Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

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

1 files changed, 2740 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
new file mode 100644
index 000000000..a2155ac1d
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -0,0 +1,2740 @@
+use super::pat::Expected;
+use super::{
+    BlockMode, CommaRecoveryMode, Parser, PathStyle, Restrictions, SemiColonMode, SeqSep,
+    TokenExpectType, TokenType,
+};
+
+use crate::lexer::UnmatchedBrace;
+use rustc_ast as ast;
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, Delimiter, Lit, LitKind, TokenKind};
+use rustc_ast::util::parser::AssocOp;
+use rustc_ast::{
+    AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingMode, Block,
+    BlockCheckMode, Expr, ExprKind, GenericArg, Generics, Item, ItemKind, Mutability, Param, Pat,
+    PatKind, Path, PathSegment, QSelf, Ty, TyKind,
+};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{
+    fluent, Applicability, DiagnosticBuilder, DiagnosticMessage, Handler, MultiSpan, PResult,
+};
+use rustc_errors::{pluralize, struct_span_err, Diagnostic, EmissionGuarantee, ErrorGuaranteed};
+use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
+use rustc_span::source_map::Spanned;
+use rustc_span::symbol::{kw, Ident};
+use rustc_span::{Span, SpanSnippetError, DUMMY_SP};
+use std::ops::{Deref, DerefMut};
+
+use std::mem::take;
+
+use crate::parser;
+use tracing::{debug, trace};
+
+const TURBOFISH_SUGGESTION_STR: &str =
+    "use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments";
+
+/// Creates a placeholder argument.
+pub(super) fn dummy_arg(ident: Ident) -> Param {
+    let pat = P(Pat {
+        id: ast::DUMMY_NODE_ID,
+        kind: PatKind::Ident(BindingMode::ByValue(Mutability::Not), ident, None),
+        span: ident.span,
+        tokens: None,
+    });
+    let ty = Ty { kind: TyKind::Err, span: ident.span, id: ast::DUMMY_NODE_ID, tokens: None };
+    Param {
+        attrs: AttrVec::default(),
+        id: ast::DUMMY_NODE_ID,
+        pat,
+        span: ident.span,
+        ty: P(ty),
+        is_placeholder: false,
+    }
+}
+
+pub enum Error {
+    UselessDocComment,
+}
+
+impl Error {
+    fn span_err(
+        self,
+        sp: impl Into<MultiSpan>,
+        handler: &Handler,
+    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+        match self {
+            Error::UselessDocComment => {
+                let mut err = struct_span_err!(
+                    handler,
+                    sp,
+                    E0585,
+                    "found a documentation comment that doesn't document anything",
+                );
+                err.help(
+                    "doc comments must come before what they document, maybe a comment was \
+                          intended with `//`?",
+                );
+                err
+            }
+        }
+    }
+}
+
+pub(super) trait RecoverQPath: Sized + 'static {
+    const PATH_STYLE: PathStyle = PathStyle::Expr;
+    fn to_ty(&self) -> Option<P<Ty>>;
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self;
+}
+
+impl RecoverQPath for Ty {
+    const PATH_STYLE: PathStyle = PathStyle::Type;
+    fn to_ty(&self) -> Option<P<Ty>> {
+        Some(P(self.clone()))
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: TyKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+impl RecoverQPath for Pat {
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: PatKind::Path(qself, path),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+impl RecoverQPath for Expr {
+    fn to_ty(&self) -> Option<P<Ty>> {
+        self.to_ty()
+    }
+    fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
+        Self {
+            span: path.span,
+            kind: ExprKind::Path(qself, path),
+            attrs: AttrVec::new(),
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        }
+    }
+}
+
+/// Control whether the closing delimiter should be consumed when calling `Parser::consume_block`.
+pub(crate) enum ConsumeClosingDelim {
+    Yes,
+    No,
+}
+
+#[derive(Clone, Copy)]
+pub enum AttemptLocalParseRecovery {
+    Yes,
+    No,
+}
+
+impl AttemptLocalParseRecovery {
+    pub fn yes(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => true,
+            AttemptLocalParseRecovery::No => false,
+        }
+    }
+
+    pub fn no(&self) -> bool {
+        match self {
+            AttemptLocalParseRecovery::Yes => false,
+            AttemptLocalParseRecovery::No => true,
+        }
+    }
+}
+
+/// Information for emitting suggestions and recovering from
+/// C-style `i++`, `--i`, etc.
+#[derive(Debug, Copy, Clone)]
+struct IncDecRecovery {
+    /// Is this increment/decrement its own statement?
+    standalone: IsStandalone,
+    /// Is this an increment or decrement?
+    op: IncOrDec,
+    /// Is this pre- or postfix?
+    fixity: UnaryFixity,
+}
+
+/// Is an increment or decrement expression its own statement?
+#[derive(Debug, Copy, Clone)]
+enum IsStandalone {
+    /// It's standalone, i.e., its own statement.
+    Standalone,
+    /// It's a subexpression, i.e., *not* standalone.
+    Subexpr,
+    /// It's maybe standalone; we're not sure.
+    Maybe,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum IncOrDec {
+    Inc,
+    // FIXME: `i--` recovery isn't implemented yet
+    #[allow(dead_code)]
+    Dec,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum UnaryFixity {
+    Pre,
+    Post,
+}
+
+impl IncOrDec {
+    fn chr(&self) -> char {
+        match self {
+            Self::Inc => '+',
+            Self::Dec => '-',
+        }
+    }
+
+    fn name(&self) -> &'static str {
+        match self {
+            Self::Inc => "increment",
+            Self::Dec => "decrement",
+        }
+    }
+}
+
+impl std::fmt::Display for UnaryFixity {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Pre => write!(f, "prefix"),
+            Self::Post => write!(f, "postfix"),
+        }
+    }
+}
+
+struct MultiSugg {
+    msg: String,
+    patches: Vec<(Span, String)>,
+    applicability: Applicability,
+}
+
+impl MultiSugg {
+    fn emit<G: EmissionGuarantee>(self, err: &mut DiagnosticBuilder<'_, G>) {
+        err.multipart_suggestion(&self.msg, self.patches, self.applicability);
+    }
+
+    /// Overrides individual messages and applicabilities.
+    fn emit_many<G: EmissionGuarantee>(
+        err: &mut DiagnosticBuilder<'_, G>,
+        msg: &str,
+        applicability: Applicability,
+        suggestions: impl Iterator<Item = Self>,
+    ) {
+        err.multipart_suggestions(msg, suggestions.map(|s| s.patches), applicability);
+    }
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::maybe_report_ambiguous_plus)]
+struct AmbiguousPlus {
+    pub sum_ty: String,
+    #[primary_span]
+    #[suggestion(code = "({sum_ty})")]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::maybe_recover_from_bad_type_plus, code = "E0178")]
+struct BadTypePlus {
+    pub ty: String,
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: BadTypePlusSub,
+}
+
+#[derive(SessionSubdiagnostic)]
+pub enum BadTypePlusSub {
+    #[suggestion(
+        parser::add_paren,
+        code = "{sum_with_parens}",
+        applicability = "machine-applicable"
+    )]
+    AddParen {
+        sum_with_parens: String,
+        #[primary_span]
+        span: Span,
+    },
+    #[label(parser::forgot_paren)]
+    ForgotParen {
+        #[primary_span]
+        span: Span,
+    },
+    #[label(parser::expect_path)]
+    ExpectPath {
+        #[primary_span]
+        span: Span,
+    },
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::maybe_recover_from_bad_qpath_stage_2)]
+struct BadQPathStage2 {
+    #[primary_span]
+    #[suggestion(applicability = "maybe-incorrect")]
+    span: Span,
+    ty: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::incorrect_semicolon)]
+struct IncorrectSemicolon<'a> {
+    #[primary_span]
+    #[suggestion_short(applicability = "machine-applicable")]
+    span: Span,
+    #[help]
+    opt_help: Option<()>,
+    name: &'a str,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::incorrect_use_of_await)]
+struct IncorrectUseOfAwait {
+    #[primary_span]
+    #[suggestion(parser::parentheses_suggestion, applicability = "machine-applicable")]
+    span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::incorrect_use_of_await)]
+struct IncorrectAwait {
+    #[primary_span]
+    span: Span,
+    #[suggestion(parser::postfix_suggestion, code = "{expr}.await{question_mark}")]
+    sugg_span: (Span, Applicability),
+    expr: String,
+    question_mark: &'static str,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(parser::in_in_typo)]
+struct InInTypo {
+    #[primary_span]
+    span: Span,
+    #[suggestion(applicability = "machine-applicable")]
+    sugg_span: Span,
+}
+
+// SnapshotParser is used to create a snapshot of the parser
+// without causing duplicate errors being emitted when the `Parser`
+// is dropped.
+pub struct SnapshotParser<'a> {
+    parser: Parser<'a>,
+    unclosed_delims: Vec<UnmatchedBrace>,
+}
+
+impl<'a> Deref for SnapshotParser<'a> {
+    type Target = Parser<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.parser
+    }
+}
+
+impl<'a> DerefMut for SnapshotParser<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.parser
+    }
+}
+
+impl<'a> Parser<'a> {
+    #[rustc_lint_diagnostics]
+    pub(super) fn span_err<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        err: Error,
+    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        err.span_err(sp, self.diagnostic())
+    }
+
+    #[rustc_lint_diagnostics]
+    pub fn struct_span_err<S: Into<MultiSpan>>(
+        &self,
+        sp: S,
+        m: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        self.sess.span_diagnostic.struct_span_err(sp, m)
+    }
+
+    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: impl Into<DiagnosticMessage>) -> ! {
+        self.sess.span_diagnostic.span_bug(sp, m)
+    }
+
+    pub(super) fn diagnostic(&self) -> &'a Handler {
+        &self.sess.span_diagnostic
+    }
+
+    /// Replace `self` with `snapshot.parser` and extend `unclosed_delims` with `snapshot.unclosed_delims`.
+    /// This is to avoid losing unclosed delims errors `create_snapshot_for_diagnostic` clears.
+    pub(super) fn restore_snapshot(&mut self, snapshot: SnapshotParser<'a>) {
+        *self = snapshot.parser;
+        self.unclosed_delims.extend(snapshot.unclosed_delims.clone());
+    }
+
+    pub fn unclosed_delims(&self) -> &[UnmatchedBrace] {
+        &self.unclosed_delims
+    }
+
+    /// Create a snapshot of the `Parser`.
+    pub fn create_snapshot_for_diagnostic(&self) -> SnapshotParser<'a> {
+        let mut snapshot = self.clone();
+        let unclosed_delims = self.unclosed_delims.clone();
+        // Clear `unclosed_delims` in snapshot to avoid
+        // duplicate errors being emitted when the `Parser`
+        // is dropped (which may or may not happen, depending
+        // if the parsing the snapshot is created for is successful)
+        snapshot.unclosed_delims.clear();
+        SnapshotParser { parser: snapshot, unclosed_delims }
+    }
+
+    pub(super) fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
+        self.sess.source_map().span_to_snippet(span)
+    }
+
+    pub(super) fn expected_ident_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        let mut err = self.struct_span_err(
+            self.token.span,
+            &format!("expected identifier, found {}", super::token_descr(&self.token)),
+        );
+        let valid_follow = &[
+            TokenKind::Eq,
+            TokenKind::Colon,
+            TokenKind::Comma,
+            TokenKind::Semi,
+            TokenKind::ModSep,
+            TokenKind::OpenDelim(Delimiter::Brace),
+            TokenKind::OpenDelim(Delimiter::Parenthesis),
+            TokenKind::CloseDelim(Delimiter::Brace),
+            TokenKind::CloseDelim(Delimiter::Parenthesis),
+        ];
+        match self.token.ident() {
+            Some((ident, false))
+                if ident.is_raw_guess()
+                    && self.look_ahead(1, |t| valid_follow.contains(&t.kind)) =>
+            {
+                err.span_suggestion_verbose(
+                    ident.span.shrink_to_lo(),
+                    &format!("escape `{}` to use it as an identifier", ident.name),
+                    "r#",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            _ => {}
+        }
+        if let Some(token_descr) = super::token_descr_opt(&self.token) {
+            err.span_label(self.token.span, format!("expected identifier, found {}", token_descr));
+        } else {
+            err.span_label(self.token.span, "expected identifier");
+            if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
+                err.span_suggestion(
+                    self.token.span,
+                    "remove this comma",
+                    "",
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        err
+    }
+
+    pub(super) fn expected_one_of_not_found(
+        &mut self,
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
+    ) -> PResult<'a, bool /* recovered */> {
+        debug!("expected_one_of_not_found(edible: {:?}, inedible: {:?})", edible, inedible);
+        fn tokens_to_string(tokens: &[TokenType]) -> String {
+            let mut i = tokens.iter();
+            // This might be a sign we need a connect method on `Iterator`.
+            let b = i.next().map_or_else(String::new, |t| t.to_string());
+            i.enumerate().fold(b, |mut b, (i, a)| {
+                if tokens.len() > 2 && i == tokens.len() - 2 {
+                    b.push_str(", or ");
+                } else if tokens.len() == 2 && i == tokens.len() - 2 {
+                    b.push_str(" or ");
+                } else {
+                    b.push_str(", ");
+                }
+                b.push_str(&a.to_string());
+                b
+            })
+        }
+
+        let mut expected = edible
+            .iter()
+            .map(|x| TokenType::Token(x.clone()))
+            .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
+            .chain(self.expected_tokens.iter().cloned())
+            .filter_map(|token| {
+                // filter out suggestions which suggest the same token which was found and deemed incorrect
+                fn is_ident_eq_keyword(found: &TokenKind, expected: &TokenType) -> bool {
+                    if let TokenKind::Ident(current_sym, _) = found {
+                        if let TokenType::Keyword(suggested_sym) = expected {
+                            return current_sym == suggested_sym;
+                        }
+                    }
+                    false
+                }
+                if token != parser::TokenType::Token(self.token.kind.clone()) {
+                    let eq = is_ident_eq_keyword(&self.token.kind, &token);
+                    // if the suggestion is a keyword and the found token is an ident,
+                    // the content of which are equal to the suggestion's content,
+                    // we can remove that suggestion (see the return None statement below)
+
+                    // if this isn't the case however, and the suggestion is a token the
+                    // content of which is the same as the found token's, we remove it as well
+                    if !eq {
+                        if let TokenType::Token(kind) = &token {
+                            if kind == &self.token.kind {
+                                return None;
+                            }
+                        }
+                        return Some(token);
+                    }
+                }
+                return None;
+            })
+            .collect::<Vec<_>>();
+        expected.sort_by_cached_key(|x| x.to_string());
+        expected.dedup();
+
+        let sm = self.sess.source_map();
+        let msg = format!("expected `;`, found {}", super::token_descr(&self.token));
+        let appl = Applicability::MachineApplicable;
+        if expected.contains(&TokenType::Token(token::Semi)) {
+            if self.token.span == DUMMY_SP || self.prev_token.span == DUMMY_SP {
+                // Likely inside a macro, can't provide meaningful suggestions.
+            } else if !sm.is_multiline(self.prev_token.span.until(self.token.span)) {
+                // The current token is in the same line as the prior token, not recoverable.
+            } else if [token::Comma, token::Colon].contains(&self.token.kind)
+                && self.prev_token.kind == token::CloseDelim(Delimiter::Parenthesis)
+            {
+                // Likely typo: The current token is on a new line and is expected to be
+                // `.`, `;`, `?`, or an operator after a close delimiter token.
+                //
+                // let a = std::process::Command::new("echo")
+                //         .arg("1")
+                //         ,arg("2")
+                //         ^
+                // https://github.com/rust-lang/rust/issues/72253
+            } else if self.look_ahead(1, |t| {
+                t == &token::CloseDelim(Delimiter::Brace)
+                    || t.can_begin_expr() && t.kind != token::Colon
+            }) && [token::Comma, token::Colon].contains(&self.token.kind)
+            {
+                // Likely typo: `,` → `;` or `:` → `;`. This is triggered if the current token is
+                // either `,` or `:`, and the next token could either start a new statement or is a
+                // block close. For example:
+                //
+                //   let x = 32:
+                //   let y = 42;
+                self.bump();
+                let sp = self.prev_token.span;
+                self.struct_span_err(sp, &msg)
+                    .span_suggestion_short(sp, "change this to `;`", ";", appl)
+                    .emit();
+                return Ok(true);
+            } else if self.look_ahead(0, |t| {
+                t == &token::CloseDelim(Delimiter::Brace)
+                    || (t.can_begin_expr() && t != &token::Semi && t != &token::Pound)
+                    // Avoid triggering with too many trailing `#` in raw string.
+                    || (sm.is_multiline(
+                        self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo())
+                    ) && t == &token::Pound)
+            }) && !expected.contains(&TokenType::Token(token::Comma))
+            {
+                // Missing semicolon typo. This is triggered if the next token could either start a
+                // new statement or is a block close. For example:
+                //
+                //   let x = 32
+                //   let y = 42;
+                let sp = self.prev_token.span.shrink_to_hi();
+                self.struct_span_err(sp, &msg)
+                    .span_label(self.token.span, "unexpected token")
+                    .span_suggestion_short(sp, "add `;` here", ";", appl)
+                    .emit();
+                return Ok(true);
+            }
+        }
+
+        let expect = tokens_to_string(&expected);
+        let actual = super::token_descr(&self.token);
+        let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
+            let short_expect = if expected.len() > 6 {
+                format!("{} possible tokens", expected.len())
+            } else {
+                expect.clone()
+            };
+            (
+                format!("expected one of {expect}, found {actual}"),
+                (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")),
+            )
+        } else if expected.is_empty() {
+            (
+                format!("unexpected token: {}", actual),
+                (self.prev_token.span, "unexpected token after this".to_string()),
+            )
+        } else {
+            (
+                format!("expected {expect}, found {actual}"),
+                (self.prev_token.span.shrink_to_hi(), format!("expected {expect}")),
+            )
+        };
+        self.last_unexpected_token_span = Some(self.token.span);
+        let mut err = self.struct_span_err(self.token.span, &msg_exp);
+
+        if let TokenKind::Ident(symbol, _) = &self.prev_token.kind {
+            if symbol.as_str() == "public" {
+                err.span_suggestion_short(
+                    self.prev_token.span,
+                    "write `pub` instead of `public` to make the item public",
+                    "pub",
+                    appl,
+                );
+            }
+        }
+
+        // Add suggestion for a missing closing angle bracket if '>' is included in expected_tokens
+        // there are unclosed angle brackets
+        if self.unmatched_angle_bracket_count > 0
+            && self.token.kind == TokenKind::Eq
+            && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Gt)))
+        {
+            err.span_label(self.prev_token.span, "maybe try to close unmatched angle bracket");
+        }
+
+        let sp = if self.token == token::Eof {
+            // This is EOF; don't want to point at the following char, but rather the last token.
+            self.prev_token.span
+        } else {
+            label_sp
+        };
+        match self.recover_closing_delimiter(
+            &expected
+                .iter()
+                .filter_map(|tt| match tt {
+                    TokenType::Token(t) => Some(t.clone()),
+                    _ => None,
+                })
+                .collect::<Vec<_>>(),
+            err,
+        ) {
+            Err(e) => err = e,
+            Ok(recovered) => {
+                return Ok(recovered);
+            }
+        }
+
+        if self.check_too_many_raw_str_terminators(&mut err) {
+            if expected.contains(&TokenType::Token(token::Semi)) && self.eat(&token::Semi) {
+                err.emit();
+                return Ok(true);
+            } else {
+                return Err(err);
+            }
+        }
+
+        if self.prev_token.span == DUMMY_SP {
+            // Account for macro context where the previous span might not be
+            // available to avoid incorrect output (#54841).
+            err.span_label(self.token.span, label_exp);
+        } else if !sm.is_multiline(self.token.span.shrink_to_hi().until(sp.shrink_to_lo())) {
+            // When the spans are in the same line, it means that the only content between
+            // them is whitespace, point at the found token in that case:
+            //
+            // X |     () => { syntax error };
+            //   |                    ^^^^^ expected one of 8 possible tokens here
+            //
+            // instead of having:
+            //
+            // X |     () => { syntax error };
+            //   |                   -^^^^^ unexpected token
+            //   |                   |
+            //   |                   expected one of 8 possible tokens here
+            err.span_label(self.token.span, label_exp);
+        } else {
+            err.span_label(sp, label_exp);
+            err.span_label(self.token.span, "unexpected token");
+        }
+        self.maybe_annotate_with_ascription(&mut err, false);
+        Err(err)
+    }
+
+    fn check_too_many_raw_str_terminators(&mut self, err: &mut Diagnostic) -> bool {
+        let sm = self.sess.source_map();
+        match (&self.prev_token.kind, &self.token.kind) {
+            (
+                TokenKind::Literal(Lit {
+                    kind: LitKind::StrRaw(n_hashes) | LitKind::ByteStrRaw(n_hashes),
+                    ..
+                }),
+                TokenKind::Pound,
+            ) if !sm.is_multiline(
+                self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo()),
+            ) =>
+            {
+                let n_hashes: u8 = *n_hashes;
+                err.set_primary_message("too many `#` when terminating raw string");
+                let str_span = self.prev_token.span;
+                let mut span = self.token.span;
+                let mut count = 0;
+                while self.token.kind == TokenKind::Pound
+                    && !sm.is_multiline(span.shrink_to_hi().until(self.token.span.shrink_to_lo()))
+                {
+                    span = span.with_hi(self.token.span.hi());
+                    self.bump();
+                    count += 1;
+                }
+                err.set_span(span);
+                err.span_suggestion(
+                    span,
+                    &format!("remove the extra `#`{}", pluralize!(count)),
+                    "",
+                    Applicability::MachineApplicable,
+                );
+                err.span_label(
+                    str_span,
+                    &format!("this raw string started with {n_hashes} `#`{}", pluralize!(n_hashes)),
+                );
+                true
+            }
+            _ => false,
+        }
+    }
+
+    pub fn maybe_suggest_struct_literal(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode,
+    ) -> Option<PResult<'a, P<Block>>> {
+        if self.token.is_ident() && self.look_ahead(1, |t| t == &token::Colon) {
+            // We might be having a struct literal where people forgot to include the path:
+            // fn foo() -> Foo {
+            //     field: value,
+            // }
+            let mut snapshot = self.create_snapshot_for_diagnostic();
+            let path =
+                Path { segments: vec![], span: self.prev_token.span.shrink_to_lo(), tokens: None };
+            let struct_expr = snapshot.parse_struct_expr(None, path, AttrVec::new(), false);
+            let block_tail = self.parse_block_tail(lo, s, AttemptLocalParseRecovery::No);
+            return Some(match (struct_expr, block_tail) {
+                (Ok(expr), Err(mut err)) => {
+                    // We have encountered the following:
+                    // fn foo() -> Foo {
+                    //     field: value,
+                    // }
+                    // Suggest:
+                    // fn foo() -> Foo { Path {
+                    //     field: value,
+                    // } }
+                    err.delay_as_bug();
+                    self.struct_span_err(
+                        expr.span,
+                        fluent::parser::struct_literal_body_without_path,
+                    )
+                    .multipart_suggestion(
+                        fluent::parser::suggestion,
+                        vec![
+                            (expr.span.shrink_to_lo(), "{ SomeStruct ".to_string()),
+                            (expr.span.shrink_to_hi(), " }".to_string()),
+                        ],
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit();
+                    self.restore_snapshot(snapshot);
+                    let mut tail = self.mk_block(
+                        vec![self.mk_stmt_err(expr.span)],
+                        s,
+                        lo.to(self.prev_token.span),
+                    );
+                    tail.could_be_bare_literal = true;
+                    Ok(tail)
+                }
+                (Err(err), Ok(tail)) => {
+                    // We have a block tail that contains a somehow valid type ascription expr.
+                    err.cancel();
+                    Ok(tail)
+                }
+                (Err(snapshot_err), Err(err)) => {
+                    // We don't know what went wrong, emit the normal error.
+                    snapshot_err.cancel();
+                    self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
+                    Err(err)
+                }
+                (Ok(_), Ok(mut tail)) => {
+                    tail.could_be_bare_literal = true;
+                    Ok(tail)
+                }
+            });
+        }
+        None
+    }
+
+    pub fn maybe_annotate_with_ascription(
+        &mut self,
+        err: &mut Diagnostic,
+        maybe_expected_semicolon: bool,
+    ) {
+        if let Some((sp, likely_path)) = self.last_type_ascription.take() {
+            let sm = self.sess.source_map();
+            let next_pos = sm.lookup_char_pos(self.token.span.lo());
+            let op_pos = sm.lookup_char_pos(sp.hi());
+
+            let allow_unstable = self.sess.unstable_features.is_nightly_build();
+
+            if likely_path {
+                err.span_suggestion(
+                    sp,
+                    "maybe write a path separator here",
+                    "::",
+                    if allow_unstable {
+                        Applicability::MaybeIncorrect
+                    } else {
+                        Applicability::MachineApplicable
+                    },
+                );
+                self.sess.type_ascription_path_suggestions.borrow_mut().insert(sp);
+            } else if op_pos.line != next_pos.line && maybe_expected_semicolon {
+                err.span_suggestion(
+                    sp,
+                    "try using a semicolon",
+                    ";",
+                    Applicability::MaybeIncorrect,
+                );
+            } else if allow_unstable {
+                err.span_label(sp, "tried to parse a type due to this type ascription");
+            } else {
+                err.span_label(sp, "tried to parse a type due to this");
+            }
+            if allow_unstable {
+                // Give extra information about type ascription only if it's a nightly compiler.
+                err.note(
+                    "`#![feature(type_ascription)]` lets you annotate an expression with a type: \
+                     `<expr>: <type>`",
+                );
+                if !likely_path {
+                    // Avoid giving too much info when it was likely an unrelated typo.
+                    err.note(
+                        "see issue #23416 <https://github.com/rust-lang/rust/issues/23416> \
+                        for more information",
+                    );
+                }
+            }
+        }
+    }
+
+    /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
+    /// passes through any errors encountered. Used for error recovery.
+    pub(super) fn eat_to_tokens(&mut self, kets: &[&TokenKind]) {
+        if let Err(err) =
+            self.parse_seq_to_before_tokens(kets, SeqSep::none(), TokenExpectType::Expect, |p| {
+                Ok(p.parse_token_tree())
+            })
+        {
+            err.cancel();
+        }
+    }
+
+    /// This function checks if there are trailing angle brackets and produces
+    /// a diagnostic to suggest removing them.
+    ///
+    /// ```ignore (diagnostic)
+    /// let _ = [1, 2, 3].into_iter().collect::<Vec<usize>>>>();
+    ///                                                    ^^ help: remove extra angle brackets
+    /// ```
+    ///
+    /// If `true` is returned, then trailing brackets were recovered, tokens were consumed
+    /// up until one of the tokens in 'end' was encountered, and an error was emitted.
+    pub(super) fn check_trailing_angle_brackets(
+        &mut self,
+        segment: &PathSegment,
+        end: &[&TokenKind],
+    ) -> bool {
+        // This function is intended to be invoked after parsing a path segment where there are two
+        // cases:
+        //
+        // 1. A specific token is expected after the path segment.
+        //    eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
+        //        `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
+        // 2. No specific token is expected after the path segment.
+        //    eg. `x.foo` (field access)
+        //
+        // This function is called after parsing `.foo` and before parsing the token `end` (if
+        // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
+        // `Foo::<Bar>`.
+
+        // We only care about trailing angle brackets if we previously parsed angle bracket
+        // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
+        // removed in this case:
+        //
+        // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
+        //
+        // This case is particularly tricky as we won't notice it just looking at the tokens -
+        // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
+        // have already been parsed):
+        //
+        // `x.foo::<u32>>>(3)`
+        let parsed_angle_bracket_args =
+            segment.args.as_ref().map_or(false, |args| args.is_angle_bracketed());
+
+        debug!(
+            "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
+            parsed_angle_bracket_args,
+        );
+        if !parsed_angle_bracket_args {
+            return false;
+        }
+
+        // Keep the span at the start so we can highlight the sequence of `>` characters to be
+        // removed.
+        let lo = self.token.span;
+
+        // We need to look-ahead to see if we have `>` characters without moving the cursor forward
+        // (since we might have the field access case and the characters we're eating are
+        // actual operators and not trailing characters - ie `x.foo >> 3`).
+        let mut position = 0;
+
+        // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
+        // many of each (so we can correctly pluralize our error messages) and continue to
+        // advance.
+        let mut number_of_shr = 0;
+        let mut number_of_gt = 0;
+        while self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            if *t == token::BinOp(token::BinOpToken::Shr) {
+                number_of_shr += 1;
+                true
+            } else if *t == token::Gt {
+                number_of_gt += 1;
+                true
+            } else {
+                false
+            }
+        }) {
+            position += 1;
+        }
+
+        // If we didn't find any trailing `>` characters, then we have nothing to error about.
+        debug!(
+            "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
+            number_of_gt, number_of_shr,
+        );
+        if number_of_gt < 1 && number_of_shr < 1 {
+            return false;
+        }
+
+        // Finally, double check that we have our end token as otherwise this is the
+        // second case.
+        if self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            end.contains(&&t.kind)
+        }) {
+            // Eat from where we started until the end token so that parsing can continue
+            // as if we didn't have those extra angle brackets.
+            self.eat_to_tokens(end);
+            let span = lo.until(self.token.span);
+
+            let total_num_of_gt = number_of_gt + number_of_shr * 2;
+            self.struct_span_err(
+                span,
+                &format!("unmatched angle bracket{}", pluralize!(total_num_of_gt)),
+            )
+            .span_suggestion(
+                span,
+                &format!("remove extra angle bracket{}", pluralize!(total_num_of_gt)),
+                "",
+                Applicability::MachineApplicable,
+            )
+            .emit();
+            return true;
+        }
+        false
+    }
+
+    /// Check if a method call with an intended turbofish has been written without surrounding
+    /// angle brackets.
+    pub(super) fn check_turbofish_missing_angle_brackets(&mut self, segment: &mut PathSegment) {
+        if token::ModSep == self.token.kind && segment.args.is_none() {
+            let snapshot = self.create_snapshot_for_diagnostic();
+            self.bump();
+            let lo = self.token.span;
+            match self.parse_angle_args(None) {
+                Ok(args) => {
+                    let span = lo.to(self.prev_token.span);
+                    // Detect trailing `>` like in `x.collect::Vec<_>>()`.
+                    let mut trailing_span = self.prev_token.span.shrink_to_hi();
+                    while self.token.kind == token::BinOp(token::Shr)
+                        || self.token.kind == token::Gt
+                    {
+                        trailing_span = trailing_span.to(self.token.span);
+                        self.bump();
+                    }
+                    if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
+                        // Recover from bad turbofish: `foo.collect::Vec<_>()`.
+                        let args = AngleBracketedArgs { args, span }.into();
+                        segment.args = args;
+
+                        self.struct_span_err(
+                            span,
+                            "generic parameters without surrounding angle brackets",
+                        )
+                        .multipart_suggestion(
+                            "surround the type parameters with angle brackets",
+                            vec![
+                                (span.shrink_to_lo(), "<".to_string()),
+                                (trailing_span, ">".to_string()),
+                            ],
+                            Applicability::MachineApplicable,
+                        )
+                        .emit();
+                    } else {
+                        // This doesn't look like an invalid turbofish, can't recover parse state.
+                        self.restore_snapshot(snapshot);
+                    }
+                }
+                Err(err) => {
+                    // We couldn't parse generic parameters, unlikely to be a turbofish. Rely on
+                    // generic parse error instead.
+                    err.cancel();
+                    self.restore_snapshot(snapshot);
+                }
+            }
+        }
+    }
+
+    /// When writing a turbofish with multiple type parameters missing the leading `::`, we will
+    /// encounter a parse error when encountering the first `,`.
+    pub(super) fn check_mistyped_turbofish_with_multiple_type_params(
+        &mut self,
+        mut e: DiagnosticBuilder<'a, ErrorGuaranteed>,
+        expr: &mut P<Expr>,
+    ) -> PResult<'a, ()> {
+        if let ExprKind::Binary(binop, _, _) = &expr.kind
+            && let ast::BinOpKind::Lt = binop.node
+            && self.eat(&token::Comma)
+        {
+            let x = self.parse_seq_to_before_end(
+                &token::Gt,
+                SeqSep::trailing_allowed(token::Comma),
+                |p| p.parse_generic_arg(None),
+            );
+            match x {
+                Ok((_, _, false)) => {
+                    if self.eat(&token::Gt) {
+                        e.span_suggestion_verbose(
+                            binop.span.shrink_to_lo(),
+                            TURBOFISH_SUGGESTION_STR,
+                            "::",
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                        match self.parse_expr() {
+                            Ok(_) => {
+                                *expr =
+                                    self.mk_expr_err(expr.span.to(self.prev_token.span));
+                                return Ok(());
+                            }
+                            Err(err) => {
+                                *expr = self.mk_expr_err(expr.span);
+                                err.cancel();
+                            }
+                        }
+                    }
+                }
+                Err(err) => {
+                    err.cancel();
+                }
+                _ => {}
+            }
+        }
+        Err(e)
+    }
+
+    /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
+    /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
+    /// parenthesising the leftmost comparison.
+    fn attempt_chained_comparison_suggestion(
+        &mut self,
+        err: &mut Diagnostic,
+        inner_op: &Expr,
+        outer_op: &Spanned<AssocOp>,
+    ) -> bool /* advanced the cursor */ {
+        if let ExprKind::Binary(op, ref l1, ref r1) = inner_op.kind {
+            if let ExprKind::Field(_, ident) = l1.kind
+                && ident.as_str().parse::<i32>().is_err()
+                && !matches!(r1.kind, ExprKind::Lit(_))
+            {
+                // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
+                // suggestion being the only one to apply is high.
+                return false;
+            }
+            let mut enclose = |left: Span, right: Span| {
+                err.multipart_suggestion(
+                    "parenthesize the comparison",
+                    vec![
+                        (left.shrink_to_lo(), "(".to_string()),
+                        (right.shrink_to_hi(), ")".to_string()),
+                    ],
+                    Applicability::MaybeIncorrect,
+                );
+            };
+            return match (op.node, &outer_op.node) {
+                // `x == y == z`
+                (BinOpKind::Eq, AssocOp::Equal) |
+                // `x < y < z` and friends.
+                (BinOpKind::Lt, AssocOp::Less | AssocOp::LessEqual) |
+                (BinOpKind::Le, AssocOp::LessEqual | AssocOp::Less) |
+                // `x > y > z` and friends.
+                (BinOpKind::Gt, AssocOp::Greater | AssocOp::GreaterEqual) |
+                (BinOpKind::Ge, AssocOp::GreaterEqual | AssocOp::Greater) => {
+                    let expr_to_str = |e: &Expr| {
+                        self.span_to_snippet(e.span)
+                            .unwrap_or_else(|_| pprust::expr_to_string(&e))
+                    };
+                    err.span_suggestion_verbose(
+                        inner_op.span.shrink_to_hi(),
+                        "split the comparison into two",
+                        format!(" && {}", expr_to_str(&r1)),
+                        Applicability::MaybeIncorrect,
+                    );
+                    false // Keep the current parse behavior, where the AST is `(x < y) < z`.
+                }
+                // `x == y < z`
+                (BinOpKind::Eq, AssocOp::Less | AssocOp::LessEqual | AssocOp::Greater | AssocOp::GreaterEqual) => {
+                    // Consume `z`/outer-op-rhs.
+                    let snapshot = self.create_snapshot_for_diagnostic();
+                    match self.parse_expr() {
+                        Ok(r2) => {
+                            // We are sure that outer-op-rhs could be consumed, the suggestion is
+                            // likely correct.
+                            enclose(r1.span, r2.span);
+                            true
+                        }
+                        Err(expr_err) => {
+                            expr_err.cancel();
+                            self.restore_snapshot(snapshot);
+                            false
+                        }
+                    }
+                }
+                // `x > y == z`
+                (BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge, AssocOp::Equal) => {
+                    let snapshot = self.create_snapshot_for_diagnostic();
+                    // At this point it is always valid to enclose the lhs in parentheses, no
+                    // further checks are necessary.
+                    match self.parse_expr() {
+                        Ok(_) => {
+                            enclose(l1.span, r1.span);
+                            true
+                        }
+                        Err(expr_err) => {
+                            expr_err.cancel();
+                            self.restore_snapshot(snapshot);
+                            false
+                        }
+                    }
+                }
+                _ => false,
+            };
+        }
+        false
+    }
+
+    /// Produces an error if comparison operators are chained (RFC #558).
+    /// We only need to check the LHS, not the RHS, because all comparison ops have same
+    /// precedence (see `fn precedence`) and are left-associative (see `fn fixity`).
+    ///
+    /// This can also be hit if someone incorrectly writes `foo<bar>()` when they should have used
+    /// the turbofish (`foo::<bar>()`) syntax. We attempt some heuristic recovery if that is the
+    /// case.
+    ///
+    /// Keep in mind that given that `outer_op.is_comparison()` holds and comparison ops are left
+    /// associative we can infer that we have:
+    ///
+    /// ```text
+    ///           outer_op
+    ///           /   \
+    ///     inner_op   r2
+    ///        /  \
+    ///      l1    r1
+    /// ```
+    pub(super) fn check_no_chained_comparison(
+        &mut self,
+        inner_op: &Expr,
+        outer_op: &Spanned<AssocOp>,
+    ) -> PResult<'a, Option<P<Expr>>> {
+        debug_assert!(
+            outer_op.node.is_comparison(),
+            "check_no_chained_comparison: {:?} is not comparison",
+            outer_op.node,
+        );
+
+        let mk_err_expr =
+            |this: &Self, span| Ok(Some(this.mk_expr(span, ExprKind::Err, AttrVec::new())));
+
+        match inner_op.kind {
+            ExprKind::Binary(op, ref l1, ref r1) if op.node.is_comparison() => {
+                let mut err = self.struct_span_err(
+                    vec![op.span, self.prev_token.span],
+                    "comparison operators cannot be chained",
+                );
+
+                let suggest = |err: &mut Diagnostic| {
+                    err.span_suggestion_verbose(
+                        op.span.shrink_to_lo(),
+                        TURBOFISH_SUGGESTION_STR,
+                        "::",
+                        Applicability::MaybeIncorrect,
+                    );
+                };
+
+                // Include `<` to provide this recommendation even in a case like
+                // `Foo<Bar<Baz<Qux, ()>>>`
+                if op.node == BinOpKind::Lt && outer_op.node == AssocOp::Less
+                    || outer_op.node == AssocOp::Greater
+                {
+                    if outer_op.node == AssocOp::Less {
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump();
+                        // So far we have parsed `foo<bar<`, consume the rest of the type args.
+                        let modifiers =
+                            [(token::Lt, 1), (token::Gt, -1), (token::BinOp(token::Shr), -2)];
+                        self.consume_tts(1, &modifiers);
+
+                        if !&[token::OpenDelim(Delimiter::Parenthesis), token::ModSep]
+                            .contains(&self.token.kind)
+                        {
+                            // We don't have `foo< bar >(` or `foo< bar >::`, so we rewind the
+                            // parser and bail out.
+                            self.restore_snapshot(snapshot);
+                        }
+                    }
+                    return if token::ModSep == self.token.kind {
+                        // We have some certainty that this was a bad turbofish at this point.
+                        // `foo< bar >::`
+                        suggest(&mut err);
+
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump(); // `::`
+
+                        // Consume the rest of the likely `foo<bar>::new()` or return at `foo<bar>`.
+                        match self.parse_expr() {
+                            Ok(_) => {
+                                // 99% certain that the suggestion is correct, continue parsing.
+                                err.emit();
+                                // FIXME: actually check that the two expressions in the binop are
+                                // paths and resynthesize new fn call expression instead of using
+                                // `ExprKind::Err` placeholder.
+                                mk_err_expr(self, inner_op.span.to(self.prev_token.span))
+                            }
+                            Err(expr_err) => {
+                                expr_err.cancel();
+                                // Not entirely sure now, but we bubble the error up with the
+                                // suggestion.
+                                self.restore_snapshot(snapshot);
+                                Err(err)
+                            }
+                        }
+                    } else if token::OpenDelim(Delimiter::Parenthesis) == self.token.kind {
+                        // We have high certainty that this was a bad turbofish at this point.
+                        // `foo< bar >(`
+                        suggest(&mut err);
+                        // Consume the fn call arguments.
+                        match self.consume_fn_args() {
+                            Err(()) => Err(err),
+                            Ok(()) => {
+                                err.emit();
+                                // FIXME: actually check that the two expressions in the binop are
+                                // paths and resynthesize new fn call expression instead of using
+                                // `ExprKind::Err` placeholder.
+                                mk_err_expr(self, inner_op.span.to(self.prev_token.span))
+                            }
+                        }
+                    } else {
+                        if !matches!(l1.kind, ExprKind::Lit(_))
+                            && !matches!(r1.kind, ExprKind::Lit(_))
+                        {
+                            // All we know is that this is `foo < bar >` and *nothing* else. Try to
+                            // be helpful, but don't attempt to recover.
+                            err.help(TURBOFISH_SUGGESTION_STR);
+                            err.help("or use `(...)` if you meant to specify fn arguments");
+                        }
+
+                        // If it looks like a genuine attempt to chain operators (as opposed to a
+                        // misformatted turbofish, for instance), suggest a correct form.
+                        if self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op)
+                        {
+                            err.emit();
+                            mk_err_expr(self, inner_op.span.to(self.prev_token.span))
+                        } else {
+                            // These cases cause too many knock-down errors, bail out (#61329).
+                            Err(err)
+                        }
+                    };
+                }
+                let recover =
+                    self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
+                err.emit();
+                if recover {
+                    return mk_err_expr(self, inner_op.span.to(self.prev_token.span));
+                }
+            }
+            _ => {}
+        }
+        Ok(None)
+    }
+
+    fn consume_fn_args(&mut self) -> Result<(), ()> {
+        let snapshot = self.create_snapshot_for_diagnostic();
+        self.bump(); // `(`
+
+        // Consume the fn call arguments.
+        let modifiers = [
+            (token::OpenDelim(Delimiter::Parenthesis), 1),
+            (token::CloseDelim(Delimiter::Parenthesis), -1),
+        ];
+        self.consume_tts(1, &modifiers);
+
+        if self.token.kind == token::Eof {
+            // Not entirely sure that what we consumed were fn arguments, rollback.
+            self.restore_snapshot(snapshot);
+            Err(())
+        } else {
+            // 99% certain that the suggestion is correct, continue parsing.
+            Ok(())
+        }
+    }
+
+    pub(super) fn maybe_report_ambiguous_plus(&mut self, impl_dyn_multi: bool, ty: &Ty) {
+        if impl_dyn_multi {
+            self.sess.emit_err(AmbiguousPlus { sum_ty: pprust::ty_to_string(&ty), span: ty.span });
+        }
+    }
+
+    /// Swift lets users write `Ty?` to mean `Option<Ty>`. Parse the construct and recover from it.
+    pub(super) fn maybe_recover_from_question_mark(&mut self, ty: P<Ty>) -> P<Ty> {
+        if self.token == token::Question {
+            self.bump();
+            self.struct_span_err(self.prev_token.span, "invalid `?` in type")
+                .span_label(self.prev_token.span, "`?` is only allowed on expressions, not types")
+                .multipart_suggestion(
+                    "if you meant to express that the type might not contain a value, use the `Option` wrapper type",
+                    vec![
+                        (ty.span.shrink_to_lo(), "Option<".to_string()),
+                        (self.prev_token.span, ">".to_string()),
+                    ],
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+            self.mk_ty(ty.span.to(self.prev_token.span), TyKind::Err)
+        } else {
+            ty
+        }
+    }
+
+    pub(super) fn maybe_recover_from_bad_type_plus(&mut self, ty: &Ty) -> PResult<'a, ()> {
+        // Do not add `+` to expected tokens.
+        if !self.token.is_like_plus() {
+            return Ok(());
+        }
+
+        self.bump(); // `+`
+        let bounds = self.parse_generic_bounds(None)?;
+        let sum_span = ty.span.to(self.prev_token.span);
+
+        let sub = match ty.kind {
+            TyKind::Rptr(ref lifetime, ref mut_ty) => {
+                let sum_with_parens = pprust::to_string(|s| {
+                    s.s.word("&");
+                    s.print_opt_lifetime(lifetime);
+                    s.print_mutability(mut_ty.mutbl, false);
+                    s.popen();
+                    s.print_type(&mut_ty.ty);
+                    if !bounds.is_empty() {
+                        s.word(" + ");
+                        s.print_type_bounds(&bounds);
+                    }
+                    s.pclose()
+                });
+
+                BadTypePlusSub::AddParen { sum_with_parens, span: sum_span }
+            }
+            TyKind::Ptr(..) | TyKind::BareFn(..) => BadTypePlusSub::ForgotParen { span: sum_span },
+            _ => BadTypePlusSub::ExpectPath { span: sum_span },
+        };
+
+        self.sess.emit_err(BadTypePlus { ty: pprust::ty_to_string(ty), span: sum_span, sub });
+
+        Ok(())
+    }
+
+    pub(super) fn recover_from_prefix_increment(
+        &mut self,
+        operand_expr: P<Expr>,
+        op_span: Span,
+        prev_is_semi: bool,
+    ) -> PResult<'a, P<Expr>> {
+        let standalone =
+            if prev_is_semi { IsStandalone::Standalone } else { IsStandalone::Subexpr };
+        let kind = IncDecRecovery { standalone, op: IncOrDec::Inc, fixity: UnaryFixity::Pre };
+
+        self.recover_from_inc_dec(operand_expr, kind, op_span)
+    }
+
+    pub(super) fn recover_from_postfix_increment(
+        &mut self,
+        operand_expr: P<Expr>,
+        op_span: Span,
+    ) -> PResult<'a, P<Expr>> {
+        let kind = IncDecRecovery {
+            standalone: IsStandalone::Maybe,
+            op: IncOrDec::Inc,
+            fixity: UnaryFixity::Post,
+        };
+
+        self.recover_from_inc_dec(operand_expr, kind, op_span)
+    }
+
+    fn recover_from_inc_dec(
+        &mut self,
+        base: P<Expr>,
+        kind: IncDecRecovery,
+        op_span: Span,
+    ) -> PResult<'a, P<Expr>> {
+        let mut err = self.struct_span_err(
+            op_span,
+            &format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
+        );
+        err.span_label(op_span, &format!("not a valid {} operator", kind.fixity));
+
+        let help_base_case = |mut err: DiagnosticBuilder<'_, _>, base| {
+            err.help(&format!("use `{}= 1` instead", kind.op.chr()));
+            err.emit();
+            Ok(base)
+        };
+
+        // (pre, post)
+        let spans = match kind.fixity {
+            UnaryFixity::Pre => (op_span, base.span.shrink_to_hi()),
+            UnaryFixity::Post => (base.span.shrink_to_lo(), op_span),
+        };
+
+        match kind.standalone {
+            IsStandalone::Standalone => self.inc_dec_standalone_suggest(kind, spans).emit(&mut err),
+            IsStandalone::Subexpr => {
+                let Ok(base_src) = self.span_to_snippet(base.span)
+                    else { return help_base_case(err, base) };
+                match kind.fixity {
+                    UnaryFixity::Pre => {
+                        self.prefix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
+                    }
+                    UnaryFixity::Post => {
+                        self.postfix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
+                    }
+                }
+            }
+            IsStandalone::Maybe => {
+                let Ok(base_src) = self.span_to_snippet(base.span)
+                    else { return help_base_case(err, base) };
+                let sugg1 = match kind.fixity {
+                    UnaryFixity::Pre => self.prefix_inc_dec_suggest(base_src, kind, spans),
+                    UnaryFixity::Post => self.postfix_inc_dec_suggest(base_src, kind, spans),
+                };
+                let sugg2 = self.inc_dec_standalone_suggest(kind, spans);
+                MultiSugg::emit_many(
+                    &mut err,
+                    "use `+= 1` instead",
+                    Applicability::Unspecified,
+                    [sugg1, sugg2].into_iter(),
+                )
+            }
+        }
+        Err(err)
+    }
+
+    fn prefix_inc_dec_suggest(
+        &mut self,
+        base_src: String,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches: vec![
+                (pre_span, "{ ".to_string()),
+                (post_span, format!(" {}= 1; {} }}", kind.op.chr(), base_src)),
+            ],
+            applicability: Applicability::MachineApplicable,
+        }
+    }
+
+    fn postfix_inc_dec_suggest(
+        &mut self,
+        base_src: String,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        let tmp_var = if base_src.trim() == "tmp" { "tmp_" } else { "tmp" };
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches: vec![
+                (pre_span, format!("{{ let {} = ", tmp_var)),
+                (post_span, format!("; {} {}= 1; {} }}", base_src, kind.op.chr(), tmp_var)),
+            ],
+            applicability: Applicability::HasPlaceholders,
+        }
+    }
+
+    fn inc_dec_standalone_suggest(
+        &mut self,
+        kind: IncDecRecovery,
+        (pre_span, post_span): (Span, Span),
+    ) -> MultiSugg {
+        MultiSugg {
+            msg: format!("use `{}= 1` instead", kind.op.chr()),
+            patches: vec![(pre_span, String::new()), (post_span, format!(" {}= 1", kind.op.chr()))],
+            applicability: Applicability::MachineApplicable,
+        }
+    }
+
+    /// Tries to recover from associated item paths like `[T]::AssocItem` / `(T, U)::AssocItem`.
