Overhaul token collection.

This commit does the following.

- Renames `collect_tokens_trailing_token` as `collect_tokens`, because
  (a) it's annoying long, and (b) the `_trailing_token` bit is less
  accurate now that its types have changed.

- In `collect_tokens`, adds a `Option<CollectPos>` argument and a
  `UsePreAttrPos` in the return type of `f`. These are used in
  `parse_expr_force_collect` (for vanilla expressions) and in
  `parse_stmt_without_recovery` (for two different cases of expression
  statements). Together these ensure are enough to fix all the problems
  with token collection and assoc expressions. The changes to the
  `stringify.rs` test demonstrate some of these.

- Adds a new test. The code in this test was causing an assertion
  failure prior to this commit, due to an invalid `NodeRange`.

The extra complexity is annoying, but necessary to fix the existing
problems.

12 files changed, 413 insertions, 291 deletions

diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 1ae26309e44..3d06017fcf3 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -10,6 +10,7 @@ use tracing::debug;
 
 use super::{
     AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, ParserRange, PathStyle, Trailing,
+    UsePreAttrPos,
 };
 use crate::{errors, fluent_generated as fluent, maybe_whole};
 
@@ -259,7 +260,8 @@ impl<'a> Parser<'a> {
     pub fn parse_attr_item(&mut self, force_collect: ForceCollect) -> PResult<'a, ast::AttrItem> {
         maybe_whole!(self, NtMeta, |attr| attr.into_inner());
 
-        let do_parse = |this: &mut Self, _empty_attrs| {
+        // Attr items don't have attributes.
+        self.collect_tokens(None, AttrWrapper::empty(), force_collect, |this, _empty_attrs| {
             let is_unsafe = this.eat_keyword(kw::Unsafe);
             let unsafety = if is_unsafe {
                 let unsafe_span = this.prev_token.span;
@@ -275,10 +277,12 @@ impl<'a> Parser<'a> {
             if is_unsafe {
                 this.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
             }
-            Ok((ast::AttrItem { unsafety, path, args, tokens: None }, Trailing::No))
-        };
-        // Attr items don't have attributes.
-        self.collect_tokens_trailing_token(AttrWrapper::empty(), force_collect, do_parse)
+            Ok((
+                ast::AttrItem { unsafety, path, args, tokens: None },
+                Trailing::No,
+                UsePreAttrPos::No,
+            ))
+        })
     }
 
     /// Parses attributes that appear after the opening of an item. These should
@@ -311,8 +315,8 @@ impl<'a> Parser<'a> {
             };
             if let Some(attr) = attr {
                 // If we are currently capturing tokens (i.e. we are within a call to
-                // `Parser::collect_tokens_trailing_tokens`) record the token positions of this
-                // inner attribute, for possible later processing in a `LazyAttrTokenStream`.
+                // `Parser::collect_tokens`) record the token positions of this inner attribute,
+                // for possible later processing in a `LazyAttrTokenStream`.
                 if let Capturing::Yes = self.capture_state.capturing {
                     let end_pos = self.num_bump_calls;
                     let parser_range = ParserRange(start_pos..end_pos);
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index 65722f2b7e3..49df2811d52 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -15,6 +15,20 @@ use super::{
     TokenCursor, Trailing,
 };
 
+// When collecting tokens, this fully captures the start point. Usually its
+// just after outer attributes, but occasionally it's before.
+#[derive(Clone, Debug)]
+pub(super) struct CollectPos {
+    start_token: (Token, Spacing),
+    cursor_snapshot: TokenCursor,
+    start_pos: u32,
+}
+
+pub(super) enum UsePreAttrPos {
+    No,
+    Yes,
+}
+
 /// 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
@@ -22,7 +36,7 @@ use super::{
 ///
 /// 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_token`.
+/// by passing an `AttrWrapper` to `collect_tokens`.
 /// This makes it difficult to accidentally construct an AST node
 /// (which stores an `ast::AttrVec`) without first collecting tokens.
 ///
@@ -33,16 +47,18 @@ pub(super) struct AttrWrapper {
     attrs: AttrVec,
     // The start of the outer attributes in the parser's token stream.
     // This lets us create a `NodeReplacement` for the entire attribute
-    // target, including outer attributes.
-    start_pos: u32,
+    // target, including outer attributes. `None` if there are no outer
+    // attributes.
+    start_pos: Option<u32>,
 }
 
 impl AttrWrapper {
     pub(super) fn new(attrs: AttrVec, start_pos: u32) -> AttrWrapper {
-        AttrWrapper { attrs, start_pos }
+        AttrWrapper { attrs, start_pos: Some(start_pos) }
     }
+
     pub(super) fn empty() -> AttrWrapper {
-        AttrWrapper { attrs: AttrVec::new(), start_pos: u32::MAX }
+        AttrWrapper { attrs: AttrVec::new(), start_pos: None }
     }
 
     pub(super) fn take_for_recovery(self, psess: &ParseSess) -> AttrVec {
@@ -77,7 +93,7 @@ fn has_cfg_or_cfg_attr(attrs: &[Attribute]) -> bool {
 }
 
