_to_tts_macro() {
+    create_default_session_globals_then(|| {
+        let stream = string_to_stream("macro_rules! zip (($a)=>($a))".to_string());
+        let tts = &stream.trees().collect::<Vec<_>>()[..];
+
+        match tts {
+            [
+                TokenTree::Token(
+                    Token { kind: token::Ident(name_macro_rules, IdentIsRaw::No), .. },
+                    _,
+                ),
+                TokenTree::Token(Token { kind: token::Not, .. }, _),
+                TokenTree::Token(Token { kind: token::Ident(name_zip, IdentIsRaw::No), .. }, _),
+                TokenTree::Delimited(.., macro_delim, macro_tts),
+            ] if name_macro_rules == &kw::MacroRules && name_zip.as_str() == "zip" => {
+                let tts = &macro_tts.trees().collect::<Vec<_>>();
+                match &tts[..] {
+                    [
+                        TokenTree::Delimited(.., first_delim, first_tts),
+                        TokenTree::Token(Token { kind: token::FatArrow, .. }, _),
+                        TokenTree::Delimited(.., second_delim, second_tts),
+                    ] if macro_delim == &Delimiter::Parenthesis => {
+                        let tts = &first_tts.trees().collect::<Vec<_>>();
+                        match &tts[..] {
+                            [
+                                TokenTree::Token(Token { kind: token::Dollar, .. }, _),
+                                TokenTree::Token(
+                                    Token { kind: token::Ident(name, IdentIsRaw::No), .. },
+                                    _,
+                                ),
+                            ] if first_delim == &Delimiter::Parenthesis && name.as_str() == "a" => {
+                            }
+                            _ => panic!("value 3: {:?} {:?}", first_delim, first_tts),
+                        }
+                        let tts = &second_tts.trees().collect::<Vec<_>>();
+                        match &tts[..] {
+                            [
+                                TokenTree::Token(Token { kind: token::Dollar, .. }, _),
+                                TokenTree::Token(
+                                    Token { kind: token::Ident(name, IdentIsRaw::No), .. },
+                                    _,
+                                ),
+                            ] if second_delim == &Delimiter::Parenthesis
+                                && name.as_str() == "a" => {}
+                            _ => panic!("value 4: {:?} {:?}", second_delim, second_tts),
+                        }
+                    }
+                    _ => panic!("value 2: {:?} {:?}", macro_delim, macro_tts),
+                }
+            }
+            _ => panic!("value: {:?}", tts),
+        }
+    })
+}
+
+#[test]
+fn string_to_tts_1() {
+    create_default_session_globals_then(|| {
+        let tts = string_to_stream("fn a(b: i32) { b; }".to_string());
+
+        let expected = TokenStream::new(vec![
+            TokenTree::token_alone(token::Ident(kw::Fn, IdentIsRaw::No), sp(0, 2)),
+            TokenTree::token_joint_hidden(
+                token::Ident(Symbol::intern("a"), IdentIsRaw::No),
+                sp(3, 4),
+            ),
+            TokenTree::Delimited(
+                DelimSpan::from_pair(sp(4, 5), sp(11, 12)),
+                // `JointHidden` because the `(` is followed immediately by
+                // `b`, `Alone` because the `)` is followed by whitespace.
+                DelimSpacing::new(Spacing::JointHidden, Spacing::Alone),
+                Delimiter::Parenthesis,
+                TokenStream::new(vec![
+                    TokenTree::token_joint(
+                        token::Ident(Symbol::intern("b"), IdentIsRaw::No),
+                        sp(5, 6),
+                    ),
+                    TokenTree::token_alone(token::Colon, sp(6, 7)),
+                    // `JointHidden` because the `i32` is immediately followed by the `)`.
+                    TokenTree::token_joint_hidden(
+                        token::Ident(sym::i32, IdentIsRaw::No),
+                        sp(8, 11),
+                    ),
+                ])
+                .into(),
+            ),
+            TokenTree::Delimited(
+                DelimSpan::from_pair(sp(13, 14), sp(18, 19)),
+                // First `Alone` because the `{` is followed by whitespace,
+                // second `Alone` because the `}` is followed immediately by
+                // EOF.
+                DelimSpacing::new(Spacing::Alone, Spacing::Alone),
+                Delimiter::Brace,
+                TokenStream::new(vec![
+                    TokenTree::token_joint(
+                        token::Ident(Symbol::intern("b"), IdentIsRaw::No),
+                        sp(15, 16),
+                    ),
+                    // `Alone` because the `;` is followed by whitespace.
+                    TokenTree::token_alone(token::Semi, sp(16, 17)),
+                ])
+                .into(),
+            ),
+        ]);
+
+        assert_eq!(tts, expected);
+    })
+}
+
+#[test]
+fn parse_use() {
+    create_default_session_globals_then(|| {
+        let use_s = "use foo::bar::baz;";
+        let vitem = string_to_item(use_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], use_s);
+
+        let use_s = "use foo::bar as baz;";
+        let vitem = string_to_item(use_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], use_s);
+    })
+}
+
+#[test]
+fn parse_extern_crate() {
+    create_default_session_globals_then(|| {
+        let ex_s = "extern crate foo;";
+        let vitem = string_to_item(ex_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], ex_s);
+
+        let ex_s = "extern crate foo as bar;";
+        let vitem = string_to_item(ex_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], ex_s);
+    })
+}
+
+fn get_spans_of_pat_idents(src: &str) -> Vec<Span> {
+    let item = string_to_item(src.to_string()).unwrap();
+
+    struct PatIdentVisitor {
+        spans: Vec<Span>,
+    }
+    impl<'a> visit::Visitor<'a> for PatIdentVisitor {
+        fn visit_pat(&mut self, p: &'a ast::Pat) {
+            match &p.kind {
+                PatKind::Ident(_, ident, _) => {
+                    self.spans.push(ident.span);
+                }
+                _ => {
+                    visit::walk_pat(self, p);
+                }
+            }
+        }
+    }
+    let mut v = PatIdentVisitor { spans: Vec::new() };
+    visit::walk_item(&mut v, &item);
+    return v.spans;
+}
+
+#[test]
+fn span_of_self_arg_pat_idents_are_correct() {
+    create_default_session_globals_then(|| {
+        let srcs = [
+            "impl z { fn a (&self, &myarg: i32) {} }",
+            "impl z { fn a (&mut self, &myarg: i32) {} }",
+            "impl z { fn a (&'a self, &myarg: i32) {} }",
+            "impl z { fn a (self, &myarg: i32) {} }",
+            "impl z { fn a (self: Foo, &myarg: i32) {} }",
+        ];
+
+        for src in srcs {
+            let spans = get_spans_of_pat_idents(src);
+            let (lo, hi) = (spans[0].lo(), spans[0].hi());
+            assert!(
+                "self" == &src[lo.to_usize()..hi.to_usize()],
+                "\"{}\" != \"self\". src=\"{}\"",
+                &src[lo.to_usize()..hi.to_usize()],
+                src
+            )
+        }
+    })
+}
+
+#[test]
+fn parse_exprs() {
+    create_default_session_globals_then(|| {
+        // just make sure that they parse....
