Auto merge of #105670 - Xiretza:rustc_parse-diagnostics-4, r=davidtwco

rustc_parse: diagnostics migration, v4

This is all the `rustc_parse` migrations I have in store right now; unfortunately life is pretty busy right now, so I won't be able to do much more in the near future.

cc #100717

r? `@davidtwco`

9 files changed, 974 insertions, 563 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index e63fc3c73b2..145611923ff 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -1,8 +1,9 @@
 use rustc_ast::token::Token;
-use rustc_ast::Path;
+use rustc_ast::{Path, Visibility};
 use rustc_errors::{fluent, AddToDiagnostic, Applicability, EmissionGuarantee, IntoDiagnostic};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::edition::{Edition, LATEST_STABLE_EDITION};
 use rustc_span::symbol::Ident;
 use rustc_span::{Span, Symbol};
 
@@ -1330,3 +1331,608 @@ pub(crate) struct WhereClauseBeforeTupleStructBodySugg {
     #[suggestion_part(code = "")]
     pub right: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_async_fn_in_2015, code = "E0670")]
+pub(crate) struct AsyncFnIn2015 {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[subdiagnostic]
+    pub help: HelpUseLatestEdition,
+}
+
+#[derive(Subdiagnostic)]
+#[label(parse_async_block_in_2015)]
+pub(crate) struct AsyncBlockIn2015 {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_self_argument_pointer)]
+pub(crate) struct SelfArgumentPointer {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_visibility_not_followed_by_item)]
+#[help]
+pub(crate) struct VisibilityNotFollowedByItem {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub vis: Visibility,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_default_not_followed_by_item)]
+#[note]
+pub(crate) struct DefaultNotFollowedByItem {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum MissingKeywordForItemDefinition {
+    #[diag(parse_missing_struct_for_struct_definition)]
+    Struct {
+        #[primary_span]
+        #[suggestion(style = "short", applicability = "maybe-incorrect", code = " struct ")]
+        span: Span,
+        ident: Ident,
+    },
+    #[diag(parse_missing_fn_for_function_definition)]
+    Function {
+        #[primary_span]
+        #[suggestion(style = "short", applicability = "maybe-incorrect", code = " fn ")]
+        span: Span,
+        ident: Ident,
+    },
+    #[diag(parse_missing_fn_for_method_definition)]
+    Method {
+        #[primary_span]
+        #[suggestion(style = "short", applicability = "maybe-incorrect", code = " fn ")]
+        span: Span,
+        ident: Ident,
+    },
+    #[diag(parse_ambiguous_missing_keyword_for_item_definition)]
+    Ambiguous {
+        #[primary_span]
+        span: Span,
+        #[subdiagnostic]
+        subdiag: Option<AmbiguousMissingKwForItemSub>,
+    },
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum AmbiguousMissingKwForItemSub {
+    #[suggestion(suggestion, applicability = "maybe-incorrect", code = "{snippet}!")]
+    SuggestMacro {
+        #[primary_span]
+        span: Span,
+        snippet: String,
+    },
+    #[help(help)]
+    HelpMacro,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_missing_trait_in_trait_impl)]
+pub(crate) struct MissingTraitInTraitImpl {
+    #[primary_span]
+    #[suggestion(suggestion_add_trait, code = " Trait ", applicability = "has-placeholders")]
+    pub span: Span,
+    #[suggestion(suggestion_remove_for, code = "", applicability = "maybe-incorrect")]
+    pub for_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_missing_for_in_trait_impl)]
+pub(crate) struct MissingForInTraitImpl {
+    #[primary_span]
+    #[suggestion(style = "short", code = " for ", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expected_trait_in_trait_impl_found_type)]
+pub(crate) struct ExpectedTraitInTraitImplFoundType {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_bounds_not_allowed_on_trait_aliases)]
+pub(crate) struct BoundsNotAllowedOnTraitAliases {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_trait_alias_cannot_be_auto)]
+pub(crate) struct TraitAliasCannotBeAuto {
+    #[primary_span]
+    #[label(parse_trait_alias_cannot_be_auto)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_trait_alias_cannot_be_unsafe)]
+pub(crate) struct TraitAliasCannotBeUnsafe {
+    #[primary_span]
+    #[label(parse_trait_alias_cannot_be_unsafe)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_associated_static_item_not_allowed)]
+pub(crate) struct AssociatedStaticItemNotAllowed {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_extern_crate_name_with_dashes)]
+pub(crate) struct ExternCrateNameWithDashes {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: ExternCrateNameWithDashesSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(suggestion, applicability = "machine-applicable")]
+pub(crate) struct ExternCrateNameWithDashesSugg {
+    #[suggestion_part(code = "_")]
+    pub dashes: Vec<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_extern_item_cannot_be_const)]
+#[note]
+pub(crate) struct ExternItemCannotBeConst {
+    #[primary_span]
+    pub ident_span: Span,
+    #[suggestion(code = "static ", applicability = "machine-applicable")]
+    pub const_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_const_global_cannot_be_mutable)]
+pub(crate) struct ConstGlobalCannotBeMutable {
+    #[primary_span]
+    #[label]
+    pub ident_span: Span,
+    #[suggestion(code = "static", applicability = "maybe-incorrect")]
+    pub const_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_missing_const_type)]
+pub(crate) struct MissingConstType {
+    #[primary_span]
+    #[suggestion(code = "{colon} <type>", applicability = "has-placeholders")]
+    pub span: Span,
+
+    pub kind: &'static str,
+    pub colon: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_enum_struct_mutually_exclusive)]
+pub(crate) struct EnumStructMutuallyExclusive {
+    #[primary_span]
+    #[suggestion(code = "enum", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum UnexpectedTokenAfterStructName {
+    #[diag(parse_unexpected_token_after_struct_name_found_reserved_identifier)]
+    ReservedIdentifier {
+        #[primary_span]
+        #[label(parse_unexpected_token_after_struct_name)]
+        span: Span,
+        token: Token,
+    },
+    #[diag(parse_unexpected_token_after_struct_name_found_keyword)]
+    Keyword {
+        #[primary_span]
+        #[label(parse_unexpected_token_after_struct_name)]
+        span: Span,
+        token: Token,
+    },
+    #[diag(parse_unexpected_token_after_struct_name_found_reserved_keyword)]
+    ReservedKeyword {
+        #[primary_span]
+        #[label(parse_unexpected_token_after_struct_name)]
+        span: Span,
+        token: Token,
+    },
+    #[diag(parse_unexpected_token_after_struct_name_found_doc_comment)]
+    DocComment {
+        #[primary_span]
+        #[label(parse_unexpected_token_after_struct_name)]
+        span: Span,
+        token: Token,
+    },
+    #[diag(parse_unexpected_token_after_struct_name_found_other)]
+    Other {
+        #[primary_span]
+        #[label(parse_unexpected_token_after_struct_name)]
+        span: Span,
+        token: Token,
+    },
+}
+
+impl UnexpectedTokenAfterStructName {
+    pub fn new(span: Span, token: Token) -> Self {
+        match TokenDescription::from_token(&token) {
+            Some(TokenDescription::ReservedIdentifier) => Self::ReservedIdentifier { span, token },
+            Some(TokenDescription::Keyword) => Self::Keyword { span, token },
+            Some(TokenDescription::ReservedKeyword) => Self::ReservedKeyword { span, token },
+            Some(TokenDescription::DocComment) => Self::DocComment { span, token },
+            None => Self::Other { span, token },
+        }
+    }
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unexpected_self_in_generic_parameters)]
+#[note]
+pub(crate) struct UnexpectedSelfInGenericParameters {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_multiple_where_clauses)]
+pub(crate) struct MultipleWhereClauses {
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub previous: Span,
+    #[suggestion(style = "verbose", code = ",", applicability = "maybe-incorrect")]
+    pub between: Span,
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum UnexpectedNonterminal {
+    #[diag(parse_nonterminal_expected_item_keyword)]
+    Item(#[primary_span] Span),
+    #[diag(parse_nonterminal_expected_statement)]
+    Statement(#[primary_span] Span),
+    #[diag(parse_nonterminal_expected_ident)]
+    Ident {
+        #[primary_span]
+        span: Span,
+        token: Token,
+    },
+    #[diag(parse_nonterminal_expected_lifetime)]
+    Lifetime {
+        #[primary_span]
+        span: Span,
+        token: Token,
+    },
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum TopLevelOrPatternNotAllowed {
+    #[diag(parse_or_pattern_not_allowed_in_let_binding)]
+    LetBinding {
+        #[primary_span]
+        span: Span,
+        #[subdiagnostic]
+        sub: Option<TopLevelOrPatternNotAllowedSugg>,
+    },
+    #[diag(parse_or_pattern_not_allowed_in_fn_parameters)]
+    FunctionParameter {
+        #[primary_span]
+        span: Span,
+        #[subdiagnostic]
+        sub: Option<TopLevelOrPatternNotAllowedSugg>,
+    },
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum TopLevelOrPatternNotAllowedSugg {
+    #[suggestion(
+        parse_sugg_remove_leading_vert_in_pattern,
+        code = "{pat}",
+        applicability = "machine-applicable"
+    )]
+    RemoveLeadingVert {
+        #[primary_span]
+        span: Span,
+        pat: String,
+    },
+    #[suggestion(
+        parse_sugg_wrap_pattern_in_parens,
+        code = "({pat})",
+        applicability = "machine-applicable"
+    )]
+    WrapInParens {
+        #[primary_span]
+        span: Span,
+        pat: String,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unexpected_vert_vert_before_function_parameter)]
+#[note(parse_note_pattern_alternatives_use_single_vert)]
+pub(crate) struct UnexpectedVertVertBeforeFunctionParam {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unexpected_vert_vert_in_pattern)]
+pub(crate) struct UnexpectedVertVertInPattern {
+    #[primary_span]
+    #[suggestion(code = "|", applicability = "machine-applicable")]
+    pub span: Span,
+    #[label(parse_label_while_parsing_or_pattern_here)]
+    pub start: Option<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_trailing_vert_not_allowed)]
+pub(crate) struct TrailingVertNotAllowed {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    #[label(parse_label_while_parsing_or_pattern_here)]
+    pub start: Option<Span>,
+    pub token: Token,
+    #[note(parse_note_pattern_alternatives_use_single_vert)]
+    pub note_double_vert: Option<()>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_dotdotdot_rest_pattern)]
+pub(crate) struct DotDotDotRestPattern {
+    #[primary_span]
+    #[suggestion(style = "short", code = "..", applicability = "machine-applicable")]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_pattern_on_wrong_side_of_at)]
+pub(crate) struct PatternOnWrongSideOfAt {
+    #[primary_span]
+    #[suggestion(code = "{whole_pat}", applicability = "machine-applicable")]
+    pub whole_span: Span,
+    pub whole_pat: String,
+    #[label(label_pattern)]
+    pub pattern: Span,
+    #[label(label_binding)]
+    pub binding: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expected_binding_left_of_at)]
+#[note]
+pub(crate) struct ExpectedBindingLeftOfAt {
+    #[primary_span]
+    pub whole_span: Span,
+    #[label(label_lhs)]
+    pub lhs: Span,
+    #[label(label_rhs)]
+    pub rhs: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_ambiguous_range_pattern)]
+pub(crate) struct AmbiguousRangePattern {
+    #[primary_span]
+    #[suggestion(code = "({pat})", applicability = "maybe-incorrect")]
+    pub span: Span,
+    pub pat: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_unexpected_lifetime_in_pattern)]
+pub(crate) struct UnexpectedLifetimeInPattern {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub symbol: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_ref_mut_order_incorrect)]
+pub(crate) struct RefMutOrderIncorrect {
+    #[primary_span]
+    #[suggestion(code = "ref mut", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum InvalidMutInPattern {
+    #[diag(parse_mut_on_nested_ident_pattern)]
+    #[note(parse_note_mut_pattern_usage)]
+    NestedIdent {
+        #[primary_span]
+        #[suggestion(code = "{pat}", applicability = "machine-applicable")]
+        span: Span,
+        pat: String,
+    },
+    #[diag(parse_mut_on_non_ident_pattern)]
+    #[note(parse_note_mut_pattern_usage)]
+    NonIdent {
+        #[primary_span]
+        #[suggestion(code = "{pat}", applicability = "machine-applicable")]
+        span: Span,
+        pat: String,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_repeated_mut_in_pattern)]
+pub(crate) struct RepeatedMutInPattern {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_dot_dot_dot_range_to_pattern_not_allowed)]
+pub(crate) struct DotDotDotRangeToPatternNotAllowed {
+    #[primary_span]
+    #[suggestion(style = "short", code = "..=", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_enum_pattern_instead_of_identifier)]
+pub(crate) struct EnumPatternInsteadOfIdentifier {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_dot_dot_dot_for_remaining_fields)]
+pub(crate) struct DotDotDotForRemainingFields {
+    #[primary_span]
+    #[suggestion(code = "..", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expected_comma_after_pattern_field)]
+pub(crate) struct ExpectedCommaAfterPatternField {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_return_types_use_thin_arrow)]
+pub(crate) struct ReturnTypesUseThinArrow {
+    #[primary_span]
+    #[suggestion(style = "short", code = "->", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_need_plus_after_trait_object_lifetime)]
+pub(crate) struct NeedPlusAfterTraitObjectLifetime {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_expected_mut_or_const_in_raw_pointer_type)]
+pub(crate) struct ExpectedMutOrConstInRawPointerType {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code("mut ", "const "), applicability = "has-placeholders")]
+    pub after_asterisk: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_lifetime_after_mut)]
+pub(crate) struct LifetimeAfterMut {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "&{snippet} mut", applicability = "maybe-incorrect")]
+    pub suggest_lifetime: Option<Span>,
+    pub snippet: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_dyn_after_mut)]
+pub(crate) struct DynAfterMut {
+    #[primary_span]
+    #[suggestion(code = "&mut dyn", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_fn_pointer_cannot_be_const)]
+pub(crate) struct FnPointerCannotBeConst {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    #[label]
+    pub qualifier: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_fn_pointer_cannot_be_async)]
+pub(crate) struct FnPointerCannotBeAsync {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    #[label]
+    pub qualifier: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_nested_c_variadic_type, code = "E0743")]
+pub(crate) struct NestedCVariadicType {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_invalid_dyn_keyword)]
+#[help]
+pub(crate) struct InvalidDynKeyword {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    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(
+    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)]
+    #[note(parse_note_edition_guide)]
+    Cargo { edition: Edition },
+    #[help(parse_help_set_edition_standalone)]
+    #[note(parse_note_edition_guide)]
+    Standalone { edition: Edition },
+}
+
+impl HelpUseLatestEdition {
+    pub fn new() -> Self {
+        let edition = LATEST_STABLE_EDITION;
+        if std::env::var_os("CARGO").is_some() {
+            Self::Cargo { edition }
+        } else {
+            Self::Standalone { edition }
+        }
+    }
+}
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index f4c08031bcc..26274822ed8 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2030,7 +2030,7 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
-        let pat = self.parse_pat_no_top_alt(Some("argument name"))?;
+        let pat = self.parse_pat_no_top_alt(Some(Expected::ArgumentName))?;
         self.expect(&token::Colon)?;
         let ty = self.parse_ty()?;
 
@@ -2397,7 +2397,7 @@ impl<'a> Parser<'a> {
     pub(crate) fn maybe_recover_colon_colon_in_pat_typo_or_anon_enum(
         &mut self,
         mut first_pat: P<Pat>,
-        expected: Expected,
+        expected: Option<Expected>,
     ) -> P<Pat> {
         if token::Colon != self.token.kind {
             return first_pat;
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 500d7d77071..b7a023868fc 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1,25 +1,26 @@
 use super::diagnostics::SnapshotParser;
-use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
+use super::pat::{CommaRecoveryMode, Expected, RecoverColon, RecoverComma};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{
     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
 };
 use crate::errors::{
-    ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
-    BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct, ComparisonInterpretedAsGeneric,
-    ComparisonOrShiftInterpretedAsGenericSugg, DoCatchSyntaxRemoved, DotDotDot, EqFieldInit,
-    ExpectedElseBlock, ExpectedEqForLetExpr, ExpectedExpressionFoundLet,
-    FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
-    IfExpressionLetSomeSub, IfExpressionMissingCondition, IfExpressionMissingThenBlock,
-    IfExpressionMissingThenBlockSub, InvalidBlockMacroSegment, InvalidComparisonOperator,
-    InvalidComparisonOperatorSub, InvalidInterpolatedExpression, InvalidLiteralSuffixOnTupleIndex,
-    InvalidLogicalOperator, InvalidLogicalOperatorSub, LabeledLoopInBreak, LeadingPlusNotSupported,
-    LeftArrowOperator, LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath,
-    MalformedLoopLabel, MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg,
-    MissingCommaAfterMatchArm, MissingDotDot, MissingInInForLoop, MissingInInForLoopSub,
-    MissingSemicolonBeforeArray, NoFieldsForFnCall, NotAsNegationOperator,
-    NotAsNegationOperatorSub, OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
+    ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncBlockIn2015,
+    AsyncMoveOrderIncorrect, BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct,
+    ComparisonInterpretedAsGeneric, ComparisonOrShiftInterpretedAsGenericSugg,
+    DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedEqForLetExpr,
+    ExpectedExpressionFoundLet, FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart,
+    FoundExprWouldBeStmt, HelpUseLatestEdition, IfExpressionLetSomeSub,
+    IfExpressionMissingCondition, IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub,
+    InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
+    InvalidInterpolatedExpression, InvalidLiteralSuffixOnTupleIndex, InvalidLogicalOperator,
+    InvalidLogicalOperatorSub, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
+    LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
+    MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
+    MissingDotDot, MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray,
+    NoFieldsForFnCall, NotAsNegationOperator, NotAsNegationOperatorSub,
+    OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
     RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
     StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedIfWithIf,
     UnexpectedTokenAfterLabel, UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
@@ -39,8 +40,8 @@ use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, R
 use rustc_ast::{ClosureBinder, MetaItemLit, StmtKind};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{
-    Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
-    StashKey,
+    AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic,
+    PResult, StashKey,
 };
 use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
@@ -2221,7 +2222,7 @@ impl<'a> Parser<'a> {
         let lo = self.token.span;
         let attrs = self.parse_outer_attributes()?;
         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
-            let pat = this.parse_pat_no_top_alt(PARAM_EXPECTED)?;
+            let pat = this.parse_pat_no_top_alt(Some(Expected::ParameterName))?;
             let ty = if this.eat(&token::Colon) {
                 this.parse_ty()?
             } else {
@@ -2926,8 +2927,8 @@ impl<'a> Parser<'a> {
 
         let mut async_block_err = |e: &mut Diagnostic, span: Span| {
             recover_async = true;
-            e.span_label(span, "`async` blocks are only allowed in Rust 2018 or later");
-            e.help_use_latest_edition();
+            AsyncBlockIn2015 { span }.add_to_diagnostic(e);
+            HelpUseLatestEdition::new().add_to_diagnostic(e);
         };
 
         while self.token != token::CloseDelim(close_delim) {
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index 8ba811715d8..585dfc518b3 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -1,4 +1,7 @@
-use crate::errors::{WhereClauseBeforeTupleStructBody, WhereClauseBeforeTupleStructBodySugg};
+use crate::errors::{
+    MultipleWhereClauses, UnexpectedSelfInGenericParameters, WhereClauseBeforeTupleStructBody,
+    WhereClauseBeforeTupleStructBodySugg,
+};
 
 use super::{ForceCollect, Parser, TrailingToken};
 
