Auto merge of #127957 - matthiaskrgr:rollup-1u5ivck, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #127350 (Parser: Suggest Placing the Return Type After Function Parameters)
 - #127621 (Rewrite and rename `issue-22131` and `issue-26006` `run-make` tests to rmake)
 - #127662 (When finding item gated behind a `cfg` flag, point at it)
 - #127903 (`force_collect` improvements)
 - #127932 (rustdoc: fix `current` class on sidebar modnav)
 - #127943 (Don't allow unsafe statics outside of extern blocks)

r? `@ghost`
`@rustbot` modify labels: rollup

8 files changed, 159 insertions, 75 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index da0701efddb..109d36fe689 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -1503,6 +1503,20 @@ pub(crate) struct FnPtrWithGenerics {
 }
 
 #[derive(Subdiagnostic)]
+#[multipart_suggestion(
+    parse_misplaced_return_type,
+    style = "verbose",
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct MisplacedReturnType {
+    #[suggestion_part(code = " {snippet}")]
+    pub fn_params_end: Span,
+    pub snippet: String,
+    #[suggestion_part(code = "")]
+    pub ret_ty_span: Span,
+}
+
+#[derive(Subdiagnostic)]
 #[multipart_suggestion(parse_suggestion, applicability = "maybe-incorrect")]
 pub(crate) struct FnPtrWithGenericsSugg {
     #[suggestion_part(code = "{snippet}")]
@@ -1516,7 +1530,6 @@ pub(crate) struct FnPtrWithGenericsSugg {
 
 pub(crate) struct FnTraitMissingParen {
     pub span: Span,
-    pub machine_applicable: bool,
 }
 
 impl Subdiagnostic for FnTraitMissingParen {
@@ -1526,16 +1539,11 @@ impl Subdiagnostic for FnTraitMissingParen {
         _: &F,
     ) {
         diag.span_label(self.span, crate::fluent_generated::parse_fn_trait_missing_paren);
-        let applicability = if self.machine_applicable {
-            Applicability::MachineApplicable
-        } else {
-            Applicability::MaybeIncorrect
-        };
         diag.span_suggestion_short(
             self.span.shrink_to_hi(),
             crate::fluent_generated::parse_add_paren,
             "()",
-            applicability,
+            Applicability::MachineApplicable,
         );
     }
 }
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index a2e40d3398a..0b2c3044039 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -124,7 +124,7 @@ impl<'a> Parser<'a> {
                 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)?;
+            let item = this.parse_attr_item(ForceCollect::No)?;
             this.expect(&token::CloseDelim(Delimiter::Bracket))?;
             let attr_sp = lo.to(this.prev_token.span);
 
@@ -248,16 +248,15 @@ impl<'a> Parser<'a> {
     ///     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> {
+    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| {
+        let do_parse = |this: &mut Self, _empty_attrs| {
             let is_unsafe = this.eat_keyword(kw::Unsafe);
             let unsafety = if is_unsafe {
                 let unsafe_span = this.prev_token.span;
                 this.psess.gated_spans.gate(sym::unsafe_attributes, unsafe_span);
                 this.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
-
                 ast::Safety::Unsafe(unsafe_span)
             } else {
                 ast::Safety::Default
@@ -268,10 +267,10 @@ impl<'a> Parser<'a> {
             if is_unsafe {
                 this.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
             }
-            Ok(ast::AttrItem { unsafety, path, args, tokens: None })
+            Ok((ast::AttrItem { unsafety, path, args, tokens: None }, false))
         };
-        // Attr items don't have attributes
-        if capture_tokens { self.collect_tokens_no_attrs(do_parse) } else { do_parse(self) }
+        // Attr items don't have attributes.
+        self.collect_tokens_trailing_token(AttrWrapper::empty(), force_collect, do_parse)
     }
 
     /// Parses attributes that appear after the opening of an item. These should
@@ -340,7 +339,7 @@ impl<'a> Parser<'a> {
         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)?;
+            let item = self.parse_attr_item(ForceCollect::Yes)?;
             expanded_attrs.push((item, lo.to(self.prev_token.span)));
             if !self.eat(&token::Comma) {
                 break;
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 326478a7175..1a0d9aa6378 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -430,7 +430,7 @@ impl<'a> Parser<'a> {
         &mut self,
         edible: &[TokenKind],
         inedible: &[TokenKind],
-    ) -> PResult<'a, Recovered> {
+    ) -> PResult<'a, ErrorGuaranteed> {
         debug!("expected_one_of_not_found(edible: {:?}, inedible: {:?})", edible, inedible);
         fn tokens_to_string(tokens: &[TokenType]) -> String {
             let mut i = tokens.iter();
@@ -533,7 +533,7 @@ impl<'a> Parser<'a> {
                     sugg: ExpectedSemiSugg::ChangeToSemi(self.token.span),
                 });
                 self.bump();
-                return Ok(Recovered::Yes(guar));
+                return Ok(guar);
             } else if self.look_ahead(0, |t| {
                 t == &token::CloseDelim(Delimiter::Brace)
                     || ((t.can_begin_expr() || t.can_begin_item())
@@ -557,7 +557,7 @@ impl<'a> Parser<'a> {
                     unexpected_token_label: Some(self.token.span),
                     sugg: ExpectedSemiSugg::AddSemi(span),
                 });
-                return Ok(Recovered::Yes(guar));
+                return Ok(guar);
             }
         }
 
