Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 263 insertions, 70 deletions

diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index e1db19557..ee0abba1c 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -422,15 +422,12 @@ impl<'a> Parser<'a> {
     }
 }
 
-pub fn maybe_needs_tokens(attrs: &[ast::Attribute]) -> bool {
-    // One of the attributes may either itself be a macro,
-    // or expand to macro attributes (`cfg_attr`).
-    attrs.iter().any(|attr| {
-        if attr.is_doc_comment() {
-            return false;
-        }
-        attr.ident().map_or(true, |ident| {
-            ident.name == sym::cfg_attr || !rustc_feature::is_builtin_attr_name(ident.name)
-        })
+/// 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
index 1e6ac5496..b579da098 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -61,8 +61,8 @@ impl AttrWrapper {
         self.attrs.is_empty()
     }
 
-    pub fn maybe_needs_tokens(&self) -> bool {
-        crate::parser::attr::maybe_needs_tokens(&self.attrs)
+    pub fn is_complete(&self) -> bool {
+        crate::parser::attr::is_complete(&self.attrs)
     }
 }
 
@@ -201,7 +201,7 @@ impl<'a> Parser<'a> {
         //    by definition
         if matches!(force_collect, ForceCollect::No)
             // None of our outer attributes can require tokens (e.g. a proc-macro)
-            && !attrs.maybe_needs_tokens()
+            && 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.
@@ -244,9 +244,9 @@ impl<'a> Parser<'a> {
         // 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.maybe_needs_tokens()` at the start of the function.
+            // 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::maybe_needs_tokens(ret.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
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index c14540396..0ce6a570d 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -605,6 +605,22 @@ impl<'a> Parser<'a> {
             }
         }
 
+        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,
+                    );
+                }
+        }
+
         // `pub` may be used for an item or `pub(crate)`
         if self.prev_token.is_ident_named(sym::public)
             && (self.token.can_begin_item()
@@ -751,13 +767,24 @@ impl<'a> Parser<'a> {
                     tail.could_be_bare_literal = true;
                     if maybe_struct_name.is_ident() && can_be_struct_literal {
                         // Account for `if Example { a: one(), }.is_pos() {}`.
-                        Err(self.sess.create_err(StructLiteralNeedingParens {
-                            span: maybe_struct_name.span.to(expr.span),
-                            sugg: StructLiteralNeedingParensSugg {
-                                before: maybe_struct_name.span.shrink_to_lo(),
-                                after: expr.span.shrink_to_hi(),
-                            },
-                        }))
+                        // 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.sess.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.sess.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.sess.emit_err(StructLiteralBodyWithoutPath {
                             span: expr.span,
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 1b28f3c97..7ede4fbc3 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -91,6 +91,18 @@ impl From<P<Expr>> for LhsExpr {
     }
 }
 
+#[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]
@@ -1001,9 +1013,15 @@ impl<'a> Parser<'a> {
     }
 
     fn error_unexpected_after_dot(&self) {
-        // FIXME Could factor this out into non_fatal_unexpected or something.
         let actual = pprust::token_to_string(&self.token);
-        self.sess.emit_err(errors::UnexpectedTokenAfterDot { span: self.token.span, actual });
+        let span = self.token.span;
+        let sm = self.sess.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.sess.emit_err(errors::UnexpectedTokenAfterDot { span, actual });
     }
 
     // We need an identifier or integer, but the next token is a float.
@@ -1013,13 +1031,8 @@ impl<'a> Parser<'a> {
     // 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).
-    fn parse_expr_tuple_field_access_float(
-        &mut self,
-        lo: Span,
-        base: P<Expr>,
-        float: Symbol,
-        suffix: Option<Symbol>,
-    ) -> P<Expr> {
+    // See also `TokenKind::break_two_token_op` which does similar splitting of `>>` into `>`.
+    fn break_up_float(&mut self, float: Symbol) -> DestructuredFloat {
         #[derive(Debug)]
         enum FloatComponent {
             IdentLike(String),
@@ -1056,7 +1069,7 @@ impl<'a> Parser<'a> {
         match &*components {
             // 1e2
             [IdentLike(i)] => {
-                self.parse_expr_tuple_field_access(lo, base, Symbol::intern(&i), suffix, None)
+                DestructuredFloat::Single(Symbol::intern(&i), span)
             }
             // 1.
             [IdentLike(i), Punct('.')] => {
@@ -1068,11 +1081,8 @@ impl<'a> Parser<'a> {
                 } else {
                     (span, span)
                 };
-                assert!(suffix.is_none());
                 let symbol = Symbol::intern(&i);
-                self.token = Token::new(token::Ident(symbol, false), ident_span);
-                let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
-                self.parse_expr_tuple_field_access(lo, base, symbol, None, Some(next_token))
+                DestructuredFloat::TrailingDot(symbol, ident_span, dot_span)
             }
             // 1.2 | 1.2e3
             [IdentLike(i1), Punct('.'), IdentLike(i2)] => {
@@ -1088,16 +1098,8 @@ impl<'a> Parser<'a> {
                     (span, span, span)
                 };
                 let symbol1 = Symbol::intern(&i1);
-                self.token = Token::new(token::Ident(symbol1, false), ident1_span);
-                // This needs to be `Spacing::Alone` to prevent regressions.
-                // See issue #76399 and PR #76285 for more details
-                let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
-                let base1 =
-                    self.parse_expr_tuple_field_access(lo, base, symbol1, None, Some(next_token1));
                 let symbol2 = Symbol::intern(&i2);
-                let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
-                self.bump_with((next_token2, self.token_spacing)); // `.`
-                self.parse_expr_tuple_field_access(lo, base1, symbol2, suffix, None)
+                DestructuredFloat::MiddleDot(symbol1, ident1_span, dot_span, symbol2, ident2_span)
             }
             // 1e+ | 1e- (recovered)
             [IdentLike(_), Punct('+' | '-')] |
@@ -1109,12 +1111,83 @@ impl<'a> Parser<'a> {
             [IdentLike(_), Punct('.'), IdentLike(_), Punct('+' | '-'), IdentLike(_)] => {
                 // See the FIXME about `TokenCursor` above.
                 self.error_unexpected_after_dot();
-                base
+                DestructuredFloat::Error
             }
             _ => panic!("unexpected components in a float token: {:?}", components),
         }
     }
 