@@ -127,12 +130,9 @@ impl<'a> Parser<'a> {
                     if this.eat_keyword_noexpect(kw::SelfUpper) {
                         // `Self` as a generic param is invalid. Here we emit the diagnostic and continue parsing
                         // as if `Self` never existed.
-                        this.struct_span_err(
-                            this.prev_token.span,
-                            "unexpected keyword `Self` in generic parameters",
-                        )
-                        .note("you cannot use `Self` as a generic parameter because it is reserved for associated items")
-                        .emit();
+                        this.sess.emit_err(UnexpectedSelfInGenericParameters {
+                            span: this.prev_token.span,
+                        });
 
                         this.eat(&token::Comma);
                     }
@@ -329,16 +329,11 @@ impl<'a> Parser<'a> {
             let ate_comma = self.eat(&token::Comma);
 
             if self.eat_keyword_noexpect(kw::Where) {
-                let msg = "cannot define duplicate `where` clauses on an item";
-                let mut err = self.struct_span_err(self.token.span, msg);
-                err.span_label(pred_lo, "previous `where` clause starts here");
-                err.span_suggestion_verbose(
-                    prev_token.shrink_to_hi().to(self.prev_token.span),
-                    "consider joining the two `where` clauses into one",
-                    ",",
-                    Applicability::MaybeIncorrect,
-                );
-                err.emit();
+                self.sess.emit_err(MultipleWhereClauses {
+                    span: self.token.span,
+                    previous: pred_lo,
+                    between: prev_token.shrink_to_hi().to(self.prev_token.span),
+                });
             } else if !ate_comma {
                 break;
             }
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 53680a82bdc..81fd084ccb3 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1,4 +1,13 @@
-use crate::errors::{DocCommentDoesNotDocumentAnything, UseEmptyBlockNotSemi};
+use crate::errors::{
+    AmbiguousMissingKwForItemSub, AssociatedStaticItemNotAllowed, AsyncFnIn2015,
+    BoundsNotAllowedOnTraitAliases, ConstGlobalCannotBeMutable, ConstLetMutuallyExclusive,
+    DefaultNotFollowedByItem, DocCommentDoesNotDocumentAnything, EnumStructMutuallyExclusive,
+    ExpectedTraitInTraitImplFoundType, ExternCrateNameWithDashes, ExternCrateNameWithDashesSugg,
+    ExternItemCannotBeConst, HelpUseLatestEdition, MissingConstType, MissingForInTraitImpl,
+    MissingKeywordForItemDefinition, MissingTraitInTraitImpl, SelfArgumentPointer,
+    TraitAliasCannotBeAuto, TraitAliasCannotBeUnsafe, UnexpectedTokenAfterStructName,
+    UseEmptyBlockNotSemi, VisibilityNotFollowedByItem,
+};
 
 use super::diagnostics::{dummy_arg, ConsumeClosingDelim};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
@@ -16,12 +25,16 @@ use rustc_ast::{EnumDef, FieldDef, Generics, TraitRef, Ty, TyKind, Variant, Vari
 use rustc_ast::{FnHeader, ForeignItem, Path, PathSegment, Visibility, VisibilityKind};
 use rustc_ast::{MacCall, MacDelimiter};
 use rustc_ast_pretty::pprust;
-use rustc_errors::{struct_span_err, Applicability, IntoDiagnostic, PResult, StashKey};
+use rustc_errors::{
+    struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
+    StashKey,
+};
 use rustc_span::edition::Edition;
 use rustc_span::lev_distance::lev_distance;
 use rustc_span::source_map::{self, Span};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
+use std::fmt::Write;
 use std::mem;
 use thin_vec::ThinVec;
 
@@ -163,35 +176,18 @@ impl<'a> Parser<'a> {
         }
 
         // At this point, we have failed to parse an item.
-        self.error_on_unmatched_vis(&vis);
-        self.error_on_unmatched_defaultness(def);
-        if !attrs_allowed {
-            self.recover_attrs_no_item(&attrs)?;
+        if !matches!(vis.kind, VisibilityKind::Inherited) {
+            self.sess.emit_err(VisibilityNotFollowedByItem { span: vis.span, vis });
         }
-        Ok(None)
-    }
 
-    /// Error in-case a non-inherited visibility was parsed but no item followed.
-    fn error_on_unmatched_vis(&self, vis: &Visibility) {
-        if let VisibilityKind::Inherited = vis.kind {
-            return;
+        if let Defaultness::Default(span) = def {
+            self.sess.emit_err(DefaultNotFollowedByItem { span });
         }
-        let vs = pprust::vis_to_string(&vis);
-        let vs = vs.trim_end();
-        self.struct_span_err(vis.span, &format!("visibility `{vs}` is not followed by an item"))
-            .span_label(vis.span, "the visibility")
-            .help(&format!("you likely meant to define an item, e.g., `{vs} fn foo() {{}}`"))
-            .emit();
-    }
 
-    /// Error in-case a `default` was parsed but no item followed.
-    fn error_on_unmatched_defaultness(&self, def: Defaultness) {
-        if let Defaultness::Default(sp) = def {
-            self.struct_span_err(sp, "`default` is not followed by an item")
-                .span_label(sp, "the `default` qualifier")
-                .note("only `fn`, `const`, `type`, or `impl` items may be prefixed by `default`")
-                .emit();
+        if !attrs_allowed {
+            self.recover_attrs_no_item(&attrs)?;
         }
+        Ok(None)
     }
 
     /// Error in-case `default` was parsed in an in-appropriate context.
@@ -384,86 +380,72 @@ impl<'a> Parser<'a> {
         let sp = self.prev_token.span.between(self.token.span);
         let full_sp = self.prev_token.span.to(self.token.span);
         let ident_sp = self.token.span;
-        if self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace)) {
+
+        let ident = if self.look_ahead(1, |t| {
+            [
+                token::Lt,
+                token::OpenDelim(Delimiter::Brace),
+                token::OpenDelim(Delimiter::Parenthesis),
+            ]
+            .contains(&t.kind)
+        }) {
+            self.parse_ident().unwrap()
+        } else {
+            return Ok(());
+        };
+
+        let mut found_generics = false;
+        if self.check(&token::Lt) {
+            found_generics = true;
+            self.eat_to_tokens(&[&token::Gt]);
+            self.bump(); // `>`
+        }
+
+        let err = if self.check(&token::OpenDelim(Delimiter::Brace)) {
             // possible public struct definition where `struct` was forgotten
-            let ident = self.parse_ident().unwrap();
-            let msg = format!("add `struct` here to parse `{ident}` as a public struct");
-            let mut err = self.struct_span_err(sp, "missing `struct` for struct definition");
-            err.span_suggestion_short(
-                sp,
-                &msg,
-                " struct ",
-                Applicability::MaybeIncorrect, // speculative
-            );
-            Err(err)
-        } else if self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Parenthesis)) {
-            let ident = self.parse_ident().unwrap();
+            Some(MissingKeywordForItemDefinition::Struct { span: sp, ident })
+        } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
+            // possible public function or tuple struct definition where `fn`/`struct` was
+            // forgotten
             self.bump(); // `(`
-            let kw_name = self.recover_first_param();
+            let is_method = self.recover_self_param();
+
             self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::Yes);
-            let (kw, kw_name, ambiguous) = if self.check(&token::RArrow) {
+
+            let err = if self.check(&token::RArrow)
+                || self.check(&token::OpenDelim(Delimiter::Brace))
+            {
                 self.eat_to_tokens(&[&token::OpenDelim(Delimiter::Brace)]);
                 self.bump(); // `{`
-                ("fn", kw_name, false)
-            } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
-                self.bump(); // `{`
-                ("fn", kw_name, false)
-            } else if self.check(&token::Colon) {
-                let kw = "struct";
-                (kw, kw, false)
-            } else {
-                ("fn` or `struct", "function or struct", true)
-            };
-
-            let msg = format!("missing `{kw}` for {kw_name} definition");
-            let mut err = self.struct_span_err(sp, &msg);
-            if !ambiguous {
                 self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
-                let suggestion =
-                    format!("add `{kw}` here to parse `{ident}` as a public {kw_name}");
-                err.span_suggestion_short(
-                    sp,
-                    &suggestion,
-                    format!(" {kw} "),
-                    Applicability::MachineApplicable,
-                );
-            } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
-                err.span_suggestion(
-                    full_sp,
-                    "if you meant to call a macro, try",
-                    format!("{}!", snippet),
-                    // this is the `ambiguous` conditional branch
-                    Applicability::MaybeIncorrect,
-                );
-            } else {
-                err.help(
-                    "if you meant to call a macro, remove the `pub` \
-                              and add a trailing `!` after the identifier",
-                );
-            }
-            Err(err)
-        } else if self.look_ahead(1, |t| *t == token::Lt) {
-            let ident = self.parse_ident().unwrap();
-            self.eat_to_tokens(&[&token::Gt]);
-            self.bump(); // `>`
-            let (kw, kw_name, ambiguous) = if self.eat(&token::OpenDelim(Delimiter::Parenthesis)) {
-                ("fn", self.recover_first_param(), false)
-            } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
-                ("struct", "struct", false)
+                if is_method {
+                    MissingKeywordForItemDefinition::Method { span: sp, ident }
+                } else {
+                    MissingKeywordForItemDefinition::Function { span: sp, ident }
+                }
+            } else if self.check(&token::Semi) {
+                MissingKeywordForItemDefinition::Struct { span: sp, ident }
             } else {
-                ("fn` or `struct", "function or struct", true)
+                MissingKeywordForItemDefinition::Ambiguous {
+                    span: sp,
+                    subdiag: if found_generics {
+                        None
+                    } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
+                        Some(AmbiguousMissingKwForItemSub::SuggestMacro { span: full_sp, snippet })
+                    } else {
+                        Some(AmbiguousMissingKwForItemSub::HelpMacro)
+                    },
+                }
             };
-            let msg = format!("missing `{kw}` for {kw_name} definition");
-            let mut err = self.struct_span_err(sp, &msg);
-            if !ambiguous {
-                err.span_suggestion_short(
-                    sp,
-                    &format!("add `{kw}` here to parse `{ident}` as a public {kw_name}"),
-                    format!(" {} ", kw),
-                    Applicability::MachineApplicable,
-                );
-            }
-            Err(err)
+            Some(err)
+        } else if found_generics {
+            Some(MissingKeywordForItemDefinition::Ambiguous { span: sp, subdiag: None })
+        } else {
+            None
+        };
+
+        if let Some(err) = err {
+            Err(err.into_diagnostic(&self.sess.span_diagnostic))
         } else {
             Ok(())
         }
@@ -512,16 +494,13 @@ impl<'a> Parser<'a> {
         let mut err = self.struct_span_err(end.span, msg);
         if end.is_doc_comment() {
             err.span_label(end.span, "this doc comment doesn't document anything");
-        }
-        if end.meta_kind().is_some() {
-            if self.token.kind == TokenKind::Semi {
-                err.span_suggestion_verbose(
-                    self.token.span,
-                    "consider removing this semicolon",
-                    "",
-                    Applicability::MaybeIncorrect,
-                );
-            }
+        } else if self.token.kind == TokenKind::Semi {
+            err.span_suggestion_verbose(
+                self.token.span,
+                "consider removing this semicolon",
+                "",
+                Applicability::MaybeIncorrect,
+            );
         }
         if let [.., penultimate, _] = attrs {
             err.span_label(start.span.to(penultimate.span), "other attributes here");
@@ -588,20 +567,9 @@ impl<'a> Parser<'a> {
         let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
         {
             let span = self.prev_token.span.between(self.token.span);
-            self.struct_span_err(span, "missing trait in a trait impl")
-                .span_suggestion(
-                    span,
-                    "add a trait here",
-                    " Trait ",
-                    Applicability::HasPlaceholders,
-                )
-                .span_suggestion(
-                    span.to(self.token.span),
-                    "for an inherent impl, drop this `for`",
-                    "",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess
+                .emit_err(MissingTraitInTraitImpl { span, for_span: span.to(self.token.span) });
+
             P(Ty {
                 kind: TyKind::Path(None, err_path(span)),
                 span,
@@ -634,14 +602,7 @@ impl<'a> Parser<'a> {
             Some(ty_second) => {
                 // impl Trait for Type
                 if !has_for {
-                    self.struct_span_err(missing_for_span, "missing `for` in a trait impl")
-                        .span_suggestion_short(
-                            missing_for_span,
-                            "add `for` here",
-                            " for ",
-                            Applicability::MachineApplicable,
-                        )
-                        .emit();
+                    self.sess.emit_err(MissingForInTraitImpl { span: missing_for_span });
                 }
 