 // From a value of this type we can reconstruct the `TokenStream` seen by the
-// `f` callback passed to a call to `Parser::collect_tokens_trailing_token`, by
+// `f` callback passed to a call to `Parser::collect_tokens`, by
 // replaying the getting of the tokens. This saves us producing a `TokenStream`
 // if it is never needed, e.g. a captured `macro_rules!` argument that is never
 // passed to a proc macro. In practice, token stream creation happens rarely
@@ -166,16 +182,30 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
 }
 
 impl<'a> Parser<'a> {
+    pub(super) fn collect_pos(&self) -> CollectPos {
+        CollectPos {
+            start_token: (self.token.clone(), self.token_spacing),
+            cursor_snapshot: self.token_cursor.clone(),
+            start_pos: self.num_bump_calls,
+        }
+    }
+
     /// Parses code with `f`. If appropriate, it records the tokens (in
     /// `LazyAttrTokenStream` form) that were parsed in the result, accessible
     /// via the `HasTokens` trait. The `Trailing` part of the callback's
     /// result indicates if an extra token should be captured, e.g. a comma or
-    /// semicolon.
+    /// semicolon. The `UsePreAttrPos` part of the callback's result indicates
+    /// if we should use `pre_attr_pos` as the collection start position (only
+    /// required in a few cases).
     ///
     /// The `attrs` passed in are in `AttrWrapper` form, which is opaque. The
     /// `AttrVec` within is passed to `f`. See the comment on `AttrWrapper` for
     /// details.
     ///
+    /// `pre_attr_pos` is the position before the outer attributes (or the node
+    /// itself, if no outer attributes are present). It is only needed if `f`
+    /// can return `UsePreAttrPos::Yes`.
+    ///
     /// Note: If your callback consumes an opening delimiter (including the
     /// case where `self.token` is an opening delimiter on entry to this
     /// function), you must also consume the corresponding closing delimiter.
@@ -197,11 +227,12 @@ impl<'a> Parser<'a> {
     ///     }                               //  32..33
     /// }                                   //  33..34
     /// ```
-    pub(super) fn collect_tokens_trailing_token<R: HasAttrs + HasTokens>(
+    pub(super) fn collect_tokens<R: HasAttrs + HasTokens>(
         &mut self,
+        pre_attr_pos: Option<CollectPos>,
         attrs: AttrWrapper,
         force_collect: ForceCollect,
-        f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, (R, Trailing)>,
+        f: impl FnOnce(&mut Self, AttrVec) -> PResult<'a, (R, Trailing, UsePreAttrPos)>,
     ) -> PResult<'a, R> {
         // We must collect if anything could observe the collected tokens, i.e.
         // if any of the following conditions hold.
@@ -220,23 +251,20 @@ impl<'a> Parser<'a> {
             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 mut collect_pos = self.collect_pos();
         let has_outer_attrs = !attrs.attrs.is_empty();
         let parser_replacements_start = self.capture_state.parser_replacements.len();
 
         // We set and restore `Capturing::Yes` on either side of the call to
-        // `f`, so we can distinguish the outermost call to
-        // `collect_tokens_trailing_token` (e.g. parsing `m` in the example
-        // above) from any inner (indirectly recursive) calls (e.g. parsing `g`
-        // in the example above). This distinction is used below and in
-        // `Parser::parse_inner_attributes`.
-        let (mut ret, capture_trailing) = {
+        // `f`, so we can distinguish the outermost call to `collect_tokens`
+        // (e.g. parsing `m` in the example above) from any inner (indirectly
+        // recursive) calls (e.g. parsing `g` in the example above). This
+        // distinction is used below and in `Parser::parse_inner_attributes`.
+        let (mut ret, capture_trailing, use_pre_attr_pos) = {
             let prev_capturing = mem::replace(&mut self.capture_state.capturing, Capturing::Yes);
-            let f_res = f(self, attrs.attrs);
+            let res = f(self, attrs.attrs);
             self.capture_state.capturing = prev_capturing;
-            f_res?
+            res?
         };
 
         // When we're not in `capture_cfg` mode, then skip collecting and
@@ -279,6 +307,14 @@ impl<'a> Parser<'a> {
             return Ok(ret);
         }
 
+        // Replace the post-attribute collection start position with the
+        // pre-attribute position supplied, if `f` indicated it is necessary.
+        // (The caller is responsible for providing a non-`None` `pre_attr_pos`
+        // if this is a possibility.)
+        if matches!(use_pre_attr_pos, UsePreAttrPos::Yes) {
+            collect_pos = pre_attr_pos.unwrap();
+        }
+
         let parser_replacements_end = self.capture_state.parser_replacements.len();
 
         assert!(
@@ -294,7 +330,7 @@ impl<'a> Parser<'a> {
             // `AttrTokenStream`, we will create the proper token.
             + self.break_last_token as u32;
 
-        let num_calls = end_pos - start_pos;
+        let num_calls = end_pos - collect_pos.start_pos;
 
         // Take the captured `ParserRange`s for any inner attributes that we parsed in
         // `Parser::parse_inner_attributes`, and pair them in a `ParserReplacement` with `None`,
@@ -328,7 +364,9 @@ impl<'a> Parser<'a> {
                 .iter()
                 .cloned()
                 .chain(inner_attr_parser_replacements.iter().cloned())
-                .map(|(parser_range, data)| (NodeRange::new(parser_range, start_pos), data))
+                .map(|(parser_range, data)| {
+                    (NodeRange::new(parser_range, collect_pos.start_pos), data)
+                })
                 .collect()
         };
 
@@ -355,9 +393,9 @@ impl<'a> Parser<'a> {
         //     - `tokens`: lazy tokens for `g` (with its inner attr deleted).
 
         let tokens = LazyAttrTokenStream::new(LazyAttrTokenStreamImpl {
-            start_token,
+            start_token: collect_pos.start_token,
+            cursor_snapshot: collect_pos.cursor_snapshot,
             num_calls,
-            cursor_snapshot,
             break_last_token: self.break_last_token,
             node_replacements,
         });
@@ -368,9 +406,9 @@ impl<'a> Parser<'a> {
         }
 
         // 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.
+        // `collect_tokens`, 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(ret.attrs())
@@ -389,7 +427,8 @@ impl<'a> Parser<'a> {
             // Set things up so that the entire AST node that we just parsed, including attributes,
             // will be replaced with `target` in the lazy token stream. This will allow us to
             // cfg-expand this AST node.
-            let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
+            let start_pos =
+                if has_outer_attrs { attrs.start_pos.unwrap() } else { collect_pos.start_pos };
             let target = AttrsTarget { attrs: ret.attrs().iter().cloned().collect(), tokens };
             self.capture_state
                 .parser_replacements
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index ba4e222a41a..ef1387c50fa 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2487,13 +2487,14 @@ impl<'a> Parser<'a> {
     pub(super) fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, P<Expr>> {
         let start = self.token.span;
         let attrs = self.parse_outer_attributes()?;
-        let expr = self.parse_expr_res(Restrictions::CONST_EXPR, attrs).map_err(|mut err| {
-            err.span_label(
-                start.shrink_to_lo(),
-                "while parsing a const generic argument starting here",
-            );
-            err
-        })?;
+        let (expr, _) =
+            self.parse_expr_res(Restrictions::CONST_EXPR, attrs).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,
@@ -2613,7 +2614,7 @@ impl<'a> Parser<'a> {
             let attrs = self.parse_outer_attributes()?;
             self.parse_expr_res(Restrictions::CONST_EXPR, attrs)
         })() {
-            Ok(expr) => {
+            Ok((expr, _)) => {
                 // Find a mistake like `MyTrait<Assoc == S::Assoc>`.
                 if snapshot.token == token::EqEq {
                     err.span_suggestion(
@@ -2671,7 +2672,7 @@ impl<'a> Parser<'a> {
         })() {
             // 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 => {
+            Ok((expr, _)) if let token::Comma | token::Gt = snapshot.token.kind => {
                 self.restore_snapshot(snapshot);
                 Some(expr)
             }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index e284c7a11bc..e0917ba43e4 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -36,7 +36,7 @@ use super::pat::{CommaRecoveryMode, Expected, RecoverColon, RecoverComma};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{
     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
-    SemiColonMode, SeqSep, TokenType, Trailing,
+    SemiColonMode, SeqSep, TokenType, Trailing, UsePreAttrPos,
 };
 use crate::{errors, maybe_recover_from_interpolated_ty_qpath};
 
@@ -59,15 +59,30 @@ impl<'a> Parser<'a> {
         self.current_closure.take();
 
         let attrs = self.parse_outer_attributes()?;
-        self.parse_expr_res(Restrictions::empty(), attrs)
+        self.parse_expr_res(Restrictions::empty(), attrs).map(|res| res.0)
     }
 
     /// Parses an expression, forcing tokens to be collected.
     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
         self.current_closure.take();
 
+        // If the expression is associative (e.g. `1 + 2`), then any preceding
+        // outer attribute actually belongs to the first inner sub-expression.
+        // In which case we must use the pre-attr pos to include the attribute
+        // in the collected tokens for the outer expression.
+        let pre_attr_pos = self.collect_pos();
         let attrs = self.parse_outer_attributes()?;
-        self.collect_tokens_no_attrs(|this| this.parse_expr_res(Restrictions::empty(), attrs))
+        self.collect_tokens(
+            Some(pre_attr_pos),
+            AttrWrapper::empty(),
+            ForceCollect::Yes,
+            |this, _empty_attrs| {
+                let (expr, is_assoc) = this.parse_expr_res(Restrictions::empty(), attrs)?;
+                let use_pre_attr_pos =
+                    if is_assoc { UsePreAttrPos::Yes } else { UsePreAttrPos::No };
+                Ok((expr, Trailing::No, use_pre_attr_pos))
+            },
+        )
     }
 
     pub fn parse_expr_anon_const(&mut self) -> PResult<'a, AnonConst> {
@@ -77,7 +92,7 @@ impl<'a> Parser<'a> {
     fn parse_expr_catch_underscore(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
         let attrs = self.parse_outer_attributes()?;
         match self.parse_expr_res(restrictions, attrs) {
-            Ok(expr) => Ok(expr),
+            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) =>
@@ -104,18 +119,20 @@ impl<'a> Parser<'a> {
         &mut self,
         r: Restrictions,
         attrs: AttrWrapper,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, (P<Expr>, bool)> {
         self.with_res(r, |this| this.parse_expr_assoc_with(0, attrs))
     }
 
     /// Parses an associative expression with operators of at least `min_prec` precedence.
+    /// The `bool` in the return value indicates if it was an assoc expr, i.e. with an operator
+    /// followed by a subexpression (e.g. `1 + 2`).
     pub(super) fn parse_expr_assoc_with(
         &mut self,
         min_prec: usize,
         attrs: AttrWrapper,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, (P<Expr>, bool)> {
         let lhs = if self.token.is_range_separator() {
-            return self.parse_expr_prefix_range(attrs);
+            return self.parse_expr_prefix_range(attrs).map(|res| (res, false));
         } else {
             self.parse_expr_prefix(attrs)?
         };
@@ -123,15 +140,17 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses the rest of an associative expression (i.e. the part after the lhs) with operators
-    /// of at least `min_prec` precedence.
+    /// of at least `min_prec` precedence. The `bool` in the return value indicates if something
+    /// was actually parsed.
     pub(super) fn parse_expr_assoc_rest_with(
         &mut self,
         min_prec: usize,
         starts_stmt: bool,
         mut lhs: P<Expr>,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, (P<Expr>, bool)> {
+        let mut parsed_something = false;
         if !self.should_continue_as_assoc_expr(&lhs) {
-            return Ok(lhs);
+            return Ok((lhs, parsed_something));
         }
 
         self.expected_tokens.push(TokenType::Operator);
@@ -156,10 +175,11 @@ impl<'a> Parser<'a> {
                 self.err_larrow_operator(self.token.span);
             }
 
+            parsed_something = true;
             self.bump();
             if op.node.is_comparison() {
                 if let Some(expr) = self.check_no_chained_comparison(&lhs, &op)? {
-                    return Ok(expr);
+                    return Ok((expr, parsed_something));
                 }
             }
 
