13 files changed, 2251 insertions, 1723 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
new file mode 100644
index 00000000000..98fee997427
--- /dev/null
+++ b/compiler/rustc_parse/src/errors.rs
@@ -0,0 +1,1251 @@
+use rustc_ast::token::Token;
+use rustc_ast::Path;
+use rustc_errors::{fluent, AddToDiagnostic, Applicability, EmissionGuarantee, IntoDiagnostic};
+use rustc_macros::{Diagnostic, Subdiagnostic};
+use rustc_session::errors::ExprParenthesesNeeded;
+use rustc_span::symbol::Ident;
+use rustc_span::{Span, Symbol};
+
+use crate::parser::TokenDescription;
+
+#[derive(Diagnostic)]
+#[diag(parser::maybe_report_ambiguous_plus)]
+pub(crate) struct AmbiguousPlus {
+    pub sum_ty: String,
+    #[primary_span]
+    #[suggestion(code = "({sum_ty})")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::maybe_recover_from_bad_type_plus, code = "E0178")]
+pub(crate) struct BadTypePlus {
+    pub ty: String,
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: BadTypePlusSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum BadTypePlusSub {
+    #[suggestion(
+        parser::add_paren,
+        code = "{sum_with_parens}",
+        applicability = "machine-applicable"
+    )]
+    AddParen {
+        sum_with_parens: String,
+        #[primary_span]
+        span: Span,
+    },
+    #[label(parser::forgot_paren)]
+    ForgotParen {
+        #[primary_span]
+        span: Span,
+    },
+    #[label(parser::expect_path)]
+    ExpectPath {
+        #[primary_span]
+        span: Span,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::maybe_recover_from_bad_qpath_stage_2)]
+pub(crate) struct BadQPathStage2 {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "maybe-incorrect")]
+    pub span: Span,
+    pub ty: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::incorrect_semicolon)]
+pub(crate) struct IncorrectSemicolon<'a> {
+    #[primary_span]
+    #[suggestion_short(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    #[help]
+    pub opt_help: Option<()>,
+    pub name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::incorrect_use_of_await)]
+pub(crate) struct IncorrectUseOfAwait {
+    #[primary_span]
+    #[suggestion(parser::parentheses_suggestion, code = "", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::incorrect_use_of_await)]
+pub(crate) struct IncorrectAwait {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(parser::postfix_suggestion, code = "{expr}.await{question_mark}")]
+    pub sugg_span: (Span, Applicability),
+    pub expr: String,
+    pub question_mark: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::in_in_typo)]
+pub(crate) struct InInTypo {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub sugg_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_variable_declaration)]
+pub(crate) struct InvalidVariableDeclaration {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: InvalidVariableDeclarationSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum InvalidVariableDeclarationSub {
+    #[suggestion(
+        parser::switch_mut_let_order,
+        applicability = "maybe-incorrect",
+        code = "let mut"
+    )]
+    SwitchMutLetOrder(#[primary_span] Span),
+    #[suggestion(
+        parser::missing_let_before_mut,
+        applicability = "machine-applicable",
+        code = "let mut"
+    )]
+    MissingLet(#[primary_span] Span),
+    #[suggestion(parser::use_let_not_auto, applicability = "machine-applicable", code = "let")]
+    UseLetNotAuto(#[primary_span] Span),
+    #[suggestion(parser::use_let_not_var, applicability = "machine-applicable", code = "let")]
+    UseLetNotVar(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_comparison_operator)]
+pub(crate) struct InvalidComparisonOperator {
+    #[primary_span]
+    pub span: Span,
+    pub invalid: String,
+    #[subdiagnostic]
+    pub sub: InvalidComparisonOperatorSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum InvalidComparisonOperatorSub {
+    #[suggestion_short(
+        parser::use_instead,
+        applicability = "machine-applicable",
+        code = "{correct}"
+    )]
+    Correctable {
+        #[primary_span]
+        span: Span,
+        invalid: String,
+        correct: String,
+    },
+    #[label(parser::spaceship_operator_invalid)]
+    Spaceship(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_logical_operator)]
+#[note]
+pub(crate) struct InvalidLogicalOperator {
+    #[primary_span]
+    pub span: Span,
+    pub incorrect: String,
+    #[subdiagnostic]
+    pub sub: InvalidLogicalOperatorSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum InvalidLogicalOperatorSub {
+    #[suggestion_short(
+        parser::use_amp_amp_for_conjunction,
+        applicability = "machine-applicable",
+        code = "&&"
+    )]
+    Conjunction(#[primary_span] Span),
+    #[suggestion_short(
+        parser::use_pipe_pipe_for_disjunction,
+        applicability = "machine-applicable",
+        code = "||"
+    )]
+    Disjunction(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::tilde_is_not_unary_operator)]
+pub(crate) struct TildeAsUnaryOperator(
+    #[primary_span]
+    #[suggestion_short(applicability = "machine-applicable", code = "!")]
+    pub Span,
+);
+
+#[derive(Diagnostic)]
+#[diag(parser::unexpected_token_after_not)]
+pub(crate) struct NotAsNegationOperator {
+    #[primary_span]
+    pub negated: Span,
+    pub negated_desc: String,
+    #[subdiagnostic]
+    pub sub: NotAsNegationOperatorSub,
+}
+
+#[derive(Subdiagnostic)]
+pub enum NotAsNegationOperatorSub {
+    #[suggestion_short(
+        parser::unexpected_token_after_not_default,
+        applicability = "machine-applicable",
+        code = "!"
+    )]
+    SuggestNotDefault(#[primary_span] Span),
+
+    #[suggestion_short(
+        parser::unexpected_token_after_not_bitwise,
+        applicability = "machine-applicable",
+        code = "!"
+    )]
+    SuggestNotBitwise(#[primary_span] Span),
+
+    #[suggestion_short(
+        parser::unexpected_token_after_not_logical,
+        applicability = "machine-applicable",
+        code = "!"
+    )]
+    SuggestNotLogical(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::malformed_loop_label)]
+pub(crate) struct MalformedLoopLabel {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "{correct_label}")]
+    pub span: Span,
+    pub correct_label: Ident,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::lifetime_in_borrow_expression)]
+pub(crate) struct LifetimeInBorrowExpression {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    #[label]
+    pub lifetime_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::field_expression_with_generic)]
+pub(crate) struct FieldExpressionWithGeneric(#[primary_span] pub Span);
+
+#[derive(Diagnostic)]
+#[diag(parser::macro_invocation_with_qualified_path)]
+pub(crate) struct MacroInvocationWithQualifiedPath(#[primary_span] pub Span);
+
+#[derive(Diagnostic)]
+#[diag(parser::unexpected_token_after_label)]
+pub(crate) struct UnexpectedTokenAfterLabel {
+    #[primary_span]
+    #[label(parser::unexpected_token_after_label)]
+    pub span: Span,
+    #[suggestion_verbose(parser::suggestion_remove_label, code = "")]
+    pub remove_label: Option<Span>,
+    #[subdiagnostic]
+    pub enclose_in_block: Option<UnexpectedTokenAfterLabelSugg>,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion_enclose_in_block, applicability = "machine-applicable")]
+pub(crate) struct UnexpectedTokenAfterLabelSugg {
+    #[suggestion_part(code = "{{ ")]
+    pub left: Span,
+    #[suggestion_part(code = " }}")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::require_colon_after_labeled_expression)]
+#[note]
+pub(crate) struct RequireColonAfterLabeledExpression {
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub label: Span,
+    #[suggestion_short(applicability = "machine-applicable", code = ": ")]
+    pub label_end: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::do_catch_syntax_removed)]
+#[note]
+pub(crate) struct DoCatchSyntaxRemoved {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "try")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::float_literal_requires_integer_part)]
+pub(crate) struct FloatLiteralRequiresIntegerPart {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "{correct}")]
+    pub span: Span,
+    pub correct: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_int_literal_width)]
+#[help]
+pub(crate) struct InvalidIntLiteralWidth {
+    #[primary_span]
+    pub span: Span,
+    pub width: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_num_literal_base_prefix)]
+#[note]
+pub(crate) struct InvalidNumLiteralBasePrefix {
+    #[primary_span]
+    #[suggestion(applicability = "maybe-incorrect", code = "{fixed}")]
+    pub span: Span,
+    pub fixed: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_num_literal_suffix)]
+#[help]
+pub(crate) struct InvalidNumLiteralSuffix {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub suffix: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_float_literal_width)]
+#[help]
+pub(crate) struct InvalidFloatLiteralWidth {
+    #[primary_span]
+    pub span: Span,
+    pub width: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_float_literal_suffix)]
+#[help]
+pub(crate) struct InvalidFloatLiteralSuffix {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub suffix: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::int_literal_too_large)]
+pub(crate) struct IntLiteralTooLarge {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::missing_semicolon_before_array)]
+pub(crate) struct MissingSemicolonBeforeArray {
+    #[primary_span]
+    pub open_delim: Span,
+    #[suggestion_verbose(applicability = "maybe-incorrect", code = ";")]
+    pub semicolon: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_block_macro_segment)]
+pub(crate) struct InvalidBlockMacroSegment {
+    #[primary_span]
+    pub span: Span,
+    #[label]
+    pub context: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::if_expression_missing_then_block)]
+pub(crate) struct IfExpressionMissingThenBlock {
+    #[primary_span]
+    pub if_span: Span,
+    #[subdiagnostic]
+    pub sub: IfExpressionMissingThenBlockSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum IfExpressionMissingThenBlockSub {
+    #[help(parser::condition_possibly_unfinished)]
+    UnfinishedCondition(#[primary_span] Span),
+    #[help(parser::add_then_block)]
+    AddThenBlock(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::if_expression_missing_condition)]
+pub(crate) struct IfExpressionMissingCondition {
+    #[primary_span]
+    #[label(parser::condition_label)]
+    pub if_span: Span,
+    #[label(parser::block_label)]
+    pub block_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::expected_expression_found_let)]
+pub(crate) struct ExpectedExpressionFoundLet {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::expected_else_block)]
+pub(crate) struct ExpectedElseBlock {
+    #[primary_span]
+    pub first_tok_span: Span,
+    pub first_tok: String,
+    #[label]
+    pub else_span: Span,
+    #[suggestion(applicability = "maybe-incorrect", code = "if ")]
+    pub condition_start: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::outer_attribute_not_allowed_on_if_else)]
+pub(crate) struct OuterAttributeNotAllowedOnIfElse {
+    #[primary_span]
+    pub last: Span,
+
+    #[label(parser::branch_label)]
+    pub branch_span: Span,
+
+    #[label(parser::ctx_label)]
+    pub ctx_span: Span,
+    pub ctx: String,
+
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    pub attributes: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::missing_in_in_for_loop)]
+pub(crate) struct MissingInInForLoop {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: MissingInInForLoopSub,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum MissingInInForLoopSub {
+    // Has been misleading, at least in the past (closed Issue #48492), thus maybe-incorrect
+    #[suggestion_short(parser::use_in_not_of, applicability = "maybe-incorrect", code = "in")]
+    InNotOf(#[primary_span] Span),
+    #[suggestion_short(parser::add_in, applicability = "maybe-incorrect", code = " in ")]
+    AddIn(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::missing_comma_after_match_arm)]
+pub(crate) struct MissingCommaAfterMatchArm {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = ",")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::catch_after_try)]
+#[help]
+pub(crate) struct CatchAfterTry {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::comma_after_base_struct)]
+#[note]
+pub(crate) struct CommaAfterBaseStruct {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion_short(applicability = "machine-applicable", code = "")]
+    pub comma: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::eq_field_init)]
+pub(crate) struct EqFieldInit {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(applicability = "machine-applicable", code = ":")]
+    pub eq: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::dotdotdot)]
+pub(crate) struct DotDotDot {
+    #[primary_span]
+    #[suggestion(parser::suggest_exclusive_range, applicability = "maybe-incorrect", code = "..")]
+    #[suggestion(parser::suggest_inclusive_range, applicability = "maybe-incorrect", code = "..=")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::left_arrow_operator)]
+pub(crate) struct LeftArrowOperator {
+    #[primary_span]
+    #[suggestion(applicability = "maybe-incorrect", code = "< -")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::remove_let)]
+pub(crate) struct RemoveLet {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::use_eq_instead)]
+pub(crate) struct UseEqInstead {
+    #[primary_span]
+    #[suggestion_short(applicability = "machine-applicable", code = "=")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::use_empty_block_not_semi)]
+pub(crate) struct UseEmptyBlockNotSemi {
+    #[primary_span]
+    #[suggestion_hidden(applicability = "machine-applicable", code = "{{}}")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::comparison_interpreted_as_generic)]
+pub(crate) struct ComparisonInterpretedAsGeneric {
+    #[primary_span]
+    #[label(parser::label_comparison)]
+    pub comparison: Span,
+    pub r#type: Path,
+    #[label(parser::label_args)]
+    pub args: Span,
+    #[subdiagnostic]
+    pub suggestion: ComparisonOrShiftInterpretedAsGenericSugg,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::shift_interpreted_as_generic)]
+pub(crate) struct ShiftInterpretedAsGeneric {
+    #[primary_span]
+    #[label(parser::label_comparison)]
+    pub shift: Span,
+    pub r#type: Path,
+    #[label(parser::label_args)]
+    pub args: Span,
+    #[subdiagnostic]
+    pub suggestion: ComparisonOrShiftInterpretedAsGenericSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct ComparisonOrShiftInterpretedAsGenericSugg {
+    #[suggestion_part(code = "(")]
+    pub left: Span,
+    #[suggestion_part(code = ")")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::found_expr_would_be_stmt)]
+pub(crate) struct FoundExprWouldBeStmt {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub token: Token,
+    #[subdiagnostic]
+    pub suggestion: ExprParenthesesNeeded,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::leading_plus_not_supported)]
+pub(crate) struct LeadingPlusNotSupported {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[suggestion_verbose(
+        parser::suggestion_remove_plus,
+        code = "",
+        applicability = "machine-applicable"
+    )]
+    pub remove_plus: Option<Span>,
+    #[subdiagnostic]
+    pub add_parentheses: Option<ExprParenthesesNeeded>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::parentheses_with_struct_fields)]
+pub(crate) struct ParenthesesWithStructFields {
+    #[primary_span]
+    pub span: Span,
+    pub r#type: Path,
+    #[subdiagnostic]
+    pub braces_for_struct: BracesForStructLiteral,
+    #[subdiagnostic]
+    pub no_fields_for_fn: NoFieldsForFnCall,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion_braces_for_struct, applicability = "maybe-incorrect")]
+pub(crate) struct BracesForStructLiteral {
+    #[suggestion_part(code = " {{ ")]
+    pub first: Span,
+    #[suggestion_part(code = " }}")]
+    pub second: Span,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion_no_fields_for_fn, applicability = "maybe-incorrect")]
+pub(crate) struct NoFieldsForFnCall {
+    #[suggestion_part(code = "")]
+    pub fields: Vec<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::labeled_loop_in_break)]
+pub(crate) struct LabeledLoopInBreak {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: WrapExpressionInParentheses,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(
+    parser::sugg_wrap_expression_in_parentheses,
+    applicability = "machine-applicable"
+)]
+pub(crate) struct WrapExpressionInParentheses {
+    #[suggestion_part(code = "(")]
+    pub left: Span,
+    #[suggestion_part(code = ")")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::array_brackets_instead_of_braces)]
+pub(crate) struct ArrayBracketsInsteadOfSpaces {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: ArrayBracketsInsteadOfSpacesSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "maybe-incorrect")]
+pub(crate) struct ArrayBracketsInsteadOfSpacesSugg {
+    #[suggestion_part(code = "[")]
+    pub left: Span,
+    #[suggestion_part(code = "]")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::match_arm_body_without_braces)]
+pub(crate) struct MatchArmBodyWithoutBraces {
+    #[primary_span]
+    #[label(parser::label_statements)]
+    pub statements: Span,
+    #[label(parser::label_arrow)]
+    pub arrow: Span,
+    pub num_statements: usize,
+    #[subdiagnostic]
+    pub sub: MatchArmBodyWithoutBracesSugg,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum MatchArmBodyWithoutBracesSugg {
+    #[multipart_suggestion(parser::suggestion_add_braces, applicability = "machine-applicable")]
+    AddBraces {
+        #[suggestion_part(code = "{{ ")]
+        left: Span,
+        #[suggestion_part(code = " }}")]
+        right: Span,
+    },
+    #[suggestion(
+        parser::suggestion_use_comma_not_semicolon,
+        code = ",",
+        applicability = "machine-applicable"
+    )]
+    UseComma {
+        #[primary_span]
+        semicolon: Span,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::struct_literal_not_allowed_here)]
+pub(crate) struct StructLiteralNotAllowedHere {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: StructLiteralNotAllowedHereSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct StructLiteralNotAllowedHereSugg {
+    #[suggestion_part(code = "(")]
+    pub left: Span,
+    #[suggestion_part(code = ")")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_interpolated_expression)]
+pub(crate) struct InvalidInterpolatedExpression {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::hexadecimal_float_literal_not_supported)]
+pub(crate) struct HexadecimalFloatLiteralNotSupported {
+    #[primary_span]
+    #[label(parser::not_supported)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::octal_float_literal_not_supported)]
+pub(crate) struct OctalFloatLiteralNotSupported {
+    #[primary_span]
+    #[label(parser::not_supported)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::binary_float_literal_not_supported)]
+pub(crate) struct BinaryFloatLiteralNotSupported {
+    #[primary_span]
+    #[label(parser::not_supported)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_literal_suffix)]
+pub(crate) struct InvalidLiteralSuffix {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    // FIXME(#100717)
+    pub kind: String,
+    pub suffix: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_literal_suffix_on_tuple_index)]
+pub(crate) struct InvalidLiteralSuffixOnTupleIndex {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub suffix: Symbol,
+    #[help(parser::tuple_exception_line_1)]
+    #[help(parser::tuple_exception_line_2)]
+    #[help(parser::tuple_exception_line_3)]
+    pub exception: Option<()>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::non_string_abi_literal)]
+pub(crate) struct NonStringAbiLiteral {
+    #[primary_span]
+    #[suggestion(code = "\"C\"", applicability = "maybe-incorrect")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::mismatched_closing_delimiter)]
+pub(crate) struct MismatchedClosingDelimiter {
+    #[primary_span]
+    pub spans: Vec<Span>,
+    pub delimiter: String,
+    #[label(parser::label_unmatched)]
+    pub unmatched: Span,
+    #[label(parser::label_opening_candidate)]
+    pub opening_candidate: Option<Span>,
+    #[label(parser::label_unclosed)]
+    pub unclosed: Option<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::incorrect_visibility_restriction, code = "E0704")]
+#[help]
+pub(crate) struct IncorrectVisibilityRestriction {
+    #[primary_span]
+    #[suggestion(code = "in {inner_str}", applicability = "machine-applicable")]
+    pub span: Span,
+    pub inner_str: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::assignment_else_not_allowed)]
+pub(crate) struct AssignmentElseNotAllowed {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::expected_statement_after_outer_attr)]
+pub(crate) struct ExpectedStatementAfterOuterAttr {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::doc_comment_does_not_document_anything, code = "E0585")]
+#[help]
+pub(crate) struct DocCommentDoesNotDocumentAnything {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = ",", applicability = "machine-applicable")]
+    pub missing_comma: Option<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::const_let_mutually_exclusive)]
+pub(crate) struct ConstLetMutuallyExclusive {
+    #[primary_span]
+    #[suggestion(code = "const", applicability = "maybe-incorrect")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_expression_in_let_else)]
+pub(crate) struct InvalidExpressionInLetElse {
+    #[primary_span]
+    pub span: Span,
+    pub operator: &'static str,
+    #[subdiagnostic]
+    pub sugg: WrapExpressionInParentheses,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_curly_in_let_else)]
+pub(crate) struct InvalidCurlyInLetElse {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: WrapExpressionInParentheses,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::compound_assignment_expression_in_let)]
+#[help]
+pub(crate) struct CompoundAssignmentExpressionInLet {
+    #[primary_span]
+    #[suggestion_short(code = "=", applicability = "maybe-incorrect")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::suffixed_literal_in_attribute)]
+#[help]
+pub(crate) struct SuffixedLiteralInAttribute {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::invalid_meta_item)]
+pub(crate) struct InvalidMetaItem {
+    #[primary_span]
+    pub span: Span,
+    pub token: Token,
+}
+
+#[derive(Subdiagnostic)]
+#[suggestion_verbose(
+    parser::sugg_escape_to_use_as_identifier,
+    applicability = "maybe-incorrect",
+    code = "r#"
+)]
+pub(crate) struct SuggEscapeToUseAsIdentifier {
+    #[primary_span]
+    pub span: Span,
+    pub ident_name: String,
+}
+
+#[derive(Subdiagnostic)]
+#[suggestion(parser::sugg_remove_comma, applicability = "machine-applicable", code = "")]
+pub(crate) struct SuggRemoveComma {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum ExpectedIdentifierFound {
+    #[label(parser::expected_identifier_found_reserved_identifier)]
+    ReservedIdentifier(#[primary_span] Span),
+    #[label(parser::expected_identifier_found_keyword)]
+    Keyword(#[primary_span] Span),
+    #[label(parser::expected_identifier_found_reserved_keyword)]
+    ReservedKeyword(#[primary_span] Span),
+    #[label(parser::expected_identifier_found_doc_comment)]
+    DocComment(#[primary_span] Span),
+    #[label(parser::expected_identifier)]
+    Other(#[primary_span] Span),
+}
+
+impl ExpectedIdentifierFound {
+    pub fn new(token_descr: Option<TokenDescription>, span: Span) -> Self {
+        (match token_descr {
+            Some(TokenDescription::ReservedIdentifier) => {
+                ExpectedIdentifierFound::ReservedIdentifier
+            }
+            Some(TokenDescription::Keyword) => ExpectedIdentifierFound::Keyword,
+            Some(TokenDescription::ReservedKeyword) => ExpectedIdentifierFound::ReservedKeyword,
+            Some(TokenDescription::DocComment) => ExpectedIdentifierFound::DocComment,
+            None => ExpectedIdentifierFound::Other,
+        })(span)
+    }
+}
+
+pub(crate) struct ExpectedIdentifier {
+    pub span: Span,
+    pub token: Token,
+    pub suggest_raw: Option<SuggEscapeToUseAsIdentifier>,
+    pub suggest_remove_comma: Option<SuggRemoveComma>,
+}
+
+impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedIdentifier {
+    fn into_diagnostic(
+        self,
+        handler: &'a rustc_errors::Handler,
+    ) -> rustc_errors::DiagnosticBuilder<'a, G> {
+        let token_descr = super::parser::TokenDescription::from_token(&self.token);
+
+        let mut diag = handler.struct_diagnostic(match token_descr {
+            Some(TokenDescription::ReservedIdentifier) => {
+                fluent::parser::expected_identifier_found_reserved_identifier_str
+            }
+            Some(TokenDescription::Keyword) => {
+                fluent::parser::expected_identifier_found_keyword_str
+            }
+            Some(TokenDescription::ReservedKeyword) => {
+                fluent::parser::expected_identifier_found_reserved_keyword_str
+            }
+            Some(TokenDescription::DocComment) => {
+                fluent::parser::expected_identifier_found_doc_comment_str
+            }
+            None => fluent::parser::expected_identifier_found_str,
+        });
+        diag.set_span(self.span);
+        diag.set_arg("token", self.token);
+
+        if let Some(sugg) = self.suggest_raw {
+            sugg.add_to_diagnostic(&mut diag);
+        }
+
+        ExpectedIdentifierFound::new(token_descr, self.span).add_to_diagnostic(&mut diag);
+
+        if let Some(sugg) = self.suggest_remove_comma {
+            sugg.add_to_diagnostic(&mut diag);
+        }
+
+        diag
+    }
+}
+
+pub(crate) struct ExpectedSemi {
+    pub span: Span,
+    pub token: Token,
+
+    pub unexpected_token_label: Option<Span>,
+    pub sugg: ExpectedSemiSugg,
+}
+
+impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for ExpectedSemi {
+    fn into_diagnostic(
+        self,
+        handler: &'a rustc_errors::Handler,
+    ) -> rustc_errors::DiagnosticBuilder<'a, G> {
+        let token_descr = super::parser::TokenDescription::from_token(&self.token);
+
+        let mut diag = handler.struct_diagnostic(match token_descr {
+            Some(TokenDescription::ReservedIdentifier) => {
+                fluent::parser::expected_semi_found_reserved_identifier_str
+            }
+            Some(TokenDescription::Keyword) => fluent::parser::expected_semi_found_keyword_str,
+            Some(TokenDescription::ReservedKeyword) => {
+                fluent::parser::expected_semi_found_reserved_keyword_str
+            }
+            Some(TokenDescription::DocComment) => {
+                fluent::parser::expected_semi_found_doc_comment_str
+            }
+            None => fluent::parser::expected_semi_found_str,
+        });
+        diag.set_span(self.span);
+        diag.set_arg("token", self.token);
+
+        if let Some(unexpected_token_label) = self.unexpected_token_label {
+            diag.span_label(unexpected_token_label, fluent::parser::label_unexpected_token);
+        }
+
+        self.sugg.add_to_diagnostic(&mut diag);
+
+        diag
+    }
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum ExpectedSemiSugg {
+    #[suggestion(
+        parser::sugg_change_this_to_semi,
+        code = ";",
+        applicability = "machine-applicable"
+    )]
+    ChangeToSemi(#[primary_span] Span),
+    #[suggestion_short(parser::sugg_add_semi, code = ";", applicability = "machine-applicable")]
+    AddSemi(#[primary_span] Span),
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::struct_literal_body_without_path)]
+pub(crate) struct StructLiteralBodyWithoutPath {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: StructLiteralBodyWithoutPathSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "has-placeholders")]
+pub(crate) struct StructLiteralBodyWithoutPathSugg {
+    #[suggestion_part(code = "{{ SomeStruct ")]
+    pub before: Span,
+    #[suggestion_part(code = " }}")]
+    pub after: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::unmatched_angle_brackets)]
+pub(crate) struct UnmatchedAngleBrackets {
+    #[primary_span]
+    #[suggestion(code = "", applicability = "machine-applicable")]
+    pub span: Span,
+    pub num_extra_brackets: usize,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::generic_parameters_without_angle_brackets)]
+pub(crate) struct GenericParamsWithoutAngleBrackets {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: GenericParamsWithoutAngleBracketsSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct GenericParamsWithoutAngleBracketsSugg {
+    #[suggestion_part(code = "<")]
+    pub left: Span,
+    #[suggestion_part(code = ">")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::comparison_operators_cannot_be_chained)]
+pub(crate) struct ComparisonOperatorsCannotBeChained {
+    #[primary_span]
+    pub span: Vec<Span>,
+    #[suggestion_verbose(
+        parser::sugg_turbofish_syntax,
+        code = "::",
+        applicability = "maybe-incorrect"
+    )]
+    pub suggest_turbofish: Option<Span>,
+    #[help(parser::sugg_turbofish_syntax)]
+    #[help(parser::sugg_parentheses_for_function_args)]
+    pub help_turbofish: Option<()>,
+    #[subdiagnostic]
+    pub chaining_sugg: Option<ComparisonOperatorsCannotBeChainedSugg>,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum ComparisonOperatorsCannotBeChainedSugg {
+    #[suggestion_verbose(
+        parser::sugg_split_comparison,
+        code = " && {middle_term}",
+        applicability = "maybe-incorrect"
+    )]
+    SplitComparison {
+        #[primary_span]
+        span: Span,
+        middle_term: String,
+    },
+    #[multipart_suggestion(parser::sugg_parenthesize, applicability = "maybe-incorrect")]
+    Parenthesize {
+        #[suggestion_part(code = "(")]
+        left: Span,
+        #[suggestion_part(code = ")")]
+        right: Span,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::question_mark_in_type)]
+pub(crate) struct QuestionMarkInType {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: QuestionMarkInTypeSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct QuestionMarkInTypeSugg {
+    #[suggestion_part(code = "Option<")]
+    pub left: Span,
+    #[suggestion_part(code = ">")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::unexpected_parentheses_in_for_head)]
+pub(crate) struct ParenthesesInForHead {
+    #[primary_span]
+    pub span: Vec<Span>,
+    #[subdiagnostic]
+    pub sugg: ParenthesesInForHeadSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct ParenthesesInForHeadSugg {
+    #[suggestion_part(code = "")]
+    pub left: Span,
+    #[suggestion_part(code = "")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::doc_comment_on_param_type)]
+pub(crate) struct DocCommentOnParamType {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::attribute_on_param_type)]
+pub(crate) struct AttributeOnParamType {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::pattern_method_param_without_body, code = "E0642")]
+pub(crate) struct PatternMethodParamWithoutBody {
+    #[primary_span]
+    #[suggestion(code = "_", applicability = "machine-applicable")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::self_param_not_first)]
+pub(crate) struct SelfParamNotFirst {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::const_generic_without_braces)]
+pub(crate) struct ConstGenericWithoutBraces {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: ConstGenericWithoutBracesSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+pub(crate) struct ConstGenericWithoutBracesSugg {
+    #[suggestion_part(code = "{{ ")]
+    pub left: Span,
+    #[suggestion_part(code = " }}")]
+    pub right: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::unexpected_const_param_declaration)]
+pub(crate) struct UnexpectedConstParamDeclaration {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: Option<UnexpectedConstParamDeclarationSugg>,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum UnexpectedConstParamDeclarationSugg {
+    #[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+    AddParam {
+        #[suggestion_part(code = "<{snippet}>")]
+        impl_generics: Span,
+        #[suggestion_part(code = "{ident}")]
+        incorrect_decl: Span,
+        snippet: String,
+        ident: String,
+    },
+    #[multipart_suggestion(parser::suggestion, applicability = "machine-applicable")]
+    AppendParam {
+        #[suggestion_part(code = ", {snippet}")]
+        impl_generics_end: Span,
+        #[suggestion_part(code = "{ident}")]
+        incorrect_decl: Span,
+        snippet: String,
+        ident: String,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::unexpected_const_in_generic_param)]
+pub(crate) struct UnexpectedConstInGenericParam {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion_verbose(code = "", applicability = "maybe-incorrect")]
+    pub to_remove: Option<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::async_move_order_incorrect)]
+pub(crate) struct AsyncMoveOrderIncorrect {
+    #[primary_span]
+    #[suggestion_verbose(code = "async move", applicability = "maybe-incorrect")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parser::double_colon_in_bound)]
+pub(crate) struct DoubleColonInBound {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(code = ": ", applicability = "machine-applicable")]
+    pub between: Span,
+}
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 63819a2f98d..88540e13ef2 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -1,10 +1,11 @@
 use crate::lexer::unicode_chars::UNICODE_ARRAY;
 use rustc_ast::ast::{self, AttrStyle};
 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
-use rustc_ast::tokenstream::{Spacing, TokenStream};
+use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
 use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
 use rustc_lexer::unescape::{self, Mode};
+use rustc_lexer::Cursor;
 use rustc_lexer::{Base, DocStyle, RawStrError};
 use rustc_session::lint::builtin::{
     RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX, TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
@@ -38,11 +39,20 @@ pub struct UnmatchedBrace {
 
