Merging upstream version 1.71.1+dfsg1.

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

19 files changed, 1088 insertions, 675 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 069217165..84494eab8 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -907,6 +907,18 @@ pub(crate) struct SuggRemoveComma {
 }
 
 #[derive(Subdiagnostic)]
+#[suggestion(
+    parse_sugg_add_let_for_stmt,
+    style = "verbose",
+    applicability = "maybe-incorrect",
+    code = "let "
+)]
+pub(crate) struct SuggAddMissingLetStmt {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Subdiagnostic)]
 pub(crate) enum ExpectedIdentifierFound {
     #[label(parse_expected_identifier_found_reserved_identifier)]
     ReservedIdentifier(#[primary_span] Span),
@@ -1341,6 +1353,28 @@ pub(crate) struct ExpectedFnPathFoundFnKeyword {
 }
 
 #[derive(Diagnostic)]
+#[diag(parse_path_single_colon)]
+pub(crate) struct PathSingleColon {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "::")]
+    pub span: Span,
+
+    #[note(parse_type_ascription_removed)]
+    pub type_ascription: Option<()>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_colon_as_semi)]
+pub(crate) struct ColonAsSemi {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = ";")]
+    pub span: Span,
+
+    #[note(parse_type_ascription_removed)]
+    pub type_ascription: Option<()>,
+}
+
+#[derive(Diagnostic)]
 #[diag(parse_where_clause_before_tuple_struct_body)]
 pub(crate) struct WhereClauseBeforeTupleStructBody {
     #[primary_span]
@@ -1486,6 +1520,16 @@ pub(crate) struct ExpectedTraitInTraitImplFoundType {
 }
 
 #[derive(Diagnostic)]
+#[diag(parse_extra_impl_keyword_in_trait_impl)]
+pub(crate) struct ExtraImplKeywordInTraitImpl {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    pub extra_impl_kw: Span,
+    #[note]
+    pub impl_trait_span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(parse_bounds_not_allowed_on_trait_aliases)]
 pub(crate) struct BoundsNotAllowedOnTraitAliases {
     #[primary_span]
@@ -2258,31 +2302,6 @@ pub(crate) struct InvalidDynKeyword {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(parse_negative_bounds_not_supported)]
-pub(crate) struct NegativeBoundsNotSupported {
-    #[primary_span]
-    pub negative_bounds: Vec<Span>,
-    #[label]
-    pub last_span: Span,
-    #[subdiagnostic]
-    pub sub: Option<NegativeBoundsNotSupportedSugg>,
-}
-
-#[derive(Subdiagnostic)]
-#[suggestion(
-    parse_suggestion,
-    style = "tool-only",
-    code = "{fixed}",
-    applicability = "machine-applicable"
-)]
-pub(crate) struct NegativeBoundsNotSupportedSugg {
-    #[primary_span]
-    pub bound_list: Span,
-    pub num_bounds: usize,
-    pub fixed: String,
-}
-
 #[derive(Subdiagnostic)]
 pub enum HelpUseLatestEdition {
     #[help(parse_help_set_edition_cargo)]
@@ -2332,3 +2351,333 @@ pub(crate) struct BadReturnTypeNotationDotDot {
     #[suggestion(code = "", applicability = "maybe-incorrect")]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_bad_assoc_type_bounds)]
+pub(crate) struct BadAssocTypeBounds {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_attr_after_generic)]
+pub(crate) struct AttrAfterGeneric {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_attr_without_generics)]
+pub(crate) struct AttrWithoutGenerics {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_where_generics)]
+pub(crate) struct WhereOnGenerics {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_generics_in_path)]
+pub(crate) struct GenericsInPath {
+    #[primary_span]
+    pub span: Vec<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_assoc_lifetime)]
+#[help]
+pub(crate) struct AssocLifetime {
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub lifetime: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_tilde_const_lifetime)]
+pub(crate) struct TildeConstLifetime {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_modifier_lifetime)]
+pub(crate) struct ModifierLifetime {
+    #[primary_span]
+    #[suggestion(style = "tool-only", applicability = "maybe-incorrect", code = "")]
+    pub span: Span,
+    pub sigil: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_parenthesized_lifetime)]
+pub(crate) struct ParenthesizedLifetime {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(style = "short", applicability = "machine-applicable", code = "{snippet}")]
+    pub sugg: Option<Span>,
+    pub snippet: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_const_bounds_missing_tilde)]
+pub(crate) struct ConstMissingTilde {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "~", applicability = "machine-applicable")]
+    pub start: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_underscore_literal_suffix)]
+pub(crate) struct UnderscoreLiteralSuffix {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expect_label_found_ident)]
+pub(crate) struct ExpectedLabelFoundIdent {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "'", applicability = "machine-applicable", style = "short")]
+    pub start: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_inappropriate_default)]
+#[note]
+pub(crate) struct InappropriateDefault {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub article: &'static str,
+    pub descr: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_recover_import_as_use)]
+pub(crate) struct RecoverImportAsUse {
+    #[primary_span]
+    #[suggestion(code = "use", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+    pub token_name: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_single_colon_import_path)]
+#[note]
+pub(crate) struct SingleColonImportPath {
+    #[primary_span]
+    #[suggestion(code = "::", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_bad_item_kind)]
+#[help]
+pub(crate) struct BadItemKind {
+    #[primary_span]
+    pub span: Span,
+    pub descr: &'static str,
+    pub ctx: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_single_colon_struct_type)]
+pub(crate) struct SingleColonStructType {
+    #[primary_span]
+    #[suggestion(code = "::", applicability = "maybe-incorrect", style = "verbose")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_equals_struct_default)]
+pub(crate) struct EqualsStructDefault {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_rules_missing_bang)]
+pub(crate) struct MacroRulesMissingBang {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "!", applicability = "machine-applicable", style = "verbose")]
+    pub hi: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_name_remove_bang)]
+pub(crate) struct MacroNameRemoveBang {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_rules_visibility)]
+pub(crate) struct MacroRulesVisibility<'a> {
+    #[primary_span]
+    #[suggestion(code = "#[macro_export]", applicability = "maybe-incorrect")]
+    pub span: Span,
+    pub vis: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_macro_invocation_visibility)]
+#[help]
+pub(crate) struct MacroInvocationVisibility<'a> {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub vis: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_nested_adt)]
+pub(crate) struct NestedAdt<'a> {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    pub item: Span,
+    pub keyword: &'a str,
+    pub kw_str: Cow<'a, str>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_function_body_equals_expr)]
+pub(crate) struct FunctionBodyEqualsExpr {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: FunctionBodyEqualsExprSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct FunctionBodyEqualsExprSugg {
+    #[suggestion_part(code = "{{")]
+    pub eq: Span,
+    #[suggestion_part(code = " }}")]
+    pub semi: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_box_not_pat)]
+pub(crate) struct BoxNotPat {
+    #[primary_span]
+    pub span: Span,
+    #[note]
+    pub kw: Span,
+    #[suggestion(code = "r#", applicability = "maybe-incorrect", style = "verbose")]
+    pub lo: Span,
+    pub descr: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unmatched_angle)]
+pub(crate) struct UnmatchedAngle {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub plural: bool,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_missing_plus_in_bounds)]
+pub(crate) struct MissingPlusBounds {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = " +", applicability = "maybe-incorrect", style = "verbose")]
+    pub hi: Span,
+    pub sym: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_incorrect_braces_trait_bounds)]
+pub(crate) struct IncorrectBracesTraitBounds {
+    #[primary_span]
+    pub span: Vec<Span>,
+    #[subdiagnostic]
+    pub sugg: IncorrectBracesTraitBoundsSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
+pub(crate) struct IncorrectBracesTraitBoundsSugg {
+    #[suggestion_part(code = " ")]
+    pub l: Span,
+    #[suggestion_part(code = "")]
+    pub r: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_kw_bad_case)]
+pub(crate) struct KwBadCase<'a> {
+    #[primary_span]
+    #[suggestion(code = "{kw}", applicability = "machine-applicable")]
+    pub span: Span,
+    pub kw: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_meta_bad_delim)]
+pub(crate) struct MetaBadDelim {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: MetaBadDelimSugg,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_cfg_attr_bad_delim)]
+pub(crate) struct CfgAttrBadDelim {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: MetaBadDelimSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parse_meta_bad_delim_suggestion, applicability = "machine-applicable")]
+pub(crate) struct MetaBadDelimSugg {
+    #[suggestion_part(code = "(")]
+    pub open: Span,
+    #[suggestion_part(code = ")")]
+    pub close: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_malformed_cfg_attr)]
+#[note]
+pub(crate) struct MalformedCfgAttr {
+    #[primary_span]
+    #[suggestion(code = "{sugg}")]
+    pub span: Span,
+    pub sugg: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unknown_builtin_construct)]
+pub(crate) struct UnknownBuiltinConstruct {
+    #[primary_span]
+    pub span: Span,
+    pub name: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expected_builtin_ident)]
+pub(crate) struct ExpectedBuiltinIdent {
+    #[primary_span]
+    pub span: Span,
+}
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 9e856c9f2..c6e6b46e4 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use crate::errors;
 use crate::lexer::unicode_chars::UNICODE_ARRAY;
 use crate::make_unclosed_delims_error;
@@ -6,7 +8,7 @@ use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
 use rustc_errors::{error_code, Applicability, Diagnostic, DiagnosticBuilder, StashKey};
-use rustc_lexer::unescape::{self, Mode};
+use rustc_lexer::unescape::{self, EscapeError, Mode};
 use rustc_lexer::Cursor;
 use rustc_lexer::{Base, DocStyle, RawStrError};
 use rustc_session::lint::builtin::{
@@ -67,7 +69,7 @@ pub(crate) fn parse_token_trees<'a>(
     match token_trees {
         Ok(stream) if unmatched_delims.is_empty() => Ok(stream),
         _ => {
-            // Return error if there are unmatched delimiters or unclosng delimiters.
+            // Return error if there are unmatched delimiters or unclosed delimiters.
             // We emit delimiter mismatch errors first, then emit the unclosing delimiter mismatch
             // because the delimiter mismatch is more likely to be the root cause of error
 
@@ -204,16 +206,15 @@ impl<'a> StringReader<'a> {
                 rustc_lexer::TokenKind::Literal { kind, suffix_start } => {
                     let suffix_start = start + BytePos(suffix_start);
                     let (kind, symbol) = self.cook_lexer_literal(start, suffix_start, kind);
+                    if let token::LitKind::CStr | token::LitKind::CStrRaw(_) = kind {
+                        self.sess.gated_spans.gate(sym::c_str_literals, self.mk_sp(start, self.pos));
+                    }
                     let suffix = if suffix_start < self.pos {
                         let string = self.str_from(suffix_start);
                         if string == "_" {
                             self.sess
                                 .span_diagnostic
-                                .struct_span_err(
-                                    self.mk_sp(suffix_start, self.pos),
-                                    "underscore literal suffix is not allowed",
-                                )
-                                .emit();
+                                .emit_err(errors::UnderscoreLiteralSuffix { span: self.mk_sp(suffix_start, self.pos) });
                             None
                         } else {
                             Some(Symbol::intern(string))
@@ -325,7 +326,7 @@ impl<'a> StringReader<'a> {
     ) -> DiagnosticBuilder<'a, !> {
         self.sess
             .span_diagnostic
-            .struct_span_fatal(self.mk_sp(from_pos, to_pos), &format!("{}: {}", m, escaped_char(c)))
+            .struct_span_fatal(self.mk_sp(from_pos, to_pos), format!("{}: {}", m, escaped_char(c)))
     }
 
     /// Detect usages of Unicode codepoints changing the direction of the text on screen and loudly
@@ -419,6 +420,16 @@ impl<'a> StringReader<'a> {
                 }
                 self.cook_quoted(token::ByteStr, Mode::ByteStr, start, end, 2, 1) // b" "
             }
+            rustc_lexer::LiteralKind::CStr { terminated } => {
+                if !terminated {
+                    self.sess.span_diagnostic.span_fatal_with_code(
+                        self.mk_sp(start + BytePos(1), end),
+                        "unterminated C string",
+                        error_code!(E0767),
+                    )
+                }
+                self.cook_c_string(token::CStr, Mode::CStr, start, end, 2, 1) // c" "
+            }
             rustc_lexer::LiteralKind::RawStr { n_hashes } => {
                 if let Some(n_hashes) = n_hashes {
                     let n = u32::from(n_hashes);
@@ -437,6 +448,15 @@ impl<'a> StringReader<'a> {
                     self.report_raw_str_error(start, 2);
                 }
             }
+            rustc_lexer::LiteralKind::RawCStr { n_hashes } => {
+                if let Some(n_hashes) = n_hashes {
+                    let n = u32::from(n_hashes);
+                    let kind = token::CStrRaw(n_hashes);
+                    self.cook_c_string(kind, Mode::RawCStr, start, end, 3 + n, 1 + n) // cr##" "##
+                } else {
+                    self.report_raw_str_error(start, 2);
+                }
+            }
             rustc_lexer::LiteralKind::Int { base, empty_int } => {
                 if empty_int {
                     let span = self.mk_sp(start, end);
@@ -546,7 +566,7 @@ impl<'a> StringReader<'a> {
         err.span_label(self.mk_sp(start, start), "unterminated raw string");
 
         if n_hashes > 0 {
-            err.note(&format!(
+            err.note(format!(
                 "this raw string should be terminated with `\"{}`",
                 "#".repeat(n_hashes as usize)
             ));
@@ -642,7 +662,7 @@ impl<'a> StringReader<'a> {
                 &RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
                 prefix_span,
                 ast::CRATE_NODE_ID,
-                &format!("prefix `{prefix}` is unknown"),
+                format!("prefix `{prefix}` is unknown"),
                 BuiltinLintDiagnostics::ReservedPrefix(prefix_span),
             );
         }
@@ -652,7 +672,7 @@ impl<'a> StringReader<'a> {
         self.sess.emit_fatal(errors::TooManyHashes { span: self.mk_sp(start, self.pos), num });
     }
 
-    fn cook_quoted(
+    fn cook_common(
         &self,
         kind: token::LitKind,
         mode: Mode,
@@ -660,12 +680,13 @@ impl<'a> StringReader<'a> {
         end: BytePos,
         prefix_len: u32,
         postfix_len: u32,
+        unescape: fn(&str, Mode, &mut dyn FnMut(Range<usize>, Result<(), EscapeError>)),
     ) -> (token::LitKind, Symbol) {
         let mut has_fatal_err = false;
         let content_start = start + BytePos(prefix_len);
         let content_end = end - BytePos(postfix_len);
         let lit_content = self.str_from_to(content_start, content_end);
-        unescape::unescape_literal(lit_content, mode, &mut |range, result| {
+        unescape(lit_content, mode, &mut |range, result| {
             // Here we only check for errors. The actual unescaping is done later.
             if let Err(err) = result {
                 let span_with_quotes = self.mk_sp(start, end);
@@ -696,6 +717,38 @@ impl<'a> StringReader<'a> {
             (token::Err, self.symbol_from_to(start, end))
         }
     }
+
+    fn cook_quoted(
+        &self,
+        kind: token::LitKind,
+        mode: Mode,
+        start: BytePos,
+        end: BytePos,
+        prefix_len: u32,
+        postfix_len: u32,
+    ) -> (token::LitKind, Symbol) {
+        self.cook_common(kind, mode, start, end, prefix_len, postfix_len, |src, mode, callback| {
+            unescape::unescape_literal(src, mode, &mut |span, result| {
+                callback(span, result.map(drop))
+            })
+        })
+    }
+
+    fn cook_c_string(
+        &self,
+        kind: token::LitKind,
+        mode: Mode,
+        start: BytePos,
+        end: BytePos,
+        prefix_len: u32,
+        postfix_len: u32,
+    ) -> (token::LitKind, Symbol) {
+        self.cook_common(kind, mode, start, end, prefix_len, postfix_len, |src, mode, callback| {
+            unescape::unescape_c_string(src, mode, &mut |span, result| {
+                callback(span, result.map(drop))
+            })
+        })
+    }
 }
 
 pub fn nfc_normalize(string: &str) -> Symbol {
diff --git a/compiler/rustc_parse/src/lexer/tokentrees.rs b/compiler/rustc_parse/src/lexer/tokentrees.rs
index 7c2c08951..318a29985 100644
--- a/compiler/rustc_parse/src/lexer/tokentrees.rs
+++ b/compiler/rustc_parse/src/lexer/tokentrees.rs
@@ -199,8 +199,7 @@ impl<'a> TokenTreesReader<'a> {
         // matching opening delimiter).
         let token_str = token_to_string(&self.token);
         let msg = format!("unexpected closing delimiter: `{}`", token_str);
-        let mut err =
-            self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, &msg);
+        let mut err = self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, msg);
 
         report_suspicious_mismatch_block(
             &mut err,
diff --git a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
index 0d12ec608..eb9625f92 100644
--- a/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
+++ b/compiler/rustc_parse/src/lexer/unescape_error_reporting.rs
@@ -78,8 +78,7 @@ pub(crate) fn emit_unescape_error(
                 }
             };
             let sugg = sugg.unwrap_or_else(|| {
-                let is_byte = mode.is_byte();
-                let prefix = if is_byte { "b" } else { "" };
+                let prefix = mode.prefix_noraw();
                 let mut escaped = String::with_capacity(lit.len());
                 let mut chrs = lit.chars().peekable();
                 while let Some(first) = chrs.next() {
@@ -97,7 +96,11 @@ pub(crate) fn emit_unescape_error(
                     };
                 }
                 let sugg = format!("{prefix}\"{escaped}\"");
-                MoreThanOneCharSugg::Quotes { span: span_with_quotes, is_byte, sugg }
+                MoreThanOneCharSugg::Quotes {
+                    span: span_with_quotes,
+                    is_byte: mode == Mode::Byte,
+                    sugg,
+                }
             });
             handler.emit_err(UnescapeError::MoreThanOneChar {
                 span: span_with_quotes,
@@ -112,7 +115,7 @@ pub(crate) fn emit_unescape_error(
                 char_span,
                 escaped_sugg: c.escape_default().to_string(),
                 escaped_msg: escaped_char(c),
-                byte: mode.is_byte(),
+                byte: mode == Mode::Byte,
             });
         }
         EscapeError::BareCarriageReturn => {
@@ -126,12 +129,15 @@ pub(crate) fn emit_unescape_error(
         EscapeError::InvalidEscape => {
             let (c, span) = last_char();
 
-            let label =
-                if mode.is_byte() { "unknown byte escape" } else { "unknown character escape" };
+            let label = if mode == Mode::Byte || mode == Mode::ByteStr {
+                "unknown byte escape"
+            } else {
+                "unknown character escape"
+            };
             let ec = escaped_char(c);
-            let mut diag = handler.struct_span_err(span, &format!("{}: `{}`", label, ec));
+            let mut diag = handler.struct_span_err(span, format!("{}: `{}`", label, ec));
             diag.span_label(span, label);
-            if c == '{' || c == '}' && !mode.is_byte() {
+            if c == '{' || c == '}' && matches!(mode, Mode::Str | Mode::RawStr) {
                 diag.help(
                     "if used in a formatting string, curly braces are escaped with `{{` and `}}`",
                 );
@@ -141,7 +147,7 @@ pub(crate) fn emit_unescape_error(
                      version control settings",
                 );
             } else {
-                if !mode.is_byte() {
+                if mode == Mode::Str || mode == Mode::Char {
                     diag.span_suggestion(
                         span_with_quotes,
                         "if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal",
@@ -180,13 +186,13 @@ pub(crate) fn emit_unescape_error(
             } else {
                 String::new()
             };
-            err.span_label(span, &format!("must be ASCII{}", postfix));
+            err.span_label(span, format!("must be ASCII{}", postfix));
             // Note: the \\xHH suggestions are not given for raw byte string
             // literals, because they are araw and so cannot use any escapes.
             if (c as u32) <= 0xFF && mode != Mode::RawByteStr {
                 err.span_suggestion(
                     span,
-                    &format!(
+                    format!(
                         "if you meant to use the unicode code point for {:?}, use a \\xHH escape",
                         c
                     ),
@@ -200,10 +206,7 @@ pub(crate) fn emit_unescape_error(
                 utf8.push(c);
                 err.span_suggestion(
                     span,
-                    &format!(
-                        "if you meant to use the UTF-8 encoding of {:?}, use \\xHH escapes",
-                        c
-                    ),
+                    format!("if you meant to use the UTF-8 encoding of {:?}, use \\xHH escapes", c),
                     utf8.as_bytes()
                         .iter()
                         .map(|b: &u8| format!("\\x{:X}", *b))
diff --git a/compiler/rustc_parse/src/lexer/unicode_chars.rs b/compiler/rustc_parse/src/lexer/unicode_chars.rs
index 1f027c08f..829d9693e 100644
--- a/compiler/rustc_parse/src/lexer/unicode_chars.rs
+++ b/compiler/rustc_parse/src/lexer/unicode_chars.rs
@@ -350,7 +350,7 @@ pub(super) fn check_for_substitution(
 
     let Some((_, ascii_name, token)) = ASCII_ARRAY.iter().find(|&&(s, _, _)| s == ascii_str) else {
         let msg = format!("substitution character not found for '{}'", ch);
-        reader.sess.span_diagnostic.span_bug_no_panic(span, &msg);
+        reader.sess.span_diagnostic.span_bug_no_panic(span, msg);
         return (None, None);
     };
 
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index 17466cd0e..25de78085 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -18,9 +18,9 @@ use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{AttrItem, Attribute, MetaItem};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Applicability, Diagnostic, FatalError, Level, PResult};
+use rustc_errors::{Diagnostic, FatalError, Level, PResult};
 use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
-use rustc_macros::fluent_messages;
+use rustc_fluent_macro::fluent_messages;
 use rustc_session::parse::ParseSess;
 use rustc_span::{FileName, SourceFile, Span};
 
@@ -153,7 +153,7 @@ fn try_file_to_source_file(
 ) -> Result<Lrc<SourceFile>, Diagnostic> {
     sess.source_map().load_file(path).map_err(|e| {
         let msg = format!("couldn't read {}: {}", path.display(), e);
-        let mut diag = Diagnostic::new(Level::Fatal, &msg);
+        let mut diag = Diagnostic::new(Level::Fatal, msg);
         if let Some(sp) = spanopt {
             diag.set_span(sp);
         }
@@ -190,7 +190,7 @@ pub fn maybe_file_to_stream(
     override_span: Option<Span>,
 ) -> Result<TokenStream, Vec<Diagnostic>> {
     let src = source_file.src.as_ref().unwrap_or_else(|| {
-        sess.span_diagnostic.bug(&format!(
+        sess.span_diagnostic.bug(format!(
             "cannot lex `source_file` without source: {}",
             sess.source_map().filename_for_diagnostics(&source_file.name)
         ));
@@ -243,12 +243,11 @@ pub fn parse_cfg_attr(
         ast::AttrArgs::Delimited(ast::DelimArgs { dspan, delim, ref tokens })
             if !tokens.is_empty() =>
         {
-            let msg = "wrong `cfg_attr` delimiters";
-            crate::validate_attr::check_meta_bad_delim(parse_sess, dspan, delim, msg);
+            crate::validate_attr::check_cfg_attr_bad_delim(parse_sess, dspan, delim);
             match parse_in(parse_sess, tokens.clone(), "`cfg_attr` input", |p| p.parse_cfg_attr()) {
                 Ok(r) => return Some(r),
                 Err(mut e) => {
-                    e.help(&format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
+                    e.help(format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
                         .note(CFG_ATTR_NOTE_REF)
                         .emit();
                 }
@@ -265,15 +264,5 @@ const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
     #the-cfg_attr-attribute>";
 
 fn error_malformed_cfg_attr_missing(span: Span, parse_sess: &ParseSess) {
-    parse_sess
-        .span_diagnostic
-        .struct_span_err(span, "malformed `cfg_attr` attribute input")
-        .span_suggestion(
-            span,
-            "missing condition and attribute",
-            CFG_ATTR_GRAMMAR_HELP,
-            Applicability::HasPlaceholders,
-        )
-        .note(CFG_ATTR_NOTE_REF)
-        .emit();
+    parse_sess.emit_err(errors::MalformedCfgAttr { span, sugg: CFG_ATTR_GRAMMAR_HELP });
 }
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index e3e7c63e3..e1db19557 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -45,10 +45,10 @@ impl<'a> Parser<'a> {
                     Some(InnerAttrForbiddenReason::AfterOuterDocComment {
                         prev_doc_comment_span: prev_outer_attr_sp.unwrap(),
                     })
-                } else if let Some(prev_outer_attr_sp) = prev_outer_attr_sp {
-                    Some(InnerAttrForbiddenReason::AfterOuterAttribute { prev_outer_attr_sp })
                 } else {
-                    None
+                    prev_outer_attr_sp.map(|prev_outer_attr_sp| {
+                        InnerAttrForbiddenReason::AfterOuterAttribute { prev_outer_attr_sp }
+                    })
                 };
                 let inner_parse_policy = InnerAttrPolicy::Forbidden(inner_error_reason);
                 just_parsed_doc_comment = false;
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index b0ab0f106..1e6ac5496 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -72,7 +72,7 @@ fn has_cfg_or_cfg_attr(attrs: &[Attribute]) -> bool {
     // Therefore, the absence of a literal `cfg` or `cfg_attr` guarantees that
     // we don't need to do any eager expansion.
     attrs.iter().any(|attr| {
-        attr.ident().map_or(false, |ident| ident.name == sym::cfg || ident.name == sym::cfg_attr)
+        attr.ident().is_some_and(|ident| ident.name == sym::cfg || ident.name == sym::cfg_attr)
     })
 }
 
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index e03ce5d71..c14540396 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -4,7 +4,7 @@ use super::{
     TokenExpectType, TokenType,
 };
 use crate::errors::{
-    AmbiguousPlus, AttributeOnParamType, BadQPathStage2, BadTypePlus, BadTypePlusSub,
+    AmbiguousPlus, AttributeOnParamType, BadQPathStage2, BadTypePlus, BadTypePlusSub, ColonAsSemi,
     ComparisonOperatorsCannotBeChained, ComparisonOperatorsCannotBeChainedSugg,
     ConstGenericWithoutBraces, ConstGenericWithoutBracesSugg, DocCommentDoesNotDocumentAnything,
     DocCommentOnParamType, DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
@@ -13,7 +13,7 @@ use crate::errors::{
     IncorrectUseOfAwait, ParenthesesInForHead, ParenthesesInForHeadSugg,
     PatternMethodParamWithoutBody, QuestionMarkInType, QuestionMarkInTypeSugg, SelfParamNotFirst,
     StructLiteralBodyWithoutPath, StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens,
-    StructLiteralNeedingParensSugg, SuggEscapeIdentifier, SuggRemoveComma,
+    StructLiteralNeedingParensSugg, SuggAddMissingLetStmt, SuggEscapeIdentifier, SuggRemoveComma,
     UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
     UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead,
 };
@@ -32,8 +32,8 @@ use rustc_ast::{
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
-    pluralize, Applicability, Diagnostic, DiagnosticBuilder, DiagnosticMessage, ErrorGuaranteed,
-    FatalError, Handler, IntoDiagnostic, MultiSpan, PResult,
+    pluralize, AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder, DiagnosticMessage,
+    ErrorGuaranteed, FatalError, Handler, IntoDiagnostic, MultiSpan, PResult,
 };
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::Spanned;
@@ -84,6 +84,7 @@ impl RecoverQPath for Ty {
 }
 
 impl RecoverQPath for Pat {
+    const PATH_STYLE: PathStyle = PathStyle::Pat;
     fn to_ty(&self) -> Option<P<Ty>> {
         self.to_ty()
     }
@@ -206,11 +207,11 @@ struct MultiSugg {
 
 impl MultiSugg {
     fn emit(self, err: &mut Diagnostic) {
-        err.multipart_suggestion(&self.msg, self.patches, self.applicability);
+        err.multipart_suggestion(self.msg, self.patches, self.applicability);
     }
 
     fn emit_verbose(self, err: &mut Diagnostic) {
-        err.multipart_suggestion_verbose(&self.msg, self.patches, self.applicability);
+        err.multipart_suggestion_verbose(self.msg, self.patches, self.applicability);
     }
 }
 
@@ -237,6 +238,7 @@ impl<'a> DerefMut for SnapshotParser<'a> {
 
 impl<'a> Parser<'a> {
     #[rustc_lint_diagnostics]
+    #[track_caller]
     pub fn struct_span_err<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -570,15 +572,13 @@ impl<'a> Parser<'a> {
         let expect = tokens_to_string(&expected);
         let actual = super::token_descr(&self.token);
         let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
+            let fmt = format!("expected one of {expect}, found {actual}");
             let short_expect = if expected.len() > 6 {
                 format!("{} possible tokens", expected.len())
             } else {
-                expect.clone()
+                expect
             };
-            (
-                format!("expected one of {expect}, found {actual}"),
-                (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")),
-            )
+            (fmt, (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")))
         } else if expected.is_empty() {
             (
                 format!("unexpected token: {actual}"),
@@ -592,13 +592,13 @@ impl<'a> Parser<'a> {
         };
         self.last_unexpected_token_span = Some(self.token.span);
         // FIXME: translation requires list formatting (for `expect`)
-        let mut err = self.struct_span_err(self.token.span, &msg_exp);
+        let mut err = self.struct_span_err(self.token.span, msg_exp);
 
         if let TokenKind::Ident(symbol, _) = &self.prev_token.kind {
             if ["def", "fun", "func", "function"].contains(&symbol.as_str()) {
                 err.span_suggestion_short(
                     self.prev_token.span,
-                    &format!("write `fn` instead of `{symbol}` to declare a function"),
+                    format!("write `fn` instead of `{symbol}` to declare a function"),
                     "fn",
                     Applicability::MachineApplicable,
                 );
@@ -665,7 +665,6 @@ impl<'a> Parser<'a> {
             err.span_label(sp, label_exp);
             err.span_label(self.token.span, "unexpected token");
         }
-        self.maybe_annotate_with_ascription(&mut err, false);
         Err(err)
     }
 
@@ -697,13 +696,13 @@ impl<'a> Parser<'a> {
                 err.set_span(span);
                 err.span_suggestion(
                     span,
-                    &format!("remove the extra `#`{}", pluralize!(count)),
+                    format!("remove the extra `#`{}", pluralize!(count)),
                     "",
                     Applicability::MachineApplicable,
                 );
                 err.span_label(
                     str_span,
-                    &format!("this raw string started with {n_hashes} `#`{}", pluralize!(n_hashes)),
+                    format!("this raw string started with {n_hashes} `#`{}", pluralize!(n_hashes)),
                 );
                 true
             }
@@ -790,59 +789,6 @@ impl<'a> Parser<'a> {
         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]) {
@@ -899,7 +845,7 @@ impl<'a> Parser<'a> {
         //
         // `x.foo::<u32>>>(3)`
         let parsed_angle_bracket_args =
-            segment.args.as_ref().map_or(false, |args| args.is_angle_bracketed());
+            segment.args.as_ref().is_some_and(|args| args.is_angle_bracketed());
 
         debug!(
             "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
@@ -1061,6 +1007,31 @@ impl<'a> Parser<'a> {
         Err(e)
     }
 
+    /// Suggest add the missing `let` before the identifier in stmt
+    /// `a: Ty = 1` -> `let a: Ty = 1`
+    pub(super) fn suggest_add_missing_let_for_stmt(
+        &mut self,
+        err: &mut DiagnosticBuilder<'a, ErrorGuaranteed>,
+    ) {
+        if self.token == token::Colon {
+            let prev_span = self.prev_token.span.shrink_to_lo();
+            let snapshot = self.create_snapshot_for_diagnostic();
+            self.bump();
+            match self.parse_ty() {
+                Ok(_) => {
+                    if self.token == token::Eq {
+                        let sugg = SuggAddMissingLetStmt { span: prev_span };
+                        sugg.add_to_diagnostic(err);
+                    }
+                }
+                Err(e) => {
+                    e.cancel();
+                }
+            }
+            self.restore_snapshot(snapshot);
+        }
+    }
+
     /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
     /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
     /// parenthesising the leftmost comparison.
@@ -1339,7 +1310,7 @@ impl<'a> Parser<'a> {
         }
 
         self.bump(); // `+`
-        let bounds = self.parse_generic_bounds(None)?;
+        let bounds = self.parse_generic_bounds()?;
         let sum_span = ty.span.to(self.prev_token.span);
 
         let sub = match &ty.kind {
@@ -1415,12 +1386,12 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, P<Expr>> {
         let mut err = self.struct_span_err(
             op_span,
-            &format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
+            format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
         );
-        err.span_label(op_span, &format!("not a valid {} operator", kind.fixity));
+        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.help(format!("use `{}= 1` instead", kind.op.chr()));
             err.emit();
             Ok(base)
         };
@@ -1609,7 +1580,7 @@ impl<'a> Parser<'a> {
                 _ => this_token_str,
             },
         );
-        let mut err = self.struct_span_err(sp, &msg);
+        let mut err = self.struct_span_err(sp, msg);
         let label_exp = format!("expected `{token_str}`");
         let sm = self.sess.source_map();
         if !sm.is_multiline(prev_sp.until(sp)) {
@@ -1624,12 +1595,36 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn expect_semi(&mut self) -> PResult<'a, ()> {
-        if self.eat(&token::Semi) {
+        if self.eat(&token::Semi) || self.recover_colon_as_semi() {
             return Ok(());
         }
         self.expect(&token::Semi).map(drop) // Error unconditionally
     }
 
+    pub(super) fn recover_colon_as_semi(&mut self) -> bool {
+        let line_idx = |span: Span| {
+            self.sess
+                .source_map()
+                .span_to_lines(span)
+                .ok()
+                .and_then(|lines| Some(lines.lines.get(0)?.line_index))
+        };
+
+        if self.may_recover()
+            && self.token == token::Colon
+            && self.look_ahead(1, |next| line_idx(self.token.span) < line_idx(next.span))
+        {
+            self.sess.emit_err(ColonAsSemi {
+                span: self.token.span,
+                type_ascription: self.sess.unstable_features.is_nightly_build().then_some(()),
+            });
+            self.bump();
+            return true;
+        }
+
+        false
+    }
+
     /// Consumes alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
     /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
     pub(super) fn recover_incorrect_await_syntax(
@@ -1648,7 +1643,7 @@ impl<'a> Parser<'a> {
             // 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),
+            _ => ExprKind::Await(expr, await_sp),
         };
         let expr = self.mk_expr(lo.to(sp), kind);
         self.maybe_recover_from_bad_qpath(expr)
@@ -1736,7 +1731,7 @@ impl<'a> Parser<'a> {
                     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.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 {
@@ -1792,24 +1787,6 @@ impl<'a> Parser<'a> {
         }
     }
 
-    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,
@@ -1904,7 +1881,6 @@ impl<'a> Parser<'a> {
                         && brace_depth == 0
                         && bracket_depth == 0 =>
                 {
-                    debug!("recover_stmt_ return - Semi");
                     break;
                 }
                 _ => self.bump(),
@@ -2110,7 +2086,7 @@ impl<'a> Parser<'a> {
                 format!("expected expression, found {}", super::token_descr(&self.token),),
             ),
         };
-        let mut err = self.struct_span_err(span, &msg);
+        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) {
             err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
@@ -2181,7 +2157,7 @@ impl<'a> Parser<'a> {
         // 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)),
+            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) {
@@ -2608,7 +2584,7 @@ impl<'a> Parser<'a> {
         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!(
+                format!(
                     "try adding parentheses to match on a tuple{}",
                     if let CommaRecoveryMode::LikelyTuple = rt { "" } else { "..." },
                 ),
@@ -2634,7 +2610,7 @@ impl<'a> Parser<'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) {
+            if qself_position.is_some_and(|pos| i < pos) {
                 continue;
             }
             if let [a, b] = segments {
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 03c82fbd3..1b28f3c97 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -174,10 +174,8 @@ impl<'a> Parser<'a> {
                 self.parse_expr_prefix(attrs)?
             }
         };
-        let last_type_ascription_set = self.last_type_ascription.is_some();
 
         if !self.should_continue_as_assoc_expr(&lhs) {
-            self.last_type_ascription = None;
             return Ok(lhs);
         }
 
@@ -301,9 +299,6 @@ impl<'a> Parser<'a> {
             if op == AssocOp::As {
                 lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
                 continue;
-            } else if op == AssocOp::Colon {
-                lhs = self.parse_assoc_op_ascribe(lhs, lhs_span)?;
-                continue;
             } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
                 // If we didn't have to handle `x..`/`x..=`, it would be pretty easy to
                 // generalise it to the Fixity::None code.
@@ -364,7 +359,7 @@ impl<'a> Parser<'a> {
                     let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
                     self.mk_expr(span, aopexpr)
                 }
-                AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
+                AssocOp::As | AssocOp::DotDot | AssocOp::DotDotEq => {
                     self.span_bug(span, "AssocOp should have been handled by special case")
                 }
             };
@@ -373,9 +368,7 @@ impl<'a> Parser<'a> {
                 break;
             }
         }
-        if last_type_ascription_set {
-            self.last_type_ascription = None;
-        }
+
         Ok(lhs)
     }
 
@@ -743,7 +736,7 @@ impl<'a> Parser<'a> {
                     (
                         // `foo: `
                         ExprKind::Path(None, ast::Path { segments, .. }),
-                        TokenKind::Ident(kw::For | kw::Loop | kw::While, false),
+                        token::Ident(kw::For | kw::Loop | kw::While, false),
                     ) if segments.len() == 1 => {
                         let snapshot = self.create_snapshot_for_diagnostic();
                         let label = Label {
@@ -838,33 +831,31 @@ impl<'a> Parser<'a> {
         &mut self,
         cast_expr: P<Expr>,
     ) -> PResult<'a, P<Expr>> {
+        if let ExprKind::Type(_, _) = cast_expr.kind {
+            panic!("ExprKind::Type must not be parsed");
+        }
+
         let span = cast_expr.span;
-        let (cast_kind, maybe_ascription_span) =
-            if let ExprKind::Type(ascripted_expr, _) = &cast_expr.kind {
-                ("type ascription", Some(ascripted_expr.span.shrink_to_hi().with_hi(span.hi())))
-            } else {
-                ("cast", None)
-            };
 
         let with_postfix = self.parse_expr_dot_or_call_with_(cast_expr, span)?;
 
         // Check if an illegal postfix operator has been added after the cast.
         // If the resulting expression is not a cast, it is an illegal postfix operator.
-        if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _)) {
+        if !matches!(with_postfix.kind, ExprKind::Cast(_, _)) {
             let msg = format!(
-                "{cast_kind} cannot be followed by {}",
+                "cast cannot be followed by {}",
                 match with_postfix.kind {
                     ExprKind::Index(_, _) => "indexing",
                     ExprKind::Try(_) => "`?`",
                     ExprKind::Field(_, _) => "a field access",
                     ExprKind::MethodCall(_) => "a method call",
                     ExprKind::Call(_, _) => "a function call",
-                    ExprKind::Await(_) => "`.await`",
+                    ExprKind::Await(_, _) => "`.await`",
                     ExprKind::Err => return Ok(with_postfix),
                     _ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
                 }
             );
-            let mut err = self.struct_span_err(span, &msg);
+            let mut err = self.struct_span_err(span, msg);
 
             let suggest_parens = |err: &mut Diagnostic| {
                 let suggestions = vec![
@@ -878,44 +869,13 @@ impl<'a> Parser<'a> {
                 );
             };
 
-            // If type ascription is "likely an error", the user will already be getting a useful
-            // help message, and doesn't need a second.
-            if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
-                self.maybe_annotate_with_ascription(&mut err, false);
-            } else if let Some(ascription_span) = maybe_ascription_span {
-                let is_nightly = self.sess.unstable_features.is_nightly_build();
-                if is_nightly {
-                    suggest_parens(&mut err);
-                }
-                err.span_suggestion(
-                    ascription_span,
-                    &format!(
-                        "{}remove the type ascription",
-                        if is_nightly { "alternatively, " } else { "" }
-                    ),
-                    "",
-                    if is_nightly {
-                        Applicability::MaybeIncorrect
-                    } else {
-                        Applicability::MachineApplicable
-                    },
-                );
-            } else {
-                suggest_parens(&mut err);
-            }
+            suggest_parens(&mut err);
+
             err.emit();
         };
         Ok(with_postfix)
     }
 
-    fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
-        let maybe_path = self.could_ascription_be_path(&lhs.kind);
-        self.last_type_ascription = Some((self.prev_token.span, maybe_path));
-        let lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
-        self.sess.gated_spans.gate(sym::type_ascription, lhs.span);
-        Ok(lhs)
-    }
-
     /// Parse `& mut? <expr>` or `& raw [ const | mut ] <expr>`.
     fn parse_expr_borrow(&mut self, lo: Span) -> PResult<'a, (Span, ExprKind)> {
         self.expect_and()?;
@@ -1010,7 +970,7 @@ impl<'a> Parser<'a> {
             };
             if has_dot {
                 // expr.f
-                e = self.parse_expr_dot_suffix(lo, e)?;
+                e = self.parse_dot_suffix_expr(lo, e)?;
                 continue;
             }
             if self.expr_is_complete(&e) {
@@ -1024,13 +984,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn look_ahead_type_ascription_as_field(&mut self) -> bool {
-        self.look_ahead(1, |t| t.is_ident())
-            && self.look_ahead(2, |t| t == &token::Colon)
-            && self.look_ahead(3, |t| t.can_begin_expr())
-    }
-
-    fn parse_expr_dot_suffix(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
+    fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
         match self.token.uninterpolate().kind {
             token::Ident(..) => self.parse_dot_suffix(base, lo),
             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
@@ -1183,9 +1137,7 @@ impl<'a> Parser<'a> {
 