@@ -263,7 +283,7 @@ impl<'a> Parser<'a> {
                 // the special cases. The code is here only for future convenience.
                 Fixity::None => 1,
             };
-            let rhs = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
+            let (rhs, _) = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
                 let attrs = this.parse_outer_attributes()?;
                 this.parse_expr_assoc_with(prec + prec_adjustment, attrs)
             })?;
@@ -319,7 +339,7 @@ impl<'a> Parser<'a> {
             }
         }
 
-        Ok(lhs)
+        Ok((lhs, parsed_something))
     }
 
     fn should_continue_as_assoc_expr(&mut self, lhs: &Expr) -> bool {
@@ -441,7 +461,8 @@ impl<'a> Parser<'a> {
             let attrs = self.parse_outer_attributes()?;
             Some(
                 self.parse_expr_assoc_with(prec + 1, attrs)
-                    .map_err(|err| self.maybe_err_dotdotlt_syntax(maybe_lt, err))?,
+                    .map_err(|err| self.maybe_err_dotdotlt_syntax(maybe_lt, err))?
+                    .0,
             )
         } else {
             None
@@ -498,7 +519,7 @@ impl<'a> Parser<'a> {
                 // RHS must be parsed with more associativity than the dots.
                 let attrs = this.parse_outer_attributes()?;
                 this.parse_expr_assoc_with(op.unwrap().precedence() + 1, attrs)
-                    .map(|x| (lo.to(x.span), Some(x)))
+                    .map(|(x, _)| (lo.to(x.span), Some(x)))
                     .map_err(|err| this.maybe_err_dotdotlt_syntax(maybe_lt, err))?
             } else {
                 (lo, None)
@@ -2335,7 +2356,7 @@ impl<'a> Parser<'a> {
                 let token = self.token.clone();
                 let attrs = self.parse_outer_attributes()?;
                 match self.parse_expr_res(restrictions, attrs) {
-                    Ok(expr) => expr,
+                    Ok((expr, _)) => expr,
                     Err(err) => self.recover_closure_body(err, before, prev, token, lo, decl_hi)?,
                 }
             }
@@ -2445,7 +2466,7 @@ impl<'a> Parser<'a> {
     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| {
+        self.collect_tokens(None, 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()?
@@ -2463,6 +2484,7 @@ impl<'a> Parser<'a> {
                     is_placeholder: false,
                 },
                 Trailing::from(this.token == token::Comma),
+                UsePreAttrPos::No,
             ))
         })
     }
@@ -2583,7 +2605,7 @@ impl<'a> Parser<'a> {
     /// Parses the condition of a `if` or `while` expression.
     fn parse_expr_cond(&mut self) -> PResult<'a, P<Expr>> {
         let attrs = self.parse_outer_attributes()?;
-        let mut cond =
+        let (mut cond, _) =
             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, attrs)?;
 
         CondChecker::new(self).visit_expr(&mut cond);
@@ -2632,7 +2654,7 @@ impl<'a> Parser<'a> {
             self.expect(&token::Eq)?;
         }
         let attrs = self.parse_outer_attributes()?;
-        let expr = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), attrs)?;
+        let (expr, _) = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), attrs)?;
         let span = lo.to(expr.span);
         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span, recovered)))
     }
@@ -2766,7 +2788,7 @@ impl<'a> Parser<'a> {
                 // 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 attrs = self.parse_outer_attributes()?;
-                let expr = match self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs) {
+                let (expr, _) = match self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs) {
                     Ok(expr) => expr,
                     Err(expr_err) => {
                         // We don't know what followed the `in`, so cancel and bubble up the
@@ -2801,7 +2823,7 @@ impl<'a> Parser<'a> {
         }
         self.check_for_for_in_in_typo(self.prev_token.span);
         let attrs = self.parse_outer_attributes()?;
-        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
+        let (expr, _) = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
         Ok((pat, expr))
     }
 
@@ -2921,7 +2943,7 @@ impl<'a> Parser<'a> {
     fn parse_expr_match(&mut self) -> PResult<'a, P<Expr>> {
         let match_span = self.prev_token.span;
         let attrs = self.parse_outer_attributes()?;
-        let scrutinee = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
+        let (scrutinee, _) = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
 
         self.parse_match_block(match_span, match_span, scrutinee, MatchKind::Prefix)
     }
@@ -3069,7 +3091,7 @@ impl<'a> Parser<'a> {
 
     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| {
+        self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
             let lo = this.token.span;
             let (pat, guard) = this.parse_match_arm_pat_and_guard()?;
 
@@ -3126,7 +3148,7 @@ impl<'a> Parser<'a> {
                 let arm_start_span = this.token.span;
 
                 let attrs = this.parse_outer_attributes()?;
-                let expr =
+                let (expr, _) =
                     this.parse_expr_res(Restrictions::STMT_EXPR, attrs).map_err(|mut err| {
                         err.span_label(arrow_span, "while parsing the `match` arm starting here");
                         err
@@ -3244,6 +3266,7 @@ impl<'a> Parser<'a> {
                     is_placeholder: false,
                 },
                 Trailing::No,
+                UsePreAttrPos::No,
             ))
         })
     }
@@ -3334,8 +3357,9 @@ impl<'a> Parser<'a> {
 
     fn parse_match_guard_condition(&mut self) -> PResult<'a, P<Expr>> {
         let attrs = self.parse_outer_attributes()?;
-        self.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, attrs).map_err(
-            |mut err| {
+        match self.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, attrs) {
+            Ok((expr, _)) => Ok(expr),
+            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
@@ -3355,9 +3379,9 @@ impl<'a> Parser<'a> {
                         err.span_suggestion_verbose(sugg_sp, msg, "=> ", applicability);
                     }
                 }
-                err
-            },
-        )
+                Err(err)
+            }
+        }
     }
 
     pub(crate) fn is_builtin(&self) -> bool {
@@ -3708,7 +3732,7 @@ impl<'a> Parser<'a> {
     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| {
+        self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
             let lo = this.token.span;
 