@@ -712,7 +712,7 @@ impl<'a> Parser<'a> {
         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));
+                return Ok(guar);
             } else {
                 return Err(err);
             }
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 78722ba26cb..fbc5b914600 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -17,6 +17,7 @@ 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::ErrorGuaranteed;
 use rustc_span::{Span, DUMMY_SP};
 use std::fmt::Write;
 use std::mem;
@@ -2332,14 +2333,106 @@ impl<'a> Parser<'a> {
                 }
             }
         };
+
+        // Store the end of function parameters to give better diagnostics
+        // inside `parse_fn_body()`.
+        let fn_params_end = self.prev_token.span.shrink_to_hi();
+
         generics.where_clause = self.parse_where_clause()?; // `where T: Ord`
 
+        // `fn_params_end` is needed only when it's followed by a where clause.
+        let fn_params_end =
+            if generics.where_clause.has_where_token { Some(fn_params_end) } else { None };
+
         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 `{ ... }`.
+        // Either `;` or `{ ... }`.
+        let body =
+            self.parse_fn_body(attrs, &ident, &mut sig_hi, fn_parse_mode.req_body, fn_params_end)?;
         let fn_sig_span = sig_lo.to(sig_hi);
         Ok((ident, FnSig { header, decl, span: fn_sig_span }, generics, body))
     }
 
+    /// Provide diagnostics when function body is not found
+    fn error_fn_body_not_found(
+        &mut self,
+        ident_span: Span,
+        req_body: bool,
+        fn_params_end: Option<Span>,
+    ) -> PResult<'a, ErrorGuaranteed> {
+        let expected = if req_body {
+            &[token::OpenDelim(Delimiter::Brace)][..]
+        } else {
+            &[token::Semi, token::OpenDelim(Delimiter::Brace)]
+        };
+        match self.expected_one_of_not_found(&[], expected) {
+            Ok(error_guaranteed) => Ok(error_guaranteed),
+            Err(mut err) => {
+                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`");
+                    Ok(err.emit())
+                } else if self.token.kind == token::RArrow
+                    && let Some(fn_params_end) = fn_params_end
+                {
+                    // Instead of a function body, the parser has encountered a right arrow
+                    // preceded by a where clause.
+
+                    // Find whether token behind the right arrow is a function trait and
+                    // store its span.
+                    let fn_trait_span =
+                        [sym::FnOnce, sym::FnMut, sym::Fn].into_iter().find_map(|symbol| {
+                            if self.prev_token.is_ident_named(symbol) {
+                                Some(self.prev_token.span)
+                            } else {
+                                None
+                            }
+                        });
+
+                    // Parse the return type (along with the right arrow) and store its span.
+                    // If there's a parse error, cancel it and return the existing error
+                    // as we are primarily concerned with the
+                    // expected-function-body-but-found-something-else error here.
+                    let arrow_span = self.token.span;
+                    let ty_span = match self.parse_ret_ty(
+                        AllowPlus::Yes,
+                        RecoverQPath::Yes,
+                        RecoverReturnSign::Yes,
+                    ) {
+                        Ok(ty_span) => ty_span.span().shrink_to_hi(),
+                        Err(parse_error) => {
+                            parse_error.cancel();
+                            return Err(err);
+                        }
+                    };
+                    let ret_ty_span = arrow_span.to(ty_span);
+
+                    if let Some(fn_trait_span) = fn_trait_span {
+                        // Typo'd Fn* trait bounds such as
+                        // fn foo<F>() where F: FnOnce -> () {}
+                        err.subdiagnostic(errors::FnTraitMissingParen { span: fn_trait_span });
+                    } else if let Ok(snippet) = self.psess.source_map().span_to_snippet(ret_ty_span)
+                    {
+                        // If token behind right arrow is not a Fn* trait, the programmer
+                        // probably misplaced the return type after the where clause like
+                        // `fn foo<T>() where T: Default -> u8 {}`
+                        err.primary_message(
+                            "return type should be specified after the function parameters",
+                        );
+                        err.subdiagnostic(errors::MisplacedReturnType {
+                            fn_params_end,
+                            snippet,
+                            ret_ty_span,
+                        });
+                    }
+                    Err(err)
+                } else {
+                    Err(err)
+                }
+            }
+        }
+    }
+
     /// 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.
@@ -2349,6 +2442,7 @@ impl<'a> Parser<'a> {
         ident: &Ident,
         sig_hi: &mut Span,
         req_body: bool,
+        fn_params_end: Option<Span>,
     ) -> PResult<'a, Option<P<Block>>> {
         let has_semi = if req_body {
             self.token.kind == TokenKind::Semi
@@ -2377,33 +2471,7 @@ impl<'a> Parser<'a> {
             });
             (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(errors::FnTraitMissingParen {
-                            span: self.prev_token.span,
-                            machine_applicable,
-                        });
-                    }
-                    return Err(err);
-                }
-            }
+            self.error_fn_body_not_found(ident.span, req_body, fn_params_end)?;
             (AttrVec::new(), None)
         };
         attrs.extend(inner_attrs);
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 06545e85dd1..7326b9ec51f 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -501,6 +501,7 @@ impl<'a> Parser<'a> {
             FatalError.raise();
         } else {
             self.expected_one_of_not_found(edible, inedible)
+                .map(|error_guaranteed| Recovered::Yes(error_guaranteed))
         }
     }
 