+        string_to_expr("3 + 4".to_string());
+        string_to_expr("a::z.froob(b,&(987+3))".to_string());
+    })
+}
+
+#[test]
+fn attrs_fix_bug() {
+    create_default_session_globals_then(|| {
+        string_to_item(
+            "pub fn mk_file_writer(path: &Path, flags: &[FileFlag])
+                -> Result<Box<Writer>, String> {
+#[cfg(windows)]
+fn wb() -> c_int {
+    (O_WRONLY | libc::consts::os::extra::O_BINARY) as c_int
+}
+
+#[cfg(unix)]
+fn wb() -> c_int { O_WRONLY as c_int }
+
+let mut fflags: c_int = wb();
+}"
+            .to_string(),
+        );
+    })
+}
+
+#[test]
+fn crlf_doc_comments() {
+    create_default_session_globals_then(|| {
+        let psess = psess();
+
+        let name_1 = FileName::Custom("crlf_source_1".to_string());
+        let source = "/// doc comment\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_1, source, &psess).unwrap().unwrap();
+        let doc = item.attrs.iter().filter_map(|at| at.doc_str()).next().unwrap();
+        assert_eq!(doc.as_str(), " doc comment");
+
+        let name_2 = FileName::Custom("crlf_source_2".to_string());
+        let source = "/// doc comment\r\n/// line 2\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_2, source, &psess).unwrap().unwrap();
+        let docs = item.attrs.iter().filter_map(|at| at.doc_str()).collect::<Vec<_>>();
+        let b: &[_] = &[Symbol::intern(" doc comment"), Symbol::intern(" line 2")];
+        assert_eq!(&docs[..], b);
+
+        let name_3 = FileName::Custom("clrf_source_3".to_string());
+        let source = "/** doc comment\r\n *  with CRLF */\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_3, source, &psess).unwrap().unwrap();
+        let doc = item.attrs.iter().filter_map(|at| at.doc_str()).next().unwrap();
+        assert_eq!(doc.as_str(), " doc comment\n *  with CRLF ");
+    });
+}
+
+#[test]
+fn ttdelim_span() {
+    fn parse_expr_from_source_str(
+        name: FileName,
+        source: String,
+        psess: &ParseSess,
+    ) -> PResult<'_, P<ast::Expr>> {
+        new_parser_from_source_str(psess, name, source).parse_expr()
+    }
+
+    create_default_session_globals_then(|| {
+        let psess = psess();
+        let expr = parse_expr_from_source_str(
+            PathBuf::from("foo").into(),
+            "foo!( fn main() { body } )".to_string(),
+            &psess,
+        )
+        .unwrap();
+
+        let ast::ExprKind::MacCall(mac) = &expr.kind else { panic!("not a macro") };
+        let span = mac.args.tokens.trees().last().unwrap().span();
+
+        match psess.source_map().span_to_snippet(span) {
+            Ok(s) => assert_eq!(&s[..], "{ body }"),
+            Err(_) => panic!("could not get snippet"),
+        }
+    });
+}
+
+// This tests that when parsing a string (rather than a file) we don't try
+// and read in a file for a module declaration and just parse a stub.
+// See `recurse_into_file_modules` in the parser.
+#[test]
+fn out_of_line_mod() {
+    create_default_session_globals_then(|| {
+        let item = parse_item_from_source_str(
+            PathBuf::from("foo").into(),
+            "mod foo { struct S; mod this_does_not_exist; }".to_owned(),
+            &psess(),
+        )
+        .unwrap()
+        .unwrap();
+
+        let ast::ItemKind::Mod(_, mod_kind) = &item.kind else { panic!() };
+        assert!(matches!(mod_kind, ast::ModKind::Loaded(items, ..) if items.len() == 2));
+    });
+}
+
+#[test]
+fn eqmodws() {
+    assert_eq!(matches_codepattern("", ""), true);
+    assert_eq!(matches_codepattern("", "a"), false);
+    assert_eq!(matches_codepattern("a", ""), false);
+    assert_eq!(matches_codepattern("a", "a"), true);
+    assert_eq!(matches_codepattern("a b", "a   \n\t\r  b"), true);
+    assert_eq!(matches_codepattern("a b ", "a   \n\t\r  b"), true);
+    assert_eq!(matches_codepattern("a b", "a   \n\t\r  b "), false);
+    assert_eq!(matches_codepattern("a   b", "a b"), true);
+    assert_eq!(matches_codepattern("ab", "a b"), false);
+    assert_eq!(matches_codepattern("a   b", "ab"), true);
+    assert_eq!(matches_codepattern(" a   b", "ab"), true);
+}
+
+#[test]
+fn pattern_whitespace() {
+    assert_eq!(matches_codepattern("", "\x0C"), false);
+    assert_eq!(matches_codepattern("a b ", "a   \u{0085}\n\t\r  b"), true);
+    assert_eq!(matches_codepattern("a b", "a   \u{0085}\n\t\r  b "), false);
+}
+
+#[test]
+fn non_pattern_whitespace() {
+    // These have the property 'White_Space' but not 'Pattern_White_Space'
+    assert_eq!(matches_codepattern("a b", "a\u{2002}b"), false);
+    assert_eq!(matches_codepattern("a   b", "a\u{2002}b"), false);
+    assert_eq!(matches_codepattern("\u{205F}a   b", "ab"), false);
+    assert_eq!(matches_codepattern("a  \u{3000}b", "ab"), false);
+}
diff --git a/compiler/rustc_parse/src/parser/tokenstream/tests.rs b/compiler/rustc_parse/src/parser/tokenstream/tests.rs
new file mode 100644
index 00000000000..9be00a14791
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/tokenstream/tests.rs
@@ -0,0 +1,108 @@
+use crate::parser::tests::string_to_stream;
+use rustc_ast::token::{self, IdentIsRaw};
+use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_span::create_default_session_globals_then;
+use rustc_span::{BytePos, Span, Symbol};
+
+fn string_to_ts(string: &str) -> TokenStream {
+    string_to_stream(string.to_owned())
+}
+
+fn sp(a: u32, b: u32) -> Span {
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
+}
+
+#[test]
+fn test_concat() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("foo::bar::baz");
+        let test_fst = string_to_ts("foo::bar");
+        let test_snd = string_to_ts("::baz");
+        let mut eq_res = TokenStream::default();
+        eq_res.push_stream(test_fst);
+        eq_res.push_stream(test_snd);
+        assert_eq!(test_res.trees().count(), 5);
+        assert_eq!(eq_res.trees().count(), 5);
+        assert_eq!(test_res.eq_unspanned(&eq_res), true);
+    })
+}
+
+#[test]
+fn test_to_from_bijection() {
+    create_default_session_globals_then(|| {
+        let test_start = string_to_ts("foo::bar(baz)");
+        let test_end = test_start.trees().cloned().collect();
+        assert_eq!(test_start, test_end)
+    })
+}
+
+#[test]
+fn test_eq_0() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("foo");
+        let test_eqs = string_to_ts("foo");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_eq_1() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("::bar::baz");
+        let test_eqs = string_to_ts("::bar::baz");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_eq_3() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("");
+        let test_eqs = string_to_ts("");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_diseq_0() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("::bar::baz");
+        let test_eqs = string_to_ts("bar::baz");
+        assert_eq!(test_res == test_eqs, false)
+    })
+}
+
+#[test]
+fn test_diseq_1() {
+    create_default_session_globals_then(|| {
+        let test_res = string_to_ts("(bar,baz)");
+        let test_eqs = string_to_ts("bar,baz");
+        assert_eq!(test_res == test_eqs, false)
+    })
+}
+
+#[test]
+fn test_is_empty() {
+    create_default_session_globals_then(|| {
+        let test0 = TokenStream::default();
+        let test1 =
+            TokenStream::token_alone(token::Ident(Symbol::intern("a"), IdentIsRaw::No), sp(0, 1));
+        let test2 = string_to_ts("foo(bar::baz)");
+
+        assert_eq!(test0.is_empty(), true);
+        assert_eq!(test1.is_empty(), false);
+        assert_eq!(test2.is_empty(), false);
+    })
+}
+
+#[test]
+fn test_dotdotdot() {
+    create_default_session_globals_then(|| {
+        let mut stream = TokenStream::default();
+        stream.push_tree(TokenTree::token_joint(token::Dot, sp(0, 1)));
+        stream.push_tree(TokenTree::token_joint(token::Dot, sp(1, 2)));
+        stream.push_tree(TokenTree::token_alone(token::Dot, sp(2, 3)));
+        assert!(stream.eq_unspanned(&string_to_ts("...")));
+        assert_eq!(stream.trees().count(), 1);
+    })
+}
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
new file mode 100644
index 00000000000..2df8f58507b
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -0,0 +1,1214 @@
+use super::{Parser, PathStyle, SeqSep, TokenType, Trailing};
+
+use crate::errors::{
+    self, DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
+    FnPointerCannotBeAsync, FnPointerCannotBeConst, FnPtrWithGenerics, FnPtrWithGenericsSugg,
+    HelpUseLatestEdition, InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime,
+    NestedCVariadicType, ReturnTypesUseThinArrow,
+};
+use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
+
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Token, TokenKind};
+use rustc_ast::util::case::Case;
+use rustc_ast::{
+    self as ast, BareFnTy, BoundAsyncness, BoundConstness, BoundPolarity, FnRetTy, GenericBound,
+    GenericBounds, GenericParam, Generics, Lifetime, MacCall, MutTy, Mutability, PolyTraitRef,
+    PreciseCapturingArg, TraitBoundModifiers, TraitObjectSyntax, Ty, TyKind, DUMMY_NODE_ID,
+};
+use rustc_errors::{Applicability, PResult};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{Span, Symbol};
+use thin_vec::{thin_vec, ThinVec};
+
+#[derive(Copy, Clone, PartialEq)]
+pub(super) enum AllowPlus {
+    Yes,
+    No,
+}
+
+#[derive(PartialEq)]
+pub(super) enum RecoverQPath {
+    Yes,
+    No,
+}
+
+pub(super) enum RecoverQuestionMark {
+    Yes,
+    No,
+}
+
+/// Signals whether parsing a type should recover `->`.
+///
+/// More specifically, when parsing a function like:
+/// ```compile_fail
+/// fn foo() => u8 { 0 }
+/// fn bar(): u8 { 0 }
+/// ```
+/// The compiler will try to recover interpreting `foo() => u8` as `foo() -> u8` when calling
+/// `parse_ty` with anything except `RecoverReturnSign::No`, and it will try to recover `bar(): u8`
+/// as `bar() -> u8` when passing `RecoverReturnSign::Yes` to `parse_ty`
+#[derive(Copy, Clone, PartialEq)]
+pub(super) enum RecoverReturnSign {
+    Yes,
+    OnlyFatArrow,
+    No,
+}
+
+impl RecoverReturnSign {
+    /// [RecoverReturnSign::Yes] allows for recovering `fn foo() => u8` and `fn foo(): u8`,
+    /// [RecoverReturnSign::OnlyFatArrow] allows for recovering only `fn foo() => u8` (recovering
+    /// colons can cause problems when parsing where clauses), and
+    /// [RecoverReturnSign::No] doesn't allow for any recovery of the return type arrow
+    fn can_recover(self, token: &TokenKind) -> bool {
+        match self {
+            Self::Yes => matches!(token, token::FatArrow | token::Colon),
+            Self::OnlyFatArrow => matches!(token, token::FatArrow),
+            Self::No => false,
+        }
+    }
+}
+
+// Is `...` (`CVarArgs`) legal at this level of type parsing?
+#[derive(PartialEq)]
+enum AllowCVariadic {
+    Yes,
+    No,
+}
+
+/// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
+/// `IDENT<<u8 as Trait>::AssocTy>`.
+///
+/// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
+/// that `IDENT` is not the ident of a fn trait.
+fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
+    t == &token::PathSep || t == &token::Lt || t == &token::BinOp(token::Shl)
+}
+
+fn can_begin_dyn_bound_in_edition_2015(t: &Token) -> bool {
+    // `Not`, `Tilde` & `Const` are deliberately not part of this list to
+    // contain the number of potential regressions esp. in MBE code.
+    // `Const` would regress `rfc-2632-const-trait-impl/mbe-dyn-const-2015.rs`.
+    // `Not` would regress `dyn!(...)` macro calls in Rust 2015.
+    t.is_path_start()
+        || t.is_lifetime()
+        || t == &TokenKind::Question
+        || t.is_keyword(kw::For)
+        || t == &TokenKind::OpenDelim(Delimiter::Parenthesis)
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a type.
+    pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::Yes,
+            AllowCVariadic::No,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            None,
+            RecoverQuestionMark::Yes,
+        )
+    }
+
+    pub(super) fn parse_ty_with_generics_recovery(
+        &mut self,
+        ty_params: &Generics,
+    ) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::Yes,
+            AllowCVariadic::No,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            Some(ty_params),
+            RecoverQuestionMark::Yes,
+        )
+    }
+
+    /// Parse a type suitable for a field definition.
+    /// The difference from `parse_ty` is that this version
+    /// allows anonymous structs and unions.
+    pub fn parse_ty_for_field_def(&mut self) -> PResult<'a, P<Ty>> {
+        if self.can_begin_anon_struct_or_union() {
+            self.parse_anon_struct_or_union()
+        } else {
+            self.parse_ty()
+        }
+    }
+
+    /// Parse a type suitable for a function or function pointer parameter.
+    /// The difference from `parse_ty` is that this version allows `...`
+    /// (`CVarArgs`) at the top level of the type.
+    pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::Yes,
+            AllowCVariadic::Yes,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            None,
+            RecoverQuestionMark::Yes,
+        )
+    }
+
+    /// Parses a type in restricted contexts where `+` is not permitted.
+    ///
+    /// Example 1: `&'a TYPE`
+    ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
+    /// Example 2: `value1 as TYPE + value2`
+    ///     `+` is prohibited to avoid interactions with expression grammar.
+    pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::No,
+            AllowCVariadic::No,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            None,
+            RecoverQuestionMark::Yes,
+        )
+    }
+
+    /// Parses a type following an `as` cast. Similar to `parse_ty_no_plus`, but signaling origin
+    /// for better diagnostics involving `?`.
+    pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::No,
+            AllowCVariadic::No,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            None,
+            RecoverQuestionMark::No,
+        )
+    }
+
+    pub(super) fn parse_ty_no_question_mark_recover(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::Yes,
+            AllowCVariadic::No,
+            RecoverQPath::Yes,
+            RecoverReturnSign::Yes,
+            None,
+            RecoverQuestionMark::No,
+        )
+    }
+
+    /// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
+    pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(
+            AllowPlus::Yes,
+            AllowCVariadic::Yes,
+            RecoverQPath::Yes,
+            RecoverReturnSign::OnlyFatArrow,
+            None,
+            RecoverQuestionMark::Yes,
+        )
+    }
+
+    /// Parses an optional return type `[ -> TY ]` in a function declaration.
+    pub(super) fn parse_ret_ty(
+        &mut self,
+        allow_plus: AllowPlus,
+        recover_qpath: RecoverQPath,
+        recover_return_sign: RecoverReturnSign,
+    ) -> PResult<'a, FnRetTy> {
+        Ok(if self.eat(&token::RArrow) {
+            // FIXME(Centril): Can we unconditionally `allow_plus`?