             // Check if a colon exists one ahead. This means we're parsing a fieldname.
@@ -3753,6 +3777,7 @@ impl<'a> Parser<'a> {
                     is_placeholder: false,
                 },
                 Trailing::from(this.token == token::Comma),
+                UsePreAttrPos::No,
             ))
         })
     }
@@ -3846,7 +3871,7 @@ impl<'a> Parser<'a> {
         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| {
+        self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
             let res = f(this, attrs)?;
             let trailing = Trailing::from(
                 this.restrictions.contains(Restrictions::STMT_EXPR)
@@ -3856,7 +3881,7 @@ impl<'a> Parser<'a> {
                 // `#[attr] expr,` always captures a trailing comma.
                 || this.token == token::Comma,
             );
-            Ok((res, trailing))
+            Ok((res, trailing, UsePreAttrPos::No))
         })
     }
 }
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index 47b801d1490..af3b6f740e3 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -7,7 +7,7 @@ use rustc_span::symbol::{kw, Ident};
 use rustc_span::Span;
 use thin_vec::ThinVec;
 
-use super::{ForceCollect, Parser, Trailing};
+use super::{ForceCollect, Parser, Trailing, UsePreAttrPos};
 use crate::errors::{
     self, MultipleWhereClauses, UnexpectedDefaultValueForLifetimeInGenericParameters,
     UnexpectedSelfInGenericParameters, WhereClauseBeforeTupleStructBody,
@@ -169,94 +169,88 @@ impl<'a> Parser<'a> {
         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,
-                        });
+            let param = self.collect_tokens(None, 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 });
+
+                    // Eat a trailing comma, if it exists.
+                    let _ = 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())
+                    };
 
-                        // Eat a trailing comma, if it exists.
-                        let _ = this.eat(&token::Comma);
+                    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,
+                        });
                     }
 
-                    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?
                         }
-
-                        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, Trailing::No));
-                            }
-                            Err(err) => {
-                                err.cancel();
-                                // FIXME - maybe we should overwrite 'self' outside of `collect_tokens`?
-                                this.restore_snapshot(snapshot);
-                                return Ok((None, Trailing::No));
-                            }
+                        Err(err) => {
+                            err.cancel();
+                            // FIXME - maybe we should overwrite 'self' outside of `collect_tokens`?
+                            this.restore_snapshot(snapshot);
                         }
-                    } 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, Trailing::No, UsePreAttrPos::No));
+                } 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, Trailing::No));
-                    };
-
-                    if !this.eat(&token::Comma) {
-                        done = true;
                     }
-                    // We just ate the comma, so no need to capture the trailing token.
-                    Ok((param, Trailing::No))
-                })?;
+                    return Ok((None, Trailing::No, UsePreAttrPos::No));
+                };
+
+                if !this.eat(&token::Comma) {
+                    done = true;
+                }
+                // We just ate the comma, so no need to capture the trailing token.
+                Ok((param, Trailing::No, UsePreAttrPos::No))
+            })?;
 
             if let Some(param) = param {
                 params.push(param);
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index fb205c5797a..47820e93c23 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -20,7 +20,9 @@ use tracing::debug;
 
 use super::diagnostics::{dummy_arg, ConsumeClosingDelim};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
-use super::{AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, Trailing};
+use super::{
+    AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, Trailing, UsePreAttrPos,
+};
 use crate::errors::{self, MacroExpandsToAdtField};
 use crate::{fluent_generated as fluent, maybe_whole};
 
@@ -127,7 +129,7 @@ impl<'a> Parser<'a> {
             Some(item.into_inner())
         });
 
-        self.collect_tokens_trailing_token(attrs, force_collect, |this, mut attrs| {
+        self.collect_tokens(None, attrs, force_collect, |this, mut attrs| {
             let lo = this.token.span;
             let vis = this.parse_visibility(FollowedByType::No)?;
             let mut def = this.parse_defaultness();
@@ -145,7 +147,7 @@ impl<'a> Parser<'a> {
                 let span = lo.to(this.prev_token.span);
                 let id = DUMMY_NODE_ID;
                 let item = Item { ident, attrs, id, kind, vis, span, tokens: None };
-                return Ok((Some(item), Trailing::No));
+                return Ok((Some(item), Trailing::No, UsePreAttrPos::No));
             }
 
             // At this point, we have failed to parse an item.
@@ -160,7 +162,7 @@ impl<'a> Parser<'a> {
             if !attrs_allowed {
                 this.recover_attrs_no_item(&attrs)?;
             }
-            Ok((None, Trailing::No))
+            Ok((None, Trailing::No, UsePreAttrPos::No))
         })
     }
 
@@ -1546,86 +1548,82 @@ impl<'a> Parser<'a> {
         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, Trailing::No));
-                }
-                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();
-                    }
+        self.collect_tokens(None, variant_attrs, ForceCollect::No, |this, variant_attrs| {
+            let vlo = this.token.span;
 
-                    this.bump();
-                    this.parse_delim_args()?;
+            let vis = this.parse_visibility(FollowedByType::No)?;
+            if !this.recover_nested_adt_item(kw::Enum)? {
+                return Ok((None, Trailing::No, UsePreAttrPos::No));
+            }
+            let ident = this.parse_field_ident("enum", vlo)?;
 
-                    return Ok((None, Trailing::from(this.token == token::Comma)));
+            if this.token == token::Not {
+                if let Err(err) = this.unexpected() {
+                    err.with_note(fluent::parse_macro_expands_to_enum_variant).emit();
                 }
 
-                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,
+                this.bump();
+                this.parse_delim_args()?;
+
+                return Ok((None, Trailing::from(this.token == token::Comma), UsePreAttrPos::No));
+            }
+
+            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::Parenthesis)]);
-                            this.bump(); // )
+                            this.eat_to_tokens(&[&token::CloseDelim(Delimiter::Brace)]);
+                            this.bump(); // }
                             err.span_label(span, "while parsing this enum");
                             err.help(help);
-                            err.emit();
-                            thin_vec![]
+                            let guar = err.emit();
+                            (thin_vec![], Recovered::Yes(guar))
                         }
                     };
-                    VariantData::Tuple(body, DUMMY_NODE_ID)
-                } else {
-                    VariantData::Unit(DUMMY_NODE_ID)
+                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 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,
-                };
+            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), Trailing::from(this.token == token::Comma)))
-            },
-        )
+            Ok((Some(vr), Trailing::from(this.token == token::Comma), UsePreAttrPos::No))
+        })
         .map_err(|mut err| {
             err.help(help);
             err
@@ -1777,7 +1775,7 @@ impl<'a> Parser<'a> {
         // 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| {
+            p.collect_tokens(None, 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
@@ -1816,6 +1814,7 @@ impl<'a> Parser<'a> {
                         is_placeholder: false,
                     },
                     Trailing::from(p.token == token::Comma),
+                    UsePreAttrPos::No,
                 ))
             })
         })
@@ -1827,11 +1826,11 @@ impl<'a> Parser<'a> {
         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| {
+        self.collect_tokens(None, 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, Trailing::No))
+                .map(|field| (field, Trailing::No, UsePreAttrPos::No))
         })
     }
 
@@ -2806,12 +2805,12 @@ impl<'a> Parser<'a> {
     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| {
+        self.collect_tokens(None, 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?, Trailing::No));
+                return Ok((res?, Trailing::No, UsePreAttrPos::No));
             }
 
             let is_name_required = match this.token.kind {
@@ -2827,7 +2826,7 @@ impl<'a> Parser<'a> {
                         this.parameter_without_type(&mut err, pat, is_name_required, first_param)
                     {
                         let guar = err.emit();
-                        Ok((dummy_arg(ident, guar), Trailing::No))
+                        Ok((dummy_arg(ident, guar), Trailing::No, UsePreAttrPos::No))
                     } else {
                         Err(err)
                     };
@@ -2871,6 +2870,7 @@ impl<'a> Parser<'a> {
             Ok((
                 Param { attrs, id: ast::DUMMY_NODE_ID, is_placeholder: false, pat, span, ty },
                 Trailing::No,
+                UsePreAttrPos::No,
             ))
         })
     }
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 6a3c4a0c106..61e3fa2e6c5 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -14,7 +14,7 @@ use std::assert_matches::debug_assert_matches;
 use std::ops::Range;
 use std::{fmt, mem, slice};
 
-use attr_wrapper::AttrWrapper;
+use attr_wrapper::{AttrWrapper, UsePreAttrPos};
 pub use diagnostics::AttemptLocalParseRecovery;
 pub(crate) use expr::ForbiddenLetReason;
 pub(crate) use item::FnParseMode;
@@ -254,7 +254,7 @@ enum Capturing {
     Yes,
 }
 
-// This state is used by `Parser::collect_tokens_trailing_token`.
+// This state is used by `Parser::collect_tokens`.
 #[derive(Clone, Debug)]
 struct CaptureState {
     capturing: Capturing,
@@ -466,8 +466,8 @@ impl<'a> Parser<'a> {
         parser.bump();
 
         // Change this from 1 back to 0 after the bump. This eases debugging of
-        // `Parser::collect_tokens_trailing_token` nicer because it makes the
-        // token positions 0-indexed which is nicer than 1-indexed.
+        // `Parser::collect_tokens` because 0-indexed token positions are nicer
+        // than 1-indexed token positions.
         parser.num_bump_calls = 0;
 
         parser
@@ -1553,11 +1553,9 @@ impl<'a> Parser<'a> {
     ) -> 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)?, Trailing::No)),
-        )
+        self.collect_tokens(None, AttrWrapper::empty(), ForceCollect::Yes, |this, _attrs| {
+            Ok((f(this)?, Trailing::No, UsePreAttrPos::No))
+        })
     }
 
     /// `::{` or `::*`
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 164be7c9496..eb9a957032f 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -13,7 +13,7 @@ use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, ErrorGuaranteed, Span};
 use thin_vec::{thin_vec, ThinVec};
 
-use super::{ForceCollect, Parser, PathStyle, Restrictions, Trailing};
+use super::{ForceCollect, Parser, PathStyle, Restrictions, Trailing, UsePreAttrPos};
 use crate::errors::{
     self, AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
     DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
@@ -403,7 +403,7 @@ impl<'a> Parser<'a> {
 
             // Parse an associative expression such as `+ expr`, `% expr`, ...
             // Assignements, ranges and `|` are disabled by [`Restrictions::IS_PAT`].
-            if let Ok(expr) =
+            if let Ok((expr, _)) =
                 snapshot.parse_expr_assoc_rest_with(0, false, expr).map_err(|err| err.cancel())
             {
                 // We got a valid expression.
@@ -1302,24 +1302,23 @@ impl<'a> Parser<'a> {
                 }
             }
 
-            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);
+            let field = self.collect_tokens(None, 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();
                         }
-                    }?;
-                    ate_comma = this.eat(&token::Comma);
+                        return Err(err);
+                    }
+                }?;
+                ate_comma = this.eat(&token::Comma);
 
-                    last_non_comma_dotdot_span = Some(this.prev_token.span);
+                last_non_comma_dotdot_span = Some(this.prev_token.span);
 