+    fn parse_expr_tuple_field_access_float(
+        &mut self,
+        lo: Span,
+        base: P<Expr>,
+        float: Symbol,
+        suffix: Option<Symbol>,
+    ) -> P<Expr> {
+        match self.break_up_float(float) {
+            // 1e2
+            DestructuredFloat::Single(sym, _sp) => {
+                self.parse_expr_tuple_field_access(lo, base, sym, suffix, None)
+            }
+            // 1.
+            DestructuredFloat::TrailingDot(sym, ident_span, dot_span) => {
+                assert!(suffix.is_none());
+                self.token = Token::new(token::Ident(sym, false), ident_span);
+                let next_token = (Token::new(token::Dot, dot_span), self.token_spacing);
+                self.parse_expr_tuple_field_access(lo, base, sym, None, Some(next_token))
+            }
+            // 1.2 | 1.2e3
+            DestructuredFloat::MiddleDot(symbol1, ident1_span, dot_span, symbol2, ident2_span) => {
+                self.token = Token::new(token::Ident(symbol1, false), ident1_span);
+                // This needs to be `Spacing::Alone` to prevent regressions.
+                // See issue #76399 and PR #76285 for more details
+                let next_token1 = (Token::new(token::Dot, dot_span), Spacing::Alone);
+                let base1 =
+                    self.parse_expr_tuple_field_access(lo, base, symbol1, None, Some(next_token1));
+                let next_token2 = Token::new(token::Ident(symbol2, false), ident2_span);
+                self.bump_with((next_token2, self.token_spacing)); // `.`
+                self.parse_expr_tuple_field_access(lo, base1, symbol2, suffix, None)
+            }
+            DestructuredFloat::Error => base,
+        }
+    }
+
+    fn parse_field_name_maybe_tuple(&mut self) -> PResult<'a, ThinVec<Ident>> {
+        let token::Literal(token::Lit { kind: token::Float, symbol, suffix }) = self.token.kind
+        else {
+            return Ok(thin_vec![self.parse_field_name()?]);
+        };
+        Ok(match self.break_up_float(symbol) {
+            // 1e2
+            DestructuredFloat::Single(sym, sp) => {
+                self.bump();
+                thin_vec![Ident::new(sym, sp)]
+            }
+            // 1.
+            DestructuredFloat::TrailingDot(sym, sym_span, dot_span) => {
+                assert!(suffix.is_none());
+                // Analogous to `Self::break_and_eat`
+                self.token_cursor.break_last_token = true;
+                // This might work, in cases like `1. 2`, and might not,
+                // in cases like `offset_of!(Ty, 1.)`. It depends on what comes
+                // after the float-like token, and therefore we have to make
+                // the other parts of the parser think that there is a dot literal.
+                self.token = Token::new(token::Ident(sym, false), sym_span);
+                self.bump_with((Token::new(token::Dot, dot_span), self.token_spacing));
+                thin_vec![Ident::new(sym, sym_span)]
+            }
+            // 1.2 | 1.2e3
+            DestructuredFloat::MiddleDot(symbol1, ident1_span, _dot_span, symbol2, ident2_span) => {
+                self.bump();
+                thin_vec![Ident::new(symbol1, ident1_span), Ident::new(symbol2, ident2_span)]
+            }
+            DestructuredFloat::Error => {
+                self.bump();
+                thin_vec![Ident::new(symbol, self.prev_token.span)]
+            }
+        })
+    }
+
     fn parse_expr_tuple_field_access(
         &mut self,
         lo: Span,
@@ -1363,6 +1436,8 @@ impl<'a> Parser<'a> {
             self.parse_expr_yield()
         } else if self.is_do_yeet() {
             self.parse_expr_yeet()
+        } else if self.eat_keyword(kw::Become) {
+            self.parse_expr_become()
         } else if self.check_keyword(kw::Let) {
             self.parse_expr_let()
         } else if self.eat_keyword(kw::Underscore) {
@@ -1679,6 +1754,16 @@ impl<'a> Parser<'a> {
         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.sess.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
@@ -1821,10 +1906,11 @@ impl<'a> Parser<'a> {
         let (fields, _trailing, _recovered) = self.parse_seq_to_before_end(
             &TokenKind::CloseDelim(Delimiter::Parenthesis),
             seq_sep,
-            Parser::parse_field_name,
+            Parser::parse_field_name_maybe_tuple,
         )?;
+        let fields = fields.into_iter().flatten().collect::<Vec<_>>();
         let span = lo.to(self.token.span);
-        Ok(self.mk_expr(span, ExprKind::OffsetOf(container, fields.to_vec().into())))
+        Ok(self.mk_expr(span, ExprKind::OffsetOf(container, fields.into())))
     }
 
     /// Returns a string literal if the next token is a string literal.
@@ -1955,17 +2041,14 @@ impl<'a> Parser<'a> {
         let recovered = self.recover_after_dot();
         let token = recovered.as_ref().unwrap_or(&self.token);
         match token::Lit::from_token(token) {
-            Some(token_lit) => {
-                match MetaItemLit::from_token_lit(token_lit, token.span) {
+            Some(lit) => {
+                match MetaItemLit::from_token_lit(lit, token.span) {
                     Ok(lit) => {
                         self.bump();
                         Some(lit)
                     }
                     Err(err) => {
-                        let span = token.span;
-                        let token::Literal(lit) = token.kind else {
-                            unreachable!();
-                        };
+                        let span = token.uninterpolated_span();
                         self.bump();
                         report_lit_error(&self.sess, err, lit, span);
                         // Pack possible quotes and prefixes from the original literal into
@@ -2109,6 +2192,10 @@ impl<'a> Parser<'a> {
             self.sess.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(),
+                },
             });
         }
 