+            let ty = self.parse_ty_common(
+                allow_plus,
+                AllowCVariadic::No,
+                recover_qpath,
+                recover_return_sign,
+                None,
+                RecoverQuestionMark::Yes,
+            )?;
+            FnRetTy::Ty(ty)
+        } else if recover_return_sign.can_recover(&self.token.kind) {
+            // Don't `eat` to prevent `=>` from being added as an expected token which isn't
+            // actually expected and could only confuse users
+            self.bump();
+            self.dcx().emit_err(ReturnTypesUseThinArrow { span: self.prev_token.span });
+            let ty = self.parse_ty_common(
+                allow_plus,
+                AllowCVariadic::No,
+                recover_qpath,
+                recover_return_sign,
+                None,
+                RecoverQuestionMark::Yes,
+            )?;
+            FnRetTy::Ty(ty)
+        } else {
+            FnRetTy::Default(self.prev_token.span.shrink_to_hi())
+        })
+    }
+
+    fn parse_ty_common(
+        &mut self,
+        allow_plus: AllowPlus,
+        allow_c_variadic: AllowCVariadic,
+        recover_qpath: RecoverQPath,
+        recover_return_sign: RecoverReturnSign,
+        ty_generics: Option<&Generics>,
+        recover_question_mark: RecoverQuestionMark,
+    ) -> PResult<'a, P<Ty>> {
+        let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
+        maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
+        maybe_whole!(self, NtTy, |ty| ty);
+
+        let lo = self.token.span;
+        let mut impl_dyn_multi = false;
+        let kind = if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            self.parse_ty_tuple_or_parens(lo, allow_plus)?
+        } else if self.eat(&token::Not) {
+            // Never type `!`
+            TyKind::Never
+        } else if self.eat(&token::BinOp(token::Star)) {
+            self.parse_ty_ptr()?
+        } else if self.eat(&token::OpenDelim(Delimiter::Bracket)) {
+            self.parse_array_or_slice_ty()?
+        } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
+            // Reference
+            self.expect_and()?;
+            self.parse_borrowed_pointee()?
+        } else if self.eat_keyword_noexpect(kw::Typeof) {
+            self.parse_typeof_ty()?
+        } else if self.eat_keyword(kw::Underscore) {
+            // A type to be inferred `_`
+            TyKind::Infer
+        } else if self.check_fn_front_matter(false, Case::Sensitive) {
+            // Function pointer type
+            self.parse_ty_bare_fn(lo, ThinVec::new(), None, recover_return_sign)?
+        } else if self.check_keyword(kw::For) {
+            let for_span = self.token.span;
+            // Function pointer type or bound list (trait object type) starting with a poly-trait.
+            //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
+            //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
+            let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+            if self.check_fn_front_matter(false, Case::Sensitive) {
+                self.parse_ty_bare_fn(
+                    lo,
+                    lifetime_defs,
+                    Some(self.prev_token.span.shrink_to_lo()),
+                    recover_return_sign,
+                )?
+            } else {
+                // Try to recover `for<'a> dyn Trait` or `for<'a> impl Trait`.
+                if self.may_recover()
+                    && (self.eat_keyword_noexpect(kw::Impl) || self.eat_keyword_noexpect(kw::Dyn))
+                {
+                    let kw = self.prev_token.ident().unwrap().0;
+                    let removal_span = kw.span.with_hi(self.token.span.lo());
+                    let path = self.parse_path(PathStyle::Type)?;
+                    let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
+                    let kind =
+                        self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?;
+                    let err = self.dcx().create_err(errors::TransposeDynOrImpl {
+                        span: kw.span,
+                        kw: kw.name.as_str(),
+                        sugg: errors::TransposeDynOrImplSugg {
+                            removal_span,
+                            insertion_span: for_span.shrink_to_lo(),
+                            kw: kw.name.as_str(),
+                        },
+                    });
+
+                    // Take the parsed bare trait object and turn it either
+                    // into a `dyn` object or an `impl Trait`.
+                    let kind = match (kind, kw.name) {
+                        (TyKind::TraitObject(bounds, _), kw::Dyn) => {
+                            TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
+                        }
+                        (TyKind::TraitObject(bounds, _), kw::Impl) => {
+                            TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds, None)
+                        }
+                        _ => return Err(err),
+                    };
+                    err.emit();
+                    kind
+                } else {
+                    let path = self.parse_path(PathStyle::Type)?;
+                    let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
+                    self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
+                }
+            }
+        } else if self.eat_keyword(kw::Impl) {
+            self.parse_impl_ty(&mut impl_dyn_multi)?
+        } else if self.is_explicit_dyn_type() {
+            self.parse_dyn_ty(&mut impl_dyn_multi)?
+        } else if self.eat_lt() {
+            // Qualified path
+            let (qself, path) = self.parse_qpath(PathStyle::Type)?;
+            TyKind::Path(Some(qself), path)
+        } else if self.check_path() {
+            self.parse_path_start_ty(lo, allow_plus, ty_generics)?
+        } else if self.can_begin_bound() {
+            self.parse_bare_trait_object(lo, allow_plus)?
+        } else if self.eat(&token::DotDotDot) {
+            match allow_c_variadic {
+                AllowCVariadic::Yes => TyKind::CVarArgs,
+                AllowCVariadic::No => {
+                    // FIXME(Centril): Should we just allow `...` syntactically
+                    // anywhere in a type and use semantic restrictions instead?
+                    let guar = self
+                        .dcx()
+                        .emit_err(NestedCVariadicType { span: lo.to(self.prev_token.span) });
+                    TyKind::Err(guar)
+                }
+            }
+        } else {
+            let msg = format!("expected type, found {}", super::token_descr(&self.token));
+            let mut err = self.dcx().struct_span_err(self.token.span, msg);
+            err.span_label(self.token.span, "expected type");
+            return Err(err);
+        };
+
+        let span = lo.to(self.prev_token.span);
+        let mut ty = self.mk_ty(span, kind);
+
+        // Try to recover from use of `+` with incorrect priority.
+        match allow_plus {
+            AllowPlus::Yes => self.maybe_recover_from_bad_type_plus(&ty)?,
+            AllowPlus::No => self.maybe_report_ambiguous_plus(impl_dyn_multi, &ty),
+        }
+        if let RecoverQuestionMark::Yes = recover_question_mark {
+            ty = self.maybe_recover_from_question_mark(ty);
+        }
+        if allow_qpath_recovery { self.maybe_recover_from_bad_qpath(ty) } else { Ok(ty) }
+    }
+
+    /// Parse an anonymous struct or union (only for field definitions):
+    /// ```ignore (feature-not-ready)
+    /// #[repr(C)]
+    /// struct Foo {
+    ///     _: struct { // anonymous struct
+    ///         x: u32,
+    ///         y: f64,
+    ///     }
+    ///     _: union { // anonymous union
+    ///         z: u32,
+    ///         w: f64,
+    ///     }
+    /// }
+    /// ```
+    fn parse_anon_struct_or_union(&mut self) -> PResult<'a, P<Ty>> {
+        assert!(self.token.is_keyword(kw::Union) || self.token.is_keyword(kw::Struct));
+        let is_union = self.token.is_keyword(kw::Union);
+
+        let lo = self.token.span;
+        self.bump();
+
+        let (fields, _recovered) =
+            self.parse_record_struct_body(if is_union { "union" } else { "struct" }, lo, false)?;
+        let span = lo.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::unnamed_fields, span);
+        let id = ast::DUMMY_NODE_ID;
+        let kind =
+            if is_union { TyKind::AnonUnion(id, fields) } else { TyKind::AnonStruct(id, fields) };
+        Ok(self.mk_ty(span, kind))
+    }
+
+    /// Parses either:
+    /// - `(TYPE)`, a parenthesized type.