-                    // We just ate a comma, so there's no need to capture a trailing token.
-                    Ok((field, Trailing::No))
-                })?;
+                // We just ate a comma, so there's no need to capture a trailing token.
+                Ok((field, Trailing::No, UsePreAttrPos::No))
+            })?;
 
             fields.push(field)
         }
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 007d760aba3..b58f398efed 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -913,7 +913,7 @@ impl<'a> Parser<'a> {
             let snapshot = self.create_snapshot_for_diagnostic();
             let attrs = self.parse_outer_attributes()?;
             match self.parse_expr_res(Restrictions::CONST_EXPR, attrs) {
-                Ok(expr) => {
+                Ok((expr, _)) => {
                     return Ok(Some(self.dummy_const_arg_needs_braces(
                         self.dcx().struct_span_err(expr.span, "invalid const generic expression"),
                         expr.span,
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index ac6a459060a..69044192780 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -21,7 +21,7 @@ use super::pat::{PatternLocation, RecoverComma};
 use super::path::PathStyle;
 use super::{
     AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
-    Trailing,
+    Trailing, UsePreAttrPos,
 };
 use crate::errors::MalformedLoopLabel;
 use crate::{errors, maybe_whole};
@@ -46,6 +46,7 @@ impl<'a> Parser<'a> {
         capture_semi: bool,
         force_collect: ForceCollect,
     ) -> PResult<'a, Option<Stmt>> {
+        let pre_attr_pos = self.collect_pos();
         let attrs = self.parse_outer_attributes()?;
         let lo = self.token.span;
 
@@ -66,11 +67,15 @@ impl<'a> Parser<'a> {
         }
 
         Ok(Some(if self.token.is_keyword(kw::Let) {
-            self.collect_tokens_trailing_token(attrs, force_collect, |this, attrs| {
+            self.collect_tokens(None, attrs, force_collect, |this, attrs| {
                 this.expect_keyword(kw::Let)?;
                 let local = this.parse_local(attrs)?;
                 let trailing = Trailing::from(capture_semi && this.token == token::Semi);
-                Ok((this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)), trailing))
+                Ok((
+                    this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
+                    trailing,
+                    UsePreAttrPos::No,
+                ))
             })?
         } else if self.is_kw_followed_by_ident(kw::Mut) && self.may_recover() {
             self.recover_stmt_local_after_let(
@@ -104,10 +109,18 @@ impl<'a> Parser<'a> {
             // 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_`.
-            let stmt = self.collect_tokens_trailing_token(
+            //
+            // `UsePreAttrPos::Yes` here means the attribute belongs unconditionally to the
+            // expression, not the statement. (But the statement attributes/tokens are obtained
+            // from the expression anyway, because `Stmt` delegates `HasAttrs`/`HasTokens` to
+            // the things within `StmtKind`.)
+            let stmt = self.collect_tokens(
+                Some(pre_attr_pos),
                 AttrWrapper::empty(),
                 force_collect,
-                |this, _empty_attrs| Ok((this.parse_stmt_path_start(lo, attrs)?, Trailing::No)),
+                |this, _empty_attrs| {
+                    Ok((this.parse_stmt_path_start(lo, attrs)?, Trailing::No, UsePreAttrPos::Yes))
+                },
             );
             match stmt {
                 Ok(stmt) => stmt,
@@ -129,12 +142,15 @@ impl<'a> Parser<'a> {
             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 = self.collect_tokens_trailing_token(
+            // Remainder are line-expr stmts. This is similar to the `parse_stmt_path_start` case
+            // above.
+            let e = self.collect_tokens(
+                Some(pre_attr_pos),
                 AttrWrapper::empty(),
                 force_collect,
                 |this, _empty_attrs| {
-                    Ok((this.parse_expr_res(Restrictions::STMT_EXPR, attrs)?, Trailing::No))
+                    let (expr, _) = this.parse_expr_res(Restrictions::STMT_EXPR, attrs)?;
+                    Ok((expr, Trailing::No, UsePreAttrPos::Yes))
                 },
             )?;
             if matches!(e.kind, ExprKind::Assign(..)) && self.eat_keyword(kw::Else) {
@@ -151,12 +167,16 @@ impl<'a> Parser<'a> {
     }
 
     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 stmt = self.collect_tokens(None, 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)?;
-                return Ok((stmt_mac, Trailing::from(this.token == token::Semi)));
+                return Ok((
+                    stmt_mac,
+                    Trailing::from(this.token == token::Semi),
+                    UsePreAttrPos::No,
+                ));
             }
 
             let expr = if this.eat(&token::OpenDelim(Delimiter::Brace)) {
@@ -170,13 +190,17 @@ impl<'a> Parser<'a> {
                 this.parse_expr_dot_or_call_with(attrs, expr, lo)
             })?;
             // `DUMMY_SP` will get overwritten later in this function
-            Ok((this.mk_stmt(rustc_span::DUMMY_SP, StmtKind::Expr(expr)), Trailing::No))
+            Ok((
+                this.mk_stmt(rustc_span::DUMMY_SP, StmtKind::Expr(expr)),
+                Trailing::No,
+                UsePreAttrPos::No,
+            ))
         })?;
 
