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Prevent where < ident > from parsing.

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In order to be forward compatible with `where<'a>` syntax for higher
rank parameters, prