Add ErrorGuaranteed to Recovered::Yes and use it more.

The starting point for this was identical comments on two different
fields, in `ast::VariantData::Struct` and `hir::VariantData::Struct`:
```
    // FIXME: investigate making this a `Option<ErrorGuaranteed>`
    recovered: bool
```
I tried that, and then found that I needed to add an `ErrorGuaranteed`
to `Recovered::Yes`. Then I ended up using `Recovered` instead of
`Option<ErrorGuaranteed>` for these two places and elsewhere, which
required moving `ErrorGuaranteed` from `rustc_parse` to `rustc_ast`.

This makes things more consistent, because `Recovered` is used in more
places, and there are fewer uses of `bool` and
`Option<ErrorGuaranteed>`. And safer, because it's difficult/impossible
to set `recovered` to `Recovered::Yes` without having emitted an error.

compiler/rustc_ast/src/ast.rs

@@ -1422,7 +1422,7 @@ pub enum ExprKind {
     /// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
     ///
     /// `Span` represents the whole `let pat = expr` statement.
-    Let(P<Pat>, P<Expr>, Span, Option<ErrorGuaranteed>),
+    Let(P<Pat>, P<Expr>, Span, Recovered),
     /// An `if` block, with an optional `else` block.
     ///
     /// `if expr { block } else { expr }`
@@ -2881,17 +2881,20 @@ pub struct FieldDef {
     pub is_placeholder: bool,
 }
 
+/// Was parsing recovery performed?
+#[derive(Copy, Clone, Debug, Encodable, Decodable, HashStable_Generic)]
+pub enum Recovered {
+    No,
+    Yes(ErrorGuaranteed),
+}
+
 /// Fields and constructor ids of enum variants and structs.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum VariantData {
     /// Struct variant.
     ///
     /// E.g., `Bar { .. }` as in `enum Foo { Bar { .. } }`.
-    Struct {
-        fields: ThinVec<FieldDef>,
-        // FIXME: investigate making this a `Option<ErrorGuaranteed>`
-        recovered: bool,
-    },
+    Struct { fields: ThinVec<FieldDef>, recovered: Recovered },
     /// Tuple variant.
     ///
     /// E.g., `Bar(..)` as in `enum Foo { Bar(..) }`.

compiler/rustc_ast_lowering/src/expr.rs

@@ -158,13 +158,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let ohs = self.lower_expr(ohs);
                     hir::ExprKind::AddrOf(*k, *m, ohs)
                 }
-                ExprKind::Let(pat, scrutinee, span, is_recovered) => {
+                ExprKind::Let(pat, scrutinee, span, recovered) => {
                     hir::ExprKind::Let(self.arena.alloc(hir::LetExpr {
                         span: self.lower_span(*span),
                         pat: self.lower_pat(pat),
                         ty: None,
                         init: self.lower_expr(scrutinee),
-                        is_recovered: *is_recovered,
+                        recovered: *recovered,
                     }))
                 }
                 ExprKind::If(cond, then, else_opt) => {

compiler/rustc_ast_lowering/src/lib.rs

@@ -1283,7 +1283,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         fields.iter().enumerate().map(|f| this.lower_field_def(f)),
                     );
                     let span = t.span;
-                    let variant_data = hir::VariantData::Struct { fields, recovered: false };
+                    let variant_data =
+                        hir::VariantData::Struct { fields, recovered: ast::Recovered::No };
                     // FIXME: capture the generics from the outer adt.
                     let generics = hir::Generics::empty();
                     let kind = match t.kind {

compiler/rustc_builtin_macros/src/format.rs

@@ -7,14 +7,13 @@ use rustc_ast::{token, StmtKind};
 use rustc_ast::{
     Expr, ExprKind, FormatAlignment, FormatArgPosition, FormatArgPositionKind, FormatArgs,
     FormatArgsPiece, FormatArgument, FormatArgumentKind, FormatArguments, FormatCount,
-    FormatDebugHex, FormatOptions, FormatPlaceholder, FormatSign, FormatTrait,
+    FormatDebugHex, FormatOptions, FormatPlaceholder, FormatSign, FormatTrait, Recovered,
 };
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{Applicability, Diag, MultiSpan, PResult, SingleLabelManySpans};
 use rustc_expand::base::*;
 use rustc_lint_defs::builtin::NAMED_ARGUMENTS_USED_POSITIONALLY;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiag, LintId};
-use rustc_parse::parser::Recovered;
 use rustc_parse_format as parse;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::{BytePos, ErrorGuaranteed, InnerSpan, Span};
@@ -112,7 +111,7 @@ fn parse_args<'a>(ecx: &ExtCtxt<'a>, sp: Span, tts: TokenStream) -> PResult<'a,
                         _ => return Err(err),
                     }
                 }
-                Ok(Recovered::Yes) => (),
+                Ok(Recovered::Yes(_)) => (),
                 Ok(Recovered::No) => unreachable!(),
             }
         }