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index cd779b0b4..8ab38c4fb 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -43,6 +43,15 @@ impl<'a> Parser<'a> {
     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 Ok(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) {
@@ -120,6 +129,41 @@ impl<'a> Parser<'a> {
         })
     }
 
+    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 };
+
+        let mut err = self.struct_span_err(
+            mistyped_const_ident.span,
+            format!("`const` keyword was mistyped as `{}`", mistyped_const_ident.as_str()),
+        );
+        err.span_suggestion_verbose(
+            mistyped_const_ident.span,
+            "use the `const` keyword",
+            kw::Const.as_str(),
+            Applicability::MachineApplicable,
+        );
+        err.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>> {
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 3783ec41b..1470180de 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -2182,7 +2182,11 @@ impl<'a> Parser<'a> {
             // `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))
+                && (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,
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index c317d9636..fdf365178 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -938,7 +938,8 @@ impl<'a> Parser<'a> {
         let mut etc = false;
         let mut ate_comma = true;
         let mut delayed_err: Option<DiagnosticBuilder<'a, ErrorGuaranteed>> = None;
-        let mut etc_span = 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() {
@@ -969,12 +970,27 @@ impl<'a> Parser<'a> {
             {
                 etc = true;
                 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
+                            .sess
+                            .source_map()
+                            .span_extend_to_line(comma_tok.span)
+                            .trim_start(comma_tok.span.shrink_to_lo())
+                            .map(|s| self.sess.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.sess.source_map().span_until_non_whitespace(etc_sp));
+                    }
+                }
 
                 self.recover_bad_dot_dot();
                 self.bump(); // `..` || `...` || `_`
 
                 if self.token == token::CloseDelim(Delimiter::Brace) {
-                    etc_span = Some(etc_sp);
                     break;
                 }
                 let token_str = super::token_descr(&self.token);
@@ -996,7 +1012,6 @@ impl<'a> Parser<'a> {
                     ate_comma = true;
                 }
 
-                etc_span = Some(etc_sp.until(self.token.span));
                 if self.token == token::CloseDelim(Delimiter::Brace) {
                     // If the struct looks otherwise well formed, recover and continue.
                     if let Some(sp) = comma_sp {
@@ -1040,6 +1055,9 @@ impl<'a> Parser<'a> {
                         }
                     }?;
                     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))
@@ -1049,15 +1067,30 @@ impl<'a> Parser<'a> {
         }
 
         if let Some(mut err) = delayed_err {
-            if let Some(etc_span) = etc_span {
-                err.multipart_suggestion(
-                    "move the `..` to the end of the field list",
-                    vec![
-                        (etc_span, String::new()),
-                        (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
-                    ],
-                    Applicability::MachineApplicable,
-                );
+            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();
         }
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 54f9fc5d2..9fcf51a04 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -23,6 +23,7 @@ use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
 use rustc_span::source_map::{BytePos, Span};
 use rustc_span::symbol::{kw, sym, Ident};
 
+use std::borrow::Cow;
 use std::mem;
 use thin_vec::{thin_vec, ThinVec};
 
@@ -364,7 +365,7 @@ impl<'a> Parser<'a> {
                         // `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(msg));
+                        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);
@@ -438,7 +439,7 @@ impl<'a> Parser<'a> {
 
     fn error_block_no_opening_brace_msg(
         &mut self,
-        msg: &str,
+        msg: Cow<'static, str>,
     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         let sp = self.token.span;
         let mut e = self.struct_span_err(sp, msg);
@@ -502,7 +503,7 @@ impl<'a> Parser<'a> {
     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(&msg))
+        Err(self.error_block_no_opening_brace_msg(Cow::from(msg)))
     }
 
     /// Parses a block. Inner attributes are allowed.