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Be more careful about interpreting a label as a mistyped char literal.
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Currently the parser will interpret any label in certain positions as a
mistyped char literal, on the assumption that the trailing single quote
was accidentally omitted. This is reasonable for a label like 'a (because
'a' would be valid) but not reasonable for a label like 'abc (because
'abc' is not valid).

This commit restricts this behaviour only to labels that would be valid
char literals, via the new `could_be_unclosed_char_literal` function.
The commit also augments the `label-is-actually-char.rs` test in a
couple of ways:
- Adds testing of labels with identifiers longer than one char, e.g.
  'abc.
- Adds a new match with simpler patterns, because the
  `recover_unclosed_char` call in `parse_pat_with_range_pat` was not
  being exercised (in this test or any other ui tests).

Fixes #120397, an assertion failure, which was caused by this behaviour
in the parser interacting with some new stricter char literal checking
added in #120329.
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nnethercote committed Jan 29, 2024
1 parent 5bda589 commit 0a568fb
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Showing 4 changed files with 112 additions and 23 deletions.
17 changes: 15 additions & 2 deletions compiler/rustc_parse/src/parser/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::{
AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder, PResult, StashKey,
};
use rustc_lexer::unescape::unescape_char;
use rustc_macros::Subdiagnostic;
use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
Expand Down Expand Up @@ -1652,6 +1653,7 @@ impl<'a> Parser<'a> {
&& self.may_recover()
&& (matches!(self.token.kind, token::CloseDelim(_) | token::Comma)
|| self.token.is_punct())
&& could_be_unclosed_char_literal(label_.ident)
{
let (lit, _) =
self.recover_unclosed_char(label_.ident, Parser::mk_token_lit_char, |self_| {
Expand Down Expand Up @@ -1744,6 +1746,7 @@ impl<'a> Parser<'a> {
mk_lit_char: impl FnOnce(Symbol, Span) -> L,
err: impl FnOnce(&Self) -> DiagnosticBuilder<'a>,
) -> L {
assert!(could_be_unclosed_char_literal(ident));
if let Some(diag) = self.dcx().steal_diagnostic(ident.span, StashKey::LifetimeIsChar) {
diag.with_span_suggestion_verbose(
ident.span.shrink_to_hi(),
Expand Down Expand Up @@ -2034,8 +2037,11 @@ impl<'a> Parser<'a> {
let msg = format!("unexpected token: {}", super::token_descr(&token));
self_.dcx().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() {
// On an error path, eagerly consider a lifetime to be an unclosed character lit, if that
// makes sense.
if let Some(ident) = self.token.lifetime()
&& could_be_unclosed_char_literal(ident)
{
let lt = self.expect_lifetime();
Ok(self.recover_unclosed_char(lt.ident, mk_lit_char, err))
} else {
Expand Down Expand Up @@ -3763,6 +3769,13 @@ impl<'a> Parser<'a> {
}
}

/// Could this lifetime/label be an unclosed char literal? For example, `'a`
/// could be, but `'abc` could not.
pub(crate) fn could_be_unclosed_char_literal(ident: Ident) -> bool {
ident.name.as_str().starts_with('\'')
&& unescape_char(ident.without_first_quote().name.as_str()).is_ok()
}

/// Used to forbid `let` expressions in certain syntactic locations.
#[derive(Clone, Copy, Subdiagnostic)]
pub(crate) enum ForbiddenLetReason {
Expand Down
4 changes: 3 additions & 1 deletion compiler/rustc_parse/src/parser/pat.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ use crate::errors::{
UnexpectedParenInRangePatSugg, UnexpectedVertVertBeforeFunctionParam,
UnexpectedVertVertInPattern,
};
use crate::parser::expr::could_be_unclosed_char_literal;
use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
use rustc_ast::mut_visit::{noop_visit_pat, MutVisitor};
use rustc_ast::ptr::P;
Expand Down Expand Up @@ -443,11 +444,12 @@ impl<'a> Parser<'a> {
} else {
PatKind::Path(qself, path)
}
} else if matches!(self.token.kind, token::Lifetime(_))
} else if let token::Lifetime(lt) = self.token.kind
// 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 = ..`
&& could_be_unclosed_char_literal(Ident::with_dummy_span(lt))
&& !self.look_ahead(1, |token| matches!(token.kind, token::Colon))
{
// Recover a `'a` as a `'a'` literal
Expand Down
41 changes: 34 additions & 7 deletions tests/ui/parser/label-is-actually-char.rs
Original file line number Diff line number Diff line change
@@ -1,16 +1,43 @@
// Note: it's ok to interpret 'a as 'a', but but not ok to interpret 'abc as
// 'abc' because 'abc' is not a valid char literal.