compiler/rustc_expand/src/placeholders.rs

@@ -174,7 +174,10 @@ pub(crate) fn placeholder(
         }]),
         AstFragmentKind::Variants => AstFragment::Variants(smallvec![ast::Variant {
             attrs: Default::default(),
-            data: ast::VariantData::Struct { fields: Default::default(), recovered: false },
+            data: ast::VariantData::Struct {
+                fields: Default::default(),
+                recovered: ast::Recovered::No
+            },
             disr_expr: None,
             id,
             ident,

compiler/rustc_hir/src/hir.rs

@@ -1308,9 +1308,9 @@ pub struct LetExpr<'hir> {
     pub pat: &'hir Pat<'hir>,
     pub ty: Option<&'hir Ty<'hir>>,
     pub init: &'hir Expr<'hir>,
-    /// `Some` when this let expressions is not in a syntanctically valid location.
+    /// `Recovered::Yes` when this let expressions is not in a syntanctically valid location.
     /// Used to prevent building MIR in such situations.
-    pub is_recovered: Option<ErrorGuaranteed>,
+    pub recovered: ast::Recovered,
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
@@ -3030,11 +3030,7 @@ pub enum VariantData<'hir> {
     /// A struct variant.
     ///
     /// E.g., `Bar { .. }` as in `enum Foo { Bar { .. } }`.
-    Struct {
-        fields: &'hir [FieldDef<'hir>],
-        // FIXME: investigate making this a `Option<ErrorGuaranteed>`
-        recovered: bool,
-    },
+    Struct { fields: &'hir [FieldDef<'hir>], recovered: ast::Recovered },
     /// A tuple variant.
     ///
     /// E.g., `Bar(..)` as in `enum Foo { Bar(..) }`.

compiler/rustc_hir/src/intravisit.rs

@@ -768,7 +768,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         ExprKind::DropTemps(ref subexpression) => {
             try_visit!(visitor.visit_expr(subexpression));
         }
-        ExprKind::Let(LetExpr { span: _, pat, ty, init, is_recovered: _ }) => {
+        ExprKind::Let(LetExpr { span: _, pat, ty, init, recovered: _ }) => {
             // match the visit order in walk_local
             try_visit!(visitor.visit_expr(init));
             try_visit!(visitor.visit_pat(pat));

compiler/rustc_hir_analysis/src/collect.rs

@@ -14,6 +14,7 @@
 //! At present, however, we do run collection across all items in the
 //! crate as a kind of pass. This should eventually be factored away.
 
+use rustc_ast::Recovered;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::unord::UnordMap;
@@ -1005,10 +1006,7 @@ fn lower_variant(
             vis: tcx.visibility(f.def_id),
         })
         .collect();
-    let recovered = match def {
-        hir::VariantData::Struct { recovered, .. } => *recovered,
-        _ => false,
-    };
+    let recovered = matches!(def, hir::VariantData::Struct { recovered: Recovered::Yes(_), .. });
     ty::VariantDef::new(
         ident.name,
         variant_did.map(LocalDefId::to_def_id),

compiler/rustc_hir_typeck/src/expr.rs

@@ -1271,7 +1271,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // otherwise check exactly as a let statement
         self.check_decl((let_expr, hir_id).into());
         // but return a bool, for this is a boolean expression
-        if let Some(error_guaranteed) = let_expr.is_recovered {
+        if let ast::Recovered::Yes(error_guaranteed) = let_expr.recovered {
             self.set_tainted_by_errors(error_guaranteed);
             Ty::new_error(self.tcx, error_guaranteed)
         } else {

compiler/rustc_hir_typeck/src/gather_locals.rs

@@ -50,7 +50,7 @@ impl<'a> From<&'a hir::LetStmt<'a>> for Declaration<'a> {
 
 impl<'a> From<(&'a hir::LetExpr<'a>, HirId)> for Declaration<'a> {
     fn from((let_expr, hir_id): (&'a hir::LetExpr<'a>, HirId)) -> Self {
-        let hir::LetExpr { pat, ty, span, init, is_recovered: _ } = *let_expr;
+        let hir::LetExpr { pat, ty, span, init, recovered: _ } = *let_expr;
         Declaration { hir_id, pat, ty, span, init: Some(init), origin: DeclOrigin::LetExpr }
     }
 }

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -22,7 +22,6 @@ use crate::fluent_generated as fluent;
 use crate::parser;
 use crate::parser::attr::InnerAttrPolicy;
 use ast::token::IdentIsRaw;
-use parser::Recovered;
 use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Lit, LitKind, Token, TokenKind};
@@ -31,7 +30,7 @@ use rustc_ast::util::parser::AssocOp;
 use rustc_ast::{
     AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingMode, Block,
     BlockCheckMode, Expr, ExprKind, GenericArg, Generics, HasTokens, Item, ItemKind, Param, Pat,
-    PatKind, Path, PathSegment, QSelf, Ty, TyKind,
+    PatKind, Path, PathSegment, QSelf, Recovered, Ty, TyKind,
 };
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
@@ -527,14 +526,14 @@ impl<'a> Parser<'a> {
                 //
                 //   let x = 32:
                 //   let y = 42;
-                self.dcx().emit_err(ExpectedSemi {
+                let guar = self.dcx().emit_err(ExpectedSemi {
                     span: self.token.span,
                     token: self.token.clone(),
                     unexpected_token_label: None,
                     sugg: ExpectedSemiSugg::ChangeToSemi(self.token.span),
                 });
                 self.bump();
-                return Ok(Recovered::Yes);
+                return Ok(Recovered::Yes(guar));
             } else if self.look_ahead(0, |t| {
                 t == &token::CloseDelim(Delimiter::Brace)
                     || ((t.can_begin_expr() || t.can_begin_item())
@@ -552,13 +551,13 @@ impl<'a> Parser<'a> {
                 //   let x = 32
                 //   let y = 42;
                 let span = self.prev_token.span.shrink_to_hi();
-                self.dcx().emit_err(ExpectedSemi {
+                let guar = self.dcx().emit_err(ExpectedSemi {
                     span,
                     token: self.token.clone(),
                     unexpected_token_label: Some(self.token.span),
                     sugg: ExpectedSemiSugg::AddSemi(span),
                 });
-                return Ok(Recovered::Yes);
+                return Ok(Recovered::Yes(guar));
             }
         }
 
@@ -712,8 +711,8 @@ impl<'a> Parser<'a> {
 
         if self.check_too_many_raw_str_terminators(&mut err) {
             if expected.contains(&TokenType::Token(token::Semi)) && self.eat(&token::Semi) {
-                err.emit();
-                return Ok(Recovered::Yes);
+                let guar = err.emit();
+                return Ok(Recovered::Yes(guar));
             } else {
                 return Err(err);
             }
@@ -1251,7 +1250,7 @@ impl<'a> Parser<'a> {
                         }
                     }
                 }
-                Ok((_, _, Recovered::Yes)) => {}
+                Ok((_, _, Recovered::Yes(_))) => {}
                 Err(err) => {
                     err.cancel();
                 }
@@ -1284,21 +1283,21 @@ impl<'a> Parser<'a> {
 
     /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
     /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
-    /// parenthesising the leftmost comparison.
+    /// parenthesising the leftmost comparison. The return value indicates if recovery happened.
     fn attempt_chained_comparison_suggestion(
         &mut self,
         err: &mut ComparisonOperatorsCannotBeChained,
         inner_op: &Expr,
         outer_op: &Spanned<AssocOp>,
-    ) -> Recovered {
+    ) -> bool {
         if let ExprKind::Binary(op, l1, r1) = &inner_op.kind {
             if let ExprKind::Field(_, ident) = l1.kind
                 && ident.as_str().parse::<i32>().is_err()
                 && !matches!(r1.kind, ExprKind::Lit(_))
             {
                 // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
                 // suggestion being the only one to apply is high.
-                return Recovered::No;
+                return false;
             }
             return match (op.node, &outer_op.node) {
                 // `x == y == z`
@@ -1317,7 +1316,7 @@ impl<'a> Parser<'a> {
                         span: inner_op.span.shrink_to_hi(),
                         middle_term: expr_to_str(r1),
                     });
-                    Recovered::No // Keep the current parse behavior, where the AST is `(x < y) < z`.
+                    false // Keep the current parse behavior, where the AST is `(x < y) < z`.
                 }
                 // `x == y < z`
                 (BinOpKind::Eq, AssocOp::Less | AssocOp::LessEqual | AssocOp::Greater | AssocOp::GreaterEqual) => {
@@ -1331,12 +1330,12 @@ impl<'a> Parser<'a> {
                                 left: r1.span.shrink_to_lo(),
                                 right: r2.span.shrink_to_hi(),
                             });
-                            Recovered::Yes
+                            true
                         }
                         Err(expr_err) => {
                             expr_err.cancel();
                             self.restore_snapshot(snapshot);
-                            Recovered::Yes
+                            true
                         }
                     }
                 }
@@ -1351,19 +1350,19 @@ impl<'a> Parser<'a> {
                                 left: l1.span.shrink_to_lo(),
                                 right: r1.span.shrink_to_hi(),
                             });
-                            Recovered::Yes
+                            true
                         }
                         Err(expr_err) => {
                             expr_err.cancel();
                             self.restore_snapshot(snapshot);
-                            Recovered::No
+                            false
                         }
                     }
                 }
-                _ => Recovered::No,
+                _ => false
             };
         }
-        Recovered::No
+        false
     }
 
     /// Produces an error if comparison operators are chained (RFC #558).
@@ -1494,7 +1493,7 @@ impl<'a> Parser<'a> {
                         // misformatted turbofish, for instance), suggest a correct form.
                         let recovered = self
                             .attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
-                        if matches!(recovered, Recovered::Yes) {
+                        if recovered {
                             let guar = self.dcx().emit_err(err);
                             mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar)
                         } else {
@@ -1503,10 +1502,10 @@ impl<'a> Parser<'a> {
                         }
                     };
                 }
-                let recover =
+                let recovered =
                     self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
                 let guar = self.dcx().emit_err(err);
-                if matches!(recover, Recovered::Yes) {
+                if recovered {
                     return mk_err_expr(self, inner_op.span.to(self.prev_token.span), guar);
                 }
             }