+    /// Attempts to convert the base expression/pattern/type into a type, parses the `::AssocItem`
+    /// tail, and combines them into a `<Ty>::AssocItem` expression/pattern/type.
+    pub(super) fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
+        &mut self,
+        base: P<T>,
+    ) -> PResult<'a, P<T>> {
+        // Do not add `::` to expected tokens.
+        if self.token == token::ModSep {
+            if let Some(ty) = base.to_ty() {
+                return self.maybe_recover_from_bad_qpath_stage_2(ty.span, ty);
+            }
+        }
+        Ok(base)
+    }
+
+    /// Given an already parsed `Ty`, parses the `::AssocItem` tail and
+    /// combines them into a `<Ty>::AssocItem` expression/pattern/type.
+    pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
+        &mut self,
+        ty_span: Span,
+        ty: P<Ty>,
+    ) -> PResult<'a, P<T>> {
+        self.expect(&token::ModSep)?;
+
+        let mut path = ast::Path { segments: Vec::new(), span: DUMMY_SP, tokens: None };
+        self.parse_path_segments(&mut path.segments, T::PATH_STYLE, None)?;
+        path.span = ty_span.to(self.prev_token.span);
+
+        let ty_str = self.span_to_snippet(ty_span).unwrap_or_else(|_| pprust::ty_to_string(&ty));
+        self.sess.emit_err(BadQPathStage2 {
+            span: path.span,
+            ty: format!("<{}>::{}", ty_str, pprust::path_to_string(&path)),
+        });
+
+        let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
+        Ok(P(T::recovered(Some(QSelf { ty, path_span, position: 0 }), path)))
+    }
+
+    pub fn maybe_consume_incorrect_semicolon(&mut self, items: &[P<Item>]) -> bool {
+        if self.token.kind == TokenKind::Semi {
+            self.bump();
+
+            let mut err =
+                IncorrectSemicolon { span: self.prev_token.span, opt_help: None, name: "" };
+
+            if !items.is_empty() {
+                let previous_item = &items[items.len() - 1];
+                let previous_item_kind_name = match previous_item.kind {
+                    // Say "braced struct" because tuple-structs and
+                    // braceless-empty-struct declarations do take a semicolon.
+                    ItemKind::Struct(..) => Some("braced struct"),
+                    ItemKind::Enum(..) => Some("enum"),
+                    ItemKind::Trait(..) => Some("trait"),
+                    ItemKind::Union(..) => Some("union"),
+                    _ => None,
+                };
+                if let Some(name) = previous_item_kind_name {
+                    err.opt_help = Some(());
+                    err.name = name;
+                }
+            }
+            self.sess.emit_err(err);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Creates a `DiagnosticBuilder` for an unexpected token `t` and tries to recover if it is a
+    /// closing delimiter.
+    pub(super) fn unexpected_try_recover(
+        &mut self,
+        t: &TokenKind,
+    ) -> PResult<'a, bool /* recovered */> {
+        let token_str = pprust::token_kind_to_string(t);
+        let this_token_str = super::token_descr(&self.token);
+        let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
+            // Point at the end of the macro call when reaching end of macro arguments.
+            (token::Eof, Some(_)) => {
+                let sp = self.sess.source_map().next_point(self.prev_token.span);
+                (sp, sp)
+            }
+            // We don't want to point at the following span after DUMMY_SP.
+            // This happens when the parser finds an empty TokenStream.
+            _ if self.prev_token.span == DUMMY_SP => (self.token.span, self.token.span),
+            // EOF, don't want to point at the following char, but rather the last token.
+            (token::Eof, None) => (self.prev_token.span, self.token.span),
+            _ => (self.prev_token.span.shrink_to_hi(), self.token.span),
+        };
+        let msg = format!(
+            "expected `{}`, found {}",
+            token_str,
+            match (&self.token.kind, self.subparser_name) {
+                (token::Eof, Some(origin)) => format!("end of {origin}"),
+                _ => this_token_str,
+            },
+        );
+        let mut err = self.struct_span_err(sp, &msg);
+        let label_exp = format!("expected `{token_str}`");
+        match self.recover_closing_delimiter(&[t.clone()], err) {
+            Err(e) => err = e,
+            Ok(recovered) => {
+                return Ok(recovered);
+            }
+        }
+        let sm = self.sess.source_map();
+        if !sm.is_multiline(prev_sp.until(sp)) {
+            // When the spans are in the same line, it means that the only content
+            // between them is whitespace, point only at the found token.
+            err.span_label(sp, label_exp);
+        } else {
+            err.span_label(prev_sp, label_exp);
+            err.span_label(sp, "unexpected token");
+        }
+        Err(err)
+    }
+
+    pub(super) fn expect_semi(&mut self) -> PResult<'a, ()> {
+        if self.eat(&token::Semi) {
+            return Ok(());
+        }
+        self.expect(&token::Semi).map(drop) // Error unconditionally
+    }
+
+    /// Consumes alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
+    /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
+    pub(super) fn recover_incorrect_await_syntax(
+        &mut self,
+        lo: Span,
+        await_sp: Span,
+        attrs: AttrVec,
+    ) -> PResult<'a, P<Expr>> {
+        let (hi, expr, is_question) = if self.token == token::Not {
+            // Handle `await!(<expr>)`.
+            self.recover_await_macro()?
+        } else {
+            self.recover_await_prefix(await_sp)?
+        };
+        let sp = self.error_on_incorrect_await(lo, hi, &expr, is_question);
+        let kind = match expr.kind {
+            // Avoid knock-down errors as we don't know whether to interpret this as `foo().await?`
+            // or `foo()?.await` (the very reason we went with postfix syntax 😅).
+            ExprKind::Try(_) => ExprKind::Err,
+            _ => ExprKind::Await(expr),
+        };
+        let expr = self.mk_expr(lo.to(sp), kind, attrs);
+        self.maybe_recover_from_bad_qpath(expr)
+    }
+
+    fn recover_await_macro(&mut self) -> PResult<'a, (Span, P<Expr>, bool)> {
+        self.expect(&token::Not)?;
+        self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
+        let expr = self.parse_expr()?;
+        self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
+        Ok((self.prev_token.span, expr, false))
+    }
+
+    fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, P<Expr>, bool)> {
+        let is_question = self.eat(&token::Question); // Handle `await? <expr>`.
+        let expr = if self.token == token::OpenDelim(Delimiter::Brace) {
+            // Handle `await { <expr> }`.
+            // This needs to be handled separately from the next arm to avoid
+            // interpreting `await { <expr> }?` as `<expr>?.await`.
+            self.parse_block_expr(None, self.token.span, BlockCheckMode::Default, AttrVec::new())
+        } else {
+            self.parse_expr()
+        }
+        .map_err(|mut err| {
+            err.span_label(await_sp, "while parsing this incorrect await expression");
+            err
+        })?;
+        Ok((expr.span, expr, is_question))
+    }
+
+    fn error_on_incorrect_await(&self, lo: Span, hi: Span, expr: &Expr, is_question: bool) -> Span {
+        let span = lo.to(hi);
+        let applicability = match expr.kind {
+            ExprKind::Try(_) => Applicability::MaybeIncorrect, // `await <expr>?`
+            _ => Applicability::MachineApplicable,
+        };
+
+        self.sess.emit_err(IncorrectAwait {
+            span,
+            sugg_span: (span, applicability),
+            expr: self.span_to_snippet(expr.span).unwrap_or_else(|_| pprust::expr_to_string(&expr)),
+            question_mark: if is_question { "?" } else { "" },
+        });
+
+        span
+    }
+
+    /// If encountering `future.await()`, consumes and emits an error.
+    pub(super) fn recover_from_await_method_call(&mut self) {
+        if self.token == token::OpenDelim(Delimiter::Parenthesis)
+            && self.look_ahead(1, |t| t == &token::CloseDelim(Delimiter::Parenthesis))
+        {
+            // future.await()
+            let lo = self.token.span;
+            self.bump(); // (
+            let span = lo.to(self.token.span);
+            self.bump(); // )
+
+            self.sess.emit_err(IncorrectUseOfAwait { span });
+        }
+    }
+
+    pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, P<Expr>> {
+        let is_try = self.token.is_keyword(kw::Try);
+        let is_questionmark = self.look_ahead(1, |t| t == &token::Not); //check for !
+        let is_open = self.look_ahead(2, |t| t == &token::OpenDelim(Delimiter::Parenthesis)); //check for (
+
+        if is_try && is_questionmark && is_open {
+            let lo = self.token.span;
+            self.bump(); //remove try
+            self.bump(); //remove !
+            let try_span = lo.to(self.token.span); //we take the try!( span
+            self.bump(); //remove (
+            let is_empty = self.token == token::CloseDelim(Delimiter::Parenthesis); //check if the block is empty
+            self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::No); //eat the block
+            let hi = self.token.span;
+            self.bump(); //remove )
+            let mut err = self.struct_span_err(lo.to(hi), "use of deprecated `try` macro");
+            err.note("in the 2018 edition `try` is a reserved keyword, and the `try!()` macro is deprecated");
+            let prefix = if is_empty { "" } else { "alternatively, " };
+            if !is_empty {
+                err.multipart_suggestion(
+                    "you can use the `?` operator instead",
+                    vec![(try_span, "".to_owned()), (hi, "?".to_owned())],
+                    Applicability::MachineApplicable,
+                );
+            }
+            err.span_suggestion(lo.shrink_to_lo(), &format!("{prefix}you can still access the deprecated `try!()` macro using the \"raw identifier\" syntax"), "r#", Applicability::MachineApplicable);
+            err.emit();
+            Ok(self.mk_expr_err(lo.to(hi)))
+        } else {
+            Err(self.expected_expression_found()) // The user isn't trying to invoke the try! macro
+        }
+    }
+
+    /// Recovers a situation like `for ( $pat in $expr )`
+    /// and suggest writing `for $pat in $expr` instead.