     /// Parse a function call expression, `expr(...)`.
     fn parse_expr_fn_call(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
-        let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis)
-            && self.look_ahead_type_ascription_as_field()
-        {
+        let snapshot = if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
         } else {
             None
@@ -1216,7 +1168,6 @@ impl<'a> Parser<'a> {
         if !self.may_recover() {
             return None;
         }
-
         match (seq.as_mut(), snapshot) {
             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
                 snapshot.bump(); // `(`
@@ -1229,11 +1180,15 @@ impl<'a> Parser<'a> {
                         self.restore_snapshot(snapshot);
                         let close_paren = self.prev_token.span;
                         let span = lo.to(close_paren);
+                        // filter shorthand fields
+                        let fields: Vec<_> =
+                            fields.into_iter().filter(|field| !field.is_shorthand).collect();
+
                         if !fields.is_empty() &&
                             // `token.kind` should not be compared here.
                             // This is because the `snapshot.token.kind` is treated as the same as
                             // that of the open delim in `TokenTreesReader::parse_token_tree`, even if they are different.
-                            self.span_to_snippet(close_paren).map_or(false, |snippet| snippet == ")")
+                            self.span_to_snippet(close_paren).is_ok_and(|snippet| snippet == ")")
                         {
                             let mut replacement_err = errors::ParenthesesWithStructFields {
                                 span,
@@ -1260,9 +1215,7 @@ impl<'a> Parser<'a> {
                         return Some(self.mk_expr_err(span));
                     }
                     Ok(_) => {}
-                    Err(mut err) => {
-                        err.emit();
-                    }
+                    Err(err) => err.cancel(),
                 }
             }
             _ => {}
@@ -1351,6 +1304,8 @@ impl<'a> Parser<'a> {
             })
         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
             self.parse_expr_array_or_repeat(Delimiter::Bracket)
+        } else if self.is_builtin() {
+            self.parse_expr_builtin()
         } else if self.check_path() {
             self.parse_expr_path_start()
         } else if self.check_keyword(kw::Move)
@@ -1499,8 +1454,19 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_expr_path_start(&mut self) -> PResult<'a, P<Expr>> {
+        let maybe_eq_tok = self.prev_token.clone();
         let (qself, path) = if self.eat_lt() {
-            let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+            let lt_span = self.prev_token.span;
+            let (qself, path) = self.parse_qpath(PathStyle::Expr).map_err(|mut err| {
+                // Suggests using '<=' if there is an error parsing qpath when the previous token
+                // is an '=' token. Only emits suggestion if the '<' token and '=' token are
+                // directly adjacent (i.e. '=<')
+                if maybe_eq_tok.kind == TokenKind::Eq && maybe_eq_tok.span.hi() == lt_span.lo() {
+                    let eq_lt = maybe_eq_tok.span.to(lt_span);
+                    err.span_suggestion(eq_lt, "did you mean", "<=", Applicability::Unspecified);
+                }
+                err
+            })?;
             (Some(qself), path)
         } else {
             (None, self.parse_path(PathStyle::Expr)?)
@@ -1516,7 +1482,6 @@ impl<'a> Parser<'a> {
             let mac = P(MacCall {
                 path,
                 args: self.parse_delim_args()?,
-                prior_type_ascription: self.last_type_ascription,
             });
             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
         } else if self.check(&token::OpenDelim(Delimiter::Brace))
@@ -1535,7 +1500,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `'label: $expr`. The label is already parsed.
-    fn parse_expr_labeled(
+    pub(super) fn parse_expr_labeled(
         &mut self,
         label_: Label,
         mut consume_colon: bool,
@@ -1807,6 +1772,61 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr)
     }
 
+    /// Parse `builtin # ident(args,*)`.
+    fn parse_expr_builtin(&mut self) -> PResult<'a, P<Expr>> {
+        self.parse_builtin(|this, lo, ident| {
+            if ident.name == sym::offset_of {
+                return Ok(Some(this.parse_expr_offset_of(lo)?));
+            }
+
+            Ok(None)
+        })
+    }
+
+    pub(crate) fn parse_builtin<T>(
+        &mut self,
+        parse: impl FnOnce(&mut Parser<'a>, Span, Ident) -> PResult<'a, Option<T>>,
+    ) -> PResult<'a, T> {
+        let lo = self.token.span;
+
+        self.bump(); // `builtin`
+        self.bump(); // `#`
+
+        let Some((ident, false)) = self.token.ident() else {
+            let err = errors::ExpectedBuiltinIdent { span: self.token.span }
+                .into_diagnostic(&self.sess.span_diagnostic);
+            return Err(err);
+        };
+        self.sess.gated_spans.gate(sym::builtin_syntax, ident.span);
+        self.bump();
+
+        self.expect(&TokenKind::OpenDelim(Delimiter::Parenthesis))?;
+        let ret = if let Some(res) = parse(self, lo, ident)? {
+            Ok(res)
+        } else {
+            let err = errors::UnknownBuiltinConstruct { span: lo.to(ident.span), name: ident.name }
+                .into_diagnostic(&self.sess.span_diagnostic);
+            return Err(err);
+        };
+        self.expect(&TokenKind::CloseDelim(Delimiter::Parenthesis))?;
+
+        ret
+    }
+
+    pub(crate) fn parse_expr_offset_of(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+        let container = self.parse_ty()?;
+        self.expect(&TokenKind::Comma)?;
+
+        let seq_sep = SeqSep { sep: Some(token::Dot), trailing_sep_allowed: false };
+        let (fields, _trailing, _recovered) = self.parse_seq_to_before_end(
+            &TokenKind::CloseDelim(Delimiter::Parenthesis),
+            seq_sep,
+            Parser::parse_field_name,
+        )?;
+        let span = lo.to(self.token.span);
+        Ok(self.mk_expr(span, ExprKind::OffsetOf(container, fields.to_vec().into())))
+    }
+
     /// Returns a string literal if the next token is a string literal.
     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
     /// and returns `None` if the next token is not literal at all.
@@ -1855,7 +1875,7 @@ impl<'a> Parser<'a> {
         let token = self.token.clone();
         let err = |self_: &Self| {
             let msg = format!("unexpected token: {}", super::token_descr(&token));
-            self_.struct_span_err(token.span, &msg)
+            self_.struct_span_err(token.span, msg)
         };
         // On an error path, eagerly consider a lifetime to be an unclosed character lit
         if self.token.is_lifetime() {
@@ -1922,6 +1942,7 @@ impl<'a> Parser<'a> {
         let recovered = self.recover_after_dot();
         let token = recovered.as_ref().unwrap_or(&self.token);
         let span = token.span;
+
         token::Lit::from_token(token).map(|token_lit| {
             self.bump();
             (token_lit, span)
@@ -2057,7 +2078,7 @@ impl<'a> Parser<'a> {
                     // Therefore, `token.kind` should not be compared here.
                     if snapshot
                         .span_to_snippet(snapshot.token.span)
-                        .map_or(false, |snippet| snippet == "]") =>
+                        .is_ok_and(|snippet| snippet == "]") =>
                 {
                     return Err(errors::MissingSemicolonBeforeArray {
                         open_delim: open_delim_span,
@@ -2752,7 +2773,7 @@ impl<'a> Parser<'a> {
                 // We might have a `=>` -> `=` or `->` typo (issue #89396).
                 if TokenKind::FatArrow
                     .similar_tokens()
-                    .map_or(false, |similar_tokens| similar_tokens.contains(&this.token.kind))
+                    .is_some_and(|similar_tokens| similar_tokens.contains(&this.token.kind))
                 {
                     err.span_suggestion(
                         this.token.span,
@@ -2875,6 +2896,10 @@ impl<'a> Parser<'a> {
         })
     }
 
+    pub(crate) fn is_builtin(&self) -> bool {
+        self.token.is_keyword(kw::Builtin) && self.look_ahead(1, |t| *t == token::Pound)
+    }
+
     /// Parses a `try {...}` expression (`try` token already eaten).
     fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
         let (attrs, body) = self.parse_inner_attrs_and_block()?;
@@ -3013,6 +3038,11 @@ impl<'a> Parser<'a> {
                     } else {
                         e.span_label(pth.span, "while parsing this struct");
                     }
+
+                    if !recover {
+                        return Err(e);
+                    }
+
                     e.emit();
 
                     // If the next token is a comma, then try to parse
@@ -3024,11 +3054,12 @@ impl<'a> Parser<'a> {
                             break;
                         }
                     }
+
                     None
                 }
             };
 
-            let is_shorthand = parsed_field.as_ref().map_or(false, |f| f.is_shorthand);
+            let is_shorthand = parsed_field.as_ref().is_some_and(|f| f.is_shorthand);
             // A shorthand field can be turned into a full field with `:`.
             // We should point this out.
             self.check_or_expected(!is_shorthand, TokenType::Token(token::Colon));
@@ -3151,14 +3182,10 @@ impl<'a> Parser<'a> {
         let label = format!("'{}", ident.name);
         let ident = Ident { name: Symbol::intern(&label), span: ident.span };
 
-        self.struct_span_err(ident.span, "expected a label, found an identifier")
-            .span_suggestion(
-                ident.span,
-                "labels start with a tick",
-                label,
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(errors::ExpectedLabelFoundIdent {
+            span: ident.span,
+            start: ident.span.shrink_to_lo(),
+        });
 
         Label { ident }
     }
@@ -3256,7 +3283,7 @@ impl<'a> Parser<'a> {
 
     fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
         let span = lo.to(self.prev_token.span);
-        let await_expr = self.mk_expr(span, ExprKind::Await(self_arg));
+        let await_expr = self.mk_expr(span, ExprKind::Await(self_arg, self.prev_token.span));
         self.recover_from_await_method_call();
         await_expr
     }
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index f8ef1307c..cd779b0b4 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -1,5 +1,5 @@
 use crate::errors::{
-    MultipleWhereClauses, UnexpectedDefaultValueForLifetimeInGenericParameters,
+    self, MultipleWhereClauses, UnexpectedDefaultValueForLifetimeInGenericParameters,
     UnexpectedSelfInGenericParameters, WhereClauseBeforeTupleStructBody,
     WhereClauseBeforeTupleStructBodySugg,
 };
@@ -78,7 +78,7 @@ impl<'a> Parser<'a> {
                 }
                 self.restore_snapshot(snapshot);
             }
-            self.parse_generic_bounds(colon_span)?
+            self.parse_generic_bounds()?
         } else {
             Vec::new()
         };
@@ -181,12 +181,9 @@ impl<'a> Parser<'a> {
                         let snapshot = this.create_snapshot_for_diagnostic();
                         match this.parse_ty_where_predicate() {
                             Ok(where_predicate) => {
-                                this.struct_span_err(
-                                    where_predicate.span(),
-                                    "bounds on associated types do not belong here",
-                                )
-                                .span_label(where_predicate.span(), "belongs in `where` clause")
-                                .emit();
+                                this.sess.emit_err(errors::BadAssocTypeBounds {
+                                    span: where_predicate.span(),
+                                });
                                 // FIXME - try to continue parsing other generics?
                                 return Ok((None, TrailingToken::None));
                             }
@@ -201,22 +198,11 @@ impl<'a> Parser<'a> {
                         // Check for trailing attributes and stop parsing.
                         if !attrs.is_empty() {
                             if !params.is_empty() {
-                                this.struct_span_err(
-                                    attrs[0].span,
-                                    "trailing attribute after generic parameter",
-                                )
-                                .span_label(attrs[0].span, "attributes must go before parameters")
-                                .emit();
+                                this.sess
+                                    .emit_err(errors::AttrAfterGeneric { span: attrs[0].span });
                             } else {
-                                this.struct_span_err(
-                                    attrs[0].span,
-                                    "attribute without generic parameters",
-                                )
-                                .span_label(
-                                    attrs[0].span,
-                                    "attributes are only permitted when preceding parameters",
-                                )
-                                .emit();
+                                this.sess
+                                    .emit_err(errors::AttrWithoutGenerics { span: attrs[0].span });
                             }
                         }
                         return Ok((None, TrailingToken::None));
@@ -304,12 +290,7 @@ impl<'a> Parser<'a> {
         // change we parse those generics now, but report an error.
         if self.choose_generics_over_qpath(0) {
             let generics = self.parse_generics()?;
-            self.struct_span_err(
-                generics.span,
-                "generic parameters on `where` clauses are reserved for future use",
-            )
-            .span_label(generics.span, "currently unsupported")
-            .emit();
+            self.sess.emit_err(errors::WhereOnGenerics { span: generics.span });
         }
 
         loop {
@@ -438,7 +419,7 @@ impl<'a> Parser<'a> {
         // or with mandatory equality sign and the second type.
         let ty = self.parse_ty_for_where_clause()?;
         if self.eat(&token::Colon) {
-            let bounds = self.parse_generic_bounds(Some(self.prev_token.span))?;
+            let bounds = self.parse_generic_bounds()?;
             Ok(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
                 span: lo.to(self.prev_token.span),
                 bound_generic_params: lifetime_defs,
@@ -472,6 +453,8 @@ impl<'a> Parser<'a> {
         //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
         //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
         //     `<` const                - generic const parameter
+        //     `<` IDENT `?`            - RECOVERY for `impl<T ?Bound` missing a `:`, meant to
+        //                                avoid the `T?` to `Option<T>` recovery for types.
         // The only truly ambiguous case is
         //     `<` IDENT `>` `::` IDENT ...
         // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
@@ -482,6 +465,9 @@ impl<'a> Parser<'a> {
                 || self.look_ahead(start + 1, |t| t.is_lifetime() || t.is_ident())
                     && self.look_ahead(start + 2, |t| {
                         matches!(t.kind, token::Gt | token::Comma | token::Colon | token::Eq)
+                        // Recovery-only branch -- this could be removed,
+                        // since it only affects diagnostics currently.
+                            || matches!(t.kind, token::Question)
                     })
                 || self.is_keyword_ahead(start + 1, &[kw::Const]))
     }
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 6422b8ac1..3783ec41b 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -71,7 +71,7 @@ impl<'a> Parser<'a> {
         if !self.eat(term) {
             let token_str = super::token_descr(&self.token);
             if !self.maybe_consume_incorrect_semicolon(&items) {
-                let msg = &format!("expected item, found {token_str}");
+                let msg = format!("expected item, found {token_str}");
                 let mut err = self.struct_span_err(self.token.span, msg);
                 let label = if self.is_kw_followed_by_ident(kw::Let) {
                     "consider using `const` or `static` instead of `let` for global variables"
@@ -181,11 +181,11 @@ impl<'a> Parser<'a> {
     /// Error in-case `default` was parsed in an in-appropriate context.
     fn error_on_unconsumed_default(&self, def: Defaultness, kind: &ItemKind) {
         if let Defaultness::Default(span) = def {
-            let msg = format!("{} {} cannot be `default`", kind.article(), kind.descr());
-            self.struct_span_err(span, &msg)
-                .span_label(span, "`default` because of this")
-                .note("only associated `fn`, `const`, and `type` items can be `default`")
-                .emit();
+            self.sess.emit_err(errors::InappropriateDefault {
+                span,
+                article: kind.article(),
+                descr: kind.descr(),
+            });
         }
     }
 
