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parser: extract maybe_recover_unexpected_comma.

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This commit is contained in:
Mazdak Farrokhzad 2019-08-18 17:11:12 +02:00
parent f852c7ce1c
commit 21d9b85c0d
1 changed files with 36 additions and 31 deletions
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67
src/libsyntax/parse/parser/pat.rs
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@ -57,40 +57,45 @@ impl<'a> Parser<'a> {
/// to subpatterns within such).
pub(super) fn parse_top_level_pat(&mut self) -> PResult<'a, P<Pat>> {
let pat = self.parse_pat(None)?;
if self.token == token::Comma {
// An unexpected comma after a top-level pattern is a clue that the
// user (perhaps more accustomed to some other language) forgot the
// parentheses in what should have been a tuple pattern; return a
// suggestion-enhanced error here rather than choking on the comma
// later.
let comma_span = self.token.span;
self.bump();
if let Err(mut err) = self.skip_pat_list() {
// We didn't expect this to work anyway; we just wanted
// to advance to the end of the comma-sequence so we know
// the span to suggest parenthesizing
err.cancel();
}
let seq_span = pat.span.to(self.prev_span);
let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
err.span_suggestion(
seq_span,
"try adding parentheses to match on a tuple..",
format!("({})", seq_snippet),
Applicability::MachineApplicable
).span_suggestion(
seq_span,
"..or a vertical bar to match on multiple alternatives",
format!("{}", seq_snippet.replace(",", " |")),
Applicability::MachineApplicable
);
}
return Err(err);
}
self.maybe_recover_unexpected_comma(pat.span)?;
Ok(pat)
}
fn maybe_recover_unexpected_comma(&mut self, lo: Span) -> PResult<'a, ()> {
if self.token != token::Comma {
return Ok(());
}
// An unexpected comma after a top-level pattern is a clue that the
// user (perhaps more accustomed to some other language) forgot the
// parentheses in what should have been a tuple pattern; return a
// suggestion-enhanced error here rather than choking on the comma later.
let comma_span = self.token.span;
self.bump();
if let Err(mut err) = self.skip_pat_list() {
// We didn't expect this to work anyway; we just wanted to advance to the
// end of the comma-sequence so we know the span to suggest parenthesizing.
err.cancel();
}
let seq_span = lo.to(self.prev_span);
let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
err.span_suggestion(
seq_span,
"try adding parentheses to match on a tuple..",
format!("({})", seq_snippet),
Applicability::MachineApplicable
)
.span_suggestion(
seq_span,
"..or a vertical bar to match on multiple alternatives",
format!("{}", seq_snippet.replace(",", " |")),
Applicability::MachineApplicable
);
}
Err(err)
}
/// Parse and throw away a parentesized comma separated
/// sequence of patterns until `)` is reached.
fn skip_pat_list(&mut self) -> PResult<'a, ()> {