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Rollup merge of #97823 - compiler-errors:missing-comma-match-arm, r=estebank

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Recover missing comma after match arm

If we're missing a comma after a match arm expression, try parsing another pattern and a following `=>`. If we find both of those, then recover by suggesting to insert a `,`.

Fixes #80112
This commit is contained in:
Dylan DPC 2022-06-08 07:37:32 +02:00 • committed by GitHub
commit a90c5a3c69
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3 changed files with 44 additions and 23 deletions
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51
compiler/rustc_parse/src/parser/expr.rs
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@ -2718,13 +2718,12 @@ impl<'a> Parser<'a> {
));
}
this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
.map_err(|mut err| {
match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) {
(Ok(ref expr_lines), Ok(ref arm_start_lines))
if arm_start_lines.lines[0].end_col
== expr_lines.lines[0].end_col
&& expr_lines.lines.len() == 2
&& this.token == token::FatArrow =>
.or_else(|mut err| {
if this.token == token::FatArrow {
if let Ok(expr_lines) = sm.span_to_lines(expr.span)
&& let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
&& arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
&& expr_lines.lines.len() == 2
{
// We check whether there's any trailing code in the parse span,
// if there isn't, we very likely have the following:
@ -2743,15 +2742,41 @@ impl<'a> Parser<'a> {
",".to_owned(),
Applicability::MachineApplicable,
);
return Err(err);
}
_ => {
err.span_label(
arrow_span,
"while parsing the `match` arm starting here",
);
} else {
// FIXME(compiler-errors): We could also recover `; PAT =>` here
// Try to parse a following `PAT =>`, if successful
// then we should recover.
let mut snapshot = this.create_snapshot_for_diagnostic();
let pattern_follows = snapshot
.parse_pat_allow_top_alt(
None,
RecoverComma::Yes,
RecoverColon::Yes,
CommaRecoveryMode::EitherTupleOrPipe,
)
.map_err(|err| err.cancel())
.is_ok();
if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
err.cancel();
this.struct_span_err(
hi.shrink_to_hi(),
"expected `,` following `match` arm",
)
.span_suggestion(
hi.shrink_to_hi(),
"missing a comma here to end this `match` arm",
",".to_owned(),
Applicability::MachineApplicable,
)
.emit();
return Ok(true);
}
}
err
err.span_label(arrow_span, "while parsing the `match` arm starting here");
Err(err)
})?;
} else {
this.eat(&token::Comma);