@@ -265,6 +265,9 @@ impl<'a> Parser<'a> {
             // UNION ITEM
             self.bump(); // `union`
             self.parse_item_union()?
+        } else if self.is_builtin() {
+            // BUILTIN# ITEM
+            return self.parse_item_builtin();
         } else if self.eat_keyword(kw::Macro) {
             // MACROS 2.0 ITEM
             self.parse_item_decl_macro(lo)?
@@ -310,14 +313,7 @@ impl<'a> Parser<'a> {
         self.bump();
         match self.parse_use_item() {
             Ok(u) => {
-                self.struct_span_err(span, format!("expected item, found {token_name}"))
-                    .span_suggestion_short(
-                        span,
-                        "items are imported using the `use` keyword",
-                        "use",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::RecoverImportAsUse { span, token_name });
                 Ok(Some(u))
             }
             Err(e) => {
@@ -441,6 +437,11 @@ impl<'a> Parser<'a> {
         }
     }
 
+    fn parse_item_builtin(&mut self) -> PResult<'a, Option<ItemInfo>> {
+        // To be expanded
+        return Ok(None);
+    }
+
     /// Parses an item macro, e.g., `item!();`.
     fn parse_item_macro(&mut self, vis: &Visibility) -> PResult<'a, MacCall> {
         let path = self.parse_path(PathStyle::Mod)?; // `foo::bar`
@@ -450,7 +451,7 @@ impl<'a> Parser<'a> {
             Ok(args) => {
                 self.eat_semi_for_macro_if_needed(&args);
                 self.complain_if_pub_macro(vis, false);
-                Ok(MacCall { path, args, prior_type_ascription: self.last_type_ascription })
+                Ok(MacCall { path, args })
             }
 
             Err(mut err) => {
@@ -602,10 +603,24 @@ impl<'a> Parser<'a> {
                 let path = match ty_first.kind {
                     // This notably includes paths passed through `ty` macro fragments (#46438).
                     TyKind::Path(None, path) => path,
-                    _ => {
-                        self.sess.emit_err(errors::ExpectedTraitInTraitImplFoundType {
-                            span: ty_first.span,
-                        });
+                    other => {
+                        if let TyKind::ImplTrait(_, bounds) = other
+                            && let [bound] = bounds.as_slice()
+                        {
+                            // Suggest removing extra `impl` keyword:
+                            // `impl<T: Default> impl Default for Wrapper<T>`
+                            //                   ^^^^^
+                            let extra_impl_kw = ty_first.span.until(bound.span());
+                            self.sess
+                                .emit_err(errors::ExtraImplKeywordInTraitImpl {
+                                    extra_impl_kw,
+                                    impl_trait_span: ty_first.span
+                                });
+                        } else {
+                            self.sess.emit_err(errors::ExpectedTraitInTraitImplFoundType {
+                                span: ty_first.span,
+                            });
+                        }
                         err_path(ty_first.span)
                     }
                 };
@@ -684,7 +699,7 @@ impl<'a> Parser<'a> {
                         // ```
                         && self
                             .span_to_snippet(self.prev_token.span)
-                            .map_or(false, |snippet| snippet == "}")
+                            .is_ok_and(|snippet| snippet == "}")
                         && self.token.kind == token::Semi;
                     let mut semicolon_span = self.token.span;
                     if !is_unnecessary_semicolon {
@@ -795,11 +810,7 @@ impl<'a> Parser<'a> {
         // Parse optional colon and supertrait bounds.
         let had_colon = self.eat(&token::Colon);
         let span_at_colon = self.prev_token.span;
-        let bounds = if had_colon {
-            self.parse_generic_bounds(Some(self.prev_token.span))?
-        } else {
-            Vec::new()
-        };
+        let bounds = if had_colon { self.parse_generic_bounds()? } else { Vec::new() };
 
         let span_before_eq = self.prev_token.span;
         if self.eat(&token::Eq) {
@@ -809,7 +820,7 @@ impl<'a> Parser<'a> {
                 self.sess.emit_err(errors::BoundsNotAllowedOnTraitAliases { span });
             }
 
-            let bounds = self.parse_generic_bounds(None)?;
+            let bounds = self.parse_generic_bounds()?;
             generics.where_clause = self.parse_where_clause()?;
             self.expect_semi()?;
 
@@ -890,7 +901,7 @@ impl<'a> Parser<'a> {
 
         // Parse optional colon and param bounds.
         let bounds =
-            if self.eat(&token::Colon) { self.parse_generic_bounds(None)? } else { Vec::new() };
+            if self.eat(&token::Colon) { self.parse_generic_bounds()? } else { Vec::new() };
         let before_where_clause = self.parse_where_clause()?;
 
         let ty = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
@@ -963,15 +974,8 @@ impl<'a> Parser<'a> {
             } else {
                 // Recover from using a colon as path separator.
                 while self.eat_noexpect(&token::Colon) {
-                    self.struct_span_err(self.prev_token.span, "expected `::`, found `:`")
-                        .span_suggestion_short(
-                            self.prev_token.span,
-                            "use double colon",
-                            "::",
-                            Applicability::MachineApplicable,
-                        )
-                        .note_once("import paths are delimited using `::`")
-                        .emit();
+                    self.sess
+                        .emit_err(errors::SingleColonImportPath { span: self.prev_token.span });
 
                     // We parse the rest of the path and append it to the original prefix.
                     self.parse_path_segments(&mut prefix.segments, PathStyle::Mod, None)?;
@@ -1134,13 +1138,11 @@ impl<'a> Parser<'a> {
         ))
     }
 
-    fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &str) -> Option<T> {
+    fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &'static str) -> Option<T> {
         // FIXME(#100717): needs variant for each `ItemKind` (instead of using `ItemKind::descr()`)
         let span = self.sess.source_map().guess_head_span(span);
         let descr = kind.descr();
-        self.struct_span_err(span, &format!("{descr} is not supported in {ctx}"))
-            .help(&format!("consider moving the {descr} out to a nearby module scope"))
-            .emit();
+        self.sess.emit_err(errors::BadItemKind { span, descr, ctx });
         None
     }
 
@@ -1282,6 +1284,7 @@ impl<'a> Parser<'a> {
             }
         }
 
+        let prev_span = self.prev_token.span;
         let id = self.parse_ident()?;
         let mut generics = self.parse_generics()?;
         generics.where_clause = self.parse_where_clause()?;
@@ -1293,10 +1296,28 @@ impl<'a> Parser<'a> {
             (thin_vec![], false)
         } else {
             self.parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant()).map_err(
-                |mut e| {
-                    e.span_label(id.span, "while parsing this enum");
+                |mut err| {
+                    err.span_label(id.span, "while parsing this enum");
+                    if self.token == token::Colon {
+                        let snapshot = self.create_snapshot_for_diagnostic();
+                        self.bump();
+                        match self.parse_ty() {
+                            Ok(_) => {
+                                err.span_suggestion_verbose(
+                                    prev_span,
+                                    "perhaps you meant to use `struct` here",
+                                    "struct".to_string(),
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                            Err(e) => {
+                                e.cancel();
+                            }
+                        }
+                        self.restore_snapshot(snapshot);
+                    }
                     self.recover_stmt();
-                    e
+                    err
                 },
             )?
         };
@@ -1445,7 +1466,7 @@ impl<'a> Parser<'a> {
             VariantData::Struct(fields, recovered)
         } else {
             let token_str = super::token_descr(&self.token);
-            let msg = &format!("expected `where` or `{{` after union name, found {token_str}");
+            let msg = format!("expected `where` or `{{` after union name, found {token_str}");
             let mut err = self.struct_span_err(self.token.span, msg);
             err.span_label(self.token.span, "expected `where` or `{` after union name");
             return Err(err);
@@ -1481,7 +1502,7 @@ impl<'a> Parser<'a> {
             self.eat(&token::CloseDelim(Delimiter::Brace));
         } else {
             let token_str = super::token_descr(&self.token);
-            let msg = &format!(
+            let msg = format!(
                 "expected {}`{{` after struct name, found {}",
                 if parsed_where { "" } else { "`where`, or " },
                 token_str
@@ -1618,7 +1639,7 @@ impl<'a> Parser<'a> {
                 let sp = self.prev_token.span.shrink_to_hi();
                 let mut err = self.struct_span_err(
                     sp,
-                    &format!("expected `,`, or `}}`, found {}", super::token_descr(&self.token)),
+                    format!("expected `,`, or `}}`, found {}", super::token_descr(&self.token)),
                 );
 
                 // Try to recover extra trailing angle brackets
@@ -1713,27 +1734,13 @@ impl<'a> Parser<'a> {
         self.expect_field_ty_separator()?;
         let ty = self.parse_ty()?;
         if self.token.kind == token::Colon && self.look_ahead(1, |tok| tok.kind != token::Colon) {
-            self.struct_span_err(self.token.span, "found single colon in a struct field type path")
-                .span_suggestion_verbose(
-                    self.token.span,
-                    "write a path separator here",
-                    "::",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess.emit_err(errors::SingleColonStructType { span: self.token.span });
         }
         if self.token.kind == token::Eq {
             self.bump();
             let const_expr = self.parse_expr_anon_const()?;
             let sp = ty.span.shrink_to_hi().to(const_expr.value.span);
-            self.struct_span_err(sp, "default values on `struct` fields aren't supported")
-                .span_suggestion(
-                    sp,
-                    "remove this unsupported default value",
-                    "",
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(errors::EqualsStructDefault { span: sp });
         }
         Ok(FieldDef {
             span: lo.to(self.prev_token.span),
@@ -1770,7 +1777,7 @@ impl<'a> Parser<'a> {
                     Ok(_) => {
                         let mut err = self.struct_span_err(
                             lo.to(self.prev_token.span),
-                            &format!("functions are not allowed in {adt_ty} definitions"),
+                            format!("functions are not allowed in {adt_ty} definitions"),
                         );
                         err.help(
                             "unlike in C++, Java, and C#, functions are declared in `impl` blocks",
@@ -1789,7 +1796,7 @@ impl<'a> Parser<'a> {
                     Ok((ident, _)) => {
                         let mut err = self.struct_span_err(
                             lo.with_hi(ident.span.hi()),
-                            &format!("structs are not allowed in {adt_ty} definitions"),
+                            format!("structs are not allowed in {adt_ty} definitions"),
                         );
                         err.help("consider creating a new `struct` definition instead of nesting");
                         err
@@ -1871,14 +1878,10 @@ impl<'a> Parser<'a> {
                 return IsMacroRulesItem::Yes { has_bang: true };
             } else if self.look_ahead(1, |t| (t.is_ident())) {
                 // macro_rules foo
-                self.struct_span_err(macro_rules_span, "expected `!` after `macro_rules`")
-                    .span_suggestion(
-                        macro_rules_span,
-                        "add a `!`",
-                        "macro_rules!",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::MacroRulesMissingBang {
+                    span: macro_rules_span,
+                    hi: macro_rules_span.shrink_to_hi(),
+                });
 
                 return IsMacroRulesItem::Yes { has_bang: false };
             }
@@ -1903,9 +1906,7 @@ impl<'a> Parser<'a> {
         if self.eat(&token::Not) {
             // Handle macro_rules! foo!
             let span = self.prev_token.span;
-            self.struct_span_err(span, "macro names aren't followed by a `!`")
-                .span_suggestion(span, "remove the `!`", "", Applicability::MachineApplicable)
-                .emit();
+            self.sess.emit_err(errors::MacroNameRemoveBang { span });
         }
 
         let body = self.parse_delim_args()?;
@@ -1925,25 +1926,9 @@ impl<'a> Parser<'a> {
         let vstr = pprust::vis_to_string(vis);
         let vstr = vstr.trim_end();
         if macro_rules {
-            let msg = format!("can't qualify macro_rules invocation with `{vstr}`");
-            self.struct_span_err(vis.span, &msg)
-                .span_suggestion(
-                    vis.span,
-                    "try exporting the macro",
-                    "#[macro_export]",
-                    Applicability::MaybeIncorrect, // speculative
-                )
-                .emit();
+            self.sess.emit_err(errors::MacroRulesVisibility { span: vis.span, vis: vstr });
         } else {
-            self.struct_span_err(vis.span, "can't qualify macro invocation with `pub`")
-                .span_suggestion(
-                    vis.span,
-                    "remove the visibility",
-                    "",
-                    Applicability::MachineApplicable,
-                )
-                .help(&format!("try adjusting the macro to put `{vstr}` inside the invocation"))
-                .emit();
+            self.sess.emit_err(errors::MacroInvocationVisibility { span: vis.span, vis: vstr });
         }
     }
 
@@ -1989,18 +1974,12 @@ impl<'a> Parser<'a> {
             let kw_token = self.token.clone();
             let kw_str = pprust::token_to_string(&kw_token);
             let item = self.parse_item(ForceCollect::No)?;
-
-            self.struct_span_err(
-                kw_token.span,
-                &format!("`{kw_str}` definition cannot be nested inside `{keyword}`"),
-            )
-            .span_suggestion(
-                item.unwrap().span,
-                &format!("consider creating a new `{kw_str}` definition instead of nesting"),
-                "",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+            self.sess.emit_err(errors::NestedAdt {
+                span: kw_token.span,
+                item: item.unwrap().span,
+                kw_str,
+                keyword: keyword.as_str(),
+            });
             // We successfully parsed the item but we must inform the caller about nested problem.
             return Ok(false);
         }
@@ -2139,13 +2118,10 @@ impl<'a> Parser<'a> {
             let _ = self.parse_expr()?;
             self.expect_semi()?; // `;`
             let span = eq_sp.to(self.prev_token.span);
-            self.struct_span_err(span, "function body cannot be `= expression;`")
-                .multipart_suggestion(
-                    "surround the expression with `{` and `}` instead of `=` and `;`",
-                    vec![(eq_sp, "{".to_string()), (self.prev_token.span, " }".to_string())],
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(errors::FunctionBodyEqualsExpr {
+                span,
+                sugg: errors::FunctionBodyEqualsExprSugg { eq: eq_sp, semi: self.prev_token.span },
+            });
             (AttrVec::new(), Some(self.mk_block_err(span)))
         } else {
             let expected = if req_body {
@@ -2289,11 +2265,11 @@ impl<'a> Parser<'a> {
 