+    ///
+    /// This should be called before parsing the `$block`.
+    pub(super) fn recover_parens_around_for_head(
+        &mut self,
+        pat: P<Pat>,
+        begin_paren: Option<Span>,
+    ) -> P<Pat> {
+        match (&self.token.kind, begin_paren) {
+            (token::CloseDelim(Delimiter::Parenthesis), Some(begin_par_sp)) => {
+                self.bump();
+
+                self.struct_span_err(
+                    MultiSpan::from_spans(vec![begin_par_sp, self.prev_token.span]),
+                    "unexpected parentheses surrounding `for` loop head",
+                )
+                .multipart_suggestion(
+                    "remove parentheses in `for` loop",
+                    vec![(begin_par_sp, String::new()), (self.prev_token.span, String::new())],
+                    // With e.g. `for (x) in y)` this would replace `(x) in y)`
+                    // with `x) in y)` which is syntactically invalid.
+                    // However, this is prevented before we get here.
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+
+                // Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
+                pat.and_then(|pat| match pat.kind {
+                    PatKind::Paren(pat) => pat,
+                    _ => P(pat),
+                })
+            }
+            _ => pat,
+        }
+    }
+
+    pub(super) fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
+        (self.token == token::Lt && // `foo:<bar`, likely a typoed turbofish.
+            self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident()))
+            || self.token.is_ident() &&
+            matches!(node, ast::ExprKind::Path(..) | ast::ExprKind::Field(..)) &&
+            !self.token.is_reserved_ident() &&           // v `foo:bar(baz)`
+            self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Parenthesis))
+            || self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Brace)) // `foo:bar {`
+            || self.look_ahead(1, |t| t == &token::Colon) &&     // `foo:bar::<baz`
+            self.look_ahead(2, |t| t == &token::Lt) &&
+            self.look_ahead(3, |t| t.is_ident())
+            || self.look_ahead(1, |t| t == &token::Colon) &&  // `foo:bar:baz`
+            self.look_ahead(2, |t| t.is_ident())
+            || self.look_ahead(1, |t| t == &token::ModSep)
+                && (self.look_ahead(2, |t| t.is_ident()) ||   // `foo:bar::baz`
+            self.look_ahead(2, |t| t == &token::Lt)) // `foo:bar::<baz>`
+    }
+
+    pub(super) fn recover_seq_parse_error(
+        &mut self,
+        delim: Delimiter,
+        lo: Span,
+        result: PResult<'a, P<Expr>>,
+    ) -> P<Expr> {
+        match result {
+            Ok(x) => x,
+            Err(mut err) => {
+                err.emit();
+                // Recover from parse error, callers expect the closing delim to be consumed.
+                self.consume_block(delim, ConsumeClosingDelim::Yes);
+                self.mk_expr(lo.to(self.prev_token.span), ExprKind::Err, AttrVec::new())
+            }
+        }
+    }
+
+    pub(super) fn recover_closing_delimiter(
+        &mut self,
+        tokens: &[TokenKind],
+        mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
+    ) -> PResult<'a, bool> {
+        let mut pos = None;
+        // We want to use the last closing delim that would apply.
+        for (i, unmatched) in self.unclosed_delims.iter().enumerate().rev() {
+            if tokens.contains(&token::CloseDelim(unmatched.expected_delim))
+                && Some(self.token.span) > unmatched.unclosed_span
+            {
+                pos = Some(i);
+            }
+        }
+        match pos {
+            Some(pos) => {
+                // Recover and assume that the detected unclosed delimiter was meant for
+                // this location. Emit the diagnostic and act as if the delimiter was
+                // present for the parser's sake.
+
+                // Don't attempt to recover from this unclosed delimiter more than once.
+                let unmatched = self.unclosed_delims.remove(pos);
+                let delim = TokenType::Token(token::CloseDelim(unmatched.expected_delim));
+                if unmatched.found_delim.is_none() {
+                    // We encountered `Eof`, set this fact here to avoid complaining about missing
+                    // `fn main()` when we found place to suggest the closing brace.
+                    *self.sess.reached_eof.borrow_mut() = true;
+                }
+
+                // We want to suggest the inclusion of the closing delimiter where it makes
+                // the most sense, which is immediately after the last token:
+                //
+                //  {foo(bar {}}
+                //      ^      ^
+                //      |      |
+                //      |      help: `)` may belong here
+                //      |
+                //      unclosed delimiter
+                if let Some(sp) = unmatched.unclosed_span {
+                    let mut primary_span: Vec<Span> =
+                        err.span.primary_spans().iter().cloned().collect();
+                    primary_span.push(sp);
+                    let mut primary_span: MultiSpan = primary_span.into();
+                    for span_label in err.span.span_labels() {
+                        if let Some(label) = span_label.label {
+                            primary_span.push_span_label(span_label.span, label);
+                        }
+                    }
+                    err.set_span(primary_span);
+                    err.span_label(sp, "unclosed delimiter");
+                }
+                // Backticks should be removed to apply suggestions.
+                let mut delim = delim.to_string();
+                delim.retain(|c| c != '`');
+                err.span_suggestion_short(
+                    self.prev_token.span.shrink_to_hi(),
+                    &format!("`{delim}` may belong here"),
+                    delim,
+                    Applicability::MaybeIncorrect,
+                );
+                if unmatched.found_delim.is_none() {
+                    // Encountered `Eof` when lexing blocks. Do not recover here to avoid knockdown
+                    // errors which would be emitted elsewhere in the parser and let other error
+                    // recovery consume the rest of the file.
+                    Err(err)
+                } else {
+                    err.emit();
+                    self.expected_tokens.clear(); // Reduce the number of errors.
+                    Ok(true)
+                }
+            }
+            _ => Err(err),
+        }
+    }
+
+    /// Eats tokens until we can be relatively sure we reached the end of the
+    /// statement. This is something of a best-effort heuristic.
+    ///
+    /// We terminate when we find an unmatched `}` (without consuming it).
+    pub(super) fn recover_stmt(&mut self) {
+        self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore)
+    }
+
+    /// If `break_on_semi` is `Break`, then we will stop consuming tokens after
+    /// finding (and consuming) a `;` outside of `{}` or `[]` (note that this is
+    /// approximate -- it can mean we break too early due to macros, but that
+    /// should only lead to sub-optimal recovery, not inaccurate parsing).
+    ///
+    /// If `break_on_block` is `Break`, then we will stop consuming tokens
+    /// after finding (and consuming) a brace-delimited block.
+    pub(super) fn recover_stmt_(
+        &mut self,
+        break_on_semi: SemiColonMode,
+        break_on_block: BlockMode,
+    ) {
+        let mut brace_depth = 0;
+        let mut bracket_depth = 0;
+        let mut in_block = false;
+        debug!("recover_stmt_ enter loop (semi={:?}, block={:?})", break_on_semi, break_on_block);
+        loop {
+            debug!("recover_stmt_ loop {:?}", self.token);
+            match self.token.kind {
+                token::OpenDelim(Delimiter::Brace) => {
+                    brace_depth += 1;
+                    self.bump();
+                    if break_on_block == BlockMode::Break && brace_depth == 1 && bracket_depth == 0
+                    {
+                        in_block = true;
+                    }
+                }
+                token::OpenDelim(Delimiter::Bracket) => {
+                    bracket_depth += 1;
+                    self.bump();
+                }
+                token::CloseDelim(Delimiter::Brace) => {
+                    if brace_depth == 0 {
+                        debug!("recover_stmt_ return - close delim {:?}", self.token);
+                        break;
+                    }
+                    brace_depth -= 1;
+                    self.bump();
+                    if in_block && bracket_depth == 0 && brace_depth == 0 {
+                        debug!("recover_stmt_ return - block end {:?}", self.token);
+                        break;
+                    }
+                }
+                token::CloseDelim(Delimiter::Bracket) => {
+                    bracket_depth -= 1;
+                    if bracket_depth < 0 {
+                        bracket_depth = 0;
+                    }
+                    self.bump();
+                }
+                token::Eof => {
+                    debug!("recover_stmt_ return - Eof");
+                    break;
+                }
+                token::Semi => {
+                    self.bump();
+                    if break_on_semi == SemiColonMode::Break
+                        && brace_depth == 0
+                        && bracket_depth == 0
+                    {
+                        debug!("recover_stmt_ return - Semi");
+                        break;
+                    }
+                }
+                token::Comma
+                    if break_on_semi == SemiColonMode::Comma
+                        && brace_depth == 0
+                        && bracket_depth == 0 =>
+                {
+                    debug!("recover_stmt_ return - Semi");
+                    break;
+                }
+                _ => self.bump(),
+            }
+        }
+    }
+
+    pub(super) fn check_for_for_in_in_typo(&mut self, in_span: Span) {
+        if self.eat_keyword(kw::In) {
+            // a common typo: `for _ in in bar {}`
+            self.sess.emit_err(InInTypo {
+                span: self.prev_token.span,
+                sugg_span: in_span.until(self.prev_token.span),
+            });
+        }
+    }
+
+    pub(super) fn eat_incorrect_doc_comment_for_param_type(&mut self) {
+        if let token::DocComment(..) = self.token.kind {
+            self.struct_span_err(
+                self.token.span,
+                "documentation comments cannot be applied to a function parameter's type",
+            )
+            .span_label(self.token.span, "doc comments are not allowed here")
+            .emit();
+            self.bump();
+        } else if self.token == token::Pound
+            && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Bracket))
+        {
+            let lo = self.token.span;
+            // Skip every token until next possible arg.
+            while self.token != token::CloseDelim(Delimiter::Bracket) {
+                self.bump();
+            }
+            let sp = lo.to(self.token.span);
+            self.bump();
+            self.struct_span_err(sp, "attributes cannot be applied to a function parameter's type")
+                .span_label(sp, "attributes are not allowed here")
+                .emit();
+        }
+    }
+
+    pub(super) fn parameter_without_type(
+        &mut self,
+        err: &mut Diagnostic,
+        pat: P<ast::Pat>,
+        require_name: bool,
+        first_param: bool,
+    ) -> Option<Ident> {
+        // If we find a pattern followed by an identifier, it could be an (incorrect)
+        // C-style parameter declaration.
+        if self.check_ident()
+            && self.look_ahead(1, |t| {
+                *t == token::Comma || *t == token::CloseDelim(Delimiter::Parenthesis)
+            })
+        {
+            // `fn foo(String s) {}`
+            let ident = self.parse_ident().unwrap();
+            let span = pat.span.with_hi(ident.span.hi());
+
+            err.span_suggestion(
+                span,
+                "declare the type after the parameter binding",
+                "<identifier>: <type>",
+                Applicability::HasPlaceholders,
+            );
+            return Some(ident);
+        } else if require_name
+            && (self.token == token::Comma
+                || self.token == token::Lt
+                || self.token == token::CloseDelim(Delimiter::Parenthesis))
+        {
+            let rfc_note = "anonymous parameters are removed in the 2018 edition (see RFC 1685)";
+
+            let (ident, self_sugg, param_sugg, type_sugg, self_span, param_span, type_span) =
+                match pat.kind {
+                    PatKind::Ident(_, ident, _) => (
+                        ident,
+                        "self: ",
+                        ": TypeName".to_string(),
+                        "_: ",
+                        pat.span.shrink_to_lo(),
+                        pat.span.shrink_to_hi(),
+                        pat.span.shrink_to_lo(),
+                    ),
+                    // Also catches `fn foo(&a)`.