fn main() {
let c = 'a;
//~^ ERROR expected `while`, `for`, `loop` or `{` after a label
//~| HELP add `'` to close the char literal
match c {

let c = 'abc;
//~^ ERROR expected `while`, `for`, `loop` or `{` after a label
//~| ERROR expected expression, found `;`
}

fn f() {
match 'a' {
'a'..='b => {}
//~^ ERROR unexpected token: `'b`
//~| HELP add `'` to close the char literal
_ => {}
'c'..='def => {}
//~^ ERROR unexpected token: `'def`
}
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
}

fn g() {
match 'g' {
'g => {}
//~^ ERROR expected pattern, found `=>`
//~| HELP add `'` to close the char literal
'hij => {}
//~^ ERROR expected pattern, found `'hij`
_ => {}
}
}

fn h() {
let x = ['a, 'b, 'cde];
//~^ ERROR expected `while`, `for`, `loop` or `{` after a label
//~| HELP add `'` to close the char literal
//~| ERROR expected `while`, `for`, `loop` or `{` after a label
//~| HELP add `'` to close the char literal
//~| ERROR expected `while`, `for`, `loop` or `{` after a label
//~| ERROR expected expression, found `]`
}
73 changes: 60 additions & 13 deletions tests/ui/parser/label-is-actually-char.stderr
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
error: expected `while`, `for`, `loop` or `{` after a label
--> $DIR/label-is-actually-char.rs:2:15
--> $DIR/label-is-actually-char.rs:5:15
|
LL | let c = 'a;
| ^ expected `while`, `for`, `loop` or `{` after a label
Expand All @@ -9,8 +9,20 @@ help: add `'` to close the char literal
LL | let c = 'a';
| +

error: expected `while`, `for`, `loop` or `{` after a label
--> $DIR/label-is-actually-char.rs:9:17
|
LL | let c = 'abc;
| ^ expected `while`, `for`, `loop` or `{` after a label

error: expected expression, found `;`
--> $DIR/label-is-actually-char.rs:9:17
|
LL | let c = 'abc;
| ^ expected expression

error: unexpected token: `'b`
--> $DIR/label-is-actually-char.rs:6:15
--> $DIR/label-is-actually-char.rs:16:15
|
LL | 'a'..='b => {}
| ^^
Expand All @@ -20,27 +32,62 @@ help: add `'` to close the char literal
LL | 'a'..='b' => {}
| +

error: unexpected token: `'def`
--> $DIR/label-is-actually-char.rs:19:15
|
LL | 'c'..='def => {}
| ^^^^

error: expected pattern, found `=>`
--> $DIR/label-is-actually-char.rs:26:11
|
LL | 'g => {}
| ^^ expected pattern
|
help: add `'` to close the char literal
|
LL | 'g' => {}
| +

error: expected pattern, found `'hij`
--> $DIR/label-is-actually-char.rs:29:8
|
LL | 'hij => {}
| ^^^^ expected pattern

error: expected `while`, `for`, `loop` or `{` after a label
--> $DIR/label-is-actually-char.rs:11:16
--> $DIR/label-is-actually-char.rs:36:15
|
LL | let x = ['a, 'b];
| ^ expected `while`, `for`, `loop` or `{` after a label
LL | let x = ['a, 'b, 'cde];
| ^ expected `while`, `for`, `loop` or `{` after a label
|
help: add `'` to close the char literal
|
LL | let x = ['a', 'b];
| +
LL | let x = ['a', 'b, 'cde];
| +

error: expected `while`, `for`, `loop` or `{` after a label
--> $DIR/label-is-actually-char.rs:11:20
--> $DIR/label-is-actually-char.rs:36:19
|
LL | let x = ['a, 'b];
| ^ expected `while`, `for`, `loop` or `{` after a label
LL | let x = ['a, 'b, 'cde];
| ^ expected `while`, `for`, `loop` or `{` after a label
|
help: add `'` to close the char literal
|
LL | let x = ['a, 'b'];
| +
LL | let x = ['a, 'b', 'cde];
| +

error: expected `while`, `for`, `loop` or `{` after a label
--> $DIR/label-is-actually-char.rs:36:25
|
LL | let x = ['a, 'b, 'cde];
| ^ expected `while`, `for`, `loop` or `{` after a label

error: expected expression, found `]`
--> $DIR/label-is-actually-char.rs:36:25
|
LL | let x = ['a, 'b, 'cde];
| ^ expected expression

error: aborting due to 4 previous errors
error: aborting due to 11 previous errors

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