                         err.span_suggestion(
                             self.token.uninterpolated_span(),
-                            &format!("`{original_kw}` already used earlier, remove this one"),
+                            format!("`{original_kw}` already used earlier, remove this one"),
                             "",
                             Applicability::MachineApplicable,
                         )
-                        .span_note(original_sp, &format!("`{original_kw}` first seen here"));
+                        .span_note(original_sp, format!("`{original_kw}` first seen here"));
                     }
                     // The keyword has not been seen yet, suggest correct placement in the function front matter
                     else if let Some(WrongKw::Misplaced(correct_pos_sp)) = wrong_kw {
@@ -2304,7 +2280,7 @@ impl<'a> Parser<'a> {
 
                             err.span_suggestion(
                                     correct_pos_sp.to(misplaced_qual_sp),
-                                    &format!("`{misplaced_qual}` must come before `{current_qual}`"),
+                                    format!("`{misplaced_qual}` must come before `{current_qual}`"),
                                     format!("{misplaced_qual} {current_qual}"),
                                     Applicability::MachineApplicable,
                                 ).note("keyword order for functions declaration is `pub`, `default`, `const`, `async`, `unsafe`, `extern`");
@@ -2328,7 +2304,7 @@ impl<'a> Parser<'a> {
                             if matches!(orig_vis.kind, VisibilityKind::Inherited) {
                                 err.span_suggestion(
                                     sp_start.to(self.prev_token.span),
-                                    &format!("visibility `{vs}` must come before `{snippet}`"),
+                                    format!("visibility `{vs}` must come before `{snippet}`"),
                                     format!("{vs} {snippet}"),
                                     Applicability::MachineApplicable,
                                 );
@@ -2577,14 +2553,12 @@ impl<'a> Parser<'a> {
     }
 
     fn recover_self_param(&mut self) -> bool {
-        match self
-            .parse_outer_attributes()
-            .and_then(|_| self.parse_self_param())
-            .map_err(|e| e.cancel())
-        {
-            Ok(Some(_)) => true,
-            _ => false,
-        }
+        matches!(
+            self.parse_outer_attributes()
+                .and_then(|_| self.parse_self_param())
+                .map_err(|e| e.cancel()),
+            Ok(Some(_))
+        )
     }
 }
 
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index aa57b8047..c23420661 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -43,7 +43,7 @@ use thin_vec::ThinVec;
 use tracing::debug;
 
 use crate::errors::{
-    IncorrectVisibilityRestriction, MismatchedClosingDelimiter, NonStringAbiLiteral,
+    self, IncorrectVisibilityRestriction, MismatchedClosingDelimiter, NonStringAbiLiteral,
 };
 
 bitflags::bitflags! {
@@ -148,9 +148,6 @@ pub struct Parser<'a> {
     max_angle_bracket_count: u32,
 
     last_unexpected_token_span: Option<Span>,
-    /// Span pointing at the `:` for the last type ascription the parser has seen, and whether it
-    /// looked like it could have been a mistyped path or literal `Option:Some(42)`).
-    pub last_type_ascription: Option<(Span, bool /* likely path typo */)>,
     /// If present, this `Parser` is not parsing Rust code but rather a macro call.
     subparser_name: Option<&'static str>,
     capture_state: CaptureState,
@@ -165,7 +162,7 @@ pub struct Parser<'a> {
 // This type is used a lot, e.g. it's cloned when matching many declarative macro rules with nonterminals. Make sure
 // it doesn't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(Parser<'_>, 288);
+rustc_data_structures::static_assert_size!(Parser<'_>, 272);
 
 /// Stores span information about a closure.
 #[derive(Clone)]
@@ -470,7 +467,6 @@ impl<'a> Parser<'a> {
             unmatched_angle_bracket_count: 0,
             max_angle_bracket_count: 0,
             last_unexpected_token_span: None,
-            last_type_ascription: None,
             subparser_name,
             capture_state: CaptureState {
                 capturing: Capturing::No,
@@ -540,7 +536,9 @@ impl<'a> Parser<'a> {
         } else if inedible.contains(&self.token.kind) {
             // leave it in the input
             Ok(false)
-        } else if self.last_unexpected_token_span == Some(self.token.span) {
+        } else if self.token.kind != token::Eof
+            && self.last_unexpected_token_span == Some(self.token.span)
+        {
             FatalError.raise();
         } else {
             self.expected_one_of_not_found(edible, inedible)
@@ -663,15 +661,10 @@ impl<'a> Parser<'a> {
         if case == Case::Insensitive
         && let Some((ident, /* is_raw */ false)) = self.token.ident()
         && ident.as_str().to_lowercase() == kw.as_str().to_lowercase() {
-            self
-                .struct_span_err(ident.span, format!("keyword `{kw}` is written in a wrong case"))
-                .span_suggestion(
-                    ident.span,
-                    "write it in the correct case",
-                    kw,
-                    Applicability::MachineApplicable
-                ).emit();
-
+            self.sess.emit_err(errors::KwBadCase {
+                span: ident.span,
+                kw: kw.as_str()
+            });
             self.bump();
             return true;
         }
@@ -914,7 +907,7 @@ impl<'a> Parser<'a> {
                                 expect_err
                                     .span_suggestion_verbose(
                                         self.prev_token.span.shrink_to_hi().until(self.token.span),
-                                        &msg,
+                                        msg,
                                         " @ ",
                                         Applicability::MaybeIncorrect,
                                     )
@@ -930,7 +923,7 @@ impl<'a> Parser<'a> {
                                     expect_err
                                         .span_suggestion_short(
                                             sp,
-                                            &format!("missing `{}`", token_str),
+                                            format!("missing `{}`", token_str),
                                             token_str,
                                             Applicability::MaybeIncorrect,
                                         )
@@ -946,10 +939,14 @@ impl<'a> Parser<'a> {
                                         // propagate the help message from sub error 'e' to main error 'expect_err;
                                         expect_err.children.push(xx.clone());
                                     }
-                                    expect_err.emit();
-
                                     e.cancel();
-                                    break;
+                                    if self.token == token::Colon {
+                                        // we will try to recover in `maybe_recover_struct_lit_bad_delims`
+                                        return Err(expect_err);
+                                    } else {
+                                        expect_err.emit();
+                                        break;
+                                    }
                                 }
                             }
                         }
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index 7a4d53ed8..adb0d372a 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -20,12 +20,10 @@ impl<'a> Parser<'a> {
     pub fn nonterminal_may_begin_with(kind: NonterminalKind, token: &Token) -> bool {
         /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
         fn may_be_ident(nt: &token::Nonterminal) -> bool {
-            match *nt {
-                token::NtItem(_) | token::NtBlock(_) | token::NtVis(_) | token::NtLifetime(_) => {
-                    false
-                }
-                _ => true,
-            }
+            !matches!(
+                *nt,
+                token::NtItem(_) | token::NtBlock(_) | token::NtVis(_) | token::NtLifetime(_)
+            )
         }
 
         match kind {
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 2246002f5..c317d9636 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,6 +1,6 @@
 use super::{ForceCollect, Parser, PathStyle, TrailingToken};
 use crate::errors::{
-    AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
+    self, AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
     DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
     ExpectedCommaAfterPatternField, InclusiveRangeExtraEquals, InclusiveRangeMatchArrow,
     InclusiveRangeNoEnd, InvalidMutInPattern, PatternOnWrongSideOfAt, RefMutOrderIncorrect,
@@ -406,11 +406,11 @@ impl<'a> Parser<'a> {
             // Parse pattern starting with a path
             let (qself, path) = if self.eat_lt() {
                 // Parse a qualified path
-                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+                let (qself, path) = self.parse_qpath(PathStyle::Pat)?;
                 (Some(qself), path)
             } else {
                 // Parse an unqualified path
-                (None, self.parse_path(PathStyle::Expr)?)
+                (None, self.parse_path(PathStyle::Pat)?)
             };
             let span = lo.to(self.prev_token.span);
 
@@ -444,7 +444,7 @@ impl<'a> Parser<'a> {
                         super::token_descr(&self_.token)
                     );
 
-                    let mut err = self_.struct_span_err(self_.token.span, &msg);
+                    let mut err = self_.struct_span_err(self_.token.span, msg);
                     err.span_label(self_.token.span, format!("expected {}", expected));
                     err
                 });
@@ -666,7 +666,7 @@ impl<'a> Parser<'a> {
     fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
         self.bump();
         let args = self.parse_delim_args()?;
-        let mac = P(MacCall { path, args, prior_type_ascription: self.last_type_ascription });
+        let mac = P(MacCall { path, args });
         Ok(PatKind::MacCall(mac))
     }
 
@@ -680,7 +680,7 @@ impl<'a> Parser<'a> {
         let expected = Expected::to_string_or_fallback(expected);
         let msg = format!("expected {}, found {}", expected, super::token_descr(&self.token));
 
-        let mut err = self.struct_span_err(self.token.span, &msg);
+        let mut err = self.struct_span_err(self.token.span, msg);
         err.span_label(self.token.span, format!("expected {}", expected));
 
         let sp = self.sess.source_map().start_point(self.token.span);
@@ -789,11 +789,11 @@ impl<'a> Parser<'a> {
             let lo = self.token.span;
             let (qself, path) = if self.eat_lt() {
                 // Parse a qualified path
-                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+                let (qself, path) = self.parse_qpath(PathStyle::Pat)?;
                 (Some(qself), path)
             } else {
                 // Parse an unqualified path
-                (None, self.parse_path(PathStyle::Expr)?)
+                (None, self.parse_path(PathStyle::Pat)?)
             };
             let hi = self.prev_token.span;
             Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path)))
@@ -908,18 +908,13 @@ impl<'a> Parser<'a> {
         let box_span = self.prev_token.span;
 
         if self.isnt_pattern_start() {
-            self.struct_span_err(
-                self.token.span,
-                format!("expected pattern, found {}", super::token_descr(&self.token)),
-            )
-            .span_note(box_span, "`box` is a reserved keyword")
-            .span_suggestion_verbose(
-                box_span.shrink_to_lo(),
-                "escape `box` to use it as an identifier",
-                "r#",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+            let descr = super::token_descr(&self.token);
+            self.sess.emit_err(errors::BoxNotPat {
+                span: self.token.span,
+                kw: box_span,
+                lo: box_span.shrink_to_lo(),
+                descr,
+            });
 
             // We cannot use `parse_pat_ident()` since it will complain `box`
             // is not an identifier.
@@ -983,7 +978,7 @@ impl<'a> Parser<'a> {
                     break;
                 }
                 let token_str = super::token_descr(&self.token);
-                let msg = &format!("expected `}}`, found {}", token_str);
+                let msg = format!("expected `}}`, found {}", token_str);
                 let mut err = self.struct_span_err(self.token.span, msg);
 
                 err.span_label(self.token.span, "expected `}`");
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index c25c23d84..feb7e829c 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -1,5 +1,6 @@
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{Parser, Restrictions, TokenType};
+use crate::errors::PathSingleColon;
 use crate::{errors, maybe_whole};
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
@@ -8,7 +9,7 @@ use rustc_ast::{
     AssocConstraintKind, BlockCheckMode, GenericArg, GenericArgs, Generics, ParenthesizedArgs,
     Path, PathSegment, QSelf,
 };
-use rustc_errors::{pluralize, Applicability, PResult};
+use rustc_errors::{Applicability, IntoDiagnostic, PResult};
 use rustc_span::source_map::{BytePos, Span};
 use rustc_span::symbol::{kw, sym, Ident};
 use std::mem;
@@ -24,7 +25,19 @@ pub enum PathStyle {
     /// In all such contexts the non-path interpretation is preferred by default for practical
     /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g.
     /// `x<y>` - comparisons, `x::<y>` - unambiguously a path.
+    ///
+    /// Also, a path may never be followed by a `:`. This means that we can eagerly recover if
+    /// we encounter it.
     Expr,
+    /// The same as `Expr`, but may be followed by a `:`.
+    /// For example, this code:
+    /// ```rust
+    /// struct S;
+    ///
+    /// let S: S;
+    /// //  ^ Followed by a `:`
+    /// ```
+    Pat,
     /// In other contexts, notably in types, no ambiguity exists and paths can be written
     /// without the disambiguator, e.g., `x<y>` - unambiguously a path.
     /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too.
@@ -38,6 +51,12 @@ pub enum PathStyle {
     Mod,
 }
 
+impl PathStyle {
+    fn has_generic_ambiguity(&self) -> bool {
+        matches!(self, Self::Expr | Self::Pat)
+    }
+}
+
 impl<'a> Parser<'a> {
     /// Parses a qualified path.
     /// Assumes that the leading `<` has been parsed already.
@@ -150,16 +169,13 @@ impl<'a> Parser<'a> {
             //
             if style == PathStyle::Mod && path.segments.iter().any(|segment| segment.args.is_some())
             {
-                parser
-                    .struct_span_err(
-                        path.segments
-                            .iter()
-                            .filter_map(|segment| segment.args.as_ref())
-                            .map(|arg| arg.span())
-                            .collect::<Vec<_>>(),
-                        "unexpected generic arguments in path",
-                    )
-                    .emit();
+                let span = path
+                    .segments
+                    .iter()
+                    .filter_map(|segment| segment.args.as_ref())
+                    .map(|arg| arg.span())
+                    .collect::<Vec<_>>();
+                parser.sess.emit_err(errors::GenericsInPath { span });
             }
         };
 
@@ -186,7 +202,6 @@ impl<'a> Parser<'a> {
             segments.push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
         }
         self.parse_path_segments(&mut segments, style, ty_generics)?;
-
         Ok(Path { segments, span: lo.to(self.prev_token.span), tokens: None })
     }
 
@@ -198,7 +213,7 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, ()> {
         loop {
             let segment = self.parse_path_segment(style, ty_generics)?;
-            if style == PathStyle::Expr {
+            if style.has_generic_ambiguity() {
                 // In order to check for trailing angle brackets, we must have finished
                 // recursing (`parse_path_segment` can indirectly call this function),
                 // that is, the next token must be the highlighted part of the below example:
@@ -220,6 +235,29 @@ impl<'a> Parser<'a> {
             segments.push(segment);
 
             if self.is_import_coupler() || !self.eat(&token::ModSep) {
+                if style == PathStyle::Expr
+                    && self.may_recover()
+                    && self.token == token::Colon
+                    && self.look_ahead(1, |token| token.is_ident() && !token.is_reserved_ident())
+                {
+                    // Emit a special error message for `a::b:c` to help users
+                    // otherwise, `a: c` might have meant to introduce a new binding
+                    if self.token.span.lo() == self.prev_token.span.hi()
+                        && self.look_ahead(1, |token| self.token.span.hi() == token.span.lo())
+                    {
+                        self.bump(); // bump past the colon
+                        self.sess.emit_err(PathSingleColon {
+                            span: self.prev_token.span,
+                            type_ascription: self
+                                .sess
+                                .unstable_features
+                                .is_nightly_build()
+                                .then_some(()),
+                        });
+                    }
+                    continue;
+                }
+
                 return Ok(());
             }
         }
@@ -273,8 +311,25 @@ impl<'a> Parser<'a> {
                         ty_generics,
                     )?;
                     self.expect_gt().map_err(|mut err| {
+                        // Try to recover a `:` into a `::`
+                        if self.token == token::Colon
+                            && self.look_ahead(1, |token| {
+                                token.is_ident() && !token.is_reserved_ident()
+                            })
+                        {
+                            err.cancel();
+                            err = PathSingleColon {
+                                span: self.token.span,
+                                type_ascription: self
+                                    .sess
+                                    .unstable_features
+                                    .is_nightly_build()
+                                    .then_some(()),
+                            }
+                            .into_diagnostic(self.diagnostic());
+                        }
                         // Attempt to find places where a missing `>` might belong.
-                        if let Some(arg) = args
+                        else if let Some(arg) = args
                             .iter()
                             .rev()
                             .find(|arg| !matches!(arg, AngleBracketedArg::Constraint(_)))
@@ -467,23 +522,10 @@ impl<'a> Parser<'a> {
                     // i.e. no multibyte characters, in this range.
                     let span =
                         lo.with_hi(lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count));
-                    self.struct_span_err(
+                    self.sess.emit_err(errors::UnmatchedAngle {
                         span,
-                        &format!(
-                            "unmatched angle bracket{}",
-                            pluralize!(snapshot.unmatched_angle_bracket_count)
-                        ),
-                    )
-                    .span_suggestion(
-                        span,
-                        &format!(
-                            "remove extra angle bracket{}",
-                            pluralize!(snapshot.unmatched_angle_bracket_count)
-                        ),
-                        "",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                        plural: snapshot.unmatched_angle_bracket_count > 1,
+                    });
 
                     // Try again without unmatched angle bracket characters.
                     self.parse_angle_args(ty_generics)
@@ -564,7 +606,7 @@ impl<'a> Parser<'a> {
                     let kind = if self.eat(&token::Colon) {
                         // Parse associated type constraint bound.
 
-                        let bounds = self.parse_generic_bounds(Some(self.prev_token.span))?;
+                        let bounds = self.parse_generic_bounds()?;
                         AssocConstraintKind::Bound { bounds }
                     } else if self.eat(&token::Eq) {
                         self.parse_assoc_equality_term(ident, self.prev_token.span)?
@@ -620,10 +662,7 @@ impl<'a> Parser<'a> {
                 c.into()
             }
             Some(GenericArg::Lifetime(lt)) => {
-                self.struct_span_err(span, "associated lifetimes are not supported")
-                    .span_label(lt.ident.span, "the lifetime is given here")
-                    .help("if you meant to specify a trait object, write `dyn Trait + 'lifetime`")
-                    .emit();
+                self.sess.emit_err(errors::AssocLifetime { span, lifetime: lt.ident.span });
                 self.mk_ty(span, ast::TyKind::Err).into()
             }
             None => {
@@ -640,14 +679,14 @@ impl<'a> Parser<'a> {
                     );
                     err.span_suggestion(
                         eq.to(before_next),
-                        &format!("remove the `=` if `{}` is a type", ident),
+                        format!("remove the `=` if `{}` is a type", ident),
                         "",
                         Applicability::MaybeIncorrect,
                     )
                 } else {
                     err.span_label(
                         self.token.span,
-                        &format!("expected type, found {}", super::token_descr(&self.token)),
+                        format!("expected type, found {}", super::token_descr(&self.token)),
                     )
                 };
                 return Err(err);
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index fbe5b88c4..54f9fc5d2 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -10,6 +10,8 @@ use super::{
 use crate::errors;
 use crate::maybe_whole;
 
+use crate::errors::MalformedLoopLabel;
+use ast::Label;
 use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, TokenKind};
@@ -19,7 +21,8 @@ use rustc_ast::{Block, BlockCheckMode, Expr, ExprKind, HasAttrs, Local, Stmt};
 use rustc_ast::{StmtKind, DUMMY_NODE_ID};
 use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
 use rustc_span::source_map::{BytePos, Span};
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::{kw, sym, Ident};
+
 use std::mem;
 use thin_vec::{thin_vec, ThinVec};
 
@@ -37,7 +40,8 @@ impl<'a> Parser<'a> {
 
     /// If `force_collect` is [`ForceCollect::Yes`], forces collection of tokens regardless of whether
     /// or not we have attributes
-    pub(crate) fn parse_stmt_without_recovery(
+    // Public for `cfg_eval` macro expansion.
+    pub fn parse_stmt_without_recovery(
         &mut self,
         capture_semi: bool,
         force_collect: ForceCollect,
@@ -87,7 +91,11 @@ impl<'a> Parser<'a> {
                 attrs,
                 errors::InvalidVariableDeclarationSub::UseLetNotVar,
             )?
-        } else if self.check_path() && !self.token.is_qpath_start() && !self.is_path_start_item() {
+        } else if self.check_path()
+            && !self.token.is_qpath_start()
+            && !self.is_path_start_item()
+            && !self.is_builtin()
+        {
             // We have avoided contextual keywords like `union`, items with `crate` visibility,
             // or `auto trait` items. We aim to parse an arbitrary path `a::b` but not something
             // that starts like a path (1 token), but it fact not a path.
@@ -96,7 +104,13 @@ impl<'a> Parser<'a> {
                 ForceCollect::Yes => {
                     self.collect_tokens_no_attrs(|this| this.parse_stmt_path_start(lo, attrs))?
                 }
-                ForceCollect::No => self.parse_stmt_path_start(lo, attrs)?,
+                ForceCollect::No => match self.parse_stmt_path_start(lo, attrs) {
+                    Ok(stmt) => stmt,
+                    Err(mut err) => {
+                        self.suggest_add_missing_let_for_stmt(&mut err);
+                        return Err(err);
+                    }
+                },
             }
         } else if let Some(item) = self.parse_item_common(
             attrs.clone(),
@@ -186,7 +200,7 @@ impl<'a> Parser<'a> {
             _ => MacStmtStyle::NoBraces,
         };
 
-        let mac = P(MacCall { path, args, prior_type_ascription: self.last_type_ascription });
+        let mac = P(MacCall { path, args });
 
         let kind = if (style == MacStmtStyle::Braces
             && self.token != token::Dot
@@ -546,10 +560,27 @@ impl<'a> Parser<'a> {
             }
             let stmt = match self.parse_full_stmt(recover) {
                 Err(mut err) if recover.yes() => {
-                    self.maybe_annotate_with_ascription(&mut err, false);
                     if let Some(ref mut snapshot) = snapshot {
                         snapshot.recover_diff_marker();
                     }
+                    if self.token == token::Colon {
+                        // if next token is following a colon, it's likely a path
+                        // and we can suggest a path separator
+                        self.bump();
+                        if self.token.span.lo() == self.prev_token.span.hi() {
+                            err.span_suggestion_verbose(
+                                self.prev_token.span,
+                                "maybe write a path separator here",
+                                "::",
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
+                        if self.sess.unstable_features.is_nightly_build() {
+                            // FIXME(Nilstrieb): Remove this again after a few months.
+                            err.note("type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>");
+                        }
+                    }
+
                     err.emit();
                     self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
                     Some(self.mk_stmt_err(self.token.span))
@@ -580,47 +611,104 @@ impl<'a> Parser<'a> {
         };
 
         let mut eat_semi = true;
+        let mut add_semi_to_stmt = false;
+
         match &mut stmt.kind {
             // Expression without semicolon.
             StmtKind::Expr(expr)
                 if self.token != token::Eof && classify::expr_requires_semi_to_be_stmt(expr) => {
                 // Just check for errors and recover; do not eat semicolon yet.
                 // `expect_one_of` returns PResult<'a, bool /* recovered */>
-                let replace_with_err =
-                    match self.expect_one_of(&[], &[token::Semi, token::CloseDelim(Delimiter::Brace)]) {
+
+                let expect_result = self.expect_one_of(&[], &[token::Semi, token::CloseDelim(Delimiter::Brace)]);
+
+                let replace_with_err = 'break_recover: {
+                    match expect_result {
                     // Recover from parser, skip type error to avoid extra errors.
-                    Ok(true) => true,
-                    Err(mut e) => {
-                        if let TokenKind::DocComment(..) = self.token.kind &&
-                            let Ok(snippet) = self.span_to_snippet(self.token.span) {
+                        Ok(true) => true,
+                        Err(mut e) => {
+                            if let TokenKind::DocComment(..) = self.token.kind
+                                && let Ok(snippet) = self.span_to_snippet(self.token.span)
+                            {
                                 let sp = self.token.span;
                                 let marker = &snippet[..3];
                                 let (comment_marker, doc_comment_marker) = marker.split_at(2);
 
                                 e.span_suggestion(
                                     sp.with_hi(sp.lo() + BytePos(marker.len() as u32)),
-                                    &format!(
+                                    format!(
                                         "add a space before `{}` to use a regular comment",
                                         doc_comment_marker,
                                     ),
                                     format!("{} {}", comment_marker, doc_comment_marker),
                                     Applicability::MaybeIncorrect,
                                 );
-                        }
+                            }
+
+                            if self.recover_colon_as_semi() {
+                                // recover_colon_as_semi has already emitted a nicer error.
+                                e.delay_as_bug();
+                                add_semi_to_stmt = true;
+                                eat_semi = false;
 
-                        if let Err(mut e) =
-                            self.check_mistyped_turbofish_with_multiple_type_params(e, expr)
-                        {
-                            if recover.no() {
-                                return Err(e);
+                                break 'break_recover false;
                             }
-                            e.emit();
-                            self.recover_stmt();
+
+                            match &expr.kind {
+                                ExprKind::Path(None, ast::Path { segments, .. }) if segments.len() == 1 => {
+                                    if self.token == token::Colon
+                                        && self.look_ahead(1, |token| {
+                                            token.is_whole_block() || matches!(
+                                                token.kind,
+                                                token::Ident(kw::For | kw::Loop | kw::While, false)
+                                                    | token::OpenDelim(Delimiter::Brace)
+                                            )
+                                        })
+                                    {
+                                        let snapshot = self.create_snapshot_for_diagnostic();
+                                        let label = Label {
+                                            ident: Ident::from_str_and_span(
+                                                &format!("'{}", segments[0].ident),
+                                                segments[0].ident.span,
+                                            ),
+                                        };
+                                        match self.parse_expr_labeled(label, false) {
+                                            Ok(labeled_expr) => {
+                                                e.delay_as_bug();
+                                                self.sess.emit_err(MalformedLoopLabel {
+                                                    span: label.ident.span,
+                                                    correct_label: label.ident,
+                                                });
+                                                *expr = labeled_expr;
+                                                break 'break_recover false;
+                                            }
+                                            Err(err) => {
+                                                err.cancel();
+                                                self.restore_snapshot(snapshot);
+                                            }
+                                        }
+                                    }
+                                }
+                                _ => {}
+                            }
+
+                            if let Err(mut e) =
+                                self.check_mistyped_turbofish_with_multiple_type_params(e, expr)
+                            {
+                                if recover.no() {
+                                    return Err(e);
+                                }
+                                e.emit();
+                                self.recover_stmt();
+                            }
+
+                            true
+
                         }
-                        true
+                        Ok(false) => false
                     }
-                    _ => false
                 };
+
                 if replace_with_err {
                     // We already emitted an error, so don't emit another type error
                     let sp = expr.span.to(self.prev_token.span);
@@ -643,9 +731,10 @@ impl<'a> Parser<'a> {
             StmtKind::Empty | StmtKind::Item(_) | StmtKind::Local(_) | StmtKind::Semi(_) => eat_semi = false,
         }
 
-        if eat_semi && self.eat(&token::Semi) {
+        if add_semi_to_stmt || (eat_semi && self.eat(&token::Semi)) {
             stmt = stmt.add_trailing_semicolon();
         }
+
         stmt.span = stmt.span.to(self.prev_token.span);
         Ok(Some(stmt))
     }
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 400c8dbe9..a29b696ae 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -1,10 +1,9 @@
 use super::{Parser, PathStyle, TokenType};
 
 use crate::errors::{
-    DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
+    self, DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
     FnPointerCannotBeAsync, FnPointerCannotBeConst, FnPtrWithGenerics, FnPtrWithGenericsSugg,
-    InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime,
-    NegativeBoundsNotSupported, NegativeBoundsNotSupportedSugg, NestedCVariadicType,
+    InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime, NestedCVariadicType,
     ReturnTypesUseThinArrow,
 };
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
@@ -14,8 +13,9 @@ use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
 use rustc_ast::util::case::Case;
 use rustc_ast::{
-    self as ast, BareFnTy, FnRetTy, GenericBound, GenericBounds, GenericParam, Generics, Lifetime,
-    MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax, Ty, TyKind,
+    self as ast, BareFnTy, BoundPolarity, FnRetTy, GenericBound, GenericBounds, GenericParam,
+    Generics, Lifetime, MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier,
+    TraitObjectSyntax, Ty, TyKind,
 };
 use rustc_errors::{Applicability, PResult};
 use rustc_span::source_map::Span;
@@ -23,10 +23,10 @@ use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Symbol;
 use thin_vec::{thin_vec, ThinVec};
 
-/// Any `?` or `~const` modifiers that appear at the start of a bound.
+/// Any `?`, `!`, or `~const` modifiers that appear at the start of a bound.
 struct BoundModifiers {
     /// `?Trait`.
-    maybe: Option<Span>,
+    bound_polarity: BoundPolarity,
 