+    /// - `(TYPE,)`, a tuple with a single field of type TYPE.
+    fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
+        let mut trailing_plus = false;
+        let (ts, trailing) = self.parse_paren_comma_seq(|p| {
+            let ty = p.parse_ty()?;
+            trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
+            Ok(ty)
+        })?;
+
+        if ts.len() == 1 && matches!(trailing, Trailing::No) {
+            let ty = ts.into_iter().next().unwrap().into_inner();
+            let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
+            match ty.kind {
+                // `(TY_BOUND_NOPAREN) + BOUND + ...`.
+                TyKind::Path(None, path) if maybe_bounds => {
+                    self.parse_remaining_bounds_path(ThinVec::new(), path, lo, true)
+                }
+                TyKind::TraitObject(bounds, TraitObjectSyntax::None)
+                    if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
+                {
+                    self.parse_remaining_bounds(bounds, true)
+                }
+                // `(TYPE)`
+                _ => Ok(TyKind::Paren(P(ty))),
+            }
+        } else {
+            Ok(TyKind::Tup(ts))
+        }
+    }
+
+    fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
+        let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
+        let bounds = self.parse_generic_bounds_common(allow_plus)?;
+        if lt_no_plus {
+            self.dcx().emit_err(NeedPlusAfterTraitObjectLifetime { span: lo });
+        }
+        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
+    }
+
+    fn parse_remaining_bounds_path(
+        &mut self,
+        generic_params: ThinVec<GenericParam>,
+        path: ast::Path,
+        lo: Span,
+        parse_plus: bool,
+    ) -> PResult<'a, TyKind> {
+        let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
+        let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifiers::NONE)];
+        self.parse_remaining_bounds(bounds, parse_plus)
+    }
+
+    /// Parse the remainder of a bare trait object type given an already parsed list.
+    fn parse_remaining_bounds(
+        &mut self,
+        mut bounds: GenericBounds,
+        plus: bool,
+    ) -> PResult<'a, TyKind> {
+        if plus {
+            self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
+            bounds.append(&mut self.parse_generic_bounds()?);
+        }
+        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
+    }
+
+    /// Parses a raw pointer type: `*[const | mut] $type`.
+    fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
+        let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
+            let span = self.prev_token.span;
+            self.dcx().emit_err(ExpectedMutOrConstInRawPointerType {
+                span,
+                after_asterisk: span.shrink_to_hi(),
+            });
+            Mutability::Not
+        });
+        let ty = self.parse_ty_no_plus()?;
+        Ok(TyKind::Ptr(MutTy { ty, mutbl }))
+    }
+
+    /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
+    /// The opening `[` bracket is already eaten.
+    fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
+        let elt_ty = match self.parse_ty() {
+            Ok(ty) => ty,
+            Err(err)
+                if self.look_ahead(1, |t| t.kind == token::CloseDelim(Delimiter::Bracket))
+                    | self.look_ahead(1, |t| t.kind == token::Semi) =>
+            {
+                // Recover from `[LIT; EXPR]` and `[LIT]`
+                self.bump();
+                let guar = err.emit();
+                self.mk_ty(self.prev_token.span, TyKind::Err(guar))
+            }
+            Err(err) => return Err(err),
+        };
+
+        let ty = if self.eat(&token::Semi) {
+            let mut length = self.parse_expr_anon_const()?;
+            if let Err(e) = self.expect(&token::CloseDelim(Delimiter::Bracket)) {
+                // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
+                self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
+                self.expect(&token::CloseDelim(Delimiter::Bracket))?;
+            }
+            TyKind::Array(elt_ty, length)
+        } else {
+            self.expect(&token::CloseDelim(Delimiter::Bracket))?;
+            TyKind::Slice(elt_ty)
+        };
+
+        Ok(ty)
+    }
+
+    fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
+        let and_span = self.prev_token.span;
+        let mut opt_lifetime = self.check_lifetime().then(|| self.expect_lifetime());
+        let mut mutbl = self.parse_mutability();
+        if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
+            // A lifetime is invalid here: it would be part of a bare trait bound, which requires
+            // it to be followed by a plus, but we disallow plus in the pointee type.
+            // So we can handle this case as an error here, and suggest `'a mut`.
+            // If there *is* a plus next though, handling the error later provides better suggestions
+            // (like adding parentheses)
+            if !self.look_ahead(1, |t| t.is_like_plus()) {
+                let lifetime_span = self.token.span;
+                let span = and_span.to(lifetime_span);
+
+                let (suggest_lifetime, snippet) =
+                    if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
+                        (Some(span), lifetime_src)
+                    } else {
+                        (None, String::new())
+                    };
+                self.dcx().emit_err(LifetimeAfterMut { span, suggest_lifetime, snippet });
+
+                opt_lifetime = Some(self.expect_lifetime());
+            }
+        } else if self.token.is_keyword(kw::Dyn)
+            && mutbl == Mutability::Not
+            && self.look_ahead(1, |t| t.is_keyword(kw::Mut))
+        {
+            // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
+            let span = and_span.to(self.look_ahead(1, |t| t.span));
+            self.dcx().emit_err(DynAfterMut { span });
+
+            // Recovery
+            mutbl = Mutability::Mut;
+            let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
+            self.bump();
+            self.bump_with((dyn_tok, dyn_tok_sp));
+        }
+        let ty = self.parse_ty_no_plus()?;
+        Ok(TyKind::Ref(opt_lifetime, MutTy { ty, mutbl }))
+    }
+
+    // Parses the `typeof(EXPR)`.
+    // To avoid ambiguity, the type is surrounded by parentheses.
+    fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
+        self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
+        let expr = self.parse_expr_anon_const()?;
+        self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+        Ok(TyKind::Typeof(expr))
+    }
+
+    /// Parses a function pointer type (`TyKind::BareFn`).
+    /// ```ignore (illustrative)
+    ///    [unsafe] [extern "ABI"] fn (S) -> T
+    /// //  ^~~~~^          ^~~~^     ^~^    ^
+    /// //    |               |        |     |
+    /// //    |               |        |   Return type
+    /// // Function Style    ABI  Parameter types
+    /// ```
+    /// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
+    fn parse_ty_bare_fn(
+        &mut self,
+        lo: Span,
+        mut params: ThinVec<GenericParam>,
+        param_insertion_point: Option<Span>,
+        recover_return_sign: RecoverReturnSign,
+    ) -> PResult<'a, TyKind> {
+        let inherited_vis = rustc_ast::Visibility {
+            span: rustc_span::DUMMY_SP,
+            kind: rustc_ast::VisibilityKind::Inherited,
+            tokens: None,
+        };
+        let span_start = self.token.span;
+        let ast::FnHeader { ext, safety, constness, coroutine_kind } =
+            self.parse_fn_front_matter(&inherited_vis, Case::Sensitive)?;
+        if self.may_recover() && self.token.kind == TokenKind::Lt {
+            self.recover_fn_ptr_with_generics(lo, &mut params, param_insertion_point)?;
+        }
+        let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
+        let whole_span = lo.to(self.prev_token.span);
+        if let ast::Const::Yes(span) = constness {
+            // If we ever start to allow `const fn()`, then update
+            // feature gating for `#![feature(const_extern_fn)]` to
+            // cover it.
+            self.dcx().emit_err(FnPointerCannotBeConst { span: whole_span, qualifier: span });
+        }
+        if let Some(ast::CoroutineKind::Async { span, .. }) = coroutine_kind {
+            self.dcx().emit_err(FnPointerCannotBeAsync { span: whole_span, qualifier: span });
+        }
+        // FIXME(gen_blocks): emit a similar error for `gen fn()`
+        let decl_span = span_start.to(self.token.span);
+        Ok(TyKind::BareFn(P(BareFnTy { ext, safety, generic_params: params, decl, decl_span })))
+    }
+
+    /// Recover from function pointer types with a generic parameter list (e.g. `fn<'a>(&'a str)`).
+    fn recover_fn_ptr_with_generics(
+        &mut self,
+        lo: Span,
+        params: &mut ThinVec<GenericParam>,
+        param_insertion_point: Option<Span>,
+    ) -> PResult<'a, ()> {
+        let generics = self.parse_generics()?;
+        let arity = generics.params.len();
+
+        let mut lifetimes: ThinVec<_> = generics
+            .params
+            .into_iter()
+            .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime))
+            .collect();
+
+        let sugg = if !lifetimes.is_empty() {
+            let snippet =
+                lifetimes.iter().map(|param| param.ident.as_str()).intersperse(", ").collect();
+
+            let (left, snippet) = if let Some(span) = param_insertion_point {
+                (span, if params.is_empty() { snippet } else { format!(", {snippet}") })
+            } else {
+                (lo.shrink_to_lo(), format!("for<{snippet}> "))
+            };
+
+            Some(FnPtrWithGenericsSugg {
+                left,
+                snippet,
+                right: generics.span,
+                arity,
+                for_param_list_exists: param_insertion_point.is_some(),
+            })
+        } else {
+            None
+        };
+
+        self.dcx().emit_err(FnPtrWithGenerics { span: generics.span, sugg });
+        params.append(&mut lifetimes);
+        Ok(())
+    }
+
+    /// Parses an `impl B0 + ... + Bn` type.
+    fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
+        if self.token.is_lifetime() {
+            self.look_ahead(1, |t| {
+                if let token::Ident(sym, _) = t.kind {
+                    // parse pattern with "'a Sized" we're supposed to give suggestion like
+                    // "'a + Sized"
+                    self.dcx().emit_err(errors::MissingPlusBounds {
+                        span: self.token.span,
+                        hi: self.token.span.shrink_to_hi(),
+                        sym,
+                    });
+                }
+            })
+        }
+
+        // parse precise captures, if any. This is `use<'lt, 'lt, P, P>`; a list of
+        // lifetimes and ident params (including SelfUpper). These are validated later
+        // for order, duplication, and whether they actually reference params.
+        let precise_capturing = if self.eat_keyword(kw::Use) {
+            let use_span = self.prev_token.span;
+            self.psess.gated_spans.gate(sym::precise_capturing, use_span);
+            let (args, args_span) = self.parse_precise_capturing_args()?;
+            Some(P((args, use_span.to(args_span))))
+        } else {
+            None
+        };
+
+        // Always parse bounds greedily for better error recovery.
+        let bounds = self.parse_generic_bounds()?;
+
+        *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
+
+        Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds, precise_capturing))
+    }
+
+    fn parse_precise_capturing_args(
+        &mut self,
+    ) -> PResult<'a, (ThinVec<PreciseCapturingArg>, Span)> {
+        let lo = self.token.span;
+        let (args, _) = self.parse_unspanned_seq(
+            &TokenKind::Lt,
+            &TokenKind::Gt,
+            SeqSep::trailing_allowed(token::Comma),
+            |self_| {
+                if self_.check_keyword(kw::SelfUpper) {
+                    self_.bump();
+                    Ok(PreciseCapturingArg::Arg(
+                        ast::Path::from_ident(self_.prev_token.ident().unwrap().0),
+                        DUMMY_NODE_ID,
+                    ))
+                } else if self_.check_ident() {
+                    Ok(PreciseCapturingArg::Arg(
+                        ast::Path::from_ident(self_.parse_ident()?),
+                        DUMMY_NODE_ID,
+                    ))
+                } else if self_.check_lifetime() {
+                    Ok(PreciseCapturingArg::Lifetime(self_.expect_lifetime()))
+                } else {
+                    self_.unexpected_any()
+                }
+            },
+        )?;
+        Ok((args, lo.to(self.prev_token.span)))
+    }
+
+    /// Is a `dyn B0 + ... + Bn` type allowed here?
+    fn is_explicit_dyn_type(&mut self) -> bool {
+        self.check_keyword(kw::Dyn)
+            && (self.token.uninterpolated_span().at_least_rust_2018()
+                || self.look_ahead(1, |t| {
+                    (can_begin_dyn_bound_in_edition_2015(t)
+                        || t.kind == TokenKind::BinOp(token::Star))
+                        && !can_continue_type_after_non_fn_ident(t)
+                }))
+    }
+
+    /// Parses a `dyn B0 + ... + Bn` type.
+    ///
+    /// Note that this does *not* parse bare trait objects.
+    fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
+        let lo = self.token.span;
+        self.bump(); // `dyn`
+
+        // parse dyn* types
+        let syntax = if self.eat(&TokenKind::BinOp(token::Star)) {
+            self.psess.gated_spans.gate(sym::dyn_star, lo.to(self.prev_token.span));
+            TraitObjectSyntax::DynStar
+        } else {
+            TraitObjectSyntax::Dyn
+        };
+
+        // Always parse bounds greedily for better error recovery.
+        let bounds = self.parse_generic_bounds()?;
+        *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
+        Ok(TyKind::TraitObject(bounds, syntax))
+    }
+
+    /// Parses a type starting with a path.
+    ///
+    /// This can be:
+    /// 1. a type macro, `mac!(...)`,
+    /// 2. a bare trait object, `B0 + ... + Bn`,
+    /// 3. or a path, `path::to::MyType`.
+    fn parse_path_start_ty(
+        &mut self,
+        lo: Span,
+        allow_plus: AllowPlus,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, TyKind> {
+        // Simple path
+        let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
+        if self.eat(&token::Not) {
+            // Macro invocation in type position
+            Ok(TyKind::MacCall(P(MacCall { path, args: self.parse_delim_args()? })))
+        } else if allow_plus == AllowPlus::Yes && self.check_plus() {
+            // `Trait1 + Trait2 + 'a`
+            self.parse_remaining_bounds_path(ThinVec::new(), path, lo, true)
+        } else {
+            // Just a type path.
+            Ok(TyKind::Path(None, path))
+        }
+    }
+
+    pub(super) fn parse_generic_bounds(&mut self) -> PResult<'a, GenericBounds> {
+        self.parse_generic_bounds_common(AllowPlus::Yes)
+    }
+
+    /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
+    ///
+    /// See `parse_generic_bound` for the `BOUND` grammar.
+    fn parse_generic_bounds_common(&mut self, allow_plus: AllowPlus) -> PResult<'a, GenericBounds> {
+        let mut bounds = Vec::new();
+
+        // In addition to looping while we find generic bounds:
+        // We continue even if we find a keyword. This is necessary for error recovery on,
+        // for example, `impl fn()`. The only keyword that can go after generic bounds is
+        // `where`, so stop if it's it.
+        // We also continue if we find types (not traits), again for error recovery.
+        while self.can_begin_bound()
+            || (self.may_recover()
+                && (self.token.can_begin_type()
+                    || (self.token.is_reserved_ident() && !self.token.is_keyword(kw::Where))))
+        {
+            if self.token.is_keyword(kw::Dyn) {
+                // Account for `&dyn Trait + dyn Other`.
+                self.dcx().emit_err(InvalidDynKeyword { span: self.token.span });
+                self.bump();
+            }
+            bounds.push(self.parse_generic_bound()?);
+            if allow_plus == AllowPlus::No || !self.eat_plus() {
+                break;
+            }
+        }
+
+        Ok(bounds)
+    }
+
+    pub(super) fn can_begin_anon_struct_or_union(&mut self) -> bool {
+        (self.token.is_keyword(kw::Struct) || self.token.is_keyword(kw::Union))
+            && self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Brace))
+    }
+
+    /// Can the current token begin a bound?
+    fn can_begin_bound(&mut self) -> bool {
+        self.check_path()
+            || self.check_lifetime()
+            || self.check(&token::Not)
+            || self.check(&token::Question)
+            || self.check(&token::Tilde)
+            || self.check_keyword(kw::For)
+            || self.check(&token::OpenDelim(Delimiter::Parenthesis))
+            || self.check_keyword(kw::Const)
+            || self.check_keyword(kw::Async)
+    }
+
+    /// Parses a bound according to the grammar:
+    /// ```ebnf
+    /// BOUND = TY_BOUND | LT_BOUND
+    /// ```
+    fn parse_generic_bound(&mut self) -> PResult<'a, GenericBound> {
+        let lo = self.token.span;
+        let leading_token = self.prev_token.clone();
+        let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
+        let inner_lo = self.token.span;
+
+        let modifiers = self.parse_trait_bound_modifiers()?;
+        let bound = if self.token.is_lifetime() {
+            self.error_lt_bound_with_modifiers(modifiers);
+            self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
+        } else {
+            self.parse_generic_ty_bound(lo, has_parens, modifiers, &leading_token)?
+        };
+
+        Ok(bound)
+    }
+
+    /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
+    /// ```ebnf
+    /// LT_BOUND = LIFETIME
+    /// ```
+    fn parse_generic_lt_bound(
+        &mut self,
+        lo: Span,
+        inner_lo: Span,
+        has_parens: bool,
+    ) -> PResult<'a, GenericBound> {
+        let bound = GenericBound::Outlives(self.expect_lifetime());
+        if has_parens {
+            // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
+            // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
+            self.recover_paren_lifetime(lo, inner_lo)?;
+        }
+        Ok(bound)
+    }
+
+    /// Emits an error if any trait bound modifiers were present.
+    fn error_lt_bound_with_modifiers(&self, modifiers: TraitBoundModifiers) {
+        match modifiers.constness {
+            BoundConstness::Never => {}
+            BoundConstness::Always(span) | BoundConstness::Maybe(span) => {
+                self.dcx().emit_err(errors::ModifierLifetime {
+                    span,
+                    modifier: modifiers.constness.as_str(),
+                });
+            }
+        }
+
+        match modifiers.polarity {
+            BoundPolarity::Positive => {}
+            BoundPolarity::Negative(span) | BoundPolarity::Maybe(span) => {
+                self.dcx().emit_err(errors::ModifierLifetime {
+                    span,
+                    modifier: modifiers.polarity.as_str(),
+                });
+            }
+        }
+    }
+
+    /// Recover on `('lifetime)` with `(` already eaten.
+    fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
+        let inner_span = inner_lo.to(self.prev_token.span);
+        self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+        let span = lo.to(self.prev_token.span);
+        let (sugg, snippet) = if let Ok(snippet) = self.span_to_snippet(inner_span) {
+            (Some(span), snippet)
+        } else {
+            (None, String::new())
+        };
+
+        self.dcx().emit_err(errors::ParenthesizedLifetime { span, sugg, snippet });
+        Ok(())
+    }
+
+    /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
+    ///
+    /// If no modifiers are present, this does not consume any tokens.
+    ///
+    /// ```ebnf
+    /// TRAIT_BOUND_MODIFIERS = [["~"] "const"] ["?" | "!"]
+    /// ```
+    fn parse_trait_bound_modifiers(&mut self) -> PResult<'a, TraitBoundModifiers> {
+        let constness = if self.eat(&token::Tilde) {
+            let tilde = self.prev_token.span;
+            self.expect_keyword(kw::Const)?;
+            let span = tilde.to(self.prev_token.span);
+            self.psess.gated_spans.gate(sym::const_trait_impl, span);
+            BoundConstness::Maybe(span)
+        } else if self.eat_keyword(kw::Const) {
+            self.psess.gated_spans.gate(sym::const_trait_impl, self.prev_token.span);
+            BoundConstness::Always(self.prev_token.span)
+        } else {
+            BoundConstness::Never
+        };
+
+        let asyncness = if self.token.uninterpolated_span().at_least_rust_2018()
+            && self.eat_keyword(kw::Async)
+        {
+            self.psess.gated_spans.gate(sym::async_closure, self.prev_token.span);
+            BoundAsyncness::Async(self.prev_token.span)
+        } else if self.may_recover()
+            && self.token.uninterpolated_span().is_rust_2015()
+            && self.is_kw_followed_by_ident(kw::Async)
+        {
+            self.bump(); // eat `async`
+            self.dcx().emit_err(errors::AsyncBoundModifierIn2015 {
+                span: self.prev_token.span,
+                help: HelpUseLatestEdition::new(),
+            });
+            self.psess.gated_spans.gate(sym::async_closure, self.prev_token.span);
+            BoundAsyncness::Async(self.prev_token.span)
+        } else {
+            BoundAsyncness::Normal
+        };
+
+        let polarity = if self.eat(&token::Question) {
+            BoundPolarity::Maybe(self.prev_token.span)
+        } else if self.eat(&token::Not) {
+            self.psess.gated_spans.gate(sym::negative_bounds, self.prev_token.span);
+            BoundPolarity::Negative(self.prev_token.span)
+        } else {
+            BoundPolarity::Positive
+        };
+
+        Ok(TraitBoundModifiers { constness, asyncness, polarity })
+    }
+
+    /// Parses a type bound according to:
+    /// ```ebnf
+    /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
+    /// TY_BOUND_NOPAREN = [TRAIT_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
+    /// ```
+    ///
+    /// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
+    fn parse_generic_ty_bound(
+        &mut self,
+        lo: Span,
+        has_parens: bool,
+        modifiers: TraitBoundModifiers,
+        leading_token: &Token,
+    ) -> PResult<'a, GenericBound> {
+        let mut lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+        let mut path = if self.token.is_keyword(kw::Fn)
+            && self.look_ahead(1, |tok| tok.kind == TokenKind::OpenDelim(Delimiter::Parenthesis))
+            && let Some(path) = self.recover_path_from_fn()
+        {
+            path
+        } else if !self.token.is_path_start() && self.token.can_begin_type() {
+            let ty = self.parse_ty_no_plus()?;
+            // Instead of finding a path (a trait), we found a type.
+            let mut err = self.dcx().struct_span_err(ty.span, "expected a trait, found type");
+
+            // If we can recover, try to extract a path from the type. Note
+            // that we do not use the try operator when parsing the type because
+            // if it fails then we get a parser error which we don't want (we're trying
+            // to recover from errors, not make more).
+            let path = if self.may_recover() {
+                let (span, message, sugg, path, applicability) = match &ty.kind {
+                    TyKind::Ptr(..) | TyKind::Ref(..)
+                        if let TyKind::Path(_, path) = &ty.peel_refs().kind =>
+                    {
+                        (
+                            ty.span.until(path.span),
+                            "consider removing the indirection",
+                            "",
+                            path,
+                            Applicability::MaybeIncorrect,
+                        )
+                    }
+                    TyKind::ImplTrait(_, bounds, None)
+                        if let [GenericBound::Trait(tr, ..), ..] = bounds.as_slice() =>
+                    {
+                        (
+                            ty.span.until(tr.span),
+                            "use the trait bounds directly",
+                            "",
+                            &tr.trait_ref.path,
+                            Applicability::MachineApplicable,
+                        )
+                    }
+                    _ => return Err(err),
+                };
+
+                err.span_suggestion_verbose(span, message, sugg, applicability);
+
+                path.clone()
+            } else {
+                return Err(err);
+            };
+
+            err.emit();
+
+            path
+        } else {
+            self.parse_path(PathStyle::Type)?
+        };
+
+        if self.may_recover() && self.token == TokenKind::OpenDelim(Delimiter::Parenthesis) {
+            self.recover_fn_trait_with_lifetime_params(&mut path, &mut lifetime_defs)?;
+        }
+
+        if has_parens {
+            // Someone has written something like `&dyn (Trait + Other)`. The correct code
+            // would be `&(dyn Trait + Other)`
+            if self.token.is_like_plus() && leading_token.is_keyword(kw::Dyn) {
+                let bounds = vec![];
+                self.parse_remaining_bounds(bounds, true)?;
+                self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+                self.dcx().emit_err(errors::IncorrectParensTraitBounds {
+                    span: vec![lo, self.prev_token.span],
+                    sugg: errors::IncorrectParensTraitBoundsSugg {
+                        wrong_span: leading_token.span.shrink_to_hi().to(lo),
+                        new_span: leading_token.span.shrink_to_lo(),
+                    },
+                });
+            } else {
+                self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+            }
+        }
+
+        let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
+        Ok(GenericBound::Trait(poly_trait, modifiers))
+    }
+
+    // recovers a `Fn(..)` parenthesized-style path from `fn(..)`
+    fn recover_path_from_fn(&mut self) -> Option<ast::Path> {
+        let fn_token_span = self.token.span;
+        self.bump();
+        let args_lo = self.token.span;
+        let snapshot = self.create_snapshot_for_diagnostic();
+        match self.parse_fn_decl(|_| false, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
+            Ok(decl) => {
+                self.dcx().emit_err(ExpectedFnPathFoundFnKeyword { fn_token_span });
+                Some(ast::Path {
+                    span: fn_token_span.to(self.prev_token.span),
+                    segments: thin_vec![ast::PathSegment {
+                        ident: Ident::new(Symbol::intern("Fn"), fn_token_span),
+                        id: DUMMY_NODE_ID,
+                        args: Some(P(ast::GenericArgs::Parenthesized(ast::ParenthesizedArgs {
+                            span: args_lo.to(self.prev_token.span),
+                            inputs: decl.inputs.iter().map(|a| a.ty.clone()).collect(),
+                            inputs_span: args_lo.until(decl.output.span()),
+                            output: decl.output.clone(),
+                        }))),
+                    }],
+                    tokens: None,
+                })
+            }
+            Err(diag) => {
+                diag.cancel();
+                self.restore_snapshot(snapshot);
+                None
+            }
+        }
+    }
+
+    /// Optionally parses `for<$generic_params>`.
+    pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, ThinVec<GenericParam>> {
+        if self.eat_keyword(kw::For) {
+            self.expect_lt()?;
+            let params = self.parse_generic_params()?;
+            self.expect_gt()?;
+            // We rely on AST validation to rule out invalid cases: There must not be type
+            // parameters, and the lifetime parameters must not have bounds.
+            Ok(params)
+        } else {
+            Ok(ThinVec::new())
+        }
+    }
+
+    /// Recover from `Fn`-family traits (Fn, FnMut, FnOnce) with lifetime arguments
+    /// (e.g. `FnOnce<'a>(&'a str) -> bool`). Up to generic arguments have already
+    /// been eaten.
+    fn recover_fn_trait_with_lifetime_params(
+        &mut self,
+        fn_path: &mut ast::Path,
+        lifetime_defs: &mut ThinVec<GenericParam>,
+    ) -> PResult<'a, ()> {
+        let fn_path_segment = fn_path.segments.last_mut().unwrap();
+        let generic_args = if let Some(p_args) = &fn_path_segment.args {
+            p_args.clone().into_inner()
+        } else {
+            // Normally it wouldn't come here because the upstream should have parsed
+            // generic parameters (otherwise it's impossible to call this function).
+            return Ok(());
+        };
+        let lifetimes =
+            if let ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs { span: _, args }) =
+                &generic_args
+            {
+                args.into_iter()
+                    .filter_map(|arg| {
+                        if let ast::AngleBracketedArg::Arg(generic_arg) = arg
+                            && let ast::GenericArg::Lifetime(lifetime) = generic_arg
+                        {
+                            Some(lifetime)
+                        } else {
+                            None
+                        }
+                    })
+                    .collect()
+            } else {
+                Vec::new()
+            };
+        // Only try to recover if the trait has lifetime params.
+        if lifetimes.is_empty() {
+            return Ok(());
+        }
+
+        // Parse `(T, U) -> R`.
+        let inputs_lo = self.token.span;
+        let inputs: ThinVec<_> =
+            self.parse_fn_params(|_| false)?.into_iter().map(|input| input.ty).collect();
+        let inputs_span = inputs_lo.to(self.prev_token.span);
+        let output = self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
+        let args = ast::ParenthesizedArgs {
+            span: fn_path_segment.span().to(self.prev_token.span),
+            inputs,
+            inputs_span,
+            output,
+        }
+        .into();
+        *fn_path_segment = ast::PathSegment {
+            ident: fn_path_segment.ident,
+            args: Some(args),
+            id: ast::DUMMY_NODE_ID,
+        };
+
+        // Convert parsed `<'a>` in `Fn<'a>` into `for<'a>`.
+        let mut generic_params = lifetimes
+            .iter()
+            .map(|lt| GenericParam {
+                id: lt.id,
+                ident: lt.ident,
+                attrs: ast::AttrVec::new(),
+                bounds: Vec::new(),
+                is_placeholder: false,
+                kind: ast::GenericParamKind::Lifetime,
+                colon_span: None,
+            })
+            .collect::<ThinVec<GenericParam>>();
+        lifetime_defs.append(&mut generic_params);
+
+        let generic_args_span = generic_args.span();
+        let snippet = format!(
+            "for<{}> ",
+            lifetimes.iter().map(|lt| lt.ident.as_str()).intersperse(", ").collect::<String>(),
+        );
+        let before_fn_path = fn_path.span.shrink_to_lo();
+        self.dcx()
+            .struct_span_err(generic_args_span, "`Fn` traits cannot take lifetime parameters")
+            .with_multipart_suggestion(
+                "consider using a higher-ranked trait bound instead",
+                vec![(generic_args_span, "".to_owned()), (before_fn_path, snippet)],
+                Applicability::MaybeIncorrect,
+            )
+            .emit();
+        Ok(())
+    }
+
+    pub(super) fn check_lifetime(&mut self) -> bool {
+        self.expected_tokens.push(TokenType::Lifetime);
+        self.token.is_lifetime()
+    }
+
+    /// Parses a single lifetime `'a` or panics.
+    pub(super) fn expect_lifetime(&mut self) -> Lifetime {
+        if let Some(ident) = self.token.lifetime() {
+            self.bump();
+            Lifetime { ident, id: ast::DUMMY_NODE_ID }
+        } else {
+            self.dcx().span_bug(self.token.span, "not a lifetime")
+        }
+    }
+
+    pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
+        P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
+    }
+}