 pub(crate) fn parse_token_trees<'a>(
     sess: &'a ParseSess,
-    src: &'a str,
-    start_pos: BytePos,
+    mut src: &'a str,
+    mut start_pos: BytePos,
     override_span: Option<Span>,
 ) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
-    StringReader { sess, start_pos, pos: start_pos, src, override_span }.into_token_trees()
+    // Skip `#!`, if present.
+    if let Some(shebang_len) = rustc_lexer::strip_shebang(src) {
+        src = &src[shebang_len..];
+        start_pos = start_pos + BytePos::from_usize(shebang_len);
+    }
+
+    let cursor = Cursor::new(src);
+    let string_reader =
+        StringReader { sess, start_pos, pos: start_pos, src, cursor, override_span };
+    tokentrees::TokenTreesReader::parse_all_token_trees(string_reader)
 }
 
 struct StringReader<'a> {
@@ -53,6 +63,8 @@ struct StringReader<'a> {
     pos: BytePos,
     /// Source text to tokenize.
     src: &'a str,
+    /// Cursor for getting lexer tokens.
+    cursor: Cursor<'a>,
     override_span: Option<Span>,
 }
 
@@ -61,42 +73,195 @@ impl<'a> StringReader<'a> {
         self.override_span.unwrap_or_else(|| Span::with_root_ctxt(lo, hi))
     }
 
-    /// Returns the next token, and info about preceding whitespace, if any.
-    fn next_token(&mut self) -> (Spacing, Token) {
-        let mut spacing = Spacing::Joint;
-
-        // Skip `#!` at the start of the file
-        if self.pos == self.start_pos
-            && let Some(shebang_len) = rustc_lexer::strip_shebang(self.src)
-        {
-            self.pos = self.pos + BytePos::from_usize(shebang_len);
-            spacing = Spacing::Alone;
-        }
+    /// Returns the next token, paired with a bool indicating if the token was
+    /// preceded by whitespace.
+    fn next_token(&mut self) -> (Token, bool) {
+        let mut preceded_by_whitespace = false;
 
         // Skip trivial (whitespace & comments) tokens
         loop {
-            let start_src_index = self.src_index(self.pos);
-            let text: &str = &self.src[start_src_index..];
-
-            if text.is_empty() {
-                let span = self.mk_sp(self.pos, self.pos);
-                return (spacing, Token::new(token::Eof, span));
-            }
-
-            let token = rustc_lexer::first_token(text);
-
+            let token = self.cursor.advance_token();
             let start = self.pos;
             self.pos = self.pos + BytePos(token.len);
 
             debug!("next_token: {:?}({:?})", token.kind, self.str_from(start));
 
-            match self.cook_lexer_token(token.kind, start) {
-                Some(kind) => {
+            // Now "cook" the token, converting the simple `rustc_lexer::TokenKind` enum into a
+            // rich `rustc_ast::TokenKind`. This turns strings into interned symbols and runs
+            // additional validation.
+            let kind = match token.kind {
+                rustc_lexer::TokenKind::LineComment { doc_style } => {
+                    // Skip non-doc comments
+                    let Some(doc_style) = doc_style else {
+                        self.lint_unicode_text_flow(start);
+                        preceded_by_whitespace = true;
+                        continue;
+                    };
+
+                    // Opening delimiter of the length 3 is not included into the symbol.
+                    let content_start = start + BytePos(3);
+                    let content = self.str_from(content_start);
+                    self.cook_doc_comment(content_start, content, CommentKind::Line, doc_style)
+                }
+                rustc_lexer::TokenKind::BlockComment { doc_style, terminated } => {
+                    if !terminated {
+                        self.report_unterminated_block_comment(start, doc_style);
+                    }
+
+                    // Skip non-doc comments
+                    let Some(doc_style) = doc_style else {
+                        self.lint_unicode_text_flow(start);
+                        preceded_by_whitespace = true;
+                        continue;
+                    };
+
+                    // Opening delimiter of the length 3 and closing delimiter of the length 2
+                    // are not included into the symbol.
+                    let content_start = start + BytePos(3);
+                    let content_end = self.pos - BytePos(if terminated { 2 } else { 0 });
+                    let content = self.str_from_to(content_start, content_end);
+                    self.cook_doc_comment(content_start, content, CommentKind::Block, doc_style)
+                }
+                rustc_lexer::TokenKind::Whitespace => {
+                    preceded_by_whitespace = true;
+                    continue;
+                }
+                rustc_lexer::TokenKind::Ident => {
+                    let sym = nfc_normalize(self.str_from(start));
                     let span = self.mk_sp(start, self.pos);
-                    return (spacing, Token::new(kind, span));
+                    self.sess.symbol_gallery.insert(sym, span);
+                    token::Ident(sym, false)
                 }
-                None => spacing = Spacing::Alone,
-            }
+                rustc_lexer::TokenKind::RawIdent => {
+                    let sym = nfc_normalize(self.str_from(start + BytePos(2)));
+                    let span = self.mk_sp(start, self.pos);
+                    self.sess.symbol_gallery.insert(sym, span);
+                    if !sym.can_be_raw() {
+                        self.err_span(span, &format!("`{}` cannot be a raw identifier", sym));
+                    }
+                    self.sess.raw_identifier_spans.borrow_mut().push(span);
+                    token::Ident(sym, true)
+                }
+                rustc_lexer::TokenKind::UnknownPrefix => {
+                    self.report_unknown_prefix(start);
+                    let sym = nfc_normalize(self.str_from(start));
+                    let span = self.mk_sp(start, self.pos);
+                    self.sess.symbol_gallery.insert(sym, span);
+                    token::Ident(sym, false)
+                }
+                rustc_lexer::TokenKind::InvalidIdent
+                    // Do not recover an identifier with emoji if the codepoint is a confusable
+                    // with a recoverable substitution token, like `➖`.
+                    if !UNICODE_ARRAY
+                        .iter()
+                        .any(|&(c, _, _)| {
+                            let sym = self.str_from(start);
+                            sym.chars().count() == 1 && c == sym.chars().next().unwrap()
+                        }) =>
+                {
+                    let sym = nfc_normalize(self.str_from(start));
+                    let span = self.mk_sp(start, self.pos);
+                    self.sess.bad_unicode_identifiers.borrow_mut().entry(sym).or_default()
+                        .push(span);
+                    token::Ident(sym, false)
+                }
+                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);
+                    let suffix = if suffix_start < self.pos {
+                        let string = self.str_from(suffix_start);
+                        if string == "_" {
+                            self.sess
+                                .span_diagnostic
+                                .struct_span_warn(
+                                    self.mk_sp(suffix_start, self.pos),
+                                    "underscore literal suffix is not allowed",
+                                )
+                                .warn(
+                                    "this was previously accepted by the compiler but is \
+                                       being phased out; it will become a hard error in \
+                                       a future release!",
+                                )
+                                .note(
+                                    "see issue #42326 \
+                                     <https://github.com/rust-lang/rust/issues/42326> \
+                                     for more information",
+                                )
+                                .emit();
+                            None
+                        } else {
+                            Some(Symbol::intern(string))
+                        }
+                    } else {
+                        None
+                    };
+                    token::Literal(token::Lit { kind, symbol, suffix })
+                }
+                rustc_lexer::TokenKind::Lifetime { starts_with_number } => {
+                    // Include the leading `'` in the real identifier, for macro
+                    // expansion purposes. See #12512 for the gory details of why
+                    // this is necessary.
+                    let lifetime_name = self.str_from(start);
+                    if starts_with_number {
+                        self.err_span_(start, self.pos, "lifetimes cannot start with a number");
+                    }
+                    let ident = Symbol::intern(lifetime_name);
+                    token::Lifetime(ident)
+                }
+                rustc_lexer::TokenKind::Semi => token::Semi,
+                rustc_lexer::TokenKind::Comma => token::Comma,
+                rustc_lexer::TokenKind::Dot => token::Dot,
+                rustc_lexer::TokenKind::OpenParen => token::OpenDelim(Delimiter::Parenthesis),
+                rustc_lexer::TokenKind::CloseParen => token::CloseDelim(Delimiter::Parenthesis),
+                rustc_lexer::TokenKind::OpenBrace => token::OpenDelim(Delimiter::Brace),
+                rustc_lexer::TokenKind::CloseBrace => token::CloseDelim(Delimiter::Brace),
+                rustc_lexer::TokenKind::OpenBracket => token::OpenDelim(Delimiter::Bracket),
+                rustc_lexer::TokenKind::CloseBracket => token::CloseDelim(Delimiter::Bracket),
+                rustc_lexer::TokenKind::At => token::At,
+                rustc_lexer::TokenKind::Pound => token::Pound,
+                rustc_lexer::TokenKind::Tilde => token::Tilde,
+                rustc_lexer::TokenKind::Question => token::Question,
+                rustc_lexer::TokenKind::Colon => token::Colon,
+                rustc_lexer::TokenKind::Dollar => token::Dollar,
+                rustc_lexer::TokenKind::Eq => token::Eq,
+                rustc_lexer::TokenKind::Bang => token::Not,
+                rustc_lexer::TokenKind::Lt => token::Lt,
+                rustc_lexer::TokenKind::Gt => token::Gt,
+                rustc_lexer::TokenKind::Minus => token::BinOp(token::Minus),
+                rustc_lexer::TokenKind::And => token::BinOp(token::And),
+                rustc_lexer::TokenKind::Or => token::BinOp(token::Or),
+                rustc_lexer::TokenKind::Plus => token::BinOp(token::Plus),
+                rustc_lexer::TokenKind::Star => token::BinOp(token::Star),
+                rustc_lexer::TokenKind::Slash => token::BinOp(token::Slash),
+                rustc_lexer::TokenKind::Caret => token::BinOp(token::Caret),
+                rustc_lexer::TokenKind::Percent => token::BinOp(token::Percent),
+
+                rustc_lexer::TokenKind::Unknown | rustc_lexer::TokenKind::InvalidIdent => {
+                    let c = self.str_from(start).chars().next().unwrap();
+                    let mut err =
+                        self.struct_err_span_char(start, self.pos, "unknown start of token", c);
+                    // FIXME: the lexer could be used to turn the ASCII version of unicode
+                    // homoglyphs, instead of keeping a table in `check_for_substitution`into the
+                    // token. Ideally, this should be inside `rustc_lexer`. However, we should
+                    // first remove compound tokens like `<<` from `rustc_lexer`, and then add
+                    // fancier error recovery to it, as there will be less overall work to do this
+                    // way.
+                    let token = unicode_chars::check_for_substitution(self, start, c, &mut err);
+                    if c == '\x00' {
+                        err.help("source files must contain UTF-8 encoded text, unexpected null bytes might occur when a different encoding is used");
+                    }
+                    err.emit();
+                    if let Some(token) = token {
+                        token
+                    } else {
+                        preceded_by_whitespace = true;
+                        continue;
+                    }
+                }
+                rustc_lexer::TokenKind::Eof => token::Eof,
+            };
+            let span = self.mk_sp(start, self.pos);
+            return (Token::new(kind, span), preceded_by_whitespace);
         }
     }
 