     /// `~const Trait`.
     maybe_const: Option<Span>,
@@ -34,11 +34,13 @@ struct BoundModifiers {
 
 impl BoundModifiers {
     fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
-        match (self.maybe, self.maybe_const) {
-            (None, None) => TraitBoundModifier::None,
-            (Some(_), None) => TraitBoundModifier::Maybe,
-            (None, Some(_)) => TraitBoundModifier::MaybeConst,
-            (Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
+        match (self.bound_polarity, self.maybe_const) {
+            (BoundPolarity::Positive, None) => TraitBoundModifier::None,
+            (BoundPolarity::Negative(_), None) => TraitBoundModifier::Negative,
+            (BoundPolarity::Maybe(_), None) => TraitBoundModifier::Maybe,
+            (BoundPolarity::Positive, Some(_)) => TraitBoundModifier::MaybeConst,
+            (BoundPolarity::Negative(_), Some(_)) => TraitBoundModifier::MaybeConstNegative,
+            (BoundPolarity::Maybe(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
         }
     }
 }
@@ -315,9 +317,8 @@ impl<'a> Parser<'a> {
             }
         } else {
             let msg = format!("expected type, found {}", super::token_descr(&self.token));
-            let mut err = self.struct_span_err(self.token.span, &msg);
+            let mut err = self.struct_span_err(self.token.span, msg);
             err.span_label(self.token.span, "expected type");
-            self.maybe_annotate_with_ascription(&mut err, true);
             return Err(err);
         };
 
@@ -369,7 +370,7 @@ impl<'a> Parser<'a> {
 
     fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
         let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
-        let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
+        let bounds = self.parse_generic_bounds_common(allow_plus)?;
         if lt_no_plus {
             self.sess.emit_err(NeedPlusAfterTraitObjectLifetime { span: lo });
         }
@@ -396,7 +397,7 @@ impl<'a> Parser<'a> {
     ) -> PResult<'a, TyKind> {
         if plus {
             self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
-            bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
+            bounds.append(&mut self.parse_generic_bounds()?);
         }
         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
     }
@@ -588,24 +589,18 @@ impl<'a> Parser<'a> {
         // Always parse bounds greedily for better error recovery.
         if self.token.is_lifetime() {
             self.look_ahead(1, |t| {
-                if let token::Ident(symname, _) = t.kind {
+                if let token::Ident(sym, _) = t.kind {
                     // parse pattern with "'a Sized" we're supposed to give suggestion like
                     // "'a + Sized"
-                    self.struct_span_err(
-                        self.token.span,
-                        &format!("expected `+` between lifetime and {}", symname),
-                    )
-                    .span_suggestion_verbose(
-                        self.token.span.shrink_to_hi(),
-                        "add `+`",
-                        " +",
-                        Applicability::MaybeIncorrect,
-                    )
-                    .emit();
+                    self.sess.emit_err(errors::MissingPlusBounds {
+                        span: self.token.span,
+                        hi: self.token.span.shrink_to_hi(),
+                        sym,
+                    });
                 }
             })
         }
-        let bounds = self.parse_generic_bounds(None)?;
+        let bounds = self.parse_generic_bounds()?;
         *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
         Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
     }
@@ -636,7 +631,7 @@ impl<'a> Parser<'a> {
         };
 
         // Always parse bounds greedily for better error recovery.
-        let bounds = self.parse_generic_bounds(None)?;
+        let bounds = self.parse_generic_bounds()?;
         *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
         Ok(TyKind::TraitObject(bounds, syntax))
     }
@@ -657,11 +652,7 @@ impl<'a> Parser<'a> {
         let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
         if self.eat(&token::Not) {
             // Macro invocation in type position
-            Ok(TyKind::MacCall(P(MacCall {
-                path,
-                args: self.parse_delim_args()?,
-                prior_type_ascription: self.last_type_ascription,
-            })))
+            Ok(TyKind::MacCall(P(MacCall { path, args: self.parse_delim_args()? })))
         } else if allow_plus == AllowPlus::Yes && self.check_plus() {
             // `Trait1 + Trait2 + 'a`
             self.parse_remaining_bounds_path(ThinVec::new(), path, lo, true)
@@ -671,23 +662,15 @@ impl<'a> Parser<'a> {
         }
     }
 
-    pub(super) fn parse_generic_bounds(
-        &mut self,
-        colon_span: Option<Span>,
-    ) -> PResult<'a, GenericBounds> {
-        self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
+    pub(super) fn parse_generic_bounds(&mut self) -> PResult<'a, GenericBounds> {
+        self.parse_generic_bounds_common(AllowPlus::Yes)
     }
 
     /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
     ///
     /// See `parse_generic_bound` for the `BOUND` grammar.
-    fn parse_generic_bounds_common(
-        &mut self,
-        allow_plus: AllowPlus,
-        colon_span: Option<Span>,
-    ) -> PResult<'a, GenericBounds> {
+    fn parse_generic_bounds_common(&mut self, allow_plus: AllowPlus) -> PResult<'a, GenericBounds> {
         let mut bounds = Vec::new();
-        let mut negative_bounds = Vec::new();
 
         // In addition to looping while we find generic bounds:
         // We continue even if we find a keyword. This is necessary for error recovery on,
@@ -704,19 +687,12 @@ impl<'a> Parser<'a> {
                 self.sess.emit_err(InvalidDynKeyword { span: self.token.span });
                 self.bump();
             }
-            match self.parse_generic_bound()? {
-                Ok(bound) => bounds.push(bound),
-                Err(neg_sp) => negative_bounds.push(neg_sp),
-            }
+            bounds.push(self.parse_generic_bound()?);
             if allow_plus == AllowPlus::No || !self.eat_plus() {
                 break;
             }
         }
 
-        if !negative_bounds.is_empty() {
-            self.error_negative_bounds(colon_span, &bounds, negative_bounds);
-        }
-
         Ok(bounds)
     }
 
@@ -724,55 +700,22 @@ impl<'a> Parser<'a> {
     fn can_begin_bound(&mut self) -> bool {
         // This needs to be synchronized with `TokenKind::can_begin_bound`.
         self.check_path()
-        || self.check_lifetime()
-        || self.check(&token::Not) // Used for error reporting only.
-        || self.check(&token::Question)
-        || self.check(&token::Tilde)
-        || self.check_keyword(kw::For)
-        || self.check(&token::OpenDelim(Delimiter::Parenthesis))
-    }
-
-    fn error_negative_bounds(
-        &self,
-        colon_span: Option<Span>,
-        bounds: &[GenericBound],
-        negative_bounds: Vec<Span>,
-    ) {
-        let sub = if let Some(bound_list) = colon_span {
-            let bound_list = bound_list.to(self.prev_token.span);
-            let mut new_bound_list = String::new();
-            if !bounds.is_empty() {
-                let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
-                while let Some(Ok(snippet)) = snippets.next() {
-                    new_bound_list.push_str(" + ");
-                    new_bound_list.push_str(&snippet);
-                }
-                new_bound_list = new_bound_list.replacen(" +", ":", 1);
-            }
-
-            Some(NegativeBoundsNotSupportedSugg {
-                bound_list,
-                num_bounds: negative_bounds.len(),
-                fixed: new_bound_list,
-            })
-        } else {
-            None
-        };
-
-        let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
-        self.sess.emit_err(NegativeBoundsNotSupported { negative_bounds, last_span, sub });
+            || self.check_lifetime()
+            || self.check(&token::Not)
+            || self.check(&token::Question)
+            || self.check(&token::Tilde)
+            || self.check_keyword(kw::For)
+            || self.check(&token::OpenDelim(Delimiter::Parenthesis))
     }
 
     /// Parses a bound according to the grammar:
     /// ```ebnf
     /// BOUND = TY_BOUND | LT_BOUND
     /// ```
-    fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
-        let anchor_lo = self.prev_token.span;
+    fn parse_generic_bound(&mut self) -> PResult<'a, GenericBound> {
         let lo = self.token.span;
         let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
         let inner_lo = self.token.span;
-        let is_negative = self.eat(&token::Not);
 
         let modifiers = self.parse_ty_bound_modifiers()?;
         let bound = if self.token.is_lifetime() {
@@ -782,7 +725,7 @@ impl<'a> Parser<'a> {
             self.parse_generic_ty_bound(lo, has_parens, modifiers)?
         };
 
-        Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
+        Ok(bound)
     }
 
     /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
@@ -807,16 +750,17 @@ impl<'a> Parser<'a> {
     /// Emits an error if any trait bound modifiers were present.
     fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
         if let Some(span) = modifiers.maybe_const {
-            self.struct_span_err(
-                span,
-                "`~const` may only modify trait bounds, not lifetime bounds",
-            )
-            .emit();
+            self.sess.emit_err(errors::TildeConstLifetime { span });
         }
 
-        if let Some(span) = modifiers.maybe {
-            self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
-                .emit();
+        match modifiers.bound_polarity {
+            BoundPolarity::Positive => {}
+            BoundPolarity::Negative(span) => {
+                self.sess.emit_err(errors::ModifierLifetime { span, sigil: "!" });
+            }
+            BoundPolarity::Maybe(span) => {
+                self.sess.emit_err(errors::ModifierLifetime { span, sigil: "?" });
+            }
         }
     }
 
@@ -824,19 +768,14 @@ impl<'a> Parser<'a> {
     fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
         let inner_span = inner_lo.to(self.prev_token.span);
         self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
-        let mut err = self.struct_span_err(
-            lo.to(self.prev_token.span),
-            "parenthesized lifetime bounds are not supported",
-        );
-        if let Ok(snippet) = self.span_to_snippet(inner_span) {
-            err.span_suggestion_short(
-                lo.to(self.prev_token.span),
-                "remove the parentheses",
-                snippet,
-                Applicability::MachineApplicable,
-            );
-        }
-        err.emit();
+        let span = lo.to(self.prev_token.span);
+        let (sugg, snippet) = if let Ok(snippet) = self.span_to_snippet(inner_span) {
+            (Some(span), snippet)
+        } else {
+            (None, String::new())
+        };
+
+        self.sess.emit_err(errors::ParenthesizedLifetime { span, sugg, snippet });
         Ok(())
     }
 
@@ -857,24 +796,23 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(kw::Const) {
             let span = self.prev_token.span;
             self.sess.gated_spans.gate(sym::const_trait_impl, span);
-
-            self.struct_span_err(span, "const bounds must start with `~`")
-                .span_suggestion(
-                    span.shrink_to_lo(),
-                    "add `~`",
-                    "~",
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(errors::ConstMissingTilde { span, start: span.shrink_to_lo() });
 
             Some(span)
         } else {
             None
         };
 
-        let maybe = self.eat(&token::Question).then_some(self.prev_token.span);
+        let bound_polarity = if self.eat(&token::Question) {
+            BoundPolarity::Maybe(self.prev_token.span)
+        } else if self.eat(&token::Not) {
+            self.sess.gated_spans.gate(sym::negative_bounds, self.prev_token.span);
+            BoundPolarity::Negative(self.prev_token.span)
+        } else {
+            BoundPolarity::Positive
+        };
 
-        Ok(BoundModifiers { maybe, maybe_const })
+        Ok(BoundModifiers { bound_polarity, maybe_const })
     }
 
     /// Parses a type bound according to:
@@ -944,14 +882,10 @@ impl<'a> Parser<'a> {
                 self.parse_remaining_bounds(bounds, true)?;
                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
                 let sp = vec![lo, self.prev_token.span];
-                let sugg = vec![(lo, String::from(" ")), (self.prev_token.span, String::new())];
-                self.struct_span_err(sp, "incorrect braces around trait bounds")
-                    .multipart_suggestion(
-                        "remove the parentheses",
-                        sugg,
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(errors::IncorrectBracesTraitBounds {
+                    span: sp,
+                    sugg: errors::IncorrectBracesTraitBoundsSugg { l: lo, r: self.prev_token.span },
+                });
             } else {
                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
             }
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 72402a200..928fdce31 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -1,6 +1,6 @@
 //! Meta-syntax validation logic of attributes for post-expansion.
 
-use crate::parse_in;
+use crate::{errors, parse_in};
 
 use rustc_ast::tokenstream::DelimSpan;
 use rustc_ast::MetaItemKind;
@@ -45,7 +45,7 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
         kind: match &item.args {
             AttrArgs::Empty => MetaItemKind::Word,
             AttrArgs::Delimited(DelimArgs { dspan, delim, tokens }) => {
-                check_meta_bad_delim(sess, *dspan, *delim, "wrong meta list delimiters");
+                check_meta_bad_delim(sess, *dspan, *delim);
                 let nmis = parse_in(sess, tokens.clone(), "meta list", |p| p.parse_meta_seq_top())?;
                 MetaItemKind::List(nmis)
             }
@@ -68,7 +68,7 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
                     }
                 } else {
                     // The non-error case can happen with e.g. `#[foo = 1+1]`. The error case can
-                    // happen with e.g. `#[foo = include_str!("non-existent-file.rs")]`; in that
+                    // happen with e.g. `#[foo = include_str!("nonexistent-file.rs")]`; in that
                     // case we delay the error because an earlier error will have already been
                     // reported.
                     let msg = format!("unexpected expression: `{}`", pprust::expr_to_string(expr));
@@ -84,19 +84,24 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
     })
 }
 
-pub fn check_meta_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter, msg: &str) {
+pub fn check_meta_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter) {
     if let ast::MacDelimiter::Parenthesis = delim {
         return;
     }
+    sess.emit_err(errors::MetaBadDelim {
+        span: span.entire(),
+        sugg: errors::MetaBadDelimSugg { open: span.open, close: span.close },
+    });
+}
 
-    sess.span_diagnostic
-        .struct_span_err(span.entire(), msg)
-        .multipart_suggestion(
-            "the delimiters should be `(` and `)`",
-            vec![(span.open, "(".to_string()), (span.close, ")".to_string())],
-            Applicability::MachineApplicable,
-        )
-        .emit();
+pub fn check_cfg_attr_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter) {
+    if let ast::MacDelimiter::Parenthesis = delim {
+        return;
+    }
+    sess.emit_err(errors::CfgAttrBadDelim {
+        span: span.entire(),
+        sugg: errors::MetaBadDelimSugg { open: span.open, close: span.close },
+    });
 }
 
 /// Checks that the given meta-item is compatible with this `AttributeTemplate`.
@@ -181,10 +186,10 @@ fn emit_malformed_attribute(
         suggestions.push(code);
     }
     if should_warn(name) {
-        sess.buffer_lint(&ILL_FORMED_ATTRIBUTE_INPUT, span, ast::CRATE_NODE_ID, &msg);
+        sess.buffer_lint(&ILL_FORMED_ATTRIBUTE_INPUT, span, ast::CRATE_NODE_ID, msg);
     } else {
         sess.span_diagnostic
-            .struct_span_err(span, &error_msg)
+            .struct_span_err(span, error_msg)
             .span_suggestions(
                 span,
                 if suggestions.len() == 1 {