Recover when unclosed char literal is parsed as a lifetime in some positions

compiler/rustc_errors/src/lib.rs

@@ -461,6 +461,9 @@ pub enum StashKey {
     UnderscoreForArrayLengths,
     EarlySyntaxWarning,
     CallIntoMethod,
+    /// When an invalid lifetime e.g. `'2` should be reinterpreted
+    /// as a char literal in the parser
+    LifetimeIsChar,
 }
 
 fn default_track_diagnostic(_: &Diagnostic) {}

compiler/rustc_parse/src/lexer/mod.rs

@@ -3,7 +3,9 @@ use rustc_ast::ast::{self, AttrStyle};
 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
-use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult};
+use rustc_errors::{
+    error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult, StashKey,
+};
 use rustc_lexer::unescape::{self, Mode};
 use rustc_lexer::Cursor;
 use rustc_lexer::{Base, DocStyle, RawStrError};
@@ -203,7 +205,10 @@ impl<'a> StringReader<'a> {
                     // 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 span = self.mk_sp(start, self.pos);
+                        let mut diag = self.sess.struct_err("lifetimes cannot start with a number");
+                        diag.set_span(span);
+                        diag.stash(span, StashKey::LifetimeIsChar);
                     }
                     let ident = Symbol::intern(lifetime_name);
                     token::Lifetime(ident)

compiler/rustc_parse/src/parser/expr.rs

@@ -42,8 +42,10 @@ use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty
 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
 use rustc_ast::{ClosureBinder, StmtKind};
 use rustc_ast_pretty::pprust;
-use rustc_errors::IntoDiagnostic;
-use rustc_errors::{Applicability, Diagnostic, PResult};
+use rustc_errors::{
+    Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
+    StashKey,
+};
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -1513,11 +1515,11 @@ impl<'a> Parser<'a> {
     /// Parse `'label: $expr`. The label is already parsed.
     fn parse_labeled_expr(
         &mut self,
-        label: Label,
+        label_: Label,
         mut consume_colon: bool,
     ) -> PResult<'a, P<Expr>> {
-        let lo = label.ident.span;
-        let label = Some(label);
+        let lo = label_.ident.span;
+        let label = Some(label_);
         let ate_colon = self.eat(&token::Colon);
         let expr = if self.eat_keyword(kw::While) {
             self.parse_while_expr(label, lo)
@@ -1529,6 +1531,19 @@ impl<'a> Parser<'a> {
             || self.token.is_whole_block()
         {
             self.parse_block_expr(label, lo, BlockCheckMode::Default)
+        } else if !ate_colon
+            && (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
+                || self.token.is_op())
+        {
+            let lit = self.recover_unclosed_char(label_.ident, |self_| {
+                self_.sess.create_err(UnexpectedTokenAfterLabel {
+                    span: self_.token.span,
+                    remove_label: None,
+                    enclose_in_block: None,
+                })
+            });
+            consume_colon = false;
+            Ok(self.mk_expr(lo, ExprKind::Lit(lit)))
         } else if !ate_colon
             && (self.check_noexpect(&TokenKind::Comma) || self.check_noexpect(&TokenKind::Gt))
         {
@@ -1603,6 +1618,39 @@ impl<'a> Parser<'a> {
         Ok(expr)
     }
 
+    /// Emit an error when a char is parsed as a lifetime because of a missing quote
+    pub(super) fn recover_unclosed_char(
+        &mut self,
+        lifetime: Ident,
+        err: impl FnOnce(&mut Self) -> DiagnosticBuilder<'a, ErrorGuaranteed>,
+    ) -> ast::Lit {
+        if let Some(mut diag) =
+            self.sess.span_diagnostic.steal_diagnostic(lifetime.span, StashKey::LifetimeIsChar)
+        {
+            diag.span_suggestion_verbose(
+                lifetime.span.shrink_to_hi(),
+                "add `'` to close the char literal",
+                "'",
+                Applicability::MaybeIncorrect,
+            )
+            .emit();
+        } else {
+            err(self)
+                .span_suggestion_verbose(
+                    lifetime.span.shrink_to_hi(),
+                    "add `'` to close the char literal",
+                    "'",
+                    Applicability::MaybeIncorrect,
+                )
+                .emit();
+        }
+        ast::Lit {
+            token_lit: token::Lit::new(token::LitKind::Char, lifetime.name, None),
+            kind: ast::LitKind::Char(lifetime.name.as_str().chars().next().unwrap_or('_')),
+            span: lifetime.span,
+        }
+    }
+
     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
     fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
         let lo = self.token.span;
@@ -1728,7 +1776,7 @@ impl<'a> Parser<'a> {
     }
 
     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
-        self.parse_opt_lit().ok_or_else(|| {
+        self.parse_opt_lit().ok_or(()).or_else(|()| {
             if let token::Interpolated(inner) = &self.token.kind {
                 let expr = match inner.as_ref() {
                     token::NtExpr(expr) => Some(expr),
@@ -1740,12 +1788,22 @@ impl<'a> Parser<'a> {
                         let mut err = InvalidInterpolatedExpression { span: self.token.span }
                             .into_diagnostic(&self.sess.span_diagnostic);
                         err.downgrade_to_delayed_bug();
-                        return err;
+                        return Err(err);
                     }
                 }
             }
-            let msg = format!("unexpected token: {}", super::token_descr(&self.token));
-            self.struct_span_err(self.token.span, &msg)
+            let token = self.token.clone();
+            let err = |self_: &mut Self| {
+                let msg = format!("unexpected token: {}", super::token_descr(&token));
+                self_.struct_span_err(token.span, &msg)
+            };
+            // On an error path, eagerly consider a lifetime to be an unclosed character lit
+            if self.token.is_lifetime() {
+                let lt = self.expect_lifetime();
+                Ok(self.recover_unclosed_char(lt.ident, err))
+            } else {
+                Err(err(self))
+            }
         })
     }
 

compiler/rustc_parse/src/parser/pat.rs

@@ -402,6 +402,25 @@ impl<'a> Parser<'a> {
             } else {
                 PatKind::Path(qself, path)
             }
+        } else if matches!(self.token.kind, token::Lifetime(_))
+            // In pattern position, we're totally fine with using "next token isn't colon"
+            // as a heuristic. We could probably just always try to recover if it's a lifetime,
+            // because we never have `'a: label {}` in a pattern position anyways, but it does
+            // keep us from suggesting something like `let 'a: Ty = ..` => `let 'a': Ty = ..`
+            && !self.look_ahead(1, |token| matches!(token.kind, token::Colon))
+        {
+            // Recover a `'a` as a `'a'` literal
+            let lt = self.expect_lifetime();
+            let lit = self.recover_unclosed_char(lt.ident, |self_| {
+                let expected = expected.unwrap_or("pattern");
+                let msg =
+                    format!("expected {}, found {}", expected, super::token_descr(&self_.token));
+
+                let mut err = self_.struct_span_err(self_.token.span, &msg);
+                err.span_label(self_.token.span, format!("expected {}", expected));
+                err
+            });
+            PatKind::Lit(self.mk_expr(lo, ExprKind::Lit(lit)))
         } else {
             // Try to parse everything else as literal with optional minus
             match self.parse_literal_maybe_minus() {
@@ -799,6 +818,7 @@ impl<'a> Parser<'a> {
                 || t.kind == token::Dot // e.g. `.5` for recovery;
                 || t.can_begin_literal_maybe_minus() // e.g. `42`.
                 || t.is_whole_expr()
+                || t.is_lifetime() // recover `'a` instead of `'a'`
             })
     }
 

src/test/ui/parser/issues/issue-93282.rs

@@ -12,4 +12,5 @@ fn foo() {
     let x = 1;
     bar('y, x);
     //~^ ERROR expected
+    //~| ERROR mismatched types
 }

src/test/ui/parser/issues/issue-93282.stderr

@@ -3,6 +3,11 @@ error: expected `while`, `for`, `loop` or `{` after a label
    |
 LL |     f<'a,>
    |         ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     f<'a',>
+   |         +
 
 error: expected one of `.`, `:`, `;`, `?`, `for`, `loop`, `while`, `}`, or an operator, found `,`
   --> $DIR/issue-93282.rs:2:9
@@ -20,6 +25,26 @@ error: expected `while`, `for`, `loop` or `{` after a label
    |
 LL |     bar('y, x);
    |           ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     bar('y', x);
+   |           +
+
+error[E0308]: mismatched types
+  --> $DIR/issue-93282.rs:13:9
+   |
+LL |     bar('y, x);
+   |     --- ^^ expected `usize`, found `char`
+   |     |
+   |     arguments to this function are incorrect
+   |
+note: function defined here
+  --> $DIR/issue-93282.rs:7:4
+   |
+LL | fn bar(a: usize, b: usize) -> usize {
+   |    ^^^ --------
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/parser/label-is-actually-char.rs