@@ -948,11 +949,10 @@ impl<'a> Parser<'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
-                });
+            let _ = self.parse_stmt_without_recovery(false, ForceCollect::No).unwrap_or_else(|e| {
+                e.cancel();
+                None
+            });
         }
 
         expect_err
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index 41e31d76d62..886d6af1735 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -171,7 +171,7 @@ impl<'a> Parser<'a> {
             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::Meta => NtMeta(P(self.parse_attr_item(ForceCollect::Yes)?)),
             NonterminalKind::Vis => {
                 NtVis(P(self
                     .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?))
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 3ec891b4eea..d8de7c1bfa1 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -72,6 +72,7 @@ impl<'a> Parser<'a> {
                 lo,
                 attrs,
                 errors::InvalidVariableDeclarationSub::MissingLet,
+                force_collect,
             )?
         } else if self.is_kw_followed_by_ident(kw::Auto) && self.may_recover() {
             self.bump(); // `auto`
@@ -79,6 +80,7 @@ impl<'a> Parser<'a> {
                 lo,
                 attrs,
                 errors::InvalidVariableDeclarationSub::UseLetNotAuto,
+                force_collect,
             )?
         } else if self.is_kw_followed_by_ident(sym::var) && self.may_recover() {
             self.bump(); // `var`
@@ -86,6 +88,7 @@ impl<'a> Parser<'a> {
                 lo,
                 attrs,
                 errors::InvalidVariableDeclarationSub::UseLetNotVar,
+                force_collect,
             )?
         } else if self.check_path()
             && !self.token.is_qpath_start()
@@ -96,17 +99,17 @@ 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_`.
-            match force_collect {
-                ForceCollect::Yes => {
-                    self.collect_tokens_no_attrs(|this| this.parse_stmt_path_start(lo, attrs))?
+            let stmt = self.collect_tokens_trailing_token(
+                AttrWrapper::empty(),
+                force_collect,
+                |this, _empty_attrs| Ok((this.parse_stmt_path_start(lo, attrs)?, false)),
+            );
+            match stmt {
+                Ok(stmt) => stmt,
+                Err(mut err) => {
+                    self.suggest_add_missing_let_for_stmt(&mut err);
+                    return Err(err);
                 }
-                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(),
@@ -123,12 +126,13 @@ impl<'a> Parser<'a> {
             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, attrs)
-                })?,
-                ForceCollect::No => self.parse_expr_res(Restrictions::STMT_EXPR, attrs)?,
-            };
+            let e = self.collect_tokens_trailing_token(
+                AttrWrapper::empty(),
+                force_collect,
+                |this, _empty_attrs| {
+                    Ok((this.parse_expr_res(Restrictions::STMT_EXPR, attrs)?, false))
+                },
+            )?;
             if matches!(e.kind, ExprKind::Assign(..)) && self.eat_keyword(kw::Else) {
                 let bl = self.parse_block()?;
                 // Destructuring assignment ... else.
@@ -231,13 +235,13 @@ impl<'a> Parser<'a> {
         lo: Span,
         attrs: AttrWrapper,
         subdiagnostic: fn(Span) -> errors::InvalidVariableDeclarationSub,
+        force_collect: ForceCollect,
     ) -> 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)), false))
-            })?;
+        let stmt = self.collect_tokens_trailing_token(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)), false))
+        })?;
         self.dcx()
             .emit_err(errors::InvalidVariableDeclaration { span: lo, sub: subdiagnostic(lo) });
         Ok(stmt)
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 68b8af7d20e..a8134110010 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -21,6 +21,11 @@ use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{ErrorGuaranteed, Span, Symbol};
 use thin_vec::{thin_vec, ThinVec};
 
+/// Signals whether parsing a type should allow `+`.
+///
+/// For example, let T be the type `impl Default + 'static`
+/// With `AllowPlus::Yes`, T will be parsed successfully
+/// With `AllowPlus::No`, parsing T will return a parse error
 #[derive(Copy, Clone, PartialEq)]
 pub(super) enum AllowPlus {
     Yes,