bjoernager/rust
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Properly calculate best failure in macro matching

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Previously, we used spans. This was not good. Sometimes, the span of the
token that failed to match may come from a position later in the file
which has been transcribed into a token stream way earlier in the file.
If precisely this token fails to match, we think that it was the best
match because its span is so high, even though other arms might have
gotten further in the token stream.

We now try to properly use the location in the token stream.
This commit is contained in:
Nilstrieb 2022-12-11 21:46:30 +01:00
parent 32da230588
commit d72a0c437b
6 changed files with 80 additions and 15 deletions
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13
compiler/rustc_expand/src/mbe/macro_parser.rs
View file

@ -310,7 +310,8 @@ pub(crate) enum ParseResult<T> {
Success(T),
/// Arm failed to match. If the second parameter is `token::Eof`, it indicates an unexpected
/// end of macro invocation. Otherwise, it indicates that no rules expected the given token.
Failure(Token, &'static str),
/// The usize is the approximate position of the token in the input token stream.
Failure(Token, usize, &'static str),
/// Fatal error (malformed macro?). Abort compilation.
Error(rustc_span::Span, String),
ErrorReported(ErrorGuaranteed),
@ -455,6 +456,7 @@ impl TtParser {
&mut self,
matcher: &'matcher [MatcherLoc],
token: &Token,
approx_position: usize,
track: &mut T,
) -> Option<NamedParseResult> {
// Matcher positions that would be valid if the macro invocation was over now. Only
@ -598,6 +600,7 @@ impl TtParser {
token::Eof,
if token.span.is_dummy() { token.span } else { token.span.shrink_to_hi() },
),
approx_position,
"missing tokens in macro arguments",
),
})
@ -627,7 +630,12 @@ impl TtParser {
// Process `cur_mps` until either we have finished the input or we need to get some
// parsing from the black-box parser done.
let res = self.parse_tt_inner(matcher, &parser.token, track);
let res = self.parse_tt_inner(
matcher,
&parser.token,
parser.approx_token_stream_pos(),
track,
);
if let Some(res) = res {
return res;
}
@ -642,6 +650,7 @@ impl TtParser {
// parser: syntax error.
return Failure(
parser.token.clone(),
parser.approx_token_stream_pos(),
"no rules expected this token in macro call",
);
}