+                    PatKind::Ref(ref inner_pat, mutab)
+                        if matches!(inner_pat.clone().into_inner().kind, PatKind::Ident(..)) =>
+                    {
+                        match inner_pat.clone().into_inner().kind {
+                            PatKind::Ident(_, ident, _) => {
+                                let mutab = mutab.prefix_str();
+                                (
+                                    ident,
+                                    "self: ",
+                                    format!("{ident}: &{mutab}TypeName"),
+                                    "_: ",
+                                    pat.span.shrink_to_lo(),
+                                    pat.span,
+                                    pat.span.shrink_to_lo(),
+                                )
+                            }
+                            _ => unreachable!(),
+                        }
+                    }
+                    _ => {
+                        // Otherwise, try to get a type and emit a suggestion.
+                        if let Some(ty) = pat.to_ty() {
+                            err.span_suggestion_verbose(
+                                pat.span,
+                                "explicitly ignore the parameter name",
+                                format!("_: {}", pprust::ty_to_string(&ty)),
+                                Applicability::MachineApplicable,
+                            );
+                            err.note(rfc_note);
+                        }
+
+                        return None;
+                    }
+                };
+
+            // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
+            if first_param {
+                err.span_suggestion(
+                    self_span,
+                    "if this is a `self` type, give it a parameter name",
+                    self_sugg,
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            // Avoid suggesting that `fn foo(HashMap<u32>)` is fixed with a change to
+            // `fn foo(HashMap: TypeName<u32>)`.
+            if self.token != token::Lt {
+                err.span_suggestion(
+                    param_span,
+                    "if this is a parameter name, give it a type",
+                    param_sugg,
+                    Applicability::HasPlaceholders,
+                );
+            }
+            err.span_suggestion(
+                type_span,
+                "if this is a type, explicitly ignore the parameter name",
+                type_sugg,
+                Applicability::MachineApplicable,
+            );
+            err.note(rfc_note);
+
+            // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
+            return if self.token == token::Lt { None } else { Some(ident) };
+        }
+        None
+    }
+
+    pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
+        let pat = self.parse_pat_no_top_alt(Some("argument name"))?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        struct_span_err!(
+            self.diagnostic(),
+            pat.span,
+            E0642,
+            "patterns aren't allowed in methods without bodies",
+        )
+        .span_suggestion_short(
+            pat.span,
+            "give this argument a name or use an underscore to ignore it",
+            "_",
+            Applicability::MachineApplicable,
+        )
+        .emit();
+
+        // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
+        let pat =
+            P(Pat { kind: PatKind::Wild, span: pat.span, id: ast::DUMMY_NODE_ID, tokens: None });
+        Ok((pat, ty))
+    }
+
+    pub(super) fn recover_bad_self_param(&mut self, mut param: Param) -> PResult<'a, Param> {
+        let sp = param.pat.span;
+        param.ty.kind = TyKind::Err;
+        self.struct_span_err(sp, "unexpected `self` parameter in function")
+            .span_label(sp, "must be the first parameter of an associated function")
+            .emit();
+        Ok(param)
+    }
+
+    pub(super) fn consume_block(&mut self, delim: Delimiter, consume_close: ConsumeClosingDelim) {
+        let mut brace_depth = 0;
+        loop {
+            if self.eat(&token::OpenDelim(delim)) {
+                brace_depth += 1;
+            } else if self.check(&token::CloseDelim(delim)) {
+                if brace_depth == 0 {
+                    if let ConsumeClosingDelim::Yes = consume_close {
+                        // Some of the callers of this method expect to be able to parse the
+                        // closing delimiter themselves, so we leave it alone. Otherwise we advance
+                        // the parser.
+                        self.bump();
+                    }
+                    return;
+                } else {
+                    self.bump();
+                    brace_depth -= 1;
+                    continue;
+                }
+            } else if self.token == token::Eof {
+                return;
+            } else {
+                self.bump();
+            }
+        }
+    }
+
+    pub(super) fn expected_expression_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        let (span, msg) = match (&self.token.kind, self.subparser_name) {
+            (&token::Eof, Some(origin)) => {
+                let sp = self.sess.source_map().next_point(self.prev_token.span);
+                (sp, format!("expected expression, found end of {origin}"))
+            }
+            _ => (
+                self.token.span,
+                format!("expected expression, found {}", super::token_descr(&self.token),),
+            ),
+        };
+        let mut err = self.struct_span_err(span, &msg);
+        let sp = self.sess.source_map().start_point(self.token.span);
+        if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            self.sess.expr_parentheses_needed(&mut err, *sp);
+        }
+        err.span_label(span, "expected expression");
+        err
+    }
+
+    fn consume_tts(
+        &mut self,
+        mut acc: i64, // `i64` because malformed code can have more closing delims than opening.
+        // Not using `FxHashMap` due to `token::TokenKind: !Eq + !Hash`.
+        modifier: &[(token::TokenKind, i64)],
+    ) {
+        while acc > 0 {
+            if let Some((_, val)) = modifier.iter().find(|(t, _)| *t == self.token.kind) {
+                acc += *val;
+            }
+            if self.token.kind == token::Eof {
+                break;
+            }
+            self.bump();
+        }
+    }
+
+    /// Replace duplicated recovered parameters with `_` pattern to avoid unnecessary errors.
+    ///
+    /// This is necessary because at this point we don't know whether we parsed a function with
+    /// anonymous parameters or a function with names but no types. In order to minimize
+    /// unnecessary errors, we assume the parameters are in the shape of `fn foo(a, b, c)` where
+    /// the parameters are *names* (so we don't emit errors about not being able to find `b` in
+    /// the local scope), but if we find the same name multiple times, like in `fn foo(i8, i8)`,
+    /// we deduplicate them to not complain about duplicated parameter names.
+    pub(super) fn deduplicate_recovered_params_names(&self, fn_inputs: &mut Vec<Param>) {
+        let mut seen_inputs = FxHashSet::default();
+        for input in fn_inputs.iter_mut() {
+            let opt_ident = if let (PatKind::Ident(_, ident, _), TyKind::Err) =
+                (&input.pat.kind, &input.ty.kind)
+            {
+                Some(*ident)
+            } else {
+                None
+            };
+            if let Some(ident) = opt_ident {
+                if seen_inputs.contains(&ident) {
+                    input.pat.kind = PatKind::Wild;
+                }
+                seen_inputs.insert(ident);
+            }
+        }
+    }
+
+    /// Handle encountering a symbol in a generic argument list that is not a `,` or `>`. In this
+    /// case, we emit an error and try to suggest enclosing a const argument in braces if it looks
+    /// like the user has forgotten them.
+    pub fn handle_ambiguous_unbraced_const_arg(
+        &mut self,
+        args: &mut Vec<AngleBracketedArg>,
+    ) -> PResult<'a, bool> {
+        // If we haven't encountered a closing `>`, then the argument is malformed.
+        // It's likely that the user has written a const expression without enclosing it
+        // in braces, so we try to recover here.
+        let arg = args.pop().unwrap();
+        // FIXME: for some reason using `unexpected` or `expected_one_of_not_found` has
+        // adverse side-effects to subsequent errors and seems to advance the parser.
+        // We are causing this error here exclusively in case that a `const` expression
+        // could be recovered from the current parser state, even if followed by more
+        // arguments after a comma.
+        let mut err = self.struct_span_err(
+            self.token.span,
+            &format!("expected one of `,` or `>`, found {}", super::token_descr(&self.token)),
+        );
+        err.span_label(self.token.span, "expected one of `,` or `>`");
+        match self.recover_const_arg(arg.span(), err) {
+            Ok(arg) => {
+                args.push(AngleBracketedArg::Arg(arg));
+                if self.eat(&token::Comma) {
+                    return Ok(true); // Continue
+                }
+            }
+            Err(mut err) => {
+                args.push(arg);
+                // We will emit a more generic error later.
+                err.delay_as_bug();
+            }
+        }
+        return Ok(false); // Don't continue.
+    }
+
+    /// Attempt to parse a generic const argument that has not been enclosed in braces.
+    /// There are a limited number of expressions that are permitted without being encoded
+    /// in braces:
+    /// - Literals.
+    /// - Single-segment paths (i.e. standalone generic const parameters).
+    /// All other expressions that can be parsed will emit an error suggesting the expression be
+    /// wrapped in braces.
+    pub fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, P<Expr>> {
+        let start = self.token.span;
+        let expr = self.parse_expr_res(Restrictions::CONST_EXPR, None).map_err(|mut err| {
+            err.span_label(
+                start.shrink_to_lo(),
+                "while parsing a const generic argument starting here",
+            );
+            err
+        })?;
+        if !self.expr_is_valid_const_arg(&expr) {
+            self.struct_span_err(
+                expr.span,
+                "expressions must be enclosed in braces to be used as const generic \
+                    arguments",
+            )
+            .multipart_suggestion(
+                "enclose the `const` expression in braces",
+                vec![
+                    (expr.span.shrink_to_lo(), "{ ".to_string()),
+                    (expr.span.shrink_to_hi(), " }".to_string()),
+                ],
+                Applicability::MachineApplicable,
+            )
+            .emit();
+        }
+        Ok(expr)
+    }
+
+    fn recover_const_param_decl(&mut self, ty_generics: Option<&Generics>) -> Option<GenericArg> {
+        let snapshot = self.create_snapshot_for_diagnostic();
+        let param = match self.parse_const_param(vec![]) {
+            Ok(param) => param,
+            Err(err) => {
+                err.cancel();
+                self.restore_snapshot(snapshot);
+                return None;
+            }
+        };
+        let mut err =
+            self.struct_span_err(param.span(), "unexpected `const` parameter declaration");
+        err.span_label(param.span(), "expected a `const` expression, not a parameter declaration");
+        if let (Some(generics), Ok(snippet)) =
+            (ty_generics, self.sess.source_map().span_to_snippet(param.span()))
+        {
+            let (span, sugg) = match &generics.params[..] {
+                [] => (generics.span, format!("<{snippet}>")),
+                [.., generic] => (generic.span().shrink_to_hi(), format!(", {snippet}")),
+            };
+            err.multipart_suggestion(
+                "`const` parameters must be declared for the `impl`",
+                vec![(span, sugg), (param.span(), param.ident.to_string())],
+                Applicability::MachineApplicable,
+            );
+        }
+        let value = self.mk_expr_err(param.span());
+        err.emit();
+        Some(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }))
+    }
+
+    pub fn recover_const_param_declaration(
+        &mut self,
+        ty_generics: Option<&Generics>,
+    ) -> PResult<'a, Option<GenericArg>> {
+        // We have to check for a few different cases.
+        if let Some(arg) = self.recover_const_param_decl(ty_generics) {
+            return Ok(Some(arg));
+        }
+
+        // We haven't consumed `const` yet.
+        let start = self.token.span;
+        self.bump(); // `const`
+
+        // Detect and recover from the old, pre-RFC2000 syntax for const generics.
+        let mut err = self
+            .struct_span_err(start, "expected lifetime, type, or constant, found keyword `const`");
+        if self.check_const_arg() {
+            err.span_suggestion_verbose(
+                start.until(self.token.span),
+                "the `const` keyword is only needed in the definition of the type",
+                "",
+                Applicability::MaybeIncorrect,
+            );
+            err.emit();
+            Ok(Some(GenericArg::Const(self.parse_const_arg()?)))
+        } else {
+            let after_kw_const = self.token.span;
+            self.recover_const_arg(after_kw_const, err).map(Some)
+        }
+    }
+
+    /// Try to recover from possible generic const argument without `{` and `}`.
+    ///
+    /// When encountering code like `foo::< bar + 3 >` or `foo::< bar - baz >` we suggest
+    /// `foo::<{ bar + 3 }>` and `foo::<{ bar - baz }>`, respectively. We only provide a suggestion
+    /// if we think that that the resulting expression would be well formed.
+    pub fn recover_const_arg(
+        &mut self,
+        start: Span,
+        mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
+    ) -> PResult<'a, GenericArg> {
+        let is_op_or_dot = AssocOp::from_token(&self.token)
+            .and_then(|op| {
+                if let AssocOp::Greater
+                | AssocOp::Less
+                | AssocOp::ShiftRight
+                | AssocOp::GreaterEqual
+                // Don't recover from `foo::<bar = baz>`, because this could be an attempt to
+                // assign a value to a defaulted generic parameter.
+                | AssocOp::Assign
+                | AssocOp::AssignOp(_) = op
+                {
+                    None
+                } else {
+                    Some(op)
+                }
+            })
+            .is_some()
+            || self.token.kind == TokenKind::Dot;
+        // This will be true when a trait object type `Foo +` or a path which was a `const fn` with
+        // type params has been parsed.
+        let was_op =
+            matches!(self.prev_token.kind, token::BinOp(token::Plus | token::Shr) | token::Gt);
+        if !is_op_or_dot && !was_op {
+            // We perform these checks and early return to avoid taking a snapshot unnecessarily.
+            return Err(err);
+        }
+        let snapshot = self.create_snapshot_for_diagnostic();
+        if is_op_or_dot {
+            self.bump();
+        }
+        match self.parse_expr_res(Restrictions::CONST_EXPR, None) {
+            Ok(expr) => {
+                // Find a mistake like `MyTrait<Assoc == S::Assoc>`.
+                if token::EqEq == snapshot.token.kind {
+                    err.span_suggestion(
+                        snapshot.token.span,
+                        "if you meant to use an associated type binding, replace `==` with `=`",
+                        "=",
+                        Applicability::MaybeIncorrect,
+                    );
+                    let value = self.mk_expr_err(start.to(expr.span));
+                    err.emit();
+                    return Ok(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }));
+                } else if token::Colon == snapshot.token.kind
+                    && expr.span.lo() == snapshot.token.span.hi()
+                    && matches!(expr.kind, ExprKind::Path(..))
+                {
+                    // Find a mistake like "foo::var:A".
+                    err.span_suggestion(
+                        snapshot.token.span,
+                        "write a path separator here",
+                        "::",
+                        Applicability::MaybeIncorrect,
+                    );
+                    err.emit();
+                    return Ok(GenericArg::Type(self.mk_ty(start.to(expr.span), TyKind::Err)));
+                } else if token::Comma == self.token.kind || self.token.kind.should_end_const_arg()
+                {
+                    // Avoid the following output by checking that we consumed a full const arg:
+                    // help: expressions must be enclosed in braces to be used as const generic
+                    //       arguments
+                    //    |
+                    // LL |     let sr: Vec<{ (u32, _, _) = vec![] };
+                    //    |                 ^                      ^
+                    return Ok(self.dummy_const_arg_needs_braces(err, start.to(expr.span)));
+                }
+            }
+            Err(err) => {
+                err.cancel();
+            }
+        }
+        self.restore_snapshot(snapshot);
+        Err(err)
+    }
+
+    /// Creates a dummy const argument, and reports that the expression must be enclosed in braces
+    pub fn dummy_const_arg_needs_braces(
+        &self,
+        mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
+        span: Span,
+    ) -> GenericArg {
+        err.multipart_suggestion(
+            "expressions must be enclosed in braces to be used as const generic \
+             arguments",
+            vec![(span.shrink_to_lo(), "{ ".to_string()), (span.shrink_to_hi(), " }".to_string())],
+            Applicability::MaybeIncorrect,
+        );
+        let value = self.mk_expr_err(span);
+        err.emit();
+        GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value })
+    }
+
+    /// Get the diagnostics for the cases where `move async` is found.
+    ///
+    /// `move_async_span` starts at the 'm' of the move keyword and ends with the 'c' of the async keyword
+    pub(super) fn incorrect_move_async_order_found(
+        &self,
+        move_async_span: Span,
+    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+        let mut err =
+            self.struct_span_err(move_async_span, "the order of `move` and `async` is incorrect");
+        err.span_suggestion_verbose(
+            move_async_span,
+            "try switching the order",
+            "async move",
+            Applicability::MaybeIncorrect,
+        );
+        err
+    }
+
+    /// Some special error handling for the "top-level" patterns in a match arm,
+    /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
+    pub(crate) fn maybe_recover_colon_colon_in_pat_typo(
+        &mut self,
+        mut first_pat: P<Pat>,
+        expected: Expected,
+    ) -> P<Pat> {
+        if token::Colon != self.token.kind {
+            return first_pat;
+        }
+        if !matches!(first_pat.kind, PatKind::Ident(_, _, None) | PatKind::Path(..))
+            || !self.look_ahead(1, |token| token.is_ident() && !token.is_reserved_ident())
+        {
+            return first_pat;
+        }
+        // The pattern looks like it might be a path with a `::` -> `:` typo:
+        // `match foo { bar:baz => {} }`
+        let span = self.token.span;
+        // We only emit "unexpected `:`" error here if we can successfully parse the
+        // whole pattern correctly in that case.
+        let snapshot = self.create_snapshot_for_diagnostic();
+
+        // Create error for "unexpected `:`".
+        match self.expected_one_of_not_found(&[], &[]) {
+            Err(mut err) => {
+                self.bump(); // Skip the `:`.
+                match self.parse_pat_no_top_alt(expected) {
+                    Err(inner_err) => {
+                        // Carry on as if we had not done anything, callers will emit a
+                        // reasonable error.
+                        inner_err.cancel();
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                    }
+                    Ok(mut pat) => {
+                        // We've parsed the rest of the pattern.
+                        let new_span = first_pat.span.to(pat.span);
+                        let mut show_sugg = false;
+                        // Try to construct a recovered pattern.
+                        match &mut pat.kind {
+                            PatKind::Struct(qself @ None, path, ..)
+                            | PatKind::TupleStruct(qself @ None, path, _)
+                            | PatKind::Path(qself @ None, path) => match &first_pat.kind {
+                                PatKind::Ident(_, ident, _) => {
+                                    path.segments.insert(0, PathSegment::from_ident(*ident));
+                                    path.span = new_span;
+                                    show_sugg = true;
+                                    first_pat = pat;
+                                }
+                                PatKind::Path(old_qself, old_path) => {
+                                    path.segments = old_path
+                                        .segments
+                                        .iter()
+                                        .cloned()
+                                        .chain(take(&mut path.segments))
+                                        .collect();
+                                    path.span = new_span;
+                                    *qself = old_qself.clone();
+                                    first_pat = pat;
+                                    show_sugg = true;
+                                }
+                                _ => {}
+                            },
+                            PatKind::Ident(BindingMode::ByValue(Mutability::Not), ident, None) => {
+                                match &first_pat.kind {
+                                    PatKind::Ident(_, old_ident, _) => {
+                                        let path = PatKind::Path(
+                                            None,
+                                            Path {
+                                                span: new_span,
+                                                segments: vec![
+                                                    PathSegment::from_ident(*old_ident),
+                                                    PathSegment::from_ident(*ident),
+                                                ],
+                                                tokens: None,
+                                            },
+                                        );
+                                        first_pat = self.mk_pat(new_span, path);
+                                        show_sugg = true;
+                                    }
+                                    PatKind::Path(old_qself, old_path) => {
+                                        let mut segments = old_path.segments.clone();
+                                        segments.push(PathSegment::from_ident(*ident));
+                                        let path = PatKind::Path(
+                                            old_qself.clone(),
+                                            Path { span: new_span, segments, tokens: None },
+                                        );
+                                        first_pat = self.mk_pat(new_span, path);
+                                        show_sugg = true;
+                                    }
+                                    _ => {}
+                                }
+                            }
+                            _ => {}
+                        }
+                        if show_sugg {
+                            err.span_suggestion(
+                                span,
+                                "maybe write a path separator here",
+                                "::",
+                                Applicability::MaybeIncorrect,
+                            );
+                        } else {
+                            first_pat = self.mk_pat(new_span, PatKind::Wild);
+                        }
+                        err.emit();
+                    }
+                }
+            }
+            _ => {
+                // Carry on as if we had not done anything. This should be unreachable.
+                self.restore_snapshot(snapshot);
+            }
+        };
+        first_pat
+    }
+
+    pub(crate) fn maybe_recover_unexpected_block_label(&mut self) -> bool {
+        let Some(label) = self.eat_label().filter(|_| {
+            self.eat(&token::Colon) && self.token.kind == token::OpenDelim(Delimiter::Brace)
+        }) else {
+            return false;
+        };
+        let span = label.ident.span.to(self.prev_token.span);
+        let mut err = self.struct_span_err(span, "block label not supported here");
+        err.span_label(span, "not supported here");
+        err.tool_only_span_suggestion(
+            label.ident.span.until(self.token.span),
+            "remove this block label",
+            "",
+            Applicability::MachineApplicable,
+        );
+        err.emit();
+        true
+    }
+
+    /// Some special error handling for the "top-level" patterns in a match arm,
+    /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
+    pub(crate) fn maybe_recover_unexpected_comma(
+        &mut self,
+        lo: Span,
+        rt: CommaRecoveryMode,
+    ) -> PResult<'a, ()> {
+        if self.token != token::Comma {
+            return Ok(());
+        }
+
+        // An unexpected comma after a top-level pattern is a clue that the
+        // user (perhaps more accustomed to some other language) forgot the
+        // parentheses in what should have been a tuple pattern; return a
+        // suggestion-enhanced error here rather than choking on the comma later.
+        let comma_span = self.token.span;
+        self.bump();
+        if let Err(err) = self.skip_pat_list() {
+            // We didn't expect this to work anyway; we just wanted to advance to the
+            // end of the comma-sequence so we know the span to suggest parenthesizing.
+            err.cancel();
+        }
+        let seq_span = lo.to(self.prev_token.span);
+        let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
+        if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
+            err.multipart_suggestion(
+                &format!(
+                    "try adding parentheses to match on a tuple{}",
+                    if let CommaRecoveryMode::LikelyTuple = rt { "" } else { "..." },
+                ),
+                vec![
+                    (seq_span.shrink_to_lo(), "(".to_string()),
+                    (seq_span.shrink_to_hi(), ")".to_string()),
+                ],
+                Applicability::MachineApplicable,
+            );
+            if let CommaRecoveryMode::EitherTupleOrPipe = rt {
+                err.span_suggestion(
+                    seq_span,
+                    "...or a vertical bar to match on multiple alternatives",
+                    seq_snippet.replace(',', " |"),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        Err(err)
+    }
+
+    pub(crate) fn maybe_recover_bounds_doubled_colon(&mut self, ty: &Ty) -> PResult<'a, ()> {
+        let TyKind::Path(qself, path) = &ty.kind else { return Ok(()) };
+        let qself_position = qself.as_ref().map(|qself| qself.position);
+        for (i, segments) in path.segments.windows(2).enumerate() {
+            if qself_position.map(|pos| i < pos).unwrap_or(false) {
+                continue;
+            }
+            if let [a, b] = segments {
+                let (a_span, b_span) = (a.span(), b.span());
+                let between_span = a_span.shrink_to_hi().to(b_span.shrink_to_lo());
+                if self.span_to_snippet(between_span).as_ref().map(|a| &a[..]) == Ok(":: ") {
+                    let mut err = self.struct_span_err(
+                        path.span.shrink_to_hi(),
+                        "expected `:` followed by trait or lifetime",
+                    );
+                    err.span_suggestion(
+                        between_span,
+                        "use single colon",
+                        ": ",
+                        Applicability::MachineApplicable,
+                    );
+                    return Err(err);
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Parse and throw away a parenthesized comma separated
+    /// sequence of patterns until `)` is reached.
+    fn skip_pat_list(&mut self) -> PResult<'a, ()> {
+        while !self.check(&token::CloseDelim(Delimiter::Parenthesis)) {
+            self.parse_pat_no_top_alt(None)?;
+            if !self.eat(&token::Comma) {
+                return Ok(());
+            }
+        }
+        Ok(())
+    }
+}