@@ -162,171 +327,6 @@ impl<'a> StringReader<'a> {
         }
     }
 
-    /// Turns simple `rustc_lexer::TokenKind` enum into a rich
-    /// `rustc_ast::TokenKind`. This turns strings into interned
-    /// symbols and runs additional validation.
-    fn cook_lexer_token(&self, token: rustc_lexer::TokenKind, start: BytePos) -> Option<TokenKind> {
-        Some(match token {
-            rustc_lexer::TokenKind::LineComment { doc_style } => {
-                // Skip non-doc comments
-                let Some(doc_style) = doc_style else {
-                    self.lint_unicode_text_flow(start);
-                    return None;
-                };
-
-                // Opening delimiter of the length 3 is not included into the symbol.
-                let content_start = start + BytePos(3);
-                let content = self.str_from(content_start);
-                self.cook_doc_comment(content_start, content, CommentKind::Line, doc_style)
-            }
-            rustc_lexer::TokenKind::BlockComment { doc_style, terminated } => {
-                if !terminated {
-                    self.report_unterminated_block_comment(start, doc_style);
-                }
-
-                // Skip non-doc comments
-                let Some(doc_style) = doc_style else {
-                    self.lint_unicode_text_flow(start);
-                    return None;
-                };
-
-                // Opening delimiter of the length 3 and closing delimiter of the length 2
-                // are not included into the symbol.
-                let content_start = start + BytePos(3);
-                let content_end = self.pos - BytePos(if terminated { 2 } else { 0 });
-                let content = self.str_from_to(content_start, content_end);
-                self.cook_doc_comment(content_start, content, CommentKind::Block, doc_style)
-            }
-            rustc_lexer::TokenKind::Whitespace => return None,
-            rustc_lexer::TokenKind::Ident
-            | rustc_lexer::TokenKind::RawIdent
-            | rustc_lexer::TokenKind::UnknownPrefix => {
-                let is_raw_ident = token == rustc_lexer::TokenKind::RawIdent;
-                let is_unknown_prefix = token == rustc_lexer::TokenKind::UnknownPrefix;
-                let mut ident_start = start;
-                if is_raw_ident {
-                    ident_start = ident_start + BytePos(2);
-                }
-                if is_unknown_prefix {
-                    self.report_unknown_prefix(start);
-                }
-                let sym = nfc_normalize(self.str_from(ident_start));
-                let span = self.mk_sp(start, self.pos);
-                self.sess.symbol_gallery.insert(sym, span);
-                if is_raw_ident {
-                    if !sym.can_be_raw() {
-                        self.err_span(span, &format!("`{}` cannot be a raw identifier", sym));
-                    }
-                    self.sess.raw_identifier_spans.borrow_mut().push(span);
-                }
-                token::Ident(sym, is_raw_ident)
-            }
-            rustc_lexer::TokenKind::InvalidIdent
-                // Do not recover an identifier with emoji if the codepoint is a confusable
-                // with a recoverable substitution token, like `➖`.
-                if !UNICODE_ARRAY
-                    .iter()
-                    .any(|&(c, _, _)| {
-                        let sym = self.str_from(start);
-                        sym.chars().count() == 1 && c == sym.chars().next().unwrap()
-                    })
-                     =>
-            {
-                let sym = nfc_normalize(self.str_from(start));
-                let span = self.mk_sp(start, self.pos);
-                self.sess.bad_unicode_identifiers.borrow_mut().entry(sym).or_default().push(span);
-                token::Ident(sym, false)
-            }
-            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);
-                let suffix = if suffix_start < self.pos {
-                    let string = self.str_from(suffix_start);
-                    if string == "_" {
-                        self.sess
-                            .span_diagnostic
-                            .struct_span_warn(
-                                self.mk_sp(suffix_start, self.pos),
-                                "underscore literal suffix is not allowed",
-                            )
-                            .warn(
-                                "this was previously accepted by the compiler but is \
-                                   being phased out; it will become a hard error in \
-                                   a future release!",
-                            )
-                            .note(
-                                "see issue #42326 \
-                                 <https://github.com/rust-lang/rust/issues/42326> \
-                                 for more information",
-                            )
-                            .emit();
-                        None
-                    } else {
-                        Some(Symbol::intern(string))
-                    }
-                } else {
-                    None
-                };
-                token::Literal(token::Lit { kind, symbol, suffix })
-            }
-            rustc_lexer::TokenKind::Lifetime { starts_with_number } => {
-                // Include the leading `'` in the real identifier, for macro
-                // expansion purposes. See #12512 for the gory details of why
-                // this is necessary.
-                let lifetime_name = self.str_from(start);
-                if starts_with_number {
-                    self.err_span_(start, self.pos, "lifetimes cannot start with a number");
-                }
-                let ident = Symbol::intern(lifetime_name);
-                token::Lifetime(ident)
-            }
-            rustc_lexer::TokenKind::Semi => token::Semi,
-            rustc_lexer::TokenKind::Comma => token::Comma,
-            rustc_lexer::TokenKind::Dot => token::Dot,
-            rustc_lexer::TokenKind::OpenParen => token::OpenDelim(Delimiter::Parenthesis),
-            rustc_lexer::TokenKind::CloseParen => token::CloseDelim(Delimiter::Parenthesis),
-            rustc_lexer::TokenKind::OpenBrace => token::OpenDelim(Delimiter::Brace),
-            rustc_lexer::TokenKind::CloseBrace => token::CloseDelim(Delimiter::Brace),
-            rustc_lexer::TokenKind::OpenBracket => token::OpenDelim(Delimiter::Bracket),
-            rustc_lexer::TokenKind::CloseBracket => token::CloseDelim(Delimiter::Bracket),
-            rustc_lexer::TokenKind::At => token::At,
-            rustc_lexer::TokenKind::Pound => token::Pound,
-            rustc_lexer::TokenKind::Tilde => token::Tilde,
-            rustc_lexer::TokenKind::Question => token::Question,
-            rustc_lexer::TokenKind::Colon => token::Colon,
-            rustc_lexer::TokenKind::Dollar => token::Dollar,
-            rustc_lexer::TokenKind::Eq => token::Eq,
-            rustc_lexer::TokenKind::Bang => token::Not,
-            rustc_lexer::TokenKind::Lt => token::Lt,
-            rustc_lexer::TokenKind::Gt => token::Gt,
-            rustc_lexer::TokenKind::Minus => token::BinOp(token::Minus),
-            rustc_lexer::TokenKind::And => token::BinOp(token::And),
-            rustc_lexer::TokenKind::Or => token::BinOp(token::Or),
-            rustc_lexer::TokenKind::Plus => token::BinOp(token::Plus),
-            rustc_lexer::TokenKind::Star => token::BinOp(token::Star),
-            rustc_lexer::TokenKind::Slash => token::BinOp(token::Slash),
-            rustc_lexer::TokenKind::Caret => token::BinOp(token::Caret),
-            rustc_lexer::TokenKind::Percent => token::BinOp(token::Percent),
-
-            rustc_lexer::TokenKind::Unknown | rustc_lexer::TokenKind::InvalidIdent => {
-                let c = self.str_from(start).chars().next().unwrap();
-                let mut err =
-                    self.struct_err_span_char(start, self.pos, "unknown start of token", c);
-                // FIXME: the lexer could be used to turn the ASCII version of unicode homoglyphs,
-                // instead of keeping a table in `check_for_substitution`into the token. Ideally,
-                // this should be inside `rustc_lexer`. However, we should first remove compound
-                // tokens like `<<` from `rustc_lexer`, and then add fancier error recovery to it,
-                // as there will be less overall work to do this way.
-                let token = unicode_chars::check_for_substitution(self, start, c, &mut err);
-                if c == '\x00' {
-                    err.help("source files must contain UTF-8 encoded text, unexpected null bytes might occur when a different encoding is used");
-                }
-                err.emit();
-                token?
-            }
-        })
-    }
-
     fn cook_doc_comment(
         &self,
         content_start: BytePos,
diff --git a/compiler/rustc_parse/src/lexer/tokentrees.rs b/compiler/rustc_parse/src/lexer/tokentrees.rs
index aa70912dcde..b2701817d48 100644
--- a/compiler/rustc_parse/src/lexer/tokentrees.rs
+++ b/compiler/rustc_parse/src/lexer/tokentrees.rs
@@ -1,31 +1,15 @@
 use super::{StringReader, UnmatchedBrace};
-
 use rustc_ast::token::{self, Delimiter, Token};
 use rustc_ast::tokenstream::{DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_ast_pretty::pprust::token_to_string;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::PResult;
+use rustc_errors::{PErr, PResult};
 use rustc_span::Span;
 
-impl<'a> StringReader<'a> {
-    pub(super) fn into_token_trees(self) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
-        let mut tt_reader = TokenTreesReader {
-            string_reader: self,
-            token: Token::dummy(),
-            open_braces: Vec::new(),
-            unmatched_braces: Vec::new(),
-            matching_delim_spans: Vec::new(),
-            last_unclosed_found_span: None,
-            last_delim_empty_block_spans: FxHashMap::default(),
-            matching_block_spans: Vec::new(),
-        };
-        let res = tt_reader.parse_all_token_trees();
-        (res, tt_reader.unmatched_braces)
-    }
-}
-
-struct TokenTreesReader<'a> {
+pub(super) struct TokenTreesReader<'a> {
     string_reader: StringReader<'a>,
+    /// The "next" token, which has been obtained from the `StringReader` but
+    /// not yet handled by the `TokenTreesReader`.
     token: Token,
     /// Stack of open delimiters and their spans. Used for error message.
     open_braces: Vec<(Delimiter, Span)>,
@@ -43,254 +27,232 @@ struct TokenTreesReader<'a> {
 }
 
 impl<'a> TokenTreesReader<'a> {
-    // Parse a stream of tokens into a list of `TokenTree`s, up to an `Eof`.
-    fn parse_all_token_trees(&mut self) -> PResult<'a, TokenStream> {
-        let mut buf = TokenStreamBuilder::default();
-
-        self.bump();
-        while self.token != token::Eof {
-            buf.push(self.parse_token_tree()?);
-        }
-
-        Ok(buf.into_token_stream())
+    pub(super) fn parse_all_token_trees(
+        string_reader: StringReader<'a>,
+    ) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
+        let mut tt_reader = TokenTreesReader {
+            string_reader,
+            token: Token::dummy(),
+            open_braces: Vec::new(),
+            unmatched_braces: Vec::new(),
+            matching_delim_spans: Vec::new(),
+            last_unclosed_found_span: None,
+            last_delim_empty_block_spans: FxHashMap::default(),
+            matching_block_spans: Vec::new(),
+        };
+        let res = tt_reader.parse_token_trees(/* is_delimited */ false);
+        (res, tt_reader.unmatched_braces)
     }
 
-    // Parse a stream of tokens into a list of `TokenTree`s, up to a `CloseDelim`.
-    fn parse_token_trees_until_close_delim(&mut self) -> TokenStream {
-        let mut buf = TokenStreamBuilder::default();
+    // Parse a stream of tokens into a list of `TokenTree`s.
+    fn parse_token_trees(&mut self, is_delimited: bool) -> PResult<'a, TokenStream> {
+        self.token = self.string_reader.next_token().0;
+        let mut buf = Vec::new();
         loop {
-            if let token::CloseDelim(..) = self.token.kind {
-                return buf.into_token_stream();
-            }
-
-            match self.parse_token_tree() {
-                Ok(tree) => buf.push(tree),
-                Err(mut e) => {
-                    e.emit();
-                    return buf.into_token_stream();
+            match self.token.kind {
+                token::OpenDelim(delim) => buf.push(self.parse_token_tree_open_delim(delim)),
+                token::CloseDelim(delim) => {
+                    return if is_delimited {
+                        Ok(TokenStream::new(buf))
+                    } else {
+                        Err(self.close_delim_err(delim))
+                    };
+                }
+                token::Eof => {
+                    if is_delimited {
+                        self.eof_err().emit();
+                    }
+                    return Ok(TokenStream::new(buf));
+                }
+                _ => {
+                    // Get the next normal token. This might require getting multiple adjacent
+                    // single-char tokens and joining them together.
+                    let (this_spacing, next_tok) = loop {
+                        let (next_tok, is_next_tok_preceded_by_whitespace) =
+                            self.string_reader.next_token();
+                        if !is_next_tok_preceded_by_whitespace {
+                            if let Some(glued) = self.token.glue(&next_tok) {
+                                self.token = glued;
+                            } else {
+                                let this_spacing =
+                                    if next_tok.is_op() { Spacing::Joint } else { Spacing::Alone };
+                                break (this_spacing, next_tok);
+                            }
+                        } else {
+                            break (Spacing::Alone, next_tok);
+                        }
+                    };
+                    let this_tok = std::mem::replace(&mut self.token, next_tok);
+                    buf.push(TokenTree::Token(this_tok, this_spacing));
                 }
             }
         }
     }
 
-    fn parse_token_tree(&mut self) -> PResult<'a, TokenTree> {
-        let sm = self.string_reader.sess.source_map();
-
-        match self.token.kind {
-            token::Eof => {
-                let msg = "this file contains an unclosed delimiter";
-                let mut err =
-                    self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, msg);
-                for &(_, sp) in &self.open_braces {
-                    err.span_label(sp, "unclosed delimiter");
-                    self.unmatched_braces.push(UnmatchedBrace {
-                        expected_delim: Delimiter::Brace,
-                        found_delim: None,
-                        found_span: self.token.span,
-                        unclosed_span: Some(sp),
-                        candidate_span: None,
-                    });
-                }
+    fn eof_err(&mut self) -> PErr<'a> {
+        let msg = "this file contains an unclosed delimiter";
+        let mut err = self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, msg);
+        for &(_, sp) in &self.open_braces {
+            err.span_label(sp, "unclosed delimiter");
+            self.unmatched_braces.push(UnmatchedBrace {
+                expected_delim: Delimiter::Brace,
+                found_delim: None,
+                found_span: self.token.span,
+                unclosed_span: Some(sp),
+                candidate_span: None,
+            });
+        }
 
-                if let Some((delim, _)) = self.open_braces.last() {
-                    if let Some((_, open_sp, close_sp)) =
-                        self.matching_delim_spans.iter().find(|(d, open_sp, close_sp)| {
-                            if let Some(close_padding) = sm.span_to_margin(*close_sp) {
-                                if let Some(open_padding) = sm.span_to_margin(*open_sp) {
-                                    return delim == d && close_padding != open_padding;
-                                }
-                            }
-                            false
-                        })
-                    // these are in reverse order as they get inserted on close, but
-                    {
-                        // we want the last open/first close
-                        err.span_label(*open_sp, "this delimiter might not be properly closed...");
-                        err.span_label(
-                            *close_sp,
-                            "...as it matches this but it has different indentation",
-                        );
+        if let Some((delim, _)) = self.open_braces.last() {
+            if let Some((_, open_sp, close_sp)) =
+                self.matching_delim_spans.iter().find(|(d, open_sp, close_sp)| {
+                    let sm = self.string_reader.sess.source_map();
+                    if let Some(close_padding) = sm.span_to_margin(*close_sp) {
+                        if let Some(open_padding) = sm.span_to_margin(*open_sp) {
+                            return delim == d && close_padding != open_padding;
+                        }
                     }
-                }
-                Err(err)
+                    false
+                })
+            // these are in reverse order as they get inserted on close, but
+            {
+                // we want the last open/first close
+                err.span_label(*open_sp, "this delimiter might not be properly closed...");
+                err.span_label(*close_sp, "...as it matches this but it has different indentation");
             }
-            token::OpenDelim(delim) => {
-                // The span for beginning of the delimited section
-                let pre_span = self.token.span;
-
-                // Parse the open delimiter.
-                self.open_braces.push((delim, self.token.span));
-                self.bump();
+        }
+        err
+    }
 
-                // Parse the token trees within the delimiters.
-                // We stop at any delimiter so we can try to recover if the user
-                // uses an incorrect delimiter.
-                let tts = self.parse_token_trees_until_close_delim();
+    fn parse_token_tree_open_delim(&mut self, open_delim: Delimiter) -> TokenTree {
+        // The span for beginning of the delimited section
+        let pre_span = self.token.span;
 
-                // Expand to cover the entire delimited token tree
-                let delim_span = DelimSpan::from_pair(pre_span, self.token.span);
+        self.open_braces.push((open_delim, self.token.span));
 
-                match self.token.kind {
-                    // Correct delimiter.
-                    token::CloseDelim(d) if d == delim => {
-                        let (open_brace, open_brace_span) = self.open_braces.pop().unwrap();
-                        let close_brace_span = self.token.span;
+        // Parse the token trees within the delimiters.
+        // We stop at any delimiter so we can try to recover if the user
+        // uses an incorrect delimiter.
+        let tts = self.parse_token_trees(/* is_delimited */ true).unwrap();
 
-                        if tts.is_empty() {
-                            let empty_block_span = open_brace_span.to(close_brace_span);
-                            if !sm.is_multiline(empty_block_span) {
-                                // Only track if the block is in the form of `{}`, otherwise it is
-                                // likely that it was written on purpose.
-                                self.last_delim_empty_block_spans.insert(delim, empty_block_span);
-                            }
-                        }
+        // Expand to cover the entire delimited token tree
+        let delim_span = DelimSpan::from_pair(pre_span, self.token.span);
 
-                        //only add braces
-                        if let (Delimiter::Brace, Delimiter::Brace) = (open_brace, delim) {
-                            self.matching_block_spans.push((open_brace_span, close_brace_span));
-                        }
+        match self.token.kind {
+            // Correct delimiter.
+            token::CloseDelim(close_delim) if close_delim == open_delim => {
+                let (open_brace, open_brace_span) = self.open_braces.pop().unwrap();
+                let close_brace_span = self.token.span;
 
-                        if self.open_braces.is_empty() {
-                            // Clear up these spans to avoid suggesting them as we've found
-                            // properly matched delimiters so far for an entire block.
-                            self.matching_delim_spans.clear();
-                        } else {
-                            self.matching_delim_spans.push((
-                                open_brace,
-                                open_brace_span,
-                                close_brace_span,
-                            ));
-                        }
-                        // Parse the closing delimiter.
-                        self.bump();
+                if tts.is_empty() {
+                    let empty_block_span = open_brace_span.to(close_brace_span);
+                    let sm = self.string_reader.sess.source_map();
+                    if !sm.is_multiline(empty_block_span) {
+                        // Only track if the block is in the form of `{}`, otherwise it is
+                        // likely that it was written on purpose.
+                        self.last_delim_empty_block_spans.insert(open_delim, empty_block_span);
                     }
-                    // Incorrect delimiter.
-                    token::CloseDelim(other) => {
-                        let mut unclosed_delimiter = None;
-                        let mut candidate = None;
-
-                        if self.last_unclosed_found_span != Some(self.token.span) {
-                            // do not complain about the same unclosed delimiter multiple times
-                            self.last_unclosed_found_span = Some(self.token.span);
-                            // This is a conservative error: only report the last unclosed
-                            // delimiter. The previous unclosed delimiters could actually be
-                            // closed! The parser just hasn't gotten to them yet.
-                            if let Some(&(_, sp)) = self.open_braces.last() {
-                                unclosed_delimiter = Some(sp);
-                            };
-                            if let Some(current_padding) = sm.span_to_margin(self.token.span) {
-                                for (brace, brace_span) in &self.open_braces {
-                                    if let Some(padding) = sm.span_to_margin(*brace_span) {
-                                        // high likelihood of these two corresponding
-                                        if current_padding == padding && brace == &other {
-                                            candidate = Some(*brace_span);
-                                        }
-                                    }
-                                }
-                            }
-                            let (tok, _) = self.open_braces.pop().unwrap();
-                            self.unmatched_braces.push(UnmatchedBrace {
-                                expected_delim: tok,
-                                found_delim: Some(other),
-                                found_span: self.token.span,
-                                unclosed_span: unclosed_delimiter,
-                                candidate_span: candidate,
-                            });
-                        } else {
-                            self.open_braces.pop();
-                        }
+                }
 
-                        // If the incorrect delimiter matches an earlier opening
-                        // delimiter, then don't consume it (it can be used to
-                        // close the earlier one). Otherwise, consume it.
-                        // E.g., we try to recover from:
-                        // fn foo() {
-                        //     bar(baz(
-                        // }  // Incorrect delimiter but matches the earlier `{`
-                        if !self.open_braces.iter().any(|&(b, _)| b == other) {
-                            self.bump();
-                        }
-                    }
-                    token::Eof => {
-                        // Silently recover, the EOF token will be seen again
-                        // and an error emitted then. Thus we don't pop from
-                        // self.open_braces here.
-                    }
-                    _ => {}
+                //only add braces
+                if let (Delimiter::Brace, Delimiter::Brace) = (open_brace, open_delim) {
+                    self.matching_block_spans.push((open_brace_span, close_brace_span));
                 }
 
-                Ok(TokenTree::Delimited(delim_span, delim, tts))
+                if self.open_braces.is_empty() {
+                    // Clear up these spans to avoid suggesting them as we've found
+                    // properly matched delimiters so far for an entire block.
+                    self.matching_delim_spans.clear();
+                } else {
+                    self.matching_delim_spans.push((open_brace, open_brace_span, close_brace_span));
+                }
+                // Move past the closing delimiter.
+                self.token = self.string_reader.next_token().0;
             }
-            token::CloseDelim(delim) => {
-                // An unexpected closing delimiter (i.e., there is no
-                // 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);
+            // Incorrect delimiter.
+            token::CloseDelim(close_delim) => {
+                let mut unclosed_delimiter = None;
+                let mut candidate = None;
 
-                // Braces are added at the end, so the last element is the biggest block
-                if let Some(parent) = self.matching_block_spans.last() {
-                    if let Some(span) = self.last_delim_empty_block_spans.remove(&delim) {
-                        // Check if the (empty block) is in the last properly closed block
-                        if (parent.0.to(parent.1)).contains(span) {
-                            err.span_label(
-                                span,
-                                "block is empty, you might have not meant to close it",
-                            );
-                        } else {
-                            err.span_label(parent.0, "this opening brace...");
-
-                            err.span_label(parent.1, "...matches this closing brace");
+                if self.last_unclosed_found_span != Some(self.token.span) {
+                    // do not complain about the same unclosed delimiter multiple times
+                    self.last_unclosed_found_span = Some(self.token.span);
+                    // This is a conservative error: only report the last unclosed
+                    // delimiter. The previous unclosed delimiters could actually be
+                    // closed! The parser just hasn't gotten to them yet.
+                    if let Some(&(_, sp)) = self.open_braces.last() {
+                        unclosed_delimiter = Some(sp);
+                    };
+                    let sm = self.string_reader.sess.source_map();
+                    if let Some(current_padding) = sm.span_to_margin(self.token.span) {
+                        for (brace, brace_span) in &self.open_braces {
+                            if let Some(padding) = sm.span_to_margin(*brace_span) {
+                                // high likelihood of these two corresponding
+                                if current_padding == padding && brace == &close_delim {
+                                    candidate = Some(*brace_span);
+                                }
+                            }
                         }
-                    } else {
-                        err.span_label(parent.0, "this opening brace...");
-
-                        err.span_label(parent.1, "...matches this closing brace");
                     }
+                    let (tok, _) = self.open_braces.pop().unwrap();
+                    self.unmatched_braces.push(UnmatchedBrace {
+                        expected_delim: tok,
+                        found_delim: Some(close_delim),
+                        found_span: self.token.span,
+                        unclosed_span: unclosed_delimiter,
+                        candidate_span: candidate,
+                    });
+                } else {
+                    self.open_braces.pop();
                 }
 
-                err.span_label(self.token.span, "unexpected closing delimiter");
-                Err(err)
-            }
-            _ => {
-                let tok = self.token.take();
-                let mut spacing = self.bump();
-                if !self.token.is_op() {
-                    spacing = Spacing::Alone;
+                // If the incorrect delimiter matches an earlier opening
+                // delimiter, then don't consume it (it can be used to
+                // close the earlier one). Otherwise, consume it.
+                // E.g., we try to recover from:
+                // fn foo() {
+                //     bar(baz(
+                // }  // Incorrect delimiter but matches the earlier `{`
+                if !self.open_braces.iter().any(|&(b, _)| b == close_delim) {
+                    self.token = self.string_reader.next_token().0;
                 }
-                Ok(TokenTree::Token(tok, spacing))
             }
+            token::Eof => {
+                // Silently recover, the EOF token will be seen again
+                // and an error emitted then. Thus we don't pop from
+                // self.open_braces here.
+            }
+            _ => unreachable!(),
         }
-    }
 
-    fn bump(&mut self) -> Spacing {
-        let (spacing, token) = self.string_reader.next_token();
-        self.token = token;
-        spacing
+        TokenTree::Delimited(delim_span, open_delim, tts)
     }
-}
 
-#[derive(Default)]
-struct TokenStreamBuilder {
-    buf: Vec<TokenTree>,
-}
+    fn close_delim_err(&mut self, delim: Delimiter) -> PErr<'a> {
+        // An unexpected closing delimiter (i.e., there is no
+        // 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);
 
-impl TokenStreamBuilder {
-    #[inline(always)]
-    fn push(&mut self, tree: TokenTree) {
-        if let Some(TokenTree::Token(prev_token, Spacing::Joint)) = self.buf.last()
-            && let TokenTree::Token(token, joint) = &tree
-            && let Some(glued) = prev_token.glue(token)
-        {
-            self.buf.pop();
-            self.buf.push(TokenTree::Token(glued, *joint));
-        } else {
-            self.buf.push(tree)
+        // Braces are added at the end, so the last element is the biggest block
+        if let Some(parent) = self.matching_block_spans.last() {
+            if let Some(span) = self.last_delim_empty_block_spans.remove(&delim) {
+                // Check if the (empty block) is in the last properly closed block
+                if (parent.0.to(parent.1)).contains(span) {
+                    err.span_label(span, "block is empty, you might have not meant to close it");
+                } else {
+                    err.span_label(parent.0, "this opening brace...");
+                    err.span_label(parent.1, "...matches this closing brace");
+                }
+            } else {
+                err.span_label(parent.0, "this opening brace...");
+                err.span_label(parent.1, "...matches this closing brace");
+            }
         }
-    }
 
-    fn into_token_stream(self) -> TokenStream {
-        TokenStream::new(self.buf)
+        err.span_label(self.token.span, "unexpected closing delimiter");
+        err
     }
 }
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index a37327f4294..0bdfe10359c 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -4,7 +4,6 @@
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
-#![cfg_attr(bootstrap, feature(let_else))]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![recursion_limit = "256"]
@@ -33,6 +32,8 @@ use parser::{emit_unclosed_delims, make_unclosed_delims_error, Parser};
 pub mod lexer;
 pub mod validate_attr;
 
+mod errors;
+
 // A bunch of utility functions of the form `parse_<thing>_from_<source>`
 // where <thing> includes crate, expr, item, stmt, tts, and one that
 // uses a HOF to parse anything, and <source> includes file and
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 5fd69b15ecc..58be348883c 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -1,27 +1,26 @@
+use crate::errors::{InvalidMetaItem, SuffixedLiteralInAttribute};
+
 use super::{AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle};
 use rustc_ast as ast;
 use rustc_ast::attr;
 use rustc_ast::token::{self, Delimiter, Nonterminal};
-use rustc_ast_pretty::pprust;
-use rustc_errors::{error_code, Diagnostic, PResult};
+use rustc_errors::{error_code, fluent, Diagnostic, IntoDiagnostic, PResult};
 use rustc_span::{sym, BytePos, Span};
 use std::convert::TryInto;
 
 // Public for rustfmt usage
 #[derive(Debug)]
-pub enum InnerAttrPolicy<'a> {
+pub enum InnerAttrPolicy {
     Permitted,
-    Forbidden { reason: &'a str, saw_doc_comment: bool, prev_outer_attr_sp: Option<Span> },
+    Forbidden(Option<InnerAttrForbiddenReason>),
 }
 
-const DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG: &str = "an inner attribute is not \
-                                                     permitted in this context";
-
-pub(super) const DEFAULT_INNER_ATTR_FORBIDDEN: InnerAttrPolicy<'_> = InnerAttrPolicy::Forbidden {
-    reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG,
-    saw_doc_comment: false,
-    prev_outer_attr_sp: None,
-};
+#[derive(Clone, Copy, Debug)]
+pub enum InnerAttrForbiddenReason {
+    InCodeBlock,
+    AfterOuterDocComment { prev_doc_comment_span: Span },
+    AfterOuterAttribute { prev_outer_attr_sp: Span },
+}
 
 enum OuterAttributeType {
     DocComment,
@@ -40,17 +39,15 @@ impl<'a> Parser<'a> {
                 let prev_outer_attr_sp = outer_attrs.last().map(|attr| attr.span);
 
                 let inner_error_reason = if just_parsed_doc_comment {
-                    "an inner attribute is not permitted following an outer doc comment"
-                } else if prev_outer_attr_sp.is_some() {
-                    "an inner attribute is not permitted following an outer attribute"
+                    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 {
-                    DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG
-                };
-                let inner_parse_policy = InnerAttrPolicy::Forbidden {
-                    reason: inner_error_reason,
-                    saw_doc_comment: just_parsed_doc_comment,
-                    prev_outer_attr_sp,
+                    None
                 };
+                let inner_parse_policy = InnerAttrPolicy::Forbidden(inner_error_reason);
                 just_parsed_doc_comment = false;
                 Some(self.parse_attribute(inner_parse_policy)?)
             } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
@@ -58,7 +55,7 @@ impl<'a> Parser<'a> {
                     let span = self.token.span;
                     let mut err = self.sess.span_diagnostic.struct_span_err_with_code(
                         span,
-                        "expected outer doc comment",
+                        fluent::parser::inner_doc_comment_not_permitted,
                         error_code!(E0753),
                     );
                     if let Some(replacement_span) = self.annotate_following_item_if_applicable(
@@ -69,13 +66,10 @@ impl<'a> Parser<'a> {
                             token::CommentKind::Block => OuterAttributeType::DocBlockComment,
                         },
                     ) {
-                        err.note(
-                            "inner doc comments like this (starting with `//!` or `/*!`) can \
-                            only appear before items",
-                        );
+                        err.note(fluent::parser::note);
                         err.span_suggestion_verbose(
                             replacement_span,
-                            "you might have meant to write a regular comment",
+                            fluent::parser::suggestion,
                             "",
                             rustc_errors::Applicability::MachineApplicable,
                         );
@@ -113,7 +107,7 @@ impl<'a> Parser<'a> {
     // Public for rustfmt usage.
     pub fn parse_attribute(
         &mut self,
-        inner_parse_policy: InnerAttrPolicy<'_>,
+        inner_parse_policy: InnerAttrPolicy,
     ) -> PResult<'a, ast::Attribute> {
         debug!(
             "parse_attribute: inner_parse_policy={:?} self.token={:?}",
@@ -122,35 +116,22 @@ impl<'a> Parser<'a> {
         let lo = self.token.span;
         // Attributes can't have attributes of their own [Editor's note: not with that attitude]
         self.collect_tokens_no_attrs(|this| {
-            if this.eat(&token::Pound) {
-                let style = if this.eat(&token::Not) {
-                    ast::AttrStyle::Inner
-                } else {
-                    ast::AttrStyle::Outer
-                };
+            assert!(this.eat(&token::Pound), "parse_attribute called in non-attribute position");
 
-                this.expect(&token::OpenDelim(Delimiter::Bracket))?;
-                let item = this.parse_attr_item(false)?;
-                this.expect(&token::CloseDelim(Delimiter::Bracket))?;
-                let attr_sp = lo.to(this.prev_token.span);
+            let style =
+                if this.eat(&token::Not) { ast::AttrStyle::Inner } else { ast::AttrStyle::Outer };
 
-                // Emit error if inner attribute is encountered and forbidden.
-                if style == ast::AttrStyle::Inner {
-                    this.error_on_forbidden_inner_attr(attr_sp, inner_parse_policy);
-                }
+            this.expect(&token::OpenDelim(Delimiter::Bracket))?;
+            let item = this.parse_attr_item(false)?;
+            this.expect(&token::CloseDelim(Delimiter::Bracket))?;
+            let attr_sp = lo.to(this.prev_token.span);
 
-                Ok(attr::mk_attr_from_item(
-                    &self.sess.attr_id_generator,
-                    item,
-                    None,
-                    style,
-                    attr_sp,
-                ))
-            } else {
-                let token_str = pprust::token_to_string(&this.token);
-                let msg = &format!("expected `#`, found `{token_str}`");
-                Err(this.struct_span_err(this.token.span, msg))
+            // Emit error if inner attribute is encountered and forbidden.
+            if style == ast::AttrStyle::Inner {
+                this.error_on_forbidden_inner_attr(attr_sp, inner_parse_policy);
             }
+
+            Ok(attr::mk_attr_from_item(&self.sess.attr_id_generator, item, None, style, attr_sp))
         })
     }
 
@@ -190,21 +171,12 @@ impl<'a> Parser<'a> {
             ForceCollect::No,
         ) {
             Ok(Some(item)) => {
-                let attr_name = match attr_type {
-                    OuterAttributeType::Attribute => "attribute",
-                    _ => "doc comment",
-                };
-                err.span_label(
-                    item.span,
-                    &format!("the inner {} doesn't annotate this {}", attr_name, item.kind.descr()),
-                );
+                // FIXME(#100717)
+                err.set_arg("item", item.kind.descr());
+                err.span_label(item.span, fluent::parser::label_does_not_annotate_this);
                 err.span_suggestion_verbose(
                     replacement_span,
-                    &format!(
-                        "to annotate the {}, change the {} from inner to outer style",
-                        item.kind.descr(),
-                        attr_name
-                    ),
+                    fluent::parser::sugg_change_inner_to_outer,
                     match attr_type {
                         OuterAttributeType::Attribute => "",
                         OuterAttributeType::DocBlockComment => "*",
@@ -222,22 +194,33 @@ impl<'a> Parser<'a> {
         Some(replacement_span)
     }
 
-    pub(super) fn error_on_forbidden_inner_attr(&self, attr_sp: Span, policy: InnerAttrPolicy<'_>) {
-        if let InnerAttrPolicy::Forbidden { reason, saw_doc_comment, prev_outer_attr_sp } = policy {
-            let prev_outer_attr_note =
-                if saw_doc_comment { "previous doc comment" } else { "previous outer attribute" };
-
-            let mut diag = self.struct_span_err(attr_sp, reason);
-
-            if let Some(prev_outer_attr_sp) = prev_outer_attr_sp {
-                diag.span_label(attr_sp, "not permitted following an outer attribute")
-                    .span_label(prev_outer_attr_sp, prev_outer_attr_note);
-            }
+    pub(super) fn error_on_forbidden_inner_attr(&self, attr_sp: Span, policy: InnerAttrPolicy) {
+        if let InnerAttrPolicy::Forbidden(reason) = policy {
+            let mut diag = match reason.as_ref().copied() {
+                Some(InnerAttrForbiddenReason::AfterOuterDocComment { prev_doc_comment_span }) => {
+                    let mut diag = self.struct_span_err(
+                        attr_sp,
+                        fluent::parser::inner_attr_not_permitted_after_outer_doc_comment,
+                    );
+                    diag.span_label(attr_sp, fluent::parser::label_attr)
+                        .span_label(prev_doc_comment_span, fluent::parser::label_prev_doc_comment);
+                    diag
+                }
+                Some(InnerAttrForbiddenReason::AfterOuterAttribute { prev_outer_attr_sp }) => {
+                    let mut diag = self.struct_span_err(
+                        attr_sp,
+                        fluent::parser::inner_attr_not_permitted_after_outer_attr,
+                    );
+                    diag.span_label(attr_sp, fluent::parser::label_attr)
+                        .span_label(prev_outer_attr_sp, fluent::parser::label_prev_attr);
+                    diag
+                }
+                Some(InnerAttrForbiddenReason::InCodeBlock) | None => {
+                    self.struct_span_err(attr_sp, fluent::parser::inner_attr_not_permitted)
+                }
+            };
 
-            diag.note(
-                "inner attributes, like `#![no_std]`, annotate the item enclosing them, and \
-                are usually found at the beginning of source files",
-            );
+            diag.note(fluent::parser::inner_attr_explanation);
             if self
                 .annotate_following_item_if_applicable(
                     &mut diag,
@@ -246,7 +229,7 @@ impl<'a> Parser<'a> {
                 )
                 .is_some()
             {
-                diag.note("outer attributes, like `#[test]`, annotate the item following them");
+                diag.note(fluent::parser::outer_attr_explanation);
             };
             diag.emit();
         }
@@ -337,12 +320,7 @@ impl<'a> Parser<'a> {
         debug!("checking if {:?} is unusuffixed", lit);
 
         if !lit.kind.is_unsuffixed() {
-            self.struct_span_err(lit.span, "suffixed literals are not allowed in attributes")
-                .help(
-                    "instead of using a suffixed literal (`1u8`, `1.0f32`, etc.), \
-                    use an unsuffixed version (`1`, `1.0`, etc.)",
-                )
-                .emit();
+            self.sess.emit_err(SuffixedLiteralInAttribute { span: lit.span });
         }
 
         Ok(lit)
@@ -435,9 +413,8 @@ impl<'a> Parser<'a> {
             Err(err) => err.cancel(),
         }
 
-        let found = pprust::token_to_string(&self.token);
-        let msg = format!("expected unsuffixed literal or identifier, found `{found}`");
-        Err(self.struct_span_err(self.token.span, &msg))
+        Err(InvalidMetaItem { span: self.token.span, token: self.token.clone() }
+            .into_diagnostic(&self.sess.span_diagnostic))
     }
 }
 
diff --git a/compiler/rustc_parse/src/parser/attr_wrapper.rs b/compiler/rustc_parse/src/parser/attr_wrapper.rs
index 86c386b94c8..0dc05475ce9 100644
--- a/compiler/rustc_parse/src/parser/attr_wrapper.rs
+++ b/compiler/rustc_parse/src/parser/attr_wrapper.rs
@@ -32,11 +32,6 @@ pub struct AttrWrapper {
     start_pos: usize,
 }
 
-// This struct is passed around very frequently,
-// so make sure it doesn't accidentally get larger
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(AttrWrapper, 16);
-
 impl AttrWrapper {
     pub(super) fn new(attrs: AttrVec, start_pos: usize) -> AttrWrapper {
         AttrWrapper { attrs, start_pos }
@@ -96,9 +91,6 @@ struct LazyAttrTokenStreamImpl {
     replace_ranges: Box<[ReplaceRange]>,
 }
 
-#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(LazyAttrTokenStreamImpl, 144);
-
 impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
     fn to_attr_token_stream(&self) -> AttrTokenStream {
         // The token produced by the final call to `{,inlined_}next` was not
@@ -461,3 +453,13 @@ fn make_token_stream(
     }
     AttrTokenStream::new(final_buf.inner)
 }
+
+// Some types are used a lot. Make sure they don't unintentionally get bigger.
+#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
+mod size_asserts {
+    use super::*;
+    use rustc_data_structures::static_assert_size;
+    // These are in alphabetical order, which is easy to maintain.
+    static_assert_size!(AttrWrapper, 16);
+    static_assert_size!(LazyAttrTokenStreamImpl, 144);
+}
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index dcea11eadcb..f57bd9cec19 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -3,6 +3,19 @@ use super::{
     BlockMode, CommaRecoveryMode, Parser, PathStyle, Restrictions, SemiColonMode, SeqSep,
     TokenExpectType, TokenType,
 };
+use crate::errors::{
+    AmbiguousPlus, AttributeOnParamType, BadQPathStage2, BadTypePlus, BadTypePlusSub,
+    ComparisonOperatorsCannotBeChained, ComparisonOperatorsCannotBeChainedSugg,
+    ConstGenericWithoutBraces, ConstGenericWithoutBracesSugg, DocCommentOnParamType,
+    DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
+    GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg, InInTypo,
+    IncorrectAwait, IncorrectSemicolon, IncorrectUseOfAwait, ParenthesesInForHead,
+    ParenthesesInForHeadSugg, PatternMethodParamWithoutBody, QuestionMarkInType,
+    QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
+    StructLiteralBodyWithoutPathSugg, SuggEscapeToUseAsIdentifier, SuggRemoveComma,
+    UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
+    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead,
+};
 
 use crate::lexer::UnmatchedBrace;
 use rustc_ast as ast;
@@ -19,8 +32,8 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{
     fluent, Applicability, DiagnosticBuilder, DiagnosticMessage, Handler, MultiSpan, PResult,
 };
-use rustc_errors::{pluralize, struct_span_err, Diagnostic, ErrorGuaranteed};
-use rustc_macros::{Diagnostic, Subdiagnostic};
+use rustc_errors::{pluralize, Diagnostic, ErrorGuaranteed, IntoDiagnostic};
+use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{Span, SpanSnippetError, DUMMY_SP};
@@ -30,9 +43,6 @@ use std::mem::take;
 
 use crate::parser;
 
-const TURBOFISH_SUGGESTION_STR: &str =
-    "use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments";
-
 /// Creates a placeholder argument.
 pub(super) fn dummy_arg(ident: Ident) -> Param {
     let pat = P(Pat {
@@ -52,34 +62,6 @@ pub(super) fn dummy_arg(ident: Ident) -> Param {
     }
 }
 
-pub enum Error {
-    UselessDocComment,
-}
-
-impl Error {
-    fn span_err(
-        self,
-        sp: impl Into<MultiSpan>,
-        handler: &Handler,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
-        match self {
-            Error::UselessDocComment => {
-                let mut err = struct_span_err!(
-                    handler,
-                    sp,
-                    E0585,
-                    "found a documentation comment that doesn't document anything",
-                );
-                err.help(
-                    "doc comments must come before what they document, maybe a comment was \
-                          intended with `//`?",
-                );
-                err
-            }
-        }
-    }
-}
-
 pub(super) trait RecoverQPath: Sized + 'static {
     const PATH_STYLE: PathStyle = PathStyle::Expr;
     fn to_ty(&self) -> Option<P<Ty>>;
@@ -242,509 +224,6 @@ impl MultiSugg {
     }
 }
 
-#[derive(Diagnostic)]
-#[diag(parser::maybe_report_ambiguous_plus)]
-struct AmbiguousPlus {
-    pub sum_ty: String,
-    #[primary_span]
-    #[suggestion(code = "({sum_ty})")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::maybe_recover_from_bad_type_plus, code = "E0178")]
-struct BadTypePlus {
-    pub ty: String,
-    #[primary_span]
-    pub span: Span,
-    #[subdiagnostic]
-    pub sub: BadTypePlusSub,
-}
-
-#[derive(Subdiagnostic)]
-pub enum BadTypePlusSub {
-    #[suggestion(
-        parser::add_paren,
-        code = "{sum_with_parens}",
-        applicability = "machine-applicable"
-    )]
-    AddParen {
-        sum_with_parens: String,
-        #[primary_span]
-        span: Span,
-    },
-    #[label(parser::forgot_paren)]
-    ForgotParen {
-        #[primary_span]
-        span: Span,
-    },
-    #[label(parser::expect_path)]
-    ExpectPath {
-        #[primary_span]
-        span: Span,
-    },
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::maybe_recover_from_bad_qpath_stage_2)]
-struct BadQPathStage2 {
-    #[primary_span]
-    #[suggestion(applicability = "maybe-incorrect")]
-    span: Span,
-    ty: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::incorrect_semicolon)]
-struct IncorrectSemicolon<'a> {
-    #[primary_span]
-    #[suggestion_short(applicability = "machine-applicable")]
-    span: Span,
-    #[help]
-    opt_help: Option<()>,
-    name: &'a str,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::incorrect_use_of_await)]
-struct IncorrectUseOfAwait {
-    #[primary_span]
-    #[suggestion(parser::parentheses_suggestion, applicability = "machine-applicable")]
-    span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::incorrect_use_of_await)]
-struct IncorrectAwait {
-    #[primary_span]
-    span: Span,
-    #[suggestion(parser::postfix_suggestion, code = "{expr}.await{question_mark}")]
-    sugg_span: (Span, Applicability),
-    expr: String,
-    question_mark: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::in_in_typo)]
-struct InInTypo {
-    #[primary_span]
-    span: Span,
-    #[suggestion(applicability = "machine-applicable")]
-    sugg_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_variable_declaration)]
-pub struct InvalidVariableDeclaration {
-    #[primary_span]
-    pub span: Span,
-    #[subdiagnostic]
-    pub sub: InvalidVariableDeclarationSub,
-}
-
-#[derive(Subdiagnostic)]
-pub enum InvalidVariableDeclarationSub {
-    #[suggestion(
-        parser::switch_mut_let_order,
-        applicability = "maybe-incorrect",
-        code = "let mut"
-    )]
-    SwitchMutLetOrder(#[primary_span] Span),
-    #[suggestion(
-        parser::missing_let_before_mut,
-        applicability = "machine-applicable",
-        code = "let mut"
-    )]
-    MissingLet(#[primary_span] Span),
-    #[suggestion(parser::use_let_not_auto, applicability = "machine-applicable", code = "let")]
-    UseLetNotAuto(#[primary_span] Span),
-    #[suggestion(parser::use_let_not_var, applicability = "machine-applicable", code = "let")]
-    UseLetNotVar(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_comparison_operator)]
-pub(crate) struct InvalidComparisonOperator {
-    #[primary_span]
-    pub span: Span,
-    pub invalid: String,
-    #[subdiagnostic]
-    pub sub: InvalidComparisonOperatorSub,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum InvalidComparisonOperatorSub {
-    #[suggestion_short(
-        parser::use_instead,
-        applicability = "machine-applicable",
-        code = "{correct}"
-    )]
-    Correctable {
-        #[primary_span]
-        span: Span,
-        invalid: String,
-        correct: String,
-    },
-    #[label(parser::spaceship_operator_invalid)]
-    Spaceship(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_logical_operator)]
-#[note]
-pub(crate) struct InvalidLogicalOperator {
-    #[primary_span]
-    pub span: Span,
-    pub incorrect: String,
-    #[subdiagnostic]
-    pub sub: InvalidLogicalOperatorSub,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum InvalidLogicalOperatorSub {
-    #[suggestion_short(
-        parser::use_amp_amp_for_conjunction,
-        applicability = "machine-applicable",
-        code = "&&"
-    )]
-    Conjunction(#[primary_span] Span),
-    #[suggestion_short(
-        parser::use_pipe_pipe_for_disjunction,
-        applicability = "machine-applicable",
-        code = "||"
-    )]
-    Disjunction(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::tilde_is_not_unary_operator)]
-pub(crate) struct TildeAsUnaryOperator(
-    #[primary_span]
-    #[suggestion_short(applicability = "machine-applicable", code = "!")]
-    pub Span,
-);
-
-#[derive(Diagnostic)]
-#[diag(parser::unexpected_token_after_not)]
-pub(crate) struct NotAsNegationOperator {
-    #[primary_span]
-    pub negated: Span,
-    pub negated_desc: String,
-    #[subdiagnostic]
-    pub sub: NotAsNegationOperatorSub,
-}
-
-#[derive(Subdiagnostic)]
-pub enum NotAsNegationOperatorSub {
-    #[suggestion_short(
-        parser::unexpected_token_after_not_default,
-        applicability = "machine-applicable",
-        code = "!"
-    )]
-    SuggestNotDefault(#[primary_span] Span),
-
-    #[suggestion_short(
-        parser::unexpected_token_after_not_bitwise,
-        applicability = "machine-applicable",
-        code = "!"
-    )]
-    SuggestNotBitwise(#[primary_span] Span),
-
-    #[suggestion_short(
-        parser::unexpected_token_after_not_logical,
-        applicability = "machine-applicable",
-        code = "!"
-    )]
-    SuggestNotLogical(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::malformed_loop_label)]
-pub(crate) struct MalformedLoopLabel {
-    #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = "{correct_label}")]
-    pub span: Span,
-    pub correct_label: Ident,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::lifetime_in_borrow_expression)]
-pub(crate) struct LifetimeInBorrowExpression {
-    #[primary_span]
-    pub span: Span,
-    #[suggestion(applicability = "machine-applicable", code = "")]
-    #[label]
-    pub lifetime_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::field_expression_with_generic)]
-pub(crate) struct FieldExpressionWithGeneric(#[primary_span] pub Span);
-
-#[derive(Diagnostic)]
-#[diag(parser::macro_invocation_with_qualified_path)]
-pub(crate) struct MacroInvocationWithQualifiedPath(#[primary_span] pub Span);
-
-#[derive(Diagnostic)]
-#[diag(parser::unexpected_token_after_label)]
-pub(crate) struct UnexpectedTokenAfterLabel(
-    #[primary_span]
-    #[label(parser::unexpected_token_after_label)]
-    pub Span,
-);
-
-#[derive(Diagnostic)]
-#[diag(parser::require_colon_after_labeled_expression)]
-#[note]
-pub(crate) struct RequireColonAfterLabeledExpression {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub label: Span,
-    #[suggestion_short(applicability = "machine-applicable", code = ": ")]
-    pub label_end: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::do_catch_syntax_removed)]
-#[note]
-pub(crate) struct DoCatchSyntaxRemoved {
-    #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = "try")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::float_literal_requires_integer_part)]
-pub(crate) struct FloatLiteralRequiresIntegerPart {
-    #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = "{correct}")]
-    pub span: Span,
-    pub correct: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_int_literal_width)]
-#[help]
-pub(crate) struct InvalidIntLiteralWidth {
-    #[primary_span]
-    pub span: Span,
-    pub width: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_num_literal_base_prefix)]
-#[note]
-pub(crate) struct InvalidNumLiteralBasePrefix {
-    #[primary_span]
-    #[suggestion(applicability = "maybe-incorrect", code = "{fixed}")]
-    pub span: Span,
-    pub fixed: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_num_literal_suffix)]
-#[help]
-pub(crate) struct InvalidNumLiteralSuffix {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-    pub suffix: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_float_literal_width)]
-#[help]
-pub(crate) struct InvalidFloatLiteralWidth {
-    #[primary_span]
-    pub span: Span,
-    pub width: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_float_literal_suffix)]
-#[help]
-pub(crate) struct InvalidFloatLiteralSuffix {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-    pub suffix: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::int_literal_too_large)]
-pub(crate) struct IntLiteralTooLarge {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::missing_semicolon_before_array)]
-pub(crate) struct MissingSemicolonBeforeArray {
-    #[primary_span]
-    pub open_delim: Span,
-    #[suggestion_verbose(applicability = "maybe-incorrect", code = ";")]
-    pub semicolon: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::invalid_block_macro_segment)]
-pub(crate) struct InvalidBlockMacroSegment {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub context: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::if_expression_missing_then_block)]
-pub(crate) struct IfExpressionMissingThenBlock {
-    #[primary_span]
-    pub if_span: Span,
-    #[subdiagnostic]
-    pub sub: IfExpressionMissingThenBlockSub,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum IfExpressionMissingThenBlockSub {
-    #[help(parser::condition_possibly_unfinished)]
-    UnfinishedCondition(#[primary_span] Span),
-    #[help(parser::add_then_block)]
-    AddThenBlock(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::if_expression_missing_condition)]
-pub(crate) struct IfExpressionMissingCondition {
-    #[primary_span]
-    #[label(parser::condition_label)]
-    pub if_span: Span,
-    #[label(parser::block_label)]
-    pub block_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::expected_expression_found_let)]
-pub(crate) struct ExpectedExpressionFoundLet {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::expected_else_block)]
-pub(crate) struct ExpectedElseBlock {
-    #[primary_span]
-    pub first_tok_span: Span,
-    pub first_tok: String,
-    #[label]
-    pub else_span: Span,
-    #[suggestion(applicability = "maybe-incorrect", code = "if ")]
-    pub condition_start: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::outer_attribute_not_allowed_on_if_else)]
-pub(crate) struct OuterAttributeNotAllowedOnIfElse {
-    #[primary_span]
-    pub last: Span,
-
-    #[label(parser::branch_label)]
-    pub branch_span: Span,
-
-    #[label(parser::ctx_label)]
-    pub ctx_span: Span,
-    pub ctx: String,
-
-    #[suggestion(applicability = "machine-applicable", code = "")]
-    pub attributes: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::missing_in_in_for_loop)]
-pub(crate) struct MissingInInForLoop {
-    #[primary_span]
-    pub span: Span,
-    #[subdiagnostic]
-    pub sub: MissingInInForLoopSub,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum MissingInInForLoopSub {
-    // Has been misleading, at least in the past (closed Issue #48492), thus maybe-incorrect
-    #[suggestion_short(parser::use_in_not_of, applicability = "maybe-incorrect", code = "in")]
-    InNotOf(#[primary_span] Span),
-    #[suggestion_short(parser::add_in, applicability = "maybe-incorrect", code = " in ")]
-    AddIn(#[primary_span] Span),
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::missing_comma_after_match_arm)]
-pub(crate) struct MissingCommaAfterMatchArm {
-    #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = ",")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::catch_after_try)]
-#[help]
-pub(crate) struct CatchAfterTry {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::comma_after_base_struct)]
-#[note]
-pub(crate) struct CommaAfterBaseStruct {
-    #[primary_span]
-    pub span: Span,
-    #[suggestion_short(applicability = "machine-applicable", code = "")]
-    pub comma: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::eq_field_init)]
-pub(crate) struct EqFieldInit {
-    #[primary_span]
-    pub span: Span,
-    #[suggestion(applicability = "machine-applicable", code = ":")]
-    pub eq: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::dotdotdot)]
-pub(crate) struct DotDotDot {
-    #[primary_span]
-    #[suggestion(parser::suggest_exclusive_range, applicability = "maybe-incorrect", code = "..")]
-    #[suggestion(parser::suggest_inclusive_range, applicability = "maybe-incorrect", code = "..=")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::left_arrow_operator)]
-pub(crate) struct LeftArrowOperator {
-    #[primary_span]
-    #[suggestion(applicability = "maybe-incorrect", code = "< -")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::remove_let)]
-pub(crate) struct RemoveLet {
-    #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = "")]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(parser::use_eq_instead)]
-pub(crate) struct UseEqInstead {
-    #[primary_span]
-    #[suggestion_short(applicability = "machine-applicable", code = "=")]
-    pub span: Span,
-}
-
 // SnapshotParser is used to create a snapshot of the parser
 // without causing duplicate errors being emitted when the `Parser`
 // is dropped.
@@ -769,15 +248,6 @@ impl<'a> DerefMut for SnapshotParser<'a> {
 
 impl<'a> Parser<'a> {
     #[rustc_lint_diagnostics]
-    pub(super) fn span_err<S: Into<MultiSpan>>(
-        &self,
-        sp: S,
-        err: Error,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        err.span_err(sp, self.diagnostic())
-    }
-
-    #[rustc_lint_diagnostics]
     pub fn struct_span_err<S: Into<MultiSpan>>(
         &self,
         sp: S,
@@ -822,10 +292,6 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn expected_ident_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        let mut err = self.struct_span_err(
-            self.token.span,
-            &format!("expected identifier, found {}", super::token_descr(&self.token)),
-        );
         let valid_follow = &[
             TokenKind::Eq,
             TokenKind::Colon,
@@ -837,34 +303,35 @@ impl<'a> Parser<'a> {
             TokenKind::CloseDelim(Delimiter::Brace),
             TokenKind::CloseDelim(Delimiter::Parenthesis),
         ];
-        match self.token.ident() {
+        let suggest_raw = match self.token.ident() {
             Some((ident, false))
                 if ident.is_raw_guess()
                     && self.look_ahead(1, |t| valid_follow.contains(&t.kind)) =>
             {
-                err.span_suggestion_verbose(
-                    ident.span.shrink_to_lo(),
-                    &format!("escape `{}` to use it as an identifier", ident.name),
-                    "r#",
-                    Applicability::MaybeIncorrect,
-                );
+                Some(SuggEscapeToUseAsIdentifier {
+                    span: ident.span.shrink_to_lo(),
+                    // `Symbol::to_string()` is different from `Symbol::into_diagnostic_arg()`,
+                    // which uses `Symbol::to_ident_string()` and "helpfully" adds an implicit `r#`
+                    ident_name: ident.name.to_string(),
+                })
             }
-            _ => {}
-        }
-        if let Some(token_descr) = super::token_descr_opt(&self.token) {
-            err.span_label(self.token.span, format!("expected identifier, found {}", token_descr));
-        } else {
-            err.span_label(self.token.span, "expected identifier");
+            _ => None,
+        };
+
+        let suggest_remove_comma =
             if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
-                err.span_suggestion(
-                    self.token.span,
-                    "remove this comma",
-                    "",
-                    Applicability::MachineApplicable,
-                );
-            }
-        }
-        err
+                Some(SuggRemoveComma { span: self.token.span })
+            } else {
+                None
+            };
+
+        let err = ExpectedIdentifier {
+            span: self.token.span,
+            token: self.token.clone(),
+            suggest_raw,
+            suggest_remove_comma,
+        };
+        err.into_diagnostic(&self.sess.span_diagnostic)
     }
 
     pub(super) fn expected_one_of_not_found(
@@ -929,8 +396,8 @@ impl<'a> Parser<'a> {
         expected.dedup();
 
         let sm = self.sess.source_map();
-        let msg = format!("expected `;`, found {}", super::token_descr(&self.token));
-        let appl = Applicability::MachineApplicable;
+
+        // Special-case "expected `;`" errors
         if expected.contains(&TokenType::Token(token::Semi)) {
             if self.token.span == DUMMY_SP || self.prev_token.span == DUMMY_SP {
                 // Likely inside a macro, can't provide meaningful suggestions.
@@ -958,11 +425,13 @@ impl<'a> Parser<'a> {
                 //
                 //   let x = 32:
                 //   let y = 42;
+                self.sess.emit_err(ExpectedSemi {
+                    span: self.token.span,
+                    token: self.token.clone(),
+                    unexpected_token_label: None,
+                    sugg: ExpectedSemiSugg::ChangeToSemi(self.token.span),
+                });
                 self.bump();
-                let sp = self.prev_token.span;
-                self.struct_span_err(sp, &msg)
-                    .span_suggestion_short(sp, "change this to `;`", ";", appl)
-                    .emit();
                 return Ok(true);
             } else if self.look_ahead(0, |t| {
                 t == &token::CloseDelim(Delimiter::Brace)
@@ -980,11 +449,13 @@ impl<'a> Parser<'a> {
                 //
                 //   let x = 32
                 //   let y = 42;
-                let sp = self.prev_token.span.shrink_to_hi();
-                self.struct_span_err(sp, &msg)
-                    .span_label(self.token.span, "unexpected token")
-                    .span_suggestion_short(sp, "add `;` here", ";", appl)
-                    .emit();
+                let span = self.prev_token.span.shrink_to_hi();
+                self.sess.emit_err(ExpectedSemi {
+                    span,
+                    token: self.token.clone(),
+                    unexpected_token_label: Some(self.token.span),
+                    sugg: ExpectedSemiSugg::AddSemi(span),
+                });
                 return Ok(true);
             }
         }
@@ -1021,6 +492,7 @@ 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);
 
         if let TokenKind::Ident(symbol, _) = &self.prev_token.kind {
@@ -1029,7 +501,7 @@ impl<'a> Parser<'a> {
                     self.prev_token.span,
                     &format!("write `fn` instead of `{symbol}` to declare a function"),
                     "fn",
-                    appl,
+                    Applicability::MachineApplicable,
                 );
             }
         }
@@ -1043,7 +515,7 @@ impl<'a> Parser<'a> {
                 self.prev_token.span,
                 "write `pub` instead of `public` to make the item public",
                 "pub",
-                appl,
+                Applicability::MachineApplicable,
             );
         }
 
@@ -1181,19 +653,13 @@ impl<'a> Parser<'a> {
                     //     field: value,
                     // } }
                     err.delay_as_bug();
-                    self.struct_span_err(
-                        expr.span,
-                        fluent::parser::struct_literal_body_without_path,
-                    )
-                    .multipart_suggestion(
-                        fluent::parser::suggestion,
-                        vec![
-                            (expr.span.shrink_to_lo(), "{ SomeStruct ".to_string()),
-                            (expr.span.shrink_to_hi(), " }".to_string()),
-                        ],
-                        Applicability::MaybeIncorrect,
-                    )
-                    .emit();
+                    self.sess.emit_err(StructLiteralBodyWithoutPath {
+                        span: expr.span,
+                        sugg: StructLiteralBodyWithoutPathSugg {
+                            before: expr.span.shrink_to_lo(),
+                            after: expr.span.shrink_to_hi(),
+                        },
+                    });
                     self.restore_snapshot(snapshot);
                     let mut tail = self.mk_block(
                         vec![self.mk_stmt_err(expr.span)],
@@ -1387,18 +853,8 @@ impl<'a> Parser<'a> {
             self.eat_to_tokens(end);
             let span = lo.until(self.token.span);
 
-            let total_num_of_gt = number_of_gt + number_of_shr * 2;
-            self.struct_span_err(
-                span,
-                &format!("unmatched angle bracket{}", pluralize!(total_num_of_gt)),
-            )
-            .span_suggestion(
-                span,
-                &format!("remove extra angle bracket{}", pluralize!(total_num_of_gt)),
-                "",
-                Applicability::MachineApplicable,
-            )
-            .emit();
+            let num_extra_brackets = number_of_gt + number_of_shr * 2;
+            self.sess.emit_err(UnmatchedAngleBrackets { span, num_extra_brackets });
             return true;
         }
         false
@@ -1427,19 +883,13 @@ impl<'a> Parser<'a> {
                         let args = AngleBracketedArgs { args, span }.into();
                         segment.args = args;
 
-                        self.struct_span_err(
+                        self.sess.emit_err(GenericParamsWithoutAngleBrackets {
                             span,
-                            "generic parameters without surrounding angle brackets",
-                        )
-                        .multipart_suggestion(
-                            "surround the type parameters with angle brackets",
-                            vec![
-                                (span.shrink_to_lo(), "<".to_string()),
-                                (trailing_span, ">".to_string()),
-                            ],
-                            Applicability::MachineApplicable,
-                        )
-                        .emit();
+                            sugg: GenericParamsWithoutAngleBracketsSugg {
+                                left: span.shrink_to_lo(),
+                                right: trailing_span,
+                            },
+                        });
                     } else {
                         // This doesn't look like an invalid turbofish, can't recover parse state.
                         self.restore_snapshot(snapshot);
@@ -1476,7 +926,7 @@ impl<'a> Parser<'a> {
                     if self.eat(&token::Gt) {
                         e.span_suggestion_verbose(
                             binop.span.shrink_to_lo(),
-                            TURBOFISH_SUGGESTION_STR,
+                            fluent::parser::sugg_turbofish_syntax,
                             "::",
                             Applicability::MaybeIncorrect,
                         )
@@ -1508,7 +958,7 @@ impl<'a> Parser<'a> {
     /// parenthesising the leftmost comparison.
     fn attempt_chained_comparison_suggestion(
         &mut self,
-        err: &mut Diagnostic,
+        err: &mut ComparisonOperatorsCannotBeChained,
         inner_op: &Expr,
         outer_op: &Spanned<AssocOp>,
     ) -> bool /* advanced the cursor */ {
@@ -1521,16 +971,6 @@ impl<'a> Parser<'a> {
                 // suggestion being the only one to apply is high.
                 return false;
             }
-            let mut enclose = |left: Span, right: Span| {
-                err.multipart_suggestion(
-                    "parenthesize the comparison",
-                    vec![
-                        (left.shrink_to_lo(), "(".to_string()),
-                        (right.shrink_to_hi(), ")".to_string()),
-                    ],
-                    Applicability::MaybeIncorrect,
-                );
-            };
             return match (op.node, &outer_op.node) {
                 // `x == y == z`
                 (BinOpKind::Eq, AssocOp::Equal) |
@@ -1544,12 +984,10 @@ impl<'a> Parser<'a> {
                         self.span_to_snippet(e.span)
                             .unwrap_or_else(|_| pprust::expr_to_string(&e))
                     };
-                    err.span_suggestion_verbose(
-                        inner_op.span.shrink_to_hi(),
-                        "split the comparison into two",
-                        format!(" && {}", expr_to_str(&r1)),
-                        Applicability::MaybeIncorrect,
-                    );
+                    err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::SplitComparison {
+                        span: inner_op.span.shrink_to_hi(),
+                        middle_term: expr_to_str(&r1),
+                    });
                     false // Keep the current parse behavior, where the AST is `(x < y) < z`.
                 }
                 // `x == y < z`
@@ -1560,7 +998,10 @@ impl<'a> Parser<'a> {
                         Ok(r2) => {
                             // We are sure that outer-op-rhs could be consumed, the suggestion is
                             // likely correct.
-                            enclose(r1.span, r2.span);
+                            err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::Parenthesize {
+                                left: r1.span.shrink_to_lo(),
+                                right: r2.span.shrink_to_hi(),
+                            });
                             true
                         }
                         Err(expr_err) => {
@@ -1577,7 +1018,10 @@ impl<'a> Parser<'a> {
                     // further checks are necessary.
                     match self.parse_expr() {
                         Ok(_) => {
-                            enclose(l1.span, r1.span);
+                            err.chaining_sugg = Some(ComparisonOperatorsCannotBeChainedSugg::Parenthesize {
+                                left: l1.span.shrink_to_lo(),
+                                right: r1.span.shrink_to_hi(),
+                            });
                             true
                         }
                         Err(expr_err) => {
@@ -1626,18 +1070,11 @@ impl<'a> Parser<'a> {
 
         match inner_op.kind {
             ExprKind::Binary(op, ref l1, ref r1) if op.node.is_comparison() => {
-                let mut err = self.struct_span_err(
-                    vec![op.span, self.prev_token.span],
-                    "comparison operators cannot be chained",
-                );
-
-                let suggest = |err: &mut Diagnostic| {
-                    err.span_suggestion_verbose(
-                        op.span.shrink_to_lo(),
-                        TURBOFISH_SUGGESTION_STR,
-                        "::",
-                        Applicability::MaybeIncorrect,
-                    );
+                let mut err = ComparisonOperatorsCannotBeChained {
+                    span: vec![op.span, self.prev_token.span],
+                    suggest_turbofish: None,
+                    help_turbofish: None,
+                    chaining_sugg: None,
                 };
 
                 // Include `<` to provide this recommendation even in a case like
@@ -1664,7 +1101,7 @@ impl<'a> Parser<'a> {
                     return if token::ModSep == self.token.kind {
                         // We have some certainty that this was a bad turbofish at this point.
                         // `foo< bar >::`
-                        suggest(&mut err);
+                        err.suggest_turbofish = Some(op.span.shrink_to_lo());
 
                         let snapshot = self.create_snapshot_for_diagnostic();
                         self.bump(); // `::`
@@ -1673,7 +1110,7 @@ impl<'a> Parser<'a> {
                         match self.parse_expr() {
                             Ok(_) => {
                                 // 99% certain that the suggestion is correct, continue parsing.
-                                err.emit();
+                                self.sess.emit_err(err);
                                 // FIXME: actually check that the two expressions in the binop are
                                 // paths and resynthesize new fn call expression instead of using
                                 // `ExprKind::Err` placeholder.
@@ -1684,18 +1121,18 @@ impl<'a> Parser<'a> {
                                 // Not entirely sure now, but we bubble the error up with the
                                 // suggestion.
                                 self.restore_snapshot(snapshot);
-                                Err(err)
+                                Err(err.into_diagnostic(&self.sess.span_diagnostic))
                             }
                         }
                     } else if token::OpenDelim(Delimiter::Parenthesis) == self.token.kind {
                         // We have high certainty that this was a bad turbofish at this point.
                         // `foo< bar >(`
-                        suggest(&mut err);
+                        err.suggest_turbofish = Some(op.span.shrink_to_lo());
                         // Consume the fn call arguments.
                         match self.consume_fn_args() {
-                            Err(()) => Err(err),
+                            Err(()) => Err(err.into_diagnostic(&self.sess.span_diagnostic)),
                             Ok(()) => {
-                                err.emit();
+                                self.sess.emit_err(err);
                                 // FIXME: actually check that the two expressions in the binop are
                                 // paths and resynthesize new fn call expression instead of using
                                 // `ExprKind::Err` placeholder.
@@ -1708,25 +1145,24 @@ impl<'a> Parser<'a> {
                         {
                             // All we know is that this is `foo < bar >` and *nothing* else. Try to
                             // be helpful, but don't attempt to recover.
-                            err.help(TURBOFISH_SUGGESTION_STR);
-                            err.help("or use `(...)` if you meant to specify fn arguments");
+                            err.help_turbofish = Some(());
                         }
 
                         // If it looks like a genuine attempt to chain operators (as opposed to a
                         // misformatted turbofish, for instance), suggest a correct form.
                         if self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op)
                         {
-                            err.emit();
+                            self.sess.emit_err(err);
                             mk_err_expr(self, inner_op.span.to(self.prev_token.span))
                         } else {
                             // These cases cause too many knock-down errors, bail out (#61329).
-                            Err(err)
+                            Err(err.into_diagnostic(&self.sess.span_diagnostic))
                         }
                     };
                 }
                 let recover =
                     self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
-                err.emit();
+                self.sess.emit_err(err);
                 if recover {
                     return mk_err_expr(self, inner_op.span.to(self.prev_token.span));
                 }
@@ -1767,17 +1203,13 @@ impl<'a> Parser<'a> {
     pub(super) fn maybe_recover_from_question_mark(&mut self, ty: P<Ty>) -> P<Ty> {
         if self.token == token::Question {
             self.bump();
-            self.struct_span_err(self.prev_token.span, "invalid `?` in type")
-                .span_label(self.prev_token.span, "`?` is only allowed on expressions, not types")
-                .multipart_suggestion(
-                    "if you meant to express that the type might not contain a value, use the `Option` wrapper type",
-                    vec![
-                        (ty.span.shrink_to_lo(), "Option<".to_string()),
-                        (self.prev_token.span, ">".to_string()),
-                    ],
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+            self.sess.emit_err(QuestionMarkInType {
+                span: self.prev_token.span,
+                sugg: QuestionMarkInTypeSugg {
+                    left: ty.span.shrink_to_lo(),
+                    right: self.prev_token.span,
+                },
+            });
             self.mk_ty(ty.span.to(self.prev_token.span), TyKind::Err)
         } else {
             ty
@@ -2201,19 +1633,16 @@ impl<'a> Parser<'a> {
             (token::CloseDelim(Delimiter::Parenthesis), Some(begin_par_sp)) => {
                 self.bump();
 
-                self.struct_span_err(
-                    MultiSpan::from_spans(vec![begin_par_sp, self.prev_token.span]),
-                    "unexpected parentheses surrounding `for` loop head",
-                )
-                .multipart_suggestion(
-                    "remove parentheses in `for` loop",
-                    vec![(begin_par_sp, String::new()), (self.prev_token.span, String::new())],
+                self.sess.emit_err(ParenthesesInForHead {
+                    span: vec![begin_par_sp, self.prev_token.span],
                     // With e.g. `for (x) in y)` this would replace `(x) in y)`
                     // with `x) in y)` which is syntactically invalid.
                     // However, this is prevented before we get here.
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+                    sugg: ParenthesesInForHeadSugg {
+                        left: begin_par_sp,
+                        right: self.prev_token.span,
+                    },
+                });
 
                 // Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
                 pat.and_then(|pat| match pat.kind {
@@ -2432,12 +1861,7 @@ impl<'a> Parser<'a> {
 
     pub(super) fn eat_incorrect_doc_comment_for_param_type(&mut self) {
         if let token::DocComment(..) = self.token.kind {
-            self.struct_span_err(
-                self.token.span,
-                "documentation comments cannot be applied to a function parameter's type",
-            )
-            .span_label(self.token.span, "doc comments are not allowed here")
-            .emit();
+            self.sess.emit_err(DocCommentOnParamType { span: self.token.span });
             self.bump();
         } else if self.token == token::Pound
             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Bracket))
@@ -2449,9 +1873,7 @@ impl<'a> Parser<'a> {
             }
             let sp = lo.to(self.token.span);
             self.bump();
-            self.struct_span_err(sp, "attributes cannot be applied to a function parameter's type")
-                .span_label(sp, "attributes are not allowed here")
-                .emit();
+            self.sess.emit_err(AttributeOnParamType { span: sp });
         }
     }
 
@@ -2572,19 +1994,7 @@ impl<'a> Parser<'a> {
         self.expect(&token::Colon)?;
         let ty = self.parse_ty()?;
 
-        struct_span_err!(
-            self.diagnostic(),
-            pat.span,
-            E0642,
-            "patterns aren't allowed in methods without bodies",
-        )
-        .span_suggestion_short(
-            pat.span,
-            "give this argument a name or use an underscore to ignore it",
-            "_",
-            Applicability::MachineApplicable,
-        )
-        .emit();
+        self.sess.emit_err(PatternMethodParamWithoutBody { span: pat.span });
 
         // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
         let pat =
@@ -2593,11 +2003,9 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn recover_bad_self_param(&mut self, mut param: Param) -> PResult<'a, Param> {
-        let sp = param.pat.span;
+        let span = param.pat.span;
         param.ty.kind = TyKind::Err;
-        self.struct_span_err(sp, "unexpected `self` parameter in function")
-            .span_label(sp, "must be the first parameter of an associated function")
-            .emit();
+        self.sess.emit_err(SelfParamNotFirst { span });
         Ok(param)
     }
 
@@ -2642,7 +2050,7 @@ impl<'a> Parser<'a> {
         let mut err = self.struct_span_err(span, &msg);
         let sp = self.sess.source_map().start_point(self.token.span);
         if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-            self.sess.expr_parentheses_needed(&mut err, *sp);
+            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
         }
         err.span_label(span, "expected expression");
         err
@@ -2746,20 +2154,13 @@ impl<'a> Parser<'a> {
             err
         })?;
         if !self.expr_is_valid_const_arg(&expr) {
-            self.struct_span_err(
-                expr.span,
-                "expressions must be enclosed in braces to be used as const generic \
-                    arguments",
-            )
-            .multipart_suggestion(
-                "enclose the `const` expression in braces",
-                vec![
-                    (expr.span.shrink_to_lo(), "{ ".to_string()),
-                    (expr.span.shrink_to_hi(), " }".to_string()),
-                ],
-                Applicability::MachineApplicable,
-            )
-            .emit();
+            self.sess.emit_err(ConstGenericWithoutBraces {
+                span: expr.span,
+                sugg: ConstGenericWithoutBracesSugg {
+                    left: expr.span.shrink_to_lo(),
+                    right: expr.span.shrink_to_hi(),
+                },
+            });
         }
         Ok(expr)
     }
@@ -2774,24 +2175,30 @@ impl<'a> Parser<'a> {
                 return None;
             }
         };
-        let mut err =
-            self.struct_span_err(param.span(), "unexpected `const` parameter declaration");
-        err.span_label(param.span(), "expected a `const` expression, not a parameter declaration");
-        if let (Some(generics), Ok(snippet)) =
-            (ty_generics, self.sess.source_map().span_to_snippet(param.span()))
-        {
-            let (span, sugg) = match &generics.params[..] {
-                [] => (generics.span, format!("<{snippet}>")),
-                [.., generic] => (generic.span().shrink_to_hi(), format!(", {snippet}")),
-            };
-            err.multipart_suggestion(
-                "`const` parameters must be declared for the `impl`",
-                vec![(span, sugg), (param.span(), param.ident.to_string())],
-                Applicability::MachineApplicable,
-            );
-        }
+
+        let ident = param.ident.to_string();
+        let sugg = match (ty_generics, self.sess.source_map().span_to_snippet(param.span())) {
+            (Some(Generics { params, span: impl_generics, .. }), Ok(snippet)) => {
+                Some(match &params[..] {
+                    [] => UnexpectedConstParamDeclarationSugg::AddParam {
+                        impl_generics: *impl_generics,
+                        incorrect_decl: param.span(),
+                        snippet,
+                        ident,
+                    },
+                    [.., generic] => UnexpectedConstParamDeclarationSugg::AppendParam {
+                        impl_generics_end: generic.span().shrink_to_hi(),
+                        incorrect_decl: param.span(),
+                        snippet,
+                        ident,
+                    },
+                })
+            }
+            _ => None,
+        };
+        self.sess.emit_err(UnexpectedConstParamDeclaration { span: param.span(), sugg });
+
         let value = self.mk_expr_err(param.span());
-        err.emit();
         Some(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }))
     }
 
@@ -2809,20 +2216,15 @@ impl<'a> Parser<'a> {
         self.bump(); // `const`
 
         // Detect and recover from the old, pre-RFC2000 syntax for const generics.
-        let mut err = self
-            .struct_span_err(start, "expected lifetime, type, or constant, found keyword `const`");
+        let mut err = UnexpectedConstInGenericParam { span: start, to_remove: None };
         if self.check_const_arg() {
-            err.span_suggestion_verbose(
-                start.until(self.token.span),
-                "the `const` keyword is only needed in the definition of the type",
-                "",
-                Applicability::MaybeIncorrect,
-            );
-            err.emit();
+            err.to_remove = Some(start.until(self.token.span));
+            self.sess.emit_err(err);
             Ok(Some(GenericArg::Const(self.parse_const_arg()?)))
         } else {
             let after_kw_const = self.token.span;
-            self.recover_const_arg(after_kw_const, err).map(Some)
+            self.recover_const_arg(after_kw_const, err.into_diagnostic(&self.sess.span_diagnostic))
+                .map(Some)
         }
     }
 
@@ -2928,24 +2330,6 @@ impl<'a> Parser<'a> {
         GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value })
     }
 
-    /// Get the diagnostics for the cases where `move async` is found.
-    ///
-    /// `move_async_span` starts at the 'm' of the move keyword and ends with the 'c' of the async keyword
-    pub(super) fn incorrect_move_async_order_found(
-        &self,
-        move_async_span: Span,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
-        let mut err =
-            self.struct_span_err(move_async_span, "the order of `move` and `async` is incorrect");
-        err.span_suggestion_verbose(
-            move_async_span,
-            "try switching the order",
-            "async move",
-            Applicability::MaybeIncorrect,
-        );
-        err
-    }
-
     /// Some special error handling for the "top-level" patterns in a match arm,
     /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
     pub(crate) fn maybe_recover_colon_colon_in_pat_typo(
@@ -3141,17 +2525,11 @@ impl<'a> Parser<'a> {
                 let (a_span, b_span) = (a.span(), b.span());
                 let between_span = a_span.shrink_to_hi().to(b_span.shrink_to_lo());
                 if self.span_to_snippet(between_span).as_ref().map(|a| &a[..]) == Ok(":: ") {
-                    let mut err = self.struct_span_err(
-                        path.span.shrink_to_hi(),
-                        "expected `:` followed by trait or lifetime",
-                    );
-                    err.span_suggestion(
-                        between_span,
-                        "use single colon",
-                        ": ",
-                        Applicability::MachineApplicable,
-                    );
-                    return Err(err);
+                    return Err(DoubleColonInBound {
+                        span: path.span.shrink_to_hi(),
+                        between: between_span,
+                    }
+                    .into_diagnostic(&self.sess.span_diagnostic));
                 }
             }
         }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index ae77961b7bc..11301f03e48 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1,27 +1,33 @@
-use super::diagnostics::{
-    CatchAfterTry, CommaAfterBaseStruct, DoCatchSyntaxRemoved, DotDotDot, EqFieldInit,
-    ExpectedElseBlock, ExpectedExpressionFoundLet, FieldExpressionWithGeneric,
-    FloatLiteralRequiresIntegerPart, IfExpressionMissingCondition, IfExpressionMissingThenBlock,
-    IfExpressionMissingThenBlockSub, InvalidBlockMacroSegment, InvalidComparisonOperator,
-    InvalidComparisonOperatorSub, InvalidLogicalOperator, InvalidLogicalOperatorSub,
-    LeftArrowOperator, LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath,
-    MalformedLoopLabel, MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray,
-    NotAsNegationOperator, NotAsNegationOperatorSub, OuterAttributeNotAllowedOnIfElse,
-    RequireColonAfterLabeledExpression, SnapshotParser, TildeAsUnaryOperator,
-    UnexpectedTokenAfterLabel,
-};
+use super::diagnostics::SnapshotParser;
 use super::pat::{CommaRecoveryMode, RecoverColon, RecoverComma, PARAM_EXPECTED};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{
     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Restrictions,
     SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
 };
-use crate::maybe_recover_from_interpolated_ty_qpath;
-use crate::parser::diagnostics::{
-    IntLiteralTooLarge, InvalidFloatLiteralSuffix, InvalidFloatLiteralWidth,
-    InvalidIntLiteralWidth, InvalidNumLiteralBasePrefix, InvalidNumLiteralSuffix,
-    MissingCommaAfterMatchArm,
+use crate::errors::{
+    ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
+    BinaryFloatLiteralNotSupported, BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct,
+    ComparisonInterpretedAsGeneric, ComparisonOrShiftInterpretedAsGenericSugg,
+    DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedExpressionFoundLet,
+    FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
+    HexadecimalFloatLiteralNotSupported, IfExpressionMissingCondition,
+    IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub, IntLiteralTooLarge,
+    InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
+    InvalidFloatLiteralSuffix, InvalidFloatLiteralWidth, InvalidIntLiteralWidth,
+    InvalidInterpolatedExpression, InvalidLiteralSuffix, InvalidLiteralSuffixOnTupleIndex,
+    InvalidLogicalOperator, InvalidLogicalOperatorSub, InvalidNumLiteralBasePrefix,
+    InvalidNumLiteralSuffix, LabeledLoopInBreak, LeadingPlusNotSupported, LeftArrowOperator,
+    LifetimeInBorrowExpression, MacroInvocationWithQualifiedPath, MalformedLoopLabel,
+    MatchArmBodyWithoutBraces, MatchArmBodyWithoutBracesSugg, MissingCommaAfterMatchArm,
+    MissingInInForLoop, MissingInInForLoopSub, MissingSemicolonBeforeArray, NoFieldsForFnCall,
+    NotAsNegationOperator, NotAsNegationOperatorSub, OctalFloatLiteralNotSupported,
+    OuterAttributeNotAllowedOnIfElse, ParenthesesWithStructFields,
+    RequireColonAfterLabeledExpression, ShiftInterpretedAsGeneric, StructLiteralNotAllowedHere,
+    StructLiteralNotAllowedHereSugg, TildeAsUnaryOperator, UnexpectedTokenAfterLabel,
+    UnexpectedTokenAfterLabelSugg, WrapExpressionInParentheses,
 };
+use crate::maybe_recover_from_interpolated_ty_qpath;
 
 use core::mem;
 use rustc_ast::ptr::P;
@@ -38,6 +44,7 @@ use rustc_ast::{ClosureBinder, StmtKind};
 use rustc_ast_pretty::pprust;
 use rustc_errors::IntoDiagnostic;
 use rustc_errors::{Applicability, Diagnostic, PResult};
+use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
 use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_span::source_map::{self, Span, Spanned};
@@ -421,13 +428,11 @@ impl<'a> Parser<'a> {
     /// but the next token implies this should be parsed as an expression.
     /// For example: `if let Some(x) = x { x } else { 0 } / 2`.
     fn error_found_expr_would_be_stmt(&self, lhs: &Expr) {
-        let mut err = self.struct_span_err(
-            self.token.span,
-            &format!("expected expression, found `{}`", pprust::token_to_string(&self.token),),
-        );
-        err.span_label(self.token.span, "expected expression");
-        self.sess.expr_parentheses_needed(&mut err, lhs.span);
-        err.emit();
+        self.sess.emit_err(FoundExprWouldBeStmt {
+            span: self.token.span,
+            token: self.token.clone(),
+            suggestion: ExprParenthesesNeeded::surrounding(lhs.span),
+        });
     }
 
     /// Possibly translate the current token to an associative operator.
@@ -578,21 +583,16 @@ impl<'a> Parser<'a> {
                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
             }
             token::BinOp(token::Plus) if this.look_ahead(1, |tok| tok.is_numeric_lit()) => {
-                let mut err = this.struct_span_err(lo, "leading `+` is not supported");
-                err.span_label(lo, "unexpected `+`");
+                let mut err =
+                    LeadingPlusNotSupported { span: lo, remove_plus: None, add_parentheses: None };
 
                 // a block on the LHS might have been intended to be an expression instead
                 if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
-                    this.sess.expr_parentheses_needed(&mut err, *sp);
+                    err.add_parentheses = Some(ExprParenthesesNeeded::surrounding(*sp));
                 } else {
-                    err.span_suggestion_verbose(
-                        lo,
-                        "try removing the `+`",
-                        "",
-                        Applicability::MachineApplicable,
-                    );
+                    err.remove_plus = Some(lo);
                 }
-                err.emit();
+                this.sess.emit_err(err);
 
                 this.bump();
                 this.parse_prefix_expr(None)
@@ -755,9 +755,34 @@ impl<'a> Parser<'a> {
 
                 match self.parse_path(PathStyle::Expr) {
                     Ok(path) => {
-                        let (op_noun, op_verb) = match self.token.kind {
-                            token::Lt => ("comparison", "comparing"),
-                            token::BinOp(token::Shl) => ("shift", "shifting"),
+                        let span_after_type = parser_snapshot_after_type.token.span;
+                        let expr = mk_expr(
+                            self,
+                            lhs,
+                            self.mk_ty(path.span, TyKind::Path(None, path.clone())),
+                        );
+
+                        let args_span = self.look_ahead(1, |t| t.span).to(span_after_type);
+                        let suggestion = ComparisonOrShiftInterpretedAsGenericSugg {
+                            left: expr.span.shrink_to_lo(),
+                            right: expr.span.shrink_to_hi(),
+                        };
+
+                        match self.token.kind {
+                            token::Lt => self.sess.emit_err(ComparisonInterpretedAsGeneric {
+                                comparison: self.token.span,
+                                r#type: path,
+                                args: args_span,
+                                suggestion,
+                            }),
+                            token::BinOp(token::Shl) => {
+                                self.sess.emit_err(ShiftInterpretedAsGeneric {
+                                    shift: self.token.span,
+                                    r#type: path,
+                                    args: args_span,
+                                    suggestion,
+                                })
+                            }
                             _ => {
                                 // We can end up here even without `<` being the next token, for
                                 // example because `parse_ty_no_plus` returns `Err` on keywords,
@@ -771,33 +796,7 @@ impl<'a> Parser<'a> {
                         // Successfully parsed the type path leaving a `<` yet to parse.
                         type_err.cancel();
 
-                        // Report non-fatal diagnostics, keep `x as usize` as an expression
-                        // in AST and continue parsing.
-                        let msg = format!(
-                            "`<` is interpreted as a start of generic arguments for `{}`, not a {}",
-                            pprust::path_to_string(&path),
-                            op_noun,
-                        );
-                        let span_after_type = parser_snapshot_after_type.token.span;
-                        let expr =
-                            mk_expr(self, lhs, self.mk_ty(path.span, TyKind::Path(None, path)));
-
-                        self.struct_span_err(self.token.span, &msg)
-                            .span_label(
-                                self.look_ahead(1, |t| t.span).to(span_after_type),
-                                "interpreted as generic arguments",
-                            )
-                            .span_label(self.token.span, format!("not interpreted as {op_noun}"))
-                            .multipart_suggestion(
-                                &format!("try {op_verb} the cast value"),
-                                vec![
-                                    (expr.span.shrink_to_lo(), "(".to_string()),
-                                    (expr.span.shrink_to_hi(), ")".to_string()),
-                                ],
-                                Applicability::MachineApplicable,
-                            )
-                            .emit();
-
+                        // Keep `x as usize` as an expression in AST and continue parsing.
                         expr
                     }
                     Err(path_err) => {
@@ -1158,7 +1157,9 @@ impl<'a> Parser<'a> {
         }
         let span = self.prev_token.span;
         let field = ExprKind::Field(base, Ident::new(field, span));
-        self.expect_no_suffix(span, "a tuple index", suffix);
+        if let Some(suffix) = suffix {
+            self.expect_no_tuple_index_suffix(span, suffix);
+        }
         self.mk_expr(lo.to(span), field)
     }
 
@@ -1196,9 +1197,8 @@ impl<'a> Parser<'a> {
     ) -> Option<P<Expr>> {
         match (seq.as_mut(), snapshot) {
             (Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
-                let name = pprust::path_to_string(&path);
                 snapshot.bump(); // `(`
-                match snapshot.parse_struct_fields(path, false, Delimiter::Parenthesis) {
+                match snapshot.parse_struct_fields(path.clone(), false, Delimiter::Parenthesis) {
                     Ok((fields, ..))
                         if snapshot.eat(&token::CloseDelim(Delimiter::Parenthesis)) =>
                     {
@@ -1208,29 +1208,25 @@ impl<'a> Parser<'a> {
                         let close_paren = self.prev_token.span;
                         let span = lo.to(self.prev_token.span);
                         if !fields.is_empty() {
-                            let replacement_err = self.struct_span_err(
+                            let mut replacement_err = ParenthesesWithStructFields {
                                 span,
-                                "invalid `struct` delimiters or `fn` call arguments",
-                            );
-                            mem::replace(err, replacement_err).cancel();
-
-                            err.multipart_suggestion(
-                                &format!("if `{name}` is a struct, use braces as delimiters"),
-                                vec![
-                                    (open_paren, " { ".to_string()),
-                                    (close_paren, " }".to_string()),
-                                ],
-                                Applicability::MaybeIncorrect,
-                            );
-                            err.multipart_suggestion(
-                                &format!("if `{name}` is a function, use the arguments directly"),
-                                fields
-                                    .into_iter()
-                                    .map(|field| (field.span.until(field.expr.span), String::new()))
-                                    .collect(),
-                                Applicability::MaybeIncorrect,
-                            );
-                            err.emit();
+                                r#type: path,
+                                braces_for_struct: BracesForStructLiteral {
+                                    first: open_paren,
+                                    second: close_paren,
+                                },
+                                no_fields_for_fn: NoFieldsForFnCall {
+                                    fields: fields
+                                        .into_iter()
+                                        .map(|field| field.span.until(field.expr.span))
+                                        .collect(),
+                                },
+                            }
+                            .into_diagnostic(&self.sess.span_diagnostic);
+                            replacement_err.emit();
+
+                            let old_err = mem::replace(err, replacement_err);
+                            old_err.cancel();
                         } else {
                             err.emit();
                         }
@@ -1314,7 +1310,7 @@ impl<'a> Parser<'a> {
                 // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
                 // then suggest parens around the lhs.
                 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
-                    self.sess.expr_parentheses_needed(&mut err, *sp);
+                    err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
                 }
                 err
             })
@@ -1537,15 +1533,19 @@ impl<'a> Parser<'a> {
             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
         {
             // We're probably inside of a `Path<'a>` that needs a turbofish
-            self.sess.emit_err(UnexpectedTokenAfterLabel(self.token.span));
+            self.sess.emit_err(UnexpectedTokenAfterLabel {
+                span: self.token.span,
+                remove_label: None,
+                enclose_in_block: None,
+            });
             consume_colon = false;
             Ok(self.mk_expr_err(lo))
         } else {
-            // FIXME: use UnexpectedTokenAfterLabel, needs multipart suggestions
-            let msg = "expected `while`, `for`, `loop` or `{` after a label";
-
-            let mut err = self.struct_span_err(self.token.span, msg);
-            err.span_label(self.token.span, msg);
+            let mut err = UnexpectedTokenAfterLabel {
+                span: self.token.span,
+                remove_label: None,
+                enclose_in_block: None,
+            };
 
             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
             let expr = self.parse_expr().map(|expr| {
@@ -1572,28 +1572,15 @@ impl<'a> Parser<'a> {
                 // If there are no breaks that may use this label, suggest removing the label and
                 // recover to the unmodified expression.
                 if !found_labeled_breaks {
-                    let msg = "consider removing the label";
-                    err.span_suggestion_verbose(
-                        lo.until(span),
-                        msg,
-                        "",
-                        Applicability::MachineApplicable,
-                    );
+                    err.remove_label = Some(lo.until(span));
 
                     return expr;
                 }
 
-                let sugg_msg = "consider enclosing expression in a block";
-                let suggestions = vec![
-                    (span.shrink_to_lo(), "{ ".to_owned()),
-                    (span.shrink_to_hi(), " }".to_owned()),
-                ];
-
-                err.multipart_suggestion_verbose(
-                    sugg_msg,
-                    suggestions,
-                    Applicability::MachineApplicable,
-                );
+                err.enclose_in_block = Some(UnexpectedTokenAfterLabelSugg {
+                    left: span.shrink_to_lo(),
+                    right: span.shrink_to_hi(),
+                });
 
                 // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to suppress future errors about `break 'label`.
                 let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
@@ -1601,7 +1588,7 @@ impl<'a> Parser<'a> {
                 self.mk_expr(span, ExprKind::Block(blk, label))
             });
 
-            err.emit();
+            self.sess.emit_err(err);
             expr
         }?;
 
@@ -1672,19 +1659,13 @@ impl<'a> Parser<'a> {
             // The value expression can be a labeled loop, see issue #86948, e.g.:
             // `loop { break 'label: loop { break 'label 42; }; }`
             let lexpr = self.parse_labeled_expr(label.take().unwrap(), true)?;
-            self.struct_span_err(
-                lexpr.span,
-                "parentheses are required around this expression to avoid confusion with a labeled break expression",
-            )
-            .multipart_suggestion(
-                "wrap the expression in parentheses",
-                vec![
-                    (lexpr.span.shrink_to_lo(), "(".to_string()),
-                    (lexpr.span.shrink_to_hi(), ")".to_string()),
-                ],
-                Applicability::MachineApplicable,
-            )
-            .emit();
+            self.sess.emit_err(LabeledLoopInBreak {
+                span: lexpr.span,
+                sub: WrapExpressionInParentheses {
+                    left: lexpr.span.shrink_to_lo(),
+                    right: lexpr.span.shrink_to_hi(),
+                },
+            });
             Some(lexpr)
         } else if self.token != token::OpenDelim(Delimiter::Brace)
             || !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
@@ -1756,9 +1737,8 @@ impl<'a> Parser<'a> {
                 };
                 if let Some(expr) = expr {
                     if matches!(expr.kind, ExprKind::Err) {
-                        let mut err = self
-                            .diagnostic()
-                            .struct_span_err(self.token.span, "invalid interpolated expression");
+                        let mut err = InvalidInterpolatedExpression { span: self.token.span }
+                            .into_diagnostic(&self.sess.span_diagnostic);
                         err.downgrade_to_delayed_bug();
                         return err;
                     }
@@ -1790,7 +1770,10 @@ impl<'a> Parser<'a> {
             });
             if let Some(token) = &recovered {
                 self.bump();
-                self.error_float_lits_must_have_int_part(&token);
+                self.sess.emit_err(FloatLiteralRequiresIntegerPart {
+                    span: token.span,
+                    correct: pprust::token_to_string(token).into_owned(),
+                });
             }
         }
 
@@ -1818,13 +1801,6 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn error_float_lits_must_have_int_part(&self, token: &Token) {
-        self.sess.emit_err(FloatLiteralRequiresIntegerPart {
-            span: token.span,
-            correct: pprust::token_to_string(token).into_owned(),
-        });
-    }
-
     fn report_lit_error(&self, err: LitError, lit: token::Lit, span: Span) {
         // Checks if `s` looks like i32 or u1234 etc.
         fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
@@ -1853,11 +1829,13 @@ impl<'a> Parser<'a> {
             // by lexer, so here we don't report it the second time.
             LitError::LexerError => {}
             LitError::InvalidSuffix => {
-                self.expect_no_suffix(
-                    span,
-                    &format!("{} {} literal", kind.article(), kind.descr()),
-                    suffix,
-                );
+                if let Some(suffix) = suffix {
+                    self.sess.emit_err(InvalidLiteralSuffix {
+                        span,
+                        kind: format!("{}", kind.descr()),
+                        suffix,
+                    });
+                }
             }
             LitError::InvalidIntSuffix => {
                 let suf = suffix.expect("suffix error with no suffix");
@@ -1883,15 +1861,12 @@ impl<'a> Parser<'a> {
                 }
             }
             LitError::NonDecimalFloat(base) => {
-                let descr = match base {
-                    16 => "hexadecimal",
-                    8 => "octal",
-                    2 => "binary",
+                match base {
+                    16 => self.sess.emit_err(HexadecimalFloatLiteralNotSupported { span }),
+                    8 => self.sess.emit_err(OctalFloatLiteralNotSupported { span }),
+                    2 => self.sess.emit_err(BinaryFloatLiteralNotSupported { span }),
                     _ => unreachable!(),
                 };
-                self.struct_span_err(span, &format!("{descr} float literal is not supported"))
-                    .span_label(span, "not supported")
-                    .emit();
             }
             LitError::IntTooLarge => {
                 self.sess.emit_err(IntLiteralTooLarge { span });
@@ -1899,38 +1874,17 @@ impl<'a> Parser<'a> {
         }
     }
 
-    pub(super) fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<Symbol>) {
-        if let Some(suf) = suffix {
-            let mut err = if kind == "a tuple index"
-                && [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf)
-            {
-                // #59553: warn instead of reject out of hand to allow the fix to percolate
-                // through the ecosystem when people fix their macros
-                let mut err = self
-                    .sess
-                    .span_diagnostic
-                    .struct_span_warn(sp, &format!("suffixes on {kind} are invalid"));
-                err.note(&format!(
-                    "`{}` is *temporarily* accepted on tuple index fields as it was \
-                        incorrectly accepted on stable for a few releases",
-                    suf,
-                ));
-                err.help(
-                    "on proc macros, you'll want to use `syn::Index::from` or \
-                        `proc_macro::Literal::*_unsuffixed` for code that will desugar \
-                        to tuple field access",
-                );
-                err.note(
-                    "see issue #60210 <https://github.com/rust-lang/rust/issues/60210> \
-                     for more information",
-                );
-                err
-            } else {
-                self.struct_span_err(sp, &format!("suffixes on {kind} are invalid"))
-                    .forget_guarantee()
-            };
-            err.span_label(sp, format!("invalid suffix `{suf}`"));
-            err.emit();
+    pub(super) fn expect_no_tuple_index_suffix(&self, span: Span, suffix: Symbol) {
+        if [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suffix) {
+            // #59553: warn instead of reject out of hand to allow the fix to percolate
+            // through the ecosystem when people fix their macros
+            self.sess.emit_warning(InvalidLiteralSuffixOnTupleIndex {
+                span,
+                suffix,
+                exception: Some(()),
+            });
+        } else {
+            self.sess.emit_err(InvalidLiteralSuffixOnTupleIndex { span, suffix, exception: None });
         }
     }
 
@@ -1964,14 +1918,13 @@ impl<'a> Parser<'a> {
         let mut snapshot = self.create_snapshot_for_diagnostic();
         match snapshot.parse_array_or_repeat_expr(Delimiter::Brace) {
             Ok(arr) => {
-                let hi = snapshot.prev_token.span;
-                self.struct_span_err(arr.span, "this is a block expression, not an array")
-                    .multipart_suggestion(
-                        "to make an array, use square brackets instead of curly braces",
-                        vec![(lo, "[".to_owned()), (hi, "]".to_owned())],
-                        Applicability::MaybeIncorrect,
-                    )
-                    .emit();
+                self.sess.emit_err(ArrayBracketsInsteadOfSpaces {
+                    span: arr.span,
+                    sub: ArrayBracketsInsteadOfSpacesSugg {
+                        left: lo,
+                        right: snapshot.prev_token.span,
+                    },
+                });
 
                 self.restore_snapshot(snapshot);
                 Some(self.mk_expr_err(arr.span))
@@ -2134,7 +2087,8 @@ impl<'a> Parser<'a> {
             // Check for `move async` and recover
             if self.check_keyword(kw::Async) {
                 let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
-                Err(self.incorrect_move_async_order_found(move_async_span))
+                Err(AsyncMoveOrderIncorrect { span: move_async_span }
+                    .into_diagnostic(&self.sess.span_diagnostic))
             } else {
                 Ok(CaptureBy::Value)
             }
@@ -2515,39 +2469,22 @@ impl<'a> Parser<'a> {
         self.bump(); // `;`
         let mut stmts =
             vec![self.mk_stmt(first_expr.span, ast::StmtKind::Expr(first_expr.clone()))];
-        let err = |this: &mut Parser<'_>, stmts: Vec<ast::Stmt>| {
+        let err = |this: &Parser<'_>, stmts: Vec<ast::Stmt>| {
             let span = stmts[0].span.to(stmts[stmts.len() - 1].span);
-            let mut err = this.struct_span_err(span, "`match` arm body without braces");
-            let (these, s, are) =
-                if stmts.len() > 1 { ("these", "s", "are") } else { ("this", "", "is") };
-            err.span_label(
-                span,
-                &format!(
-                    "{these} statement{s} {are} not surrounded by a body",
-                    these = these,
-                    s = s,
-                    are = are
-                ),
-            );
-            err.span_label(arrow_span, "while parsing the `match` arm starting here");
-            if stmts.len() > 1 {
-                err.multipart_suggestion(
-                    &format!("surround the statement{s} with a body"),
-                    vec![
-                        (span.shrink_to_lo(), "{ ".to_string()),
-                        (span.shrink_to_hi(), " }".to_string()),
-                    ],
-                    Applicability::MachineApplicable,
-                );
-            } else {
-                err.span_suggestion(
-                    semi_sp,
-                    "use a comma to end a `match` arm expression",
-                    ",",
-                    Applicability::MachineApplicable,
-                );
-            }
-            err.emit();
+
+            this.sess.emit_err(MatchArmBodyWithoutBraces {
+                statements: span,
+                arrow: arrow_span,
+                num_statements: stmts.len(),
+                sub: if stmts.len() > 1 {
+                    MatchArmBodyWithoutBracesSugg::AddBraces {
+                        left: span.shrink_to_lo(),
+                        right: span.shrink_to_hi(),
+                    }
+                } else {
+                    MatchArmBodyWithoutBracesSugg::UseComma { semicolon: semi_sp }
+                },
+            });
             this.mk_expr_err(span)
         };
         // We might have either a `,` -> `;` typo, or a block without braces. We need
@@ -2836,23 +2773,19 @@ impl<'a> Parser<'a> {
             let expr = self.parse_struct_expr(qself.cloned(), path.clone(), true);
             if let (Ok(expr), false) = (&expr, struct_allowed) {
                 // This is a struct literal, but we don't can't accept them here.
-                self.error_struct_lit_not_allowed_here(path.span, expr.span);
+                self.sess.emit_err(StructLiteralNotAllowedHere {
+                    span: expr.span,
+                    sub: StructLiteralNotAllowedHereSugg {
+                        left: path.span.shrink_to_lo(),
+                        right: expr.span.shrink_to_hi(),
+                    },
+                });
             }
             return Some(expr);
         }
         None
     }
 
-    fn error_struct_lit_not_allowed_here(&self, lo: Span, sp: Span) {
-        self.struct_span_err(sp, "struct literals are not allowed here")
-            .multipart_suggestion(
-                "surround the struct literal with parentheses",
-                vec![(lo.shrink_to_lo(), "(".to_string()), (sp.shrink_to_hi(), ")".to_string())],
-                Applicability::MachineApplicable,
-            )
-            .emit();
-    }
-
     pub(super) fn parse_struct_fields(
         &mut self,
         pth: ast::Path,
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index e55b5ce71cd..25425fbb2c6 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1,4 +1,6 @@
-use super::diagnostics::{dummy_arg, ConsumeClosingDelim, Error};
+use crate::errors::{DocCommentDoesNotDocumentAnything, UseEmptyBlockNotSemi};
+
+use super::diagnostics::{dummy_arg, ConsumeClosingDelim};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, TrailingToken};
 
@@ -13,7 +15,7 @@ use rustc_ast::{EnumDef, FieldDef, Generics, TraitRef, Ty, TyKind, Variant, Vari
 use rustc_ast::{FnHeader, ForeignItem, Path, PathSegment, Visibility, VisibilityKind};
 use rustc_ast::{MacArgs, MacCall, MacDelimiter};
 use rustc_ast_pretty::pprust;
-use rustc_errors::{struct_span_err, Applicability, PResult, StashKey};
+use rustc_errors::{struct_span_err, Applicability, IntoDiagnostic, PResult, StashKey};
 use rustc_span::edition::Edition;
 use rustc_span::lev_distance::lev_distance;
 use rustc_span::source_map::{self, Span};
@@ -664,6 +666,14 @@ impl<'a> Parser<'a> {
         mut parse_item: impl FnMut(&mut Parser<'a>) -> PResult<'a, Option<Option<T>>>,
     ) -> PResult<'a, Vec<T>> {
         let open_brace_span = self.token.span;
+
+        // Recover `impl Ty;` instead of `impl Ty {}`
+        if self.token == TokenKind::Semi {
+            self.sess.emit_err(UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            return Ok(vec![]);
+        }
+
         self.expect(&token::OpenDelim(Delimiter::Brace))?;
         attrs.extend(self.parse_inner_attributes()?);
 
@@ -750,8 +760,8 @@ impl<'a> Parser<'a> {
                 )
                 .span_label(self.token.span, "this doc comment doesn't document anything")
                 .help(
-                    "doc comments must come before what they document, maybe a \
-                    comment was intended with `//`?",
+                    "doc comments must come before what they document, if a comment was \
+                    intended use `//`",
                 )
                 .emit();
                 self.bump();
@@ -1283,12 +1293,10 @@ impl<'a> Parser<'a> {
     /// Parses an enum declaration.
     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
         if self.token.is_keyword(kw::Struct) {
-            let mut err = self.struct_span_err(
-                self.prev_token.span.to(self.token.span),
-                "`enum` and `struct` are mutually exclusive",
-            );
+            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(
-                self.prev_token.span.to(self.token.span),
+                span,
                 "replace `enum struct` with",
                 "enum",
                 Applicability::MachineApplicable,
@@ -1305,12 +1313,20 @@ impl<'a> Parser<'a> {
         let mut generics = self.parse_generics()?;
         generics.where_clause = self.parse_where_clause()?;
 
-        let (variants, _) = self
-            .parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant())
-            .map_err(|e| {
-                self.recover_stmt();
-                e
-            })?;
+        // Possibly recover `enum Foo;` instead of `enum Foo {}`
+        let (variants, _) = if self.token == TokenKind::Semi {
+            self.sess.emit_err(UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            (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");
+                    self.recover_stmt();
+                    e
+                },
+            )?
+        };
 
         let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
         Ok((id, ItemKind::Enum(enum_definition, generics)))
@@ -1332,7 +1348,8 @@ impl<'a> Parser<'a> {
 
                 let struct_def = if this.check(&token::OpenDelim(Delimiter::Brace)) {
                     // Parse a struct variant.
-                    let (fields, recovered) = this.parse_record_struct_body("struct", false)?;
+                    let (fields, recovered) =
+                        this.parse_record_struct_body("struct", ident.span, false)?;
                     VariantData::Struct(fields, recovered)
                 } else if this.check(&token::OpenDelim(Delimiter::Parenthesis)) {
                     VariantData::Tuple(this.parse_tuple_struct_body()?, DUMMY_NODE_ID)
@@ -1386,8 +1403,11 @@ impl<'a> Parser<'a> {
                 VariantData::Unit(DUMMY_NODE_ID)
             } else {
                 // If we see: `struct Foo<T> where T: Copy { ... }`
-                let (fields, recovered) =
-                    self.parse_record_struct_body("struct", generics.where_clause.has_where_token)?;
+                let (fields, recovered) = self.parse_record_struct_body(
+                    "struct",
+                    class_name.span,
+                    generics.where_clause.has_where_token,
+                )?;
                 VariantData::Struct(fields, recovered)
             }
         // No `where` so: `struct Foo<T>;`
@@ -1395,8 +1415,11 @@ impl<'a> Parser<'a> {
             VariantData::Unit(DUMMY_NODE_ID)
         // Record-style struct definition
         } else if self.token == token::OpenDelim(Delimiter::Brace) {
-            let (fields, recovered) =
-                self.parse_record_struct_body("struct", generics.where_clause.has_where_token)?;
+            let (fields, recovered) = self.parse_record_struct_body(
+                "struct",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
             VariantData::Struct(fields, recovered)
         // Tuple-style struct definition with optional where-clause.
         } else if self.token == token::OpenDelim(Delimiter::Parenthesis) {
@@ -1425,12 +1448,18 @@ impl<'a> Parser<'a> {
 
         let vdata = if self.token.is_keyword(kw::Where) {
             generics.where_clause = self.parse_where_clause()?;
-            let (fields, recovered) =
-                self.parse_record_struct_body("union", generics.where_clause.has_where_token)?;
+            let (fields, recovered) = self.parse_record_struct_body(
+                "union",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
             VariantData::Struct(fields, recovered)
         } else if self.token == token::OpenDelim(Delimiter::Brace) {
-            let (fields, recovered) =
-                self.parse_record_struct_body("union", generics.where_clause.has_where_token)?;
+            let (fields, recovered) = self.parse_record_struct_body(
+                "union",
+                class_name.span,
+                generics.where_clause.has_where_token,
+            )?;
             VariantData::Struct(fields, recovered)
         } else {
             let token_str = super::token_descr(&self.token);
@@ -1446,6 +1475,7 @@ impl<'a> Parser<'a> {
     fn parse_record_struct_body(
         &mut self,
         adt_ty: &str,
+        ident_span: Span,
         parsed_where: bool,
     ) -> PResult<'a, (Vec<FieldDef>, /* recovered */ bool)> {
         let mut fields = Vec::new();
@@ -1460,6 +1490,7 @@ impl<'a> Parser<'a> {
                 match field {
                     Ok(field) => fields.push(field),
                     Err(mut err) => {
+                        err.span_label(ident_span, format!("while parsing this {adt_ty}"));
                         err.emit();
                         break;
                     }
@@ -1555,7 +1586,10 @@ impl<'a> Parser<'a> {
             token::CloseDelim(Delimiter::Brace) => {}
             token::DocComment(..) => {
                 let previous_span = self.prev_token.span;
-                let mut err = self.span_err(self.token.span, Error::UselessDocComment);
+                let mut err = DocCommentDoesNotDocumentAnything {
+                    span: self.token.span,
+                    missing_comma: None,
+                };
                 self.bump(); // consume the doc comment
                 let comma_after_doc_seen = self.eat(&token::Comma);
                 // `seen_comma` is always false, because we are inside doc block
@@ -1564,18 +1598,13 @@ impl<'a> Parser<'a> {
                     seen_comma = true;
                 }
                 if comma_after_doc_seen || self.token == token::CloseDelim(Delimiter::Brace) {
-                    err.emit();
+                    self.sess.emit_err(err);
                 } else {
                     if !seen_comma {
                         let sp = self.sess.source_map().next_point(previous_span);
-                        err.span_suggestion(
-                            sp,
-                            "missing comma here",
-                            ",",
-                            Applicability::MachineApplicable,
-                        );
+                        err.missing_comma = Some(sp);
                     }
-                    return Err(err);
+                    return Err(err.into_diagnostic(&self.sess.span_diagnostic));
                 }
             }
             _ => {
@@ -1715,6 +1744,7 @@ impl<'a> Parser<'a> {
     fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
         let (ident, is_raw) = self.ident_or_err()?;
         if !is_raw && ident.is_reserved() {
+            let snapshot = self.create_snapshot_for_diagnostic();
             let err = if self.check_fn_front_matter(false) {
                 let inherited_vis = Visibility {
                     span: rustc_span::DUMMY_SP,
@@ -1723,18 +1753,40 @@ impl<'a> Parser<'a> {
                 };
                 // We use `parse_fn` to get a span for the function
                 let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
-                if let Err(mut db) =
-                    self.parse_fn(&mut AttrVec::new(), fn_parse_mode, lo, &inherited_vis)
-                {
-                    db.delay_as_bug();
+                match self.parse_fn(&mut AttrVec::new(), fn_parse_mode, lo, &inherited_vis) {
+                    Ok(_) => {
+                        let mut err = self.struct_span_err(
+                            lo.to(self.prev_token.span),
+                            &format!("functions are not allowed in {adt_ty} definitions"),
+                        );
+                        err.help(
+                            "unlike in C++, Java, and C#, functions are declared in `impl` blocks",
+                        );
+                        err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
+                        err
+                    }
+                    Err(err) => {
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                        self.expected_ident_found()
+                    }
+                }
+            } else if self.eat_keyword(kw::Struct) {
+                match self.parse_item_struct() {
+                    Ok((ident, _)) => {
+                        let mut err = self.struct_span_err(
+                            lo.with_hi(ident.span.hi()),
+                            &format!("structs are not allowed in {adt_ty} definitions"),
+                        );
+                        err.help("consider creating a new `struct` definition instead of nesting");
+                        err
+                    }
+                    Err(err) => {
+                        err.cancel();
+                        self.restore_snapshot(snapshot);
+                        self.expected_ident_found()
+                    }
                 }
-                let mut err = self.struct_span_err(
-                    lo.to(self.prev_token.span),
-                    &format!("functions are not allowed in {adt_ty} definitions"),
-                );
-                err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
-                err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
-                err
             } else {
                 self.expected_ident_found()
             };
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 4cb198561e0..b934e087608 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -13,7 +13,6 @@ mod ty;
 use crate::lexer::UnmatchedBrace;
 pub use attr_wrapper::AttrWrapper;
 pub use diagnostics::AttemptLocalParseRecovery;
-use diagnostics::Error;
 pub(crate) use item::FnParseMode;
 pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 pub use path::PathStyle;
@@ -32,7 +31,7 @@ use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::PResult;
 use rustc_errors::{
-    struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, FatalError, MultiSpan,
+    Applicability, DiagnosticBuilder, ErrorGuaranteed, FatalError, IntoDiagnostic, MultiSpan,
 };
 use rustc_session::parse::ParseSess;
 use rustc_span::source_map::{Span, DUMMY_SP};
@@ -41,6 +40,11 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use std::ops::Range;
 use std::{cmp, mem, slice};
 
+use crate::errors::{
+    DocCommentDoesNotDocumentAnything, IncorrectVisibilityRestriction, MismatchedClosingDelimiter,
+    NonStringAbiLiteral,
+};
+
 bitflags::bitflags! {
     struct Restrictions: u8 {
         const STMT_EXPR         = 1 << 0;
@@ -298,7 +302,10 @@ impl TokenCursor {
 
     fn desugar(&mut self, attr_style: AttrStyle, data: Symbol, span: Span) -> (Token, Spacing) {
         // Searches for the occurrences of `"#*` and returns the minimum number of `#`s
-        // required to wrap the text.
+        // required to wrap the text. E.g.
+        // - `abc d` is wrapped as `r"abc d"` (num_of_hashes = 0)
+        // - `abc "d"` is wrapped as `r#"abc "d""#` (num_of_hashes = 1)
+        // - `abc "##d##"` is wrapped as `r###"abc "d""###` (num_of_hashes = 3)
         let mut num_of_hashes = 0;
         let mut count = 0;
         for ch in data.as_str().chars() {
@@ -310,6 +317,7 @@ impl TokenCursor {
             num_of_hashes = cmp::max(num_of_hashes, count);
         }
 
+        // `/// foo` becomes `doc = r"foo".
         let delim_span = DelimSpan::from_single(span);
         let body = TokenTree::Delimited(
             delim_span,
@@ -406,24 +414,39 @@ pub enum FollowedByType {
     No,
 }
 
-fn token_descr_opt(token: &Token) -> Option<&'static str> {
-    Some(match token.kind {
-        _ if token.is_special_ident() => "reserved identifier",
-        _ if token.is_used_keyword() => "keyword",
-        _ if token.is_unused_keyword() => "reserved keyword",
-        token::DocComment(..) => "doc comment",
-        _ => return None,
-    })
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum TokenDescription {
+    ReservedIdentifier,
+    Keyword,
+    ReservedKeyword,
+    DocComment,
 }
 
-pub(super) fn token_descr(token: &Token) -> String {
-    let token_str = pprust::token_to_string(token);
-    match token_descr_opt(token) {
-        Some(prefix) => format!("{} `{}`", prefix, token_str),
-        _ => format!("`{}`", token_str),
+impl TokenDescription {
+    pub fn from_token(token: &Token) -> Option<Self> {
+        match token.kind {
+            _ if token.is_special_ident() => Some(TokenDescription::ReservedIdentifier),
+            _ if token.is_used_keyword() => Some(TokenDescription::Keyword),
+            _ if token.is_unused_keyword() => Some(TokenDescription::ReservedKeyword),
+            token::DocComment(..) => Some(TokenDescription::DocComment),
+            _ => None,
+        }
     }
 }
 
+pub(super) fn token_descr(token: &Token) -> String {
+    let name = pprust::token_to_string(token).to_string();
+
+    let kind = TokenDescription::from_token(token).map(|kind| match kind {
+        TokenDescription::ReservedIdentifier => "reserved identifier",
+        TokenDescription::Keyword => "keyword",
+        TokenDescription::ReservedKeyword => "reserved keyword",
+        TokenDescription::DocComment => "doc comment",
+    });
+
+    if let Some(kind) = kind { format!("{} `{}`", kind, name) } else { format!("`{}`", name) }
+}
+
 impl<'a> Parser<'a> {
     pub fn new(
         sess: &'a ParseSess,
@@ -518,9 +541,11 @@ impl<'a> Parser<'a> {
 
     fn ident_or_err(&mut self) -> PResult<'a, (Ident, /* is_raw */ bool)> {
         self.token.ident().ok_or_else(|| match self.prev_token.kind {
-            TokenKind::DocComment(..) => {
-                self.span_err(self.prev_token.span, Error::UselessDocComment)
+            TokenKind::DocComment(..) => DocCommentDoesNotDocumentAnything {
+                span: self.prev_token.span,
+                missing_comma: None,
             }
+            .into_diagnostic(&self.sess.span_diagnostic),
             _ => self.expected_ident_found(),
         })
     }
@@ -1144,7 +1169,9 @@ impl<'a> Parser<'a> {
     fn parse_field_name(&mut self) -> PResult<'a, Ident> {
         if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = self.token.kind
         {
-            self.expect_no_suffix(self.token.span, "a tuple index", suffix);
+            if let Some(suffix) = suffix {
+                self.expect_no_tuple_index_suffix(self.token.span, suffix);
+            }
             self.bump();
             Ok(Ident::new(symbol, self.prev_token.span))
         } else {
@@ -1342,23 +1369,8 @@ impl<'a> Parser<'a> {
         let path = self.parse_path(PathStyle::Mod)?;
         self.expect(&token::CloseDelim(Delimiter::Parenthesis))?; // `)`
 
-        let msg = "incorrect visibility restriction";
-        let suggestion = r##"some possible visibility restrictions are:
-`pub(crate)`: visible only on the current crate
-`pub(super)`: visible only in the current module's parent
-`pub(in path::to::module)`: visible only on the specified path"##;
-
         let path_str = pprust::path_to_string(&path);
-
-        struct_span_err!(self.sess.span_diagnostic, path.span, E0704, "{}", msg)
-            .help(suggestion)
-            .span_suggestion(
-                path.span,
-                &format!("make this visible only to module `{}` with `in`", path_str),
-                format!("in {}", path_str),
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        self.sess.emit_err(IncorrectVisibilityRestriction { span: path.span, inner_str: path_str });
 
         Ok(())
     }
@@ -1384,14 +1396,7 @@ impl<'a> Parser<'a> {
             Err(Some(lit)) => match lit.kind {
                 ast::LitKind::Err => None,
                 _ => {
-                    self.struct_span_err(lit.span, "non-string ABI literal")
-                        .span_suggestion(
-                            lit.span,
-                            "specify the ABI with a string literal",
-                            "\"C\"",
-                            Applicability::MaybeIncorrect,
-                        )
-                        .emit();
+                    self.sess.emit_err(NonStringAbiLiteral { span: lit.span });
                     None
                 }
             },
@@ -1432,25 +1437,18 @@ pub(crate) fn make_unclosed_delims_error(
     // `None` here means an `Eof` was found. We already emit those errors elsewhere, we add them to
     // `unmatched_braces` only for error recovery in the `Parser`.
     let found_delim = unmatched.found_delim?;
-    let span: MultiSpan = if let Some(sp) = unmatched.unclosed_span {
-        vec![unmatched.found_span, sp].into()
-    } else {
-        unmatched.found_span.into()
-    };
-    let mut err = sess.span_diagnostic.struct_span_err(
-        span,
-        &format!(
-            "mismatched closing delimiter: `{}`",
-            pprust::token_kind_to_string(&token::CloseDelim(found_delim)),
-        ),
-    );
-    err.span_label(unmatched.found_span, "mismatched closing delimiter");
-    if let Some(sp) = unmatched.candidate_span {
-        err.span_label(sp, "closing delimiter possibly meant for this");
-    }
+    let mut spans = vec![unmatched.found_span];
     if let Some(sp) = unmatched.unclosed_span {
-        err.span_label(sp, "unclosed delimiter");
-    }
+        spans.push(sp);
+    };
+    let err = MismatchedClosingDelimiter {
+        spans,
+        delimiter: pprust::token_kind_to_string(&token::CloseDelim(found_delim)).to_string(),
+        unmatched: unmatched.found_span,
+        opening_candidate: unmatched.candidate_span,
+        unclosed: unmatched.unclosed_span,
+    }
+    .into_diagnostic(&sess.span_diagnostic);
     Some(err)
 }
 
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 120a3c267f1..0250b518243 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,5 +1,5 @@
 use super::{ForceCollect, Parser, PathStyle, TrailingToken};
-use crate::parser::diagnostics::RemoveLet;
+use crate::errors::RemoveLet;
 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
 use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
 use rustc_ast::ptr::P;
@@ -10,6 +10,7 @@ use rustc_ast::{
 };
 use rustc_ast_pretty::pprust;
 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
+use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::{respan, Span, Spanned};
 use rustc_span::symbol::{kw, sym, Ident};
 
@@ -693,7 +694,7 @@ impl<'a> Parser<'a> {
 
         let sp = self.sess.source_map().start_point(self.token.span);
         if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-            self.sess.expr_parentheses_needed(&mut err, *sp);
+            err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
         }
 
         Err(err)
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 3d957406b19..a61e77b7c3b 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -1,7 +1,5 @@
-use super::attr::DEFAULT_INNER_ATTR_FORBIDDEN;
-use super::diagnostics::{
-    AttemptLocalParseRecovery, Error, InvalidVariableDeclaration, InvalidVariableDeclarationSub,
-};
+use super::attr::InnerAttrForbiddenReason;
+use super::diagnostics::AttemptLocalParseRecovery;
 use super::expr::LhsExpr;
 use super::pat::RecoverComma;
 use super::path::PathStyle;
@@ -9,6 +7,12 @@ use super::TrailingToken;
 use super::{
     AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
 };
+use crate::errors::{
+    AssignmentElseNotAllowed, CompoundAssignmentExpressionInLet, ConstLetMutuallyExclusive,
+    DocCommentDoesNotDocumentAnything, ExpectedStatementAfterOuterAttr, InvalidCurlyInLetElse,
+    InvalidExpressionInLetElse, InvalidVariableDeclaration, InvalidVariableDeclarationSub,
+    WrapExpressionInParentheses,
+};
 use crate::maybe_whole;
 
 use rustc_ast as ast;
@@ -112,11 +116,7 @@ impl<'a> Parser<'a> {
                 let bl = self.parse_block()?;
                 // Destructuring assignment ... else.
                 // This is not allowed, but point it out in a nice way.
-                let mut err = self.struct_span_err(
-                    e.span.to(bl.span),
-                    "<assignment> ... else { ... } is not allowed",
-                );
-                err.emit();
+                self.sess.emit_err(AssignmentElseNotAllowed { span: e.span.to(bl.span) });
             }
             self.mk_stmt(lo.to(e.span), StmtKind::Expr(e))
         } else {
@@ -202,9 +202,12 @@ impl<'a> Parser<'a> {
     fn error_outer_attrs(&self, attrs: &[Attribute]) {
         if let [.., last] = attrs {
             if last.is_doc_comment() {
-                self.span_err(last.span, Error::UselessDocComment).emit();
+                self.sess.emit_err(DocCommentDoesNotDocumentAnything {
+                    span: last.span,
+                    missing_comma: None,
+                });
             } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
-                self.struct_span_err(last.span, "expected statement after outer attribute").emit();
+                self.sess.emit_err(ExpectedStatementAfterOuterAttr { span: last.span });
             }
         }
     }
@@ -255,17 +258,7 @@ impl<'a> Parser<'a> {
         let lo = self.prev_token.span;
 
         if self.token.is_keyword(kw::Const) && self.look_ahead(1, |t| t.is_ident()) {
-            self.struct_span_err(
-                lo.to(self.token.span),
-                "`const` and `let` are mutually exclusive",
-            )
-            .span_suggestion(
-                lo.to(self.token.span),
-                "remove `let`",
-                "const",
-                Applicability::MaybeIncorrect,
-            )
-            .emit();
+            self.sess.emit_err(ConstLetMutuallyExclusive { span: lo.to(self.token.span) });
             self.bump();
         }
 
@@ -363,44 +356,27 @@ impl<'a> Parser<'a> {
     fn check_let_else_init_bool_expr(&self, init: &ast::Expr) {
         if let ast::ExprKind::Binary(op, ..) = init.kind {
             if op.node.lazy() {
-                let suggs = vec![
-                    (init.span.shrink_to_lo(), "(".to_string()),
-                    (init.span.shrink_to_hi(), ")".to_string()),
-                ];
-                self.struct_span_err(
-                    init.span,
-                    &format!(
-                        "a `{}` expression cannot be directly assigned in `let...else`",
-                        op.node.to_string()
-                    ),
-                )
-                .multipart_suggestion(
-                    "wrap the expression in parentheses",
-                    suggs,
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+                self.sess.emit_err(InvalidExpressionInLetElse {
+                    span: init.span,
+                    operator: op.node.to_string(),
+                    sugg: WrapExpressionInParentheses {
+                        left: init.span.shrink_to_lo(),
+                        right: init.span.shrink_to_hi(),
+                    },
+                });
             }
         }
     }
 
     fn check_let_else_init_trailing_brace(&self, init: &ast::Expr) {
         if let Some(trailing) = classify::expr_trailing_brace(init) {
-            let err_span = trailing.span.with_lo(trailing.span.hi() - BytePos(1));
-            let suggs = vec![
-                (trailing.span.shrink_to_lo(), "(".to_string()),
-                (trailing.span.shrink_to_hi(), ")".to_string()),
-            ];
-            self.struct_span_err(
-                err_span,
-                "right curly brace `}` before `else` in a `let...else` statement not allowed",
-            )
-            .multipart_suggestion(
-                "try wrapping the expression in parentheses",
-                suggs,
-                Applicability::MachineApplicable,
-            )
-            .emit();
+            self.sess.emit_err(InvalidCurlyInLetElse {
+                span: trailing.span.with_lo(trailing.span.hi() - BytePos(1)),
+                sugg: WrapExpressionInParentheses {
+                    left: trailing.span.shrink_to_lo(),
+                    right: trailing.span.shrink_to_hi(),
+                },
+            });
         }
     }
 
@@ -409,18 +385,7 @@ impl<'a> Parser<'a> {
         let eq_consumed = match self.token.kind {
             token::BinOpEq(..) => {
                 // Recover `let x <op>= 1` as `let x = 1`
-                self.struct_span_err(
-                    self.token.span,
-                    "can't reassign to an uninitialized variable",
-                )
-                .span_suggestion_short(
-                    self.token.span,
-                    "initialize the variable",
-                    "=",
-                    Applicability::MaybeIncorrect,
-                )
-                .help("if you meant to overwrite, remove the `let` binding")
-                .emit();
+                self.sess.emit_err(CompoundAssignmentExpressionInLet { span: self.token.span });
                 self.bump();
                 true
             }
@@ -434,7 +399,12 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_block(&mut self) -> PResult<'a, P<Block>> {
         let (attrs, block) = self.parse_inner_attrs_and_block()?;
         if let [.., last] = &*attrs {
-            self.error_on_forbidden_inner_attr(last.span, DEFAULT_INNER_ATTR_FORBIDDEN);
+            self.error_on_forbidden_inner_attr(
+                last.span,
+                super::attr::InnerAttrPolicy::Forbidden(Some(
+                    InnerAttrForbiddenReason::InCodeBlock,
+                )),
+            );
         }
         Ok(block)
     }
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index b47f0c09783..2a8512acf8c 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -397,10 +397,13 @@ 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;
-            let msg = "expected mut or const in raw pointer type";
-            self.struct_span_err(span, msg)
-                .span_label(span, msg)
-                .help("use `*mut T` or `*const T` as appropriate")
+            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()].into_iter(),
+                    Applicability::HasPlaceholders,
+                )
                 .emit();
             Mutability::Not
         });