@@ -0,0 +1,16 @@
+fn main() {
+    let c = 'a;
+    //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
+    //~| HELP add `'` to close the char literal
+    match c {
+        'a'..='b => {}
+        //~^ ERROR unexpected token: `'b`
+        //~| HELP add `'` to close the char literal
+        _ => {}
+    }
+    let x = ['a, 'b];
+    //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
+    //~| ERROR expected `while`, `for`, `loop` or `{` after a label
+    //~| HELP add `'` to close the char literal
+    //~| HELP add `'` to close the char literal
+}

src/test/ui/parser/label-is-actually-char.stderr

@@ -0,0 +1,46 @@
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/label-is-actually-char.rs:2:15
+   |
+LL |     let c = 'a;
+   |               ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     let c = 'a';
+   |               +
+
+error: unexpected token: `'b`
+  --> $DIR/label-is-actually-char.rs:6:15
+   |
+LL |         'a'..='b => {}
+   |               ^^
+   |
+help: add `'` to close the char literal
+   |
+LL |         'a'..='b' => {}
+   |                 +
+
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/label-is-actually-char.rs:11:16
+   |
+LL |     let x = ['a, 'b];
+   |                ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     let x = ['a', 'b];
+   |                +
+
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/label-is-actually-char.rs:11:20
+   |
+LL |     let x = ['a, 'b];
+   |                    ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     let x = ['a, 'b'];
+   |                    +
+
+error: aborting due to 4 previous errors
+

src/test/ui/parser/numeric-lifetime.stderr

@@ -1,3 +1,11 @@
+error[E0308]: mismatched types
+  --> $DIR/numeric-lifetime.rs:6:20
+   |
+LL |     let x: usize = "";
+   |            -----   ^^ expected `usize`, found `&str`
+   |            |
+   |            expected due to this
+
 error: lifetimes cannot start with a number
   --> $DIR/numeric-lifetime.rs:1:10
    |
@@ -10,14 +18,6 @@ error: lifetimes cannot start with a number
 LL | struct S<'1> { s: &'1 usize }
    |                    ^^
 
-error[E0308]: mismatched types
-  --> $DIR/numeric-lifetime.rs:6:20
-   |
-LL |     let x: usize = "";
-   |            -----   ^^ expected `usize`, found `&str`
-   |            |
-   |            expected due to this
-
 error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

src/test/ui/parser/require-parens-for-chained-comparison.rs

@@ -23,11 +23,13 @@ fn main() {
     //~^ ERROR expected one of
     //~| HELP use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
     //~| ERROR expected
+    //~| HELP add `'` to close the char literal
 
     f<'_>();
     //~^ comparison operators cannot be chained
     //~| HELP use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
     //~| ERROR expected
+    //~| HELP add `'` to close the char literal
 
     let _ = f<u8>;
     //~^ ERROR comparison operators cannot be chained

src/test/ui/parser/require-parens-for-chained-comparison.stderr

@@ -58,6 +58,11 @@ error: expected `while`, `for`, `loop` or `{` after a label
    |
 LL |     let _ = f<'_, i8>();
    |                 ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     let _ = f<'_', i8>();
+   |                 +
 
 error: expected one of `.`, `:`, `;`, `?`, `else`, `for`, `loop`, `while`, or an operator, found `,`
   --> $DIR/require-parens-for-chained-comparison.rs:22:17
@@ -71,13 +76,18 @@ LL |     let _ = f::<'_, i8>();
    |              ++
 
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/require-parens-for-chained-comparison.rs:27:9
+  --> $DIR/require-parens-for-chained-comparison.rs:28:9
    |
 LL |     f<'_>();
    |         ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: add `'` to close the char literal
+   |
+LL |     f<'_'>();
+   |         +
 
 error: comparison operators cannot be chained
-  --> $DIR/require-parens-for-chained-comparison.rs:27:6
+  --> $DIR/require-parens-for-chained-comparison.rs:28:6
    |
 LL |     f<'_>();
    |      ^  ^
@@ -88,7 +98,7 @@ LL |     f::<'_>();
    |      ++
 
 error: comparison operators cannot be chained
-  --> $DIR/require-parens-for-chained-comparison.rs:32:14
+  --> $DIR/require-parens-for-chained-comparison.rs:34:14
    |
 LL |     let _ = f<u8>;
    |              ^  ^