         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| {
+            // Perform this outside of the `collect_tokens` 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_rest_with(0, true, expr)
             })?;
             Ok(self.mk_stmt(lo.to(self.prev_token.span), StmtKind::Expr(expr)))
@@ -210,7 +234,7 @@ impl<'a> Parser<'a> {
             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(attrs, e, lo)?;
-            let e = self.parse_expr_assoc_rest_with(0, false, e)?;
+            let (e, _) = self.parse_expr_assoc_rest_with(0, false, e)?;
             StmtKind::Expr(e)
         };
         Ok(self.mk_stmt(lo.to(hi), kind))
@@ -240,10 +264,14 @@ impl<'a> Parser<'a> {
         subdiagnostic: fn(Span) -> errors::InvalidVariableDeclarationSub,
         force_collect: ForceCollect,
     ) -> PResult<'a, Stmt> {
-        let stmt = self.collect_tokens_trailing_token(attrs, force_collect, |this, attrs| {
+        let stmt = self.collect_tokens(None, attrs, force_collect, |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)), Trailing::No))
+            Ok((
+                this.mk_stmt(lo.to(this.prev_token.span), StmtKind::Let(local)),
+                Trailing::No,
+                UsePreAttrPos::No,
+            ))
         })?;
         self.dcx()
             .emit_err(errors::InvalidVariableDeclaration { span: lo, sub: subdiagnostic(lo) });
diff --git a/tests/ui/attributes/assoc-expr.rs b/tests/ui/attributes/assoc-expr.rs
new file mode 100644
index 00000000000..f39557d2ef0
--- /dev/null
+++ b/tests/ui/attributes/assoc-expr.rs
@@ -0,0 +1,42 @@
+//@ check-pass
+// This test triggered an assertion failure in token collection due to
+// mishandling of attributes on associative expressions.
+
+#![feature(cfg_eval)]
+#![feature(rustc_attrs)]
+#![feature(stmt_expr_attributes)]
+#![allow(internal_features)]
+
+fn main() {}
+
+#[cfg_eval]
+struct Foo1(
+    [ bool; {
+        let _x = 30;
+        #[cfg_attr(unix, rustc_dummy(aa))] 1
+    } ]
+);
+
+#[cfg_eval]
+struct Foo12(
+    [ bool; {
+        let _x = 30;
+        #[cfg_attr(unix, rustc_dummy(bb))] 1 + 2
+    } ]
+);
+
+#[cfg_eval]
+struct Foox(
+    [ bool; {
+        let _x = 30;
+        #[cfg_attr(unix, rustc_dummy(cc))] _x
+    } ]
+);
+
+#[cfg_eval]
+struct Foox2(
+    [ bool; {
+        let _x = 30;
+        #[cfg_attr(unix, rustc_dummy(dd))] _x + 2
+    } ]
+);
diff --git a/tests/ui/macros/stringify.rs b/tests/ui/macros/stringify.rs
index a8b73ac7e15..37409dd066d 100644
--- a/tests/ui/macros/stringify.rs
+++ b/tests/ui/macros/stringify.rs
@@ -51,14 +51,6 @@ macro_rules! c1 {
     };
 }
 
-// FIXME: temporary
-macro_rules! c2 {
-    ($frag:ident, [$($tt:tt)*], $s1:literal, $s2:literal) => {
-        assert_eq!($frag!($($tt)*), $s1);
-        assert_eq!(stringify!($($tt)*), $s2);
-    };
-}
-
 #[test]
 fn test_block() {
     c1!(block, [ {} ], "{}");
@@ -344,10 +336,10 @@ fn test_expr() {
     // Ones involving attributes.
     c1!(expr, [ #[aa] 1 ], "#[aa] 1");
     c1!(expr, [ #[aa] #[bb] x ], "#[aa] #[bb] x");
-    c2!(expr, [ #[aa] 1 + 2 ], "1 + 2", "#[aa] 1 + 2"); // FIXME
-    c2!(expr, [ #[aa] x + 2 ], "x + 2", "#[aa] x + 2"); // FIXME
-    c2!(expr, [ #[aa] 1 / #[bb] 2 ], "1 / #[bb] 2", "#[aa] 1 / #[bb] 2"); // FIXME
-    c2!(expr, [ #[aa] x / #[bb] 2 ], "x / #[bb] 2", "#[aa] x / #[bb] 2"); // FIXME
+    c1!(expr, [ #[aa] 1 + 2 ], "#[aa] 1 + 2");
+    c1!(expr, [ #[aa] x + 2 ], "#[aa] x + 2");
+    c1!(expr, [ #[aa] 1 / #[bb] 2 ], "#[aa] 1 / #[bb] 2");
+    c1!(expr, [ #[aa] x / #[bb] 2 ], "#[aa] x / #[bb] 2");
     c1!(expr, [ 1 << #[bb] 2 ], "1 << #[bb] 2");
     c1!(expr, [ x << #[bb] 2 ], "x << #[bb] 2");
     c1!(expr, [ #[aa] (1 + 2) ], "#[aa] (1 + 2)");
@@ -659,10 +651,10 @@ fn test_stmt() {
     // Ones involving attributes.
     c1!(stmt, [ #[aa] 1 ], "#[aa] 1");
     c1!(stmt, [ #[aa] #[bb] x ], "#[aa] #[bb] x");
-    c2!(stmt, [ #[aa] 1 as u32 ], "1 as u32", "#[aa] 1 as u32"); // FIXME
-    c2!(stmt, [ #[aa] x as u32 ], "x as u32", "#[aa] x as u32"); // FIXME
-    c2!(stmt, [ #[aa] 1 .. #[bb] 2 ], "1 .. #[bb] 2", "#[aa] 1 .. #[bb] 2"); // FIXME
-    c2!(stmt, [ #[aa] x .. #[bb] 2 ], "x .. #[bb] 2", "#[aa] x .. #[bb] 2"); // FIXME
+    c1!(stmt, [ #[aa] 1 as u32 ], "#[aa] 1 as u32");
+    c1!(stmt, [ #[aa] x as u32 ], "#[aa] x as u32");
+    c1!(stmt, [ #[aa] 1 .. #[bb] 2 ], "#[aa] 1 .. #[bb] 2");
+    c1!(stmt, [ #[aa] x .. #[bb] 2 ], "#[aa] x .. #[bb] 2");
     c1!(stmt, [ 1 || #[bb] 2 ], "1 || #[bb] 2");
     c1!(stmt, [ x || #[bb] 2 ], "x || #[bb] 2");
     c1!(stmt, [ #[aa] (1 + 2) ], "#[aa] (1 + 2)");