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Recover missing comma after match arm #97823

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merged 1 commit into from
Jun 8, 2022
Merged

Recover missing comma after match arm #97823

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51 changes: 38 additions & 13 deletions compiler/rustc_parse/src/parser/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand All @@ -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 {
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Can't this logic be completely replaced with the snapshot parse attempt unconditionally? Or is it that we have advanced too much already and consumed part of the pattern by now specifically because of &?

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@compiler-errors compiler-errors Jun 8, 2022 •
edited
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yeah, for example, in:

match &Foo {
  &Foo { a: 1 } => ()
  &Foo { a } => (),
}

we would have consumed the & token and Foo { .. } as the operator and RHS of operator & in the second arm before getting here, which means we have to handle it differently. Specifically, we can't recover so that the next arm parse is bound to be successful.

// 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);
Expand Down
6 changes: 3 additions & 3 deletions src/test/ui/parser/match-arm-without-braces.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,9 +45,9 @@ fn main() {
15;
}
match S::get(16) {
Some(Val::Foo) => 17
_ => 18, //~ ERROR expected one of
}
Some(Val::Foo) => 17 //~ ERROR expected `,` following `match` arm
_ => 18,
};
match S::get(19) {
Some(Val::Foo) =>
20; //~ ERROR `match` arm body without braces
Expand Down
10 changes: 3 additions & 7 deletions src/test/ui/parser/match-arm-without-braces.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -52,15 +52,11 @@ LL ~ { 14;
LL ~ 15; }
|

error: expected one of `,`, `.`, `?`, `}`, or an operator, found reserved identifier `_`
--> $DIR/match-arm-without-braces.rs:49:9
error: expected `,` following `match` arm
--> $DIR/match-arm-without-braces.rs:48:29
|
LL | Some(Val::Foo) => 17
| -- - expected one of `,`, `.`, `?`, `}`, or an operator
| |
| while parsing the `match` arm starting here
LL | _ => 18,
| ^ unexpected token
| ^ help: missing a comma here to end this `match` arm: `,`

error: `match` arm body without braces
--> $DIR/match-arm-without-braces.rs:53:11
Expand Down