                 let ty_first = ty_first.into_inner();
@@ -649,7 +610,8 @@ impl<'a> Parser<'a> {
                     // This notably includes paths passed through `ty` macro fragments (#46438).
                     TyKind::Path(None, path) => path,
                     _ => {
-                        self.struct_span_err(ty_first.span, "expected a trait, found type").emit();
+                        self.sess
+                            .emit_err(ExpectedTraitInTraitImplFoundType { span: ty_first.span });
                         err_path(ty_first.span)
                     }
                 };
@@ -783,6 +745,7 @@ impl<'a> Parser<'a> {
     fn recover_doc_comment_before_brace(&mut self) -> bool {
         if let token::DocComment(..) = self.token.kind {
             if self.look_ahead(1, |tok| tok == &token::CloseDelim(Delimiter::Brace)) {
+                // FIXME: merge with `DocCommentDoesNotDocumentAnything` (E0585)
                 struct_span_err!(
                     self.diagnostic(),
                     self.token.span,
@@ -849,7 +812,7 @@ impl<'a> Parser<'a> {
             // It's a trait alias.
             if had_colon {
                 let span = span_at_colon.to(span_before_eq);
-                self.struct_span_err(span, "bounds are not allowed on trait aliases").emit();
+                self.sess.emit_err(BoundsNotAllowedOnTraitAliases { span });
             }
 
             let bounds = self.parse_generic_bounds(None)?;
@@ -858,12 +821,10 @@ impl<'a> Parser<'a> {
 
             let whole_span = lo.to(self.prev_token.span);
             if is_auto == IsAuto::Yes {
-                let msg = "trait aliases cannot be `auto`";
-                self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
+                self.sess.emit_err(TraitAliasCannotBeAuto { span: whole_span });
             }
             if let Unsafe::Yes(_) = unsafety {
-                let msg = "trait aliases cannot be `unsafe`";
-                self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
+                self.sess.emit_err(TraitAliasCannotBeUnsafe { span: whole_span });
             }
 
             self.sess.gated_spans.gate(sym::trait_alias, whole_span);
@@ -909,8 +870,7 @@ impl<'a> Parser<'a> {
                     Ok(kind) => kind,
                     Err(kind) => match kind {
                         ItemKind::Static(a, _, b) => {
-                            self.struct_span_err(span, "associated `static` items are not allowed")
-                                .emit();
+                            self.sess.emit_err(AssociatedStaticItemNotAllowed { span });
                             AssocItemKind::Const(Defaultness::Final, a, b)
                         }
                         _ => return self.error_bad_item_kind(span, &kind, "`trait`s or `impl`s"),
@@ -1084,41 +1044,37 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, Ident> {
-        let error_msg = "crate name using dashes are not valid in `extern crate` statements";
-        let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
-                              in the code";
-        let mut ident = if self.token.is_keyword(kw::SelfLower) {
+        let ident = if self.token.is_keyword(kw::SelfLower) {
             self.parse_path_segment_ident()
         } else {
             self.parse_ident()
         }?;
-        let mut idents = vec![];
-        let mut replacement = vec![];
-        let mut fixed_crate_name = false;
-        // Accept `extern crate name-like-this` for better diagnostics.
+
         let dash = token::BinOp(token::BinOpToken::Minus);
-        if self.token == dash {
-            // Do not include `-` as part of the expected tokens list.
-            while self.eat(&dash) {
-                fixed_crate_name = true;
-                replacement.push((self.prev_token.span, "_".to_string()));
-                idents.push(self.parse_ident()?);
-            }
+        if self.token != dash {
+            return Ok(ident);
         }
-        if fixed_crate_name {
-            let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
-            let mut fixed_name = ident.name.to_string();
-            for part in idents {
-                fixed_name.push_str(&format!("_{}", part.name));
-            }
-            ident = Ident::from_str_and_span(&fixed_name, fixed_name_sp);
 
-            self.struct_span_err(fixed_name_sp, error_msg)
-                .span_label(fixed_name_sp, "dash-separated idents are not valid")
-                .multipart_suggestion(suggestion_msg, replacement, Applicability::MachineApplicable)
-                .emit();
+        // Accept `extern crate name-like-this` for better diagnostics.
+        let mut dashes = vec![];
+        let mut idents = vec![];
+        while self.eat(&dash) {
+            dashes.push(self.prev_token.span);
+            idents.push(self.parse_ident()?);
         }
-        Ok(ident)
+
+        let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
+        let mut fixed_name = ident.name.to_string();
+        for part in idents {
+            write!(fixed_name, "_{}", part.name).unwrap();
+        }
+
+        self.sess.emit_err(ExternCrateNameWithDashes {
+            span: fixed_name_sp,
+            sugg: ExternCrateNameWithDashesSugg { dashes },
+        });
+
+        Ok(Ident::from_str_and_span(&fixed_name, fixed_name_sp))
     }
 
     /// Parses `extern` for foreign ABIs modules.
@@ -1166,7 +1122,10 @@ impl<'a> Parser<'a> {
                     Ok(kind) => kind,
                     Err(kind) => match kind {
                         ItemKind::Const(_, a, b) => {
-                            self.error_on_foreign_const(span, ident);
+                            self.sess.emit_err(ExternItemCannotBeConst {
+                                ident_span: ident.span,
+                                const_span: span.with_hi(ident.span.lo()),
+                            });
                             ForeignItemKind::Static(a, Mutability::Not, b)
                         }
                         _ => return self.error_bad_item_kind(span, &kind, "`extern` blocks"),
@@ -1178,6 +1137,7 @@ impl<'a> Parser<'a> {
     }
 
     fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &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}"))
@@ -1186,18 +1146,6 @@ impl<'a> Parser<'a> {
         None
     }
 
-    fn error_on_foreign_const(&self, span: Span, ident: Ident) {
-        self.struct_span_err(ident.span, "extern items cannot be `const`")
-            .span_suggestion(
-                span.with_hi(ident.span.lo()),
-                "try using a static value",
-                "static ",
-                Applicability::MachineApplicable,
-            )
-            .note("for more information, visit https://doc.rust-lang.org/std/keyword.extern.html")
-            .emit();
-    }
-
     fn is_unsafe_foreign_mod(&self) -> bool {
         self.token.is_keyword(kw::Unsafe)
             && self.is_keyword_ahead(1, &[kw::Extern])
@@ -1225,25 +1173,10 @@ impl<'a> Parser<'a> {
     fn recover_const_mut(&mut self, const_span: Span) {
         if self.eat_keyword(kw::Mut) {
             let span = self.prev_token.span;
-            self.struct_span_err(span, "const globals cannot be mutable")
-                .span_label(span, "cannot be mutable")
-                .span_suggestion(
-                    const_span,
-                    "you might want to declare a static instead",
-                    "static",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess.emit_err(ConstGlobalCannotBeMutable { ident_span: span, const_span });
         } else if self.eat_keyword(kw::Let) {
             let span = self.prev_token.span;
-            self.struct_span_err(const_span.to(span), "`const` and `let` are mutually exclusive")
-                .span_suggestion(
-                    const_span.to(span),
-                    "remove `let`",
-                    "const",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess.emit_err(ConstLetMutuallyExclusive { span: const_span.to(span) });
         }
     }
 
@@ -1328,13 +1261,8 @@ impl<'a> Parser<'a> {
         };
 
         let span = self.prev_token.span.shrink_to_hi();
-        let mut err = self.struct_span_err(span, &format!("missing type for `{kind}` item"));
-        err.span_suggestion(
-            span,
-            "provide a type for the item",
-            format!("{colon} <type>"),
-            Applicability::HasPlaceholders,
-        );
+        let err: DiagnosticBuilder<'_, ErrorGuaranteed> =
+            MissingConstType { span, colon, kind }.into_diagnostic(&self.sess.span_diagnostic);
         err.stash(span, StashKey::ItemNoType);
 
         // The user intended that the type be inferred,
@@ -1346,18 +1274,12 @@ impl<'a> Parser<'a> {
     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
         if self.token.is_keyword(kw::Struct) {
             let span = self.prev_token.span.to(self.token.span);
-            let mut err = self.struct_span_err(span, "`enum` and `struct` are mutually exclusive");
-            err.span_suggestion(
-                span,
-                "replace `enum struct` with",
-                "enum",
-                Applicability::MachineApplicable,
-            );
+            let err = EnumStructMutuallyExclusive { span };
             if self.look_ahead(1, |t| t.is_ident()) {
                 self.bump();
-                err.emit();
+                self.sess.emit_err(err);
             } else {
-                return Err(err);
+                return Err(err.into_diagnostic(&self.sess.span_diagnostic));
             }
         }
 
@@ -1493,13 +1415,8 @@ impl<'a> Parser<'a> {
             self.expect_semi()?;
             body
         } else {
-            let token_str = super::token_descr(&self.token);
-            let msg = &format!(
-                "expected `where`, `{{`, `(`, or `;` after struct 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 struct name");
-            return Err(err);
+            let err = UnexpectedTokenAfterStructName::new(self.token.span, self.token.clone());
+            return Err(err.into_diagnostic(&self.sess.span_diagnostic));
         };
 
         Ok((class_name, ItemKind::Struct(vdata, generics)))
@@ -2330,7 +2247,9 @@ impl<'a> Parser<'a> {
         let ext = self.parse_extern(case);
 
         if let Async::Yes { span, .. } = asyncness {
-            self.ban_async_in_2015(span);
+            if span.rust_2015() {
+                self.sess.emit_err(AsyncFnIn2015 { span, help: HelpUseLatestEdition::new() });
+            }
         }
 
         if !self.eat_keyword_case(kw::Fn, case) {
@@ -2440,17 +2359,6 @@ impl<'a> Parser<'a> {
         Ok(FnHeader { constness, unsafety, asyncness, ext })
     }
 
-    /// We are parsing `async fn`. If we are on Rust 2015, emit an error.
-    fn ban_async_in_2015(&self, span: Span) {
-        if span.rust_2015() {
-            let diag = self.diagnostic();
-            struct_span_err!(diag, span, E0670, "`async fn` is not permitted in Rust 2015")
-                .span_label(span, "to use `async fn`, switch to Rust 2018 or later")
-                .help_use_latest_edition()
-                .emit();
-        }
-    }
-
     /// Parses the parameter list and result type of a function declaration.
     pub(super) fn parse_fn_decl(
         &mut self,
@@ -2593,9 +2501,7 @@ impl<'a> Parser<'a> {
         };
         // Recover for the grammar `*self`, `*const self`, and `*mut self`.
         let recover_self_ptr = |this: &mut Self| {
-            let msg = "cannot pass `self` by raw pointer";
-            let span = this.token.span;
-            this.struct_span_err(span, msg).span_label(span, msg).emit();
+            self.sess.emit_err(SelfArgumentPointer { span: this.token.span });
 
             Ok((SelfKind::Value(Mutability::Not), expect_self_ident(this), this.prev_token.span))
         };
@@ -2676,14 +2582,14 @@ impl<'a> Parser<'a> {
             && self.look_ahead(offset + 1, |t| t == &token::Colon)
     }
 
-    fn recover_first_param(&mut self) -> &'static str {
+    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(_)) => "method",
-            _ => "function",
+            Ok(Some(_)) => true,
+            _ => false,
         }
     }
 }
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index 239ed79ce2f..7a4d53ed8bb 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -2,9 +2,11 @@ use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, NonterminalKind, Token};
 use rustc_ast::HasTokens;
 use rustc_ast_pretty::pprust;
+use rustc_errors::IntoDiagnostic;
 use rustc_errors::PResult;
 use rustc_span::symbol::{kw, Ident};
 
+use crate::errors::UnexpectedNonterminal;
 use crate::parser::pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 use crate::parser::{FollowedByType, ForceCollect, NtOrTt, Parser, PathStyle};
 
@@ -113,7 +115,8 @@ impl<'a> Parser<'a> {
             NonterminalKind::Item => match self.parse_item(ForceCollect::Yes)? {
                 Some(item) => token::NtItem(item),
                 None => {
-                    return Err(self.struct_span_err(self.token.span, "expected an item keyword"));
+                    return Err(UnexpectedNonterminal::Item(self.token.span)
+                               .into_diagnostic(&self.sess.span_diagnostic));
                 }
             },
             NonterminalKind::Block => {
@@ -124,7 +127,8 @@ impl<'a> Parser<'a> {
             NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
                 Some(s) => token::NtStmt(P(s)),
                 None => {
-                    return Err(self.struct_span_err(self.token.span, "expected a statement"));
+                    return Err(UnexpectedNonterminal::Statement(self.token.span)
+                               .into_diagnostic(&self.sess.span_diagnostic));
                 }
             },
             NonterminalKind::PatParam { .. } | NonterminalKind::PatWithOr { .. } => {
@@ -160,9 +164,10 @@ impl<'a> Parser<'a> {
                 token::NtIdent(ident, is_raw)
             }
             NonterminalKind::Ident => {
-                let token_str = pprust::token_to_string(&self.token);
-                let msg = &format!("expected ident, found {}", &token_str);
-                return Err(self.struct_span_err(self.token.span, msg));
+                return Err(UnexpectedNonterminal::Ident {
+                    span: self.token.span,
+                    token: self.token.clone(),
+                }.into_diagnostic(&self.sess.span_diagnostic));
             }
             NonterminalKind::Path => token::NtPath(
                 P(self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?),
@@ -175,9 +180,10 @@ impl<'a> Parser<'a> {
                 if self.check_lifetime() {
                     token::NtLifetime(self.expect_lifetime().ident)
                 } else {
-                    let token_str = pprust::token_to_string(&self.token);
-                    let msg = &format!("expected a lifetime, found `{}`", &token_str);
-                    return Err(self.struct_span_err(self.token.span, msg));
+                    return Err(UnexpectedNonterminal::Lifetime {
+                        span: self.token.span,
+                        token: self.token.clone(),
+                    }.into_diagnostic(&self.sess.span_diagnostic));
                 }
             }
         };
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 912f7cc14f6..88c75fd81e7 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,6 +1,12 @@
 use super::{ForceCollect, Parser, PathStyle, TrailingToken};
 use crate::errors::{
-    InclusiveRangeExtraEquals, InclusiveRangeMatchArrow, InclusiveRangeNoEnd, RemoveLet,
+    AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
+    DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
+    ExpectedCommaAfterPatternField, InclusiveRangeExtraEquals, InclusiveRangeMatchArrow,
+    InclusiveRangeNoEnd, InvalidMutInPattern, PatternOnWrongSideOfAt, RefMutOrderIncorrect,
+    RemoveLet, RepeatedMutInPattern, TopLevelOrPatternNotAllowed, TopLevelOrPatternNotAllowedSugg,
+    TrailingVertNotAllowed, UnexpectedLifetimeInPattern, UnexpectedVertVertBeforeFunctionParam,
+    UnexpectedVertVertInPattern,
 };
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
@@ -11,15 +17,33 @@ use rustc_ast::{
     PatField, PatKind, Path, QSelf, RangeEnd, RangeSyntax,
 };
 use rustc_ast_pretty::pprust;
-use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
+use rustc_errors::{
+    fluent, Applicability, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
+};
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::{respan, Span, Spanned};
 use rustc_span::symbol::{kw, sym, Ident};
 
-pub(super) type Expected = Option<&'static str>;
+#[derive(PartialEq, Copy, Clone)]
+pub enum Expected {
+    ParameterName,
+    ArgumentName,
+    Identifier,
+    BindingPattern,
+}
 
-/// `Expected` for function and lambda parameter patterns.
-pub(super) const PARAM_EXPECTED: Expected = Some("parameter name");
+impl Expected {
+    // FIXME(#100717): migrate users of this to proper localization
+    fn to_string_or_fallback(expected: Option<Expected>) -> &'static str {
+        match expected {
+            Some(Expected::ParameterName) => "parameter name",
+            Some(Expected::ArgumentName) => "argument name",
+            Some(Expected::Identifier) => "identifier",
+            Some(Expected::BindingPattern) => "binding pattern",
+            None => "pattern",
+        }
+    }
+}
 
 const WHILE_PARSING_OR_MSG: &str = "while parsing this or-pattern starting here";
 
@@ -56,13 +80,19 @@ enum EatOrResult {
     None,
 }
 
+/// The syntax location of a given pattern. Used for diagnostics.
+pub(super) enum PatternLocation {
+    LetBinding,
+    FunctionParameter,
+}
+
 impl<'a> Parser<'a> {
     /// Parses a pattern.
     ///
     /// Corresponds to `pat<no_top_alt>` in RFC 2535 and does not admit or-patterns
     /// at the top level. Used when parsing the parameters of lambda expressions,
     /// functions, function pointers, and `pat` macro fragments.
-    pub fn parse_pat_no_top_alt(&mut self, expected: Expected) -> PResult<'a, P<Pat>> {
+    pub fn parse_pat_no_top_alt(&mut self, expected: Option<Expected>) -> PResult<'a, P<Pat>> {
         self.parse_pat_with_range_pat(true, expected)
     }
 
@@ -76,7 +106,7 @@ impl<'a> Parser<'a> {
     /// simplify the grammar somewhat.
     pub fn parse_pat_allow_top_alt(
         &mut self,
-        expected: Expected,
+        expected: Option<Expected>,
         rc: RecoverComma,
         ra: RecoverColon,
         rt: CommaRecoveryMode,
@@ -88,7 +118,7 @@ impl<'a> Parser<'a> {
     /// recovered).
     fn parse_pat_allow_top_alt_inner(
         &mut self,
-        expected: Expected,
+        expected: Option<Expected>,
         rc: RecoverComma,
         ra: RecoverColon,
         rt: CommaRecoveryMode,
@@ -168,9 +198,9 @@ impl<'a> Parser<'a> {
     /// otherwise).
     pub(super) fn parse_pat_before_ty(
         &mut self,
-        expected: Expected,
+        expected: Option<Expected>,
         rc: RecoverComma,
-        syntax_loc: &str,
+        syntax_loc: PatternLocation,
     ) -> PResult<'a, (P<Pat>, bool)> {
         // We use `parse_pat_allow_top_alt` regardless of whether we actually want top-level
         // or-patterns so that we can detect when a user tries to use it. This allows us to print a
@@ -184,27 +214,41 @@ impl<'a> Parser<'a> {
         let colon = self.eat(&token::Colon);
 
         if let PatKind::Or(pats) = &pat.kind {
-            let msg = format!("top-level or-patterns are not allowed in {}", syntax_loc);
-            let (help, fix) = if pats.len() == 1 {
-                // If all we have is a leading vert, then print a special message. This is the case
-                // if `parse_pat_allow_top_alt` returns an or-pattern with one variant.
-                let msg = "remove the `|`";
-                let fix = pprust::pat_to_string(&pat);
-                (msg, fix)
-            } else {
-                let msg = "wrap the pattern in parentheses";
-                let fix = format!("({})", pprust::pat_to_string(&pat));
-                (msg, fix)
-            };
+            let span = pat.span;
 
             if trailing_vert {
                 // We already emitted an error and suggestion to remove the trailing vert. Don't
                 // emit again.
-                self.sess.span_diagnostic.delay_span_bug(pat.span, &msg);
+
+                // FIXME(#100717): pass `TopLevelOrPatternNotAllowed::* { sub: None }` to
+                // `delay_span_bug()` instead of fluent message
+                self.sess.span_diagnostic.delay_span_bug(
+                    span,
+                    match syntax_loc {
+                        PatternLocation::LetBinding => {
+                            fluent::parse_or_pattern_not_allowed_in_let_binding
+                        }
+                        PatternLocation::FunctionParameter => {
+                            fluent::parse_or_pattern_not_allowed_in_fn_parameters
+                        }
+                    },
+                );
             } else {
-                self.struct_span_err(pat.span, &msg)
-                    .span_suggestion(pat.span, help, fix, Applicability::MachineApplicable)
-                    .emit();
+                let pat = pprust::pat_to_string(&pat);
+                let sub = if pats.len() == 1 {
+                    Some(TopLevelOrPatternNotAllowedSugg::RemoveLeadingVert { span, pat })
+                } else {
+                    Some(TopLevelOrPatternNotAllowedSugg::WrapInParens { span, pat })
+                };
+
+                self.sess.emit_err(match syntax_loc {
+                    PatternLocation::LetBinding => {
+                        TopLevelOrPatternNotAllowed::LetBinding { span, sub }
+                    }
+                    PatternLocation::FunctionParameter => {
+                        TopLevelOrPatternNotAllowed::FunctionParameter { span, sub }
+                    }
+                });
             }
         }
 
@@ -221,15 +265,15 @@ impl<'a> Parser<'a> {
         // a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
         // separately.
         if let token::OrOr = self.token.kind {
-            let span = self.token.span;
-            let mut err = self.struct_span_err(span, "unexpected `||` before function parameter");
-            err.span_suggestion(span, "remove the `||`", "", Applicability::MachineApplicable);
-            err.note("alternatives in or-patterns are separated with `|`, not `||`");
-            err.emit();
+            self.sess.emit_err(UnexpectedVertVertBeforeFunctionParam { span: self.token.span });
             self.bump();
         }
 
-        self.parse_pat_before_ty(PARAM_EXPECTED, RecoverComma::No, "function parameters")
+        self.parse_pat_before_ty(
+            Some(Expected::ParameterName),
+            RecoverComma::No,
+            PatternLocation::FunctionParameter,
+        )
     }
 
     /// Eat the or-pattern `|` separator.
@@ -239,7 +283,7 @@ impl<'a> Parser<'a> {
             EatOrResult::TrailingVert
         } else if matches!(self.token.kind, token::OrOr) {
             // Found `||`; Recover and pretend we parsed `|`.
-            self.ban_unexpected_or_or(lo);
+            self.sess.emit_err(UnexpectedVertVertInPattern { span: self.token.span, start: lo });
             self.bump();
             EatOrResult::AteOr
         } else if self.eat(&token::BinOp(token::Or)) {
@@ -273,7 +317,13 @@ impl<'a> Parser<'a> {
         });
         match (is_end_ahead, &self.token.kind) {
             (true, token::BinOp(token::Or) | token::OrOr) => {
-                self.ban_illegal_vert(lo, "trailing", "not allowed in an or-pattern");
+                // A `|` or possibly `||` token shouldn't be here. Ban it.
+                self.sess.emit_err(TrailingVertNotAllowed {
+                    span: self.token.span,
+                    start: lo,
+                    token: self.token.clone(),
+                    note_double_vert: matches!(self.token.kind, token::OrOr).then_some(()),
+                });
                 self.bump();
                 true
             }
@@ -281,46 +331,12 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// We have parsed `||` instead of `|`. Error and suggest `|` instead.
-    fn ban_unexpected_or_or(&mut self, lo: Option<Span>) {
-        let mut err = self.struct_span_err(self.token.span, "unexpected token `||` in pattern");
-        err.span_suggestion(
-            self.token.span,
-            "use a single `|` to separate multiple alternative patterns",
-            "|",
-            Applicability::MachineApplicable,
-        );
-        if let Some(lo) = lo {
-            err.span_label(lo, WHILE_PARSING_OR_MSG);
-        }
-        err.emit();
-    }
-
-    /// A `|` or possibly `||` token shouldn't be here. Ban it.
-    fn ban_illegal_vert(&mut self, lo: Option<Span>, pos: &str, ctx: &str) {
-        let span = self.token.span;
-        let mut err = self.struct_span_err(span, &format!("a {} `|` is {}", pos, ctx));
-        err.span_suggestion(
-            span,
-            &format!("remove the `{}`", pprust::token_to_string(&self.token)),
-            "",
-            Applicability::MachineApplicable,
-        );
-        if let Some(lo) = lo {
-            err.span_label(lo, WHILE_PARSING_OR_MSG);
-        }
-        if let token::OrOr = self.token.kind {
-            err.note("alternatives in or-patterns are separated with `|`, not `||`");
-        }
-        err.emit();
-    }
-
     /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
     /// allowed).
     fn parse_pat_with_range_pat(
         &mut self,
         allow_range_pat: bool,
-        expected: Expected,
+        expected: Option<Expected>,
     ) -> PResult<'a, P<Pat>> {
         maybe_recover_from_interpolated_ty_qpath!(self, true);
         maybe_whole!(self, NtPat, |x| x);
@@ -416,7 +432,7 @@ impl<'a> Parser<'a> {
             let lt = self.expect_lifetime();
             let (lit, _) =
                 self.recover_unclosed_char(lt.ident, Parser::mk_token_lit_char, |self_| {
-                    let expected = expected.unwrap_or("pattern");
+                    let expected = Expected::to_string_or_fallback(expected);
                     let msg = format!(
                         "expected {}, found {}",
                         expected,
@@ -457,15 +473,7 @@ impl<'a> Parser<'a> {
         self.bump(); // `...`
 
         // The user probably mistook `...` for a rest pattern `..`.
-        self.struct_span_err(lo, "unexpected `...`")
-            .span_label(lo, "not a valid pattern")
-            .span_suggestion_short(
-                lo,
-                "for a rest pattern, use `..` instead of `...`",
-                "..",
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(DotDotDotRestPattern { span: lo });
         PatKind::Rest
     }
 
@@ -490,7 +498,7 @@ impl<'a> Parser<'a> {
         // At this point we attempt to parse `@ $pat_rhs` and emit an error.
         self.bump(); // `@`
         let mut rhs = self.parse_pat_no_top_alt(None)?;
-        let sp = lhs.span.to(rhs.span);
+        let whole_span = lhs.span.to(rhs.span);
 
         if let PatKind::Ident(_, _, sub @ None) = &mut rhs.kind {
             // The user inverted the order, so help them fix that.
@@ -499,27 +507,23 @@ impl<'a> Parser<'a> {
             // The RHS is now the full pattern.
             *sub = Some(lhs);
 
-            self.struct_span_err(sp, "pattern on wrong side of `@`")
-                .span_label(lhs_span, "pattern on the left, should be on the right")
-                .span_label(rhs.span, "binding on the right, should be on the left")
-                .span_suggestion(
-                    sp,
-                    "switch the order",
-                    pprust::pat_to_string(&rhs),
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(PatternOnWrongSideOfAt {
+                whole_span,
+                whole_pat: pprust::pat_to_string(&rhs),
+                pattern: lhs_span,
+                binding: rhs.span,
+            });
         } else {
             // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
             rhs.kind = PatKind::Wild;
-            self.struct_span_err(sp, "left-hand side of `@` must be a binding")
-                .span_label(lhs.span, "interpreted as a pattern, not a binding")
-                .span_label(rhs.span, "also a pattern")
-                .note("bindings are `x`, `mut x`, `ref x`, and `ref mut x`")
-                .emit();
+            self.sess.emit_err(ExpectedBindingLeftOfAt {
+                whole_span,
+                lhs: lhs.span,
+                rhs: rhs.span,
+            });
         }
 
-        rhs.span = sp;
+        rhs.span = whole_span;
         Ok(rhs)
     }
 
@@ -534,35 +538,23 @@ impl<'a> Parser<'a> {
             _ => return,
         }
 
-        self.struct_span_err(pat.span, "the range pattern here has ambiguous interpretation")
-            .span_suggestion(
-                pat.span,
-                "add parentheses to clarify the precedence",
-                format!("({})", pprust::pat_to_string(&pat)),
-                // "ambiguous interpretation" implies that we have to be guessing
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+        self.sess
+            .emit_err(AmbiguousRangePattern { span: pat.span, pat: pprust::pat_to_string(&pat) });
     }
 
     /// Parse `&pat` / `&mut pat`.
-    fn parse_pat_deref(&mut self, expected: Expected) -> PResult<'a, PatKind> {
+    fn parse_pat_deref(&mut self, expected: Option<Expected>) -> PResult<'a, PatKind> {
         self.expect_and()?;
-        self.recover_lifetime_in_deref_pat();
-        let mutbl = self.parse_mutability();
-        let subpat = self.parse_pat_with_range_pat(false, expected)?;
-        Ok(PatKind::Ref(subpat, mutbl))
-    }
-
-    fn recover_lifetime_in_deref_pat(&mut self) {
         if let token::Lifetime(name) = self.token.kind {
             self.bump(); // `'a`
 
-            let span = self.prev_token.span;
-            self.struct_span_err(span, &format!("unexpected lifetime `{}` in pattern", name))
-                .span_suggestion(span, "remove the lifetime", "", Applicability::MachineApplicable)
-                .emit();
+            self.sess
+                .emit_err(UnexpectedLifetimeInPattern { span: self.prev_token.span, symbol: name });
         }
+
+        let mutbl = self.parse_mutability();
+        let subpat = self.parse_pat_with_range_pat(false, expected)?;
+        Ok(PatKind::Ref(subpat, mutbl))
     }
 
     /// Parse a tuple or parenthesis pattern.
@@ -590,7 +582,8 @@ impl<'a> Parser<'a> {
         let mut_span = self.prev_token.span;
 
         if self.eat_keyword(kw::Ref) {
-            return self.recover_mut_ref_ident(mut_span);
+            self.sess.emit_err(RefMutOrderIncorrect { span: mut_span.to(self.prev_token.span) });
+            return self.parse_pat_ident(BindingAnnotation::REF_MUT);
         }
 
         self.recover_additional_muts();
@@ -603,7 +596,7 @@ impl<'a> Parser<'a> {
         }
 
         // Parse the pattern we hope to be an identifier.
-        let mut pat = self.parse_pat_no_top_alt(Some("identifier"))?;
+        let mut pat = self.parse_pat_no_top_alt(Some(Expected::Identifier))?;
 
         // If we don't have `mut $ident (@ pat)?`, error.
         if let PatKind::Ident(BindingAnnotation(ByRef::No, m @ Mutability::Not), ..) = &mut pat.kind
@@ -620,22 +613,6 @@ impl<'a> Parser<'a> {
         Ok(pat.into_inner().kind)
     }
 
-    /// Recover on `mut ref? ident @ pat` and suggest
-    /// that the order of `mut` and `ref` is incorrect.
-    fn recover_mut_ref_ident(&mut self, lo: Span) -> PResult<'a, PatKind> {
-        let mutref_span = lo.to(self.prev_token.span);
-        self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
-            .span_suggestion(
-                mutref_span,
-                "try switching the order",
-                "ref mut",
-                Applicability::MachineApplicable,
-            )
-            .emit();
-
-        self.parse_pat_ident(BindingAnnotation::REF_MUT)
-    }
-
     /// Turn all by-value immutable bindings in a pattern into mutable bindings.
     /// Returns `true` if any change was made.
     fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
@@ -660,16 +637,13 @@ impl<'a> Parser<'a> {
     /// Error on `mut $pat` where `$pat` is not an ident.
     fn ban_mut_general_pat(&self, lo: Span, pat: &Pat, changed_any_binding: bool) {
         let span = lo.to(pat.span);
-        let fix = pprust::pat_to_string(&pat);
-        let (problem, suggestion) = if changed_any_binding {
-            ("`mut` must be attached to each individual binding", "add `mut` to each binding")
+        let pat = pprust::pat_to_string(&pat);
+
+        self.sess.emit_err(if changed_any_binding {
+            InvalidMutInPattern::NestedIdent { span, pat }
         } else {
-            ("`mut` must be followed by a named binding", "remove the `mut` prefix")
-        };
-        self.struct_span_err(span, problem)
-            .span_suggestion(span, suggestion, fix, Applicability::MachineApplicable)
-            .note("`mut` may be followed by `variable` and `variable @ pattern`")
-            .emit();
+            InvalidMutInPattern::NonIdent { span, pat }
+        });
     }
 
     /// Eat any extraneous `mut`s and error + recover if we ate any.
@@ -680,15 +654,7 @@ impl<'a> Parser<'a> {
             return;
         }
 
-        let span = lo.to(self.prev_token.span);
-        self.struct_span_err(span, "`mut` on a binding may not be repeated")
-            .span_suggestion(
-                span,
-                "remove the additional `mut`s",
-                "",
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(RepeatedMutInPattern { span: lo.to(self.prev_token.span) });
     }
 
     /// Parse macro invocation
@@ -702,11 +668,11 @@ impl<'a> Parser<'a> {
     fn fatal_unexpected_non_pat(
         &mut self,
         err: DiagnosticBuilder<'a, ErrorGuaranteed>,
-        expected: Expected,
+        expected: Option<Expected>,
     ) -> PResult<'a, P<Pat>> {
         err.cancel();
 
-        let expected = expected.unwrap_or("pattern");
+        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);
@@ -774,28 +740,18 @@ impl<'a> Parser<'a> {
                     let _ = self.parse_pat_range_end().map_err(|e| e.cancel());
                 }
 
-                self.error_inclusive_range_with_extra_equals(span_with_eq);
+                self.sess.emit_err(InclusiveRangeExtraEquals { span: span_with_eq });
             }
             token::Gt if no_space => {
-                self.error_inclusive_range_match_arrow(span);
+                let after_pat = span.with_hi(span.hi() - rustc_span::BytePos(1)).shrink_to_hi();
+                self.sess.emit_err(InclusiveRangeMatchArrow { span, after_pat });
+            }
+            _ => {
+                self.sess.emit_err(InclusiveRangeNoEnd { span });
             }
-            _ => self.error_inclusive_range_with_no_end(span),
         }
     }
 
-    fn error_inclusive_range_with_extra_equals(&self, span: Span) {
-        self.sess.emit_err(InclusiveRangeExtraEquals { span });
-    }
-
-    fn error_inclusive_range_match_arrow(&self, span: Span) {
-        let after_pat = span.with_hi(span.hi() - rustc_span::BytePos(1)).shrink_to_hi();
-        self.sess.emit_err(InclusiveRangeMatchArrow { span, after_pat });
-    }
-
-    fn error_inclusive_range_with_no_end(&self, span: Span) {
-        self.sess.emit_err(InclusiveRangeNoEnd { span });
-    }
-
     /// Parse a range-to pattern, `..X` or `..=X` where `X` remains to be parsed.
     ///
     /// The form `...X` is prohibited to reduce confusion with the potential
@@ -804,14 +760,7 @@ impl<'a> Parser<'a> {
         let end = self.parse_pat_range_end()?;
         if let RangeEnd::Included(syn @ RangeSyntax::DotDotDot) = &mut re.node {
             *syn = RangeSyntax::DotDotEq;
-            self.struct_span_err(re.span, "range-to patterns with `...` are not allowed")
-                .span_suggestion_short(
-                    re.span,
-                    "use `..=` instead",
-                    "..=",
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(DotDotDotRangeToPatternNotAllowed { span: re.span });
         }
         Ok(PatKind::Range(None, Some(end), re))
     }
@@ -876,7 +825,7 @@ impl<'a> Parser<'a> {
     fn parse_pat_ident(&mut self, binding_annotation: BindingAnnotation) -> PResult<'a, PatKind> {
         let ident = self.parse_ident()?;
         let sub = if self.eat(&token::At) {
-            Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
+            Some(self.parse_pat_no_top_alt(Some(Expected::BindingPattern))?)
         } else {
             None
         };
@@ -887,8 +836,8 @@ impl<'a> Parser<'a> {
         // binding mode then we do not end up here, because the lookahead
         // will direct us over to `parse_enum_variant()`.
         if self.token == token::OpenDelim(Delimiter::Parenthesis) {
-            return Err(self
-                .struct_span_err(self.prev_token.span, "expected identifier, found enum pattern"));
+            return Err(EnumPatternInsteadOfIdentifier { span: self.prev_token.span }
+                .into_diagnostic(&self.sess.span_diagnostic));
         }
 
         Ok(PatKind::Ident(binding_annotation, ident, sub))
@@ -970,7 +919,7 @@ impl<'a> Parser<'a> {
             // We cannot use `parse_pat_ident()` since it will complain `box`
             // is not an identifier.
             let sub = if self.eat(&token::At) {
-                Some(self.parse_pat_no_top_alt(Some("binding pattern"))?)
+                Some(self.parse_pat_no_top_alt(Some(Expected::BindingPattern))?)
             } else {
                 None
             };
@@ -1005,7 +954,8 @@ impl<'a> Parser<'a> {
 
             // check that a comma comes after every field
             if !ate_comma {
-                let err = self.struct_span_err(self.token.span, "expected `,`");
+                let err = ExpectedCommaAfterPatternField { span: self.token.span }
+                    .into_diagnostic(&self.sess.span_diagnostic);
                 if let Some(mut delayed) = delayed_err {
                     delayed.emit();
                 }
@@ -1118,14 +1068,7 @@ impl<'a> Parser<'a> {
             return;
         }
 
-        self.struct_span_err(self.token.span, "expected field pattern, found `...`")
-            .span_suggestion(
-                self.token.span,
-                "to omit remaining fields, use one fewer `.`",
-                "..",
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(DotDotDotForRemainingFields { span: self.token.span });
     }
 
     fn parse_pat_field(&mut self, lo: Span, attrs: AttrVec) -> PResult<'a, PatField> {
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 58c7a398f14..647639b9b62 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -1,7 +1,7 @@
 use super::attr::InnerAttrForbiddenReason;
 use super::diagnostics::AttemptLocalParseRecovery;
 use super::expr::LhsExpr;
-use super::pat::RecoverComma;
+use super::pat::{PatternLocation, RecoverComma};
 use super::path::PathStyle;
 use super::TrailingToken;
 use super::{
@@ -275,7 +275,8 @@ impl<'a> Parser<'a> {
         }
 
         self.report_invalid_identifier_error()?;
-        let (pat, colon) = self.parse_pat_before_ty(None, RecoverComma::Yes, "`let` bindings")?;
+        let (pat, colon) =
+            self.parse_pat_before_ty(None, RecoverComma::Yes, PatternLocation::LetBinding)?;
 
         let (err, ty) = if colon {
             // Save the state of the parser before parsing type normally, in case there is a `:`
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 8b4f0ab8feb..306cbcff149 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -1,6 +1,12 @@
 use super::{Parser, PathStyle, TokenType};
 
-use crate::errors::{ExpectedFnPathFoundFnKeyword, FnPtrWithGenerics, FnPtrWithGenericsSugg};
+use crate::errors::{
+    DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
+    FnPointerCannotBeAsync, FnPointerCannotBeConst, FnPtrWithGenerics, FnPtrWithGenericsSugg,
+    InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime,
+    NegativeBoundsNotSupported, NegativeBoundsNotSupportedSugg, NestedCVariadicType,
+    ReturnTypesUseThinArrow,
+};
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 
 use ast::DUMMY_NODE_ID;
@@ -12,7 +18,7 @@ use rustc_ast::{
     MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax, Ty, TyKind,
 };
 use rustc_ast_pretty::pprust;
-use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
+use rustc_errors::{Applicability, PResult};
 use rustc_span::source_map::Span;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Symbol;
@@ -233,14 +239,7 @@ impl<'a> Parser<'a> {
             // Don't `eat` to prevent `=>` from being added as an expected token which isn't
             // actually expected and could only confuse users
             self.bump();
-            self.struct_span_err(self.prev_token.span, "return types are denoted using `->`")
-                .span_suggestion_short(
-                    self.prev_token.span,
-                    "use `->` instead",
-                    "->",
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(ReturnTypesUseThinArrow { span: self.prev_token.span });
             let ty = self.parse_ty_common(
                 allow_plus,
                 AllowCVariadic::No,
@@ -328,7 +327,7 @@ impl<'a> Parser<'a> {
                 AllowCVariadic::No => {
                     // FIXME(Centril): Should we just allow `...` syntactically
                     // anywhere in a type and use semantic restrictions instead?
-                    self.error_illegal_c_varadic_ty(lo);
+                    self.sess.emit_err(NestedCVariadicType { span: lo.to(self.prev_token.span) });
                     TyKind::Err
                 }
             }
@@ -431,8 +430,7 @@ impl<'a> Parser<'a> {
         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)?;
         if lt_no_plus {
-            self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`")
-                .emit();
+            self.sess.emit_err(NeedPlusAfterTraitObjectLifetime { span: lo });
         }
         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
     }
@@ -466,14 +464,10 @@ impl<'a> Parser<'a> {
     fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
             let span = self.prev_token.span;
-            self.struct_span_err(span, "expected `mut` or `const` keyword in raw pointer type")
-                .span_suggestions(
-                    span.shrink_to_hi(),
-                    "add `mut` or `const` here",
-                    ["mut ".to_string(), "const ".to_string()],
-                    Applicability::HasPlaceholders,
-                )
-                .emit();
+            self.sess.emit_err(ExpectedMutOrConstInRawPointerType {
+                span,
+                after_asterisk: span.shrink_to_hi(),
+            });
             Mutability::Not
         });
         let ty = self.parse_ty_no_plus()?;
@@ -528,16 +522,13 @@ impl<'a> Parser<'a> {
                 let lifetime_span = self.token.span;
                 let span = and_span.to(lifetime_span);
 
-                let mut err = self.struct_span_err(span, "lifetime must precede `mut`");
-                if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
-                    err.span_suggestion(
-                        span,
-                        "place the lifetime before `mut`",
-                        format!("&{} mut", lifetime_src),
-                        Applicability::MaybeIncorrect,
-                    );
-                }
-                err.emit();
+                let (suggest_lifetime, snippet) =
+                    if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
+                        (Some(span), lifetime_src)
+                    } else {
+                        (None, String::new())
+                    };
+                self.sess.emit_err(LifetimeAfterMut { span, suggest_lifetime, snippet });
 
                 opt_lifetime = Some(self.expect_lifetime());
             }
@@ -547,14 +538,7 @@ impl<'a> Parser<'a> {
         {
             // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
             let span = and_span.to(self.look_ahead(1, |t| t.span));
-            let mut err = self.struct_span_err(span, "`mut` must precede `dyn`");
-            err.span_suggestion(
-                span,
-                "place `mut` before `dyn`",
-                "&mut dyn",
-                Applicability::MachineApplicable,
-            );
-            err.emit();
+            self.sess.emit_err(DynAfterMut { span });
 
             // Recovery
             mutbl = Mutability::Mut;
@@ -608,10 +592,10 @@ impl<'a> Parser<'a> {
             // If we ever start to allow `const fn()`, then update
             // feature gating for `#![feature(const_extern_fn)]` to
             // cover it.
-            self.error_fn_ptr_bad_qualifier(whole_span, span, "const");
+            self.sess.emit_err(FnPointerCannotBeConst { span: whole_span, qualifier: span });
         }
         if let ast::Async::Yes { span, .. } = asyncness {
-            self.error_fn_ptr_bad_qualifier(whole_span, span, "async");
+            self.sess.emit_err(FnPointerCannotBeAsync { span: whole_span, qualifier: span });
         }
         let decl_span = span_start.to(self.token.span);
         Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl, decl_span })))
@@ -659,19 +643,6 @@ impl<'a> Parser<'a> {
         Ok(())
     }
 
-    /// Emit an error for the given bad function pointer qualifier.
-    fn error_fn_ptr_bad_qualifier(&self, span: Span, qual_span: Span, qual: &str) {
-        self.struct_span_err(span, &format!("an `fn` pointer type cannot be `{}`", qual))
-            .span_label(qual_span, format!("`{}` because of this", qual))
-            .span_suggestion_short(
-                qual_span,
-                &format!("remove the `{}` qualifier", qual),
-                "",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
-    }
-
     /// Parses an `impl B0 + ... + Bn` type.
     fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
         // Always parse bounds greedily for better error recovery.
@@ -758,16 +729,6 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn error_illegal_c_varadic_ty(&self, lo: Span) {
-        struct_span_err!(
-            self.sess.span_diagnostic,
-            lo.to(self.prev_token.span),
-            E0743,
-            "C-variadic type `...` may not be nested inside another type",
-        )
-        .emit();
-    }
-
     pub(super) fn parse_generic_bounds(
         &mut self,
         colon_span: Option<Span>,
@@ -797,15 +758,7 @@ impl<'a> Parser<'a> {
         {
             if self.token.is_keyword(kw::Dyn) {
                 // Account for `&dyn Trait + dyn Other`.
-                self.struct_span_err(self.token.span, "invalid `dyn` keyword")
-                    .help("`dyn` is only needed at the start of a trait `+`-separated list")
-                    .span_suggestion(
-                        self.token.span,
-                        "remove this keyword",
-                        "",
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
+                self.sess.emit_err(InvalidDynKeyword { span: self.token.span });
                 self.bump();
             }
             match self.parse_generic_bound()? {
@@ -842,11 +795,7 @@ impl<'a> Parser<'a> {
         bounds: &[GenericBound],
         negative_bounds: Vec<Span>,
     ) {
-        let negative_bounds_len = negative_bounds.len();
-        let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
-        let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
-        err.span_label(last_span, "negative bounds are not supported");
-        if let Some(bound_list) = colon_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() {
@@ -857,14 +806,18 @@ impl<'a> Parser<'a> {
                 }
                 new_bound_list = new_bound_list.replacen(" +", ":", 1);
             }
-            err.tool_only_span_suggestion(
+
+            Some(NegativeBoundsNotSupportedSugg {
                 bound_list,
-                &format!("remove the bound{}", pluralize!(negative_bounds_len)),
-                new_bound_list,
-                Applicability::MachineApplicable,
-            );
-        }
-        err.emit();
+                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 });
     }
 
     /// Parses a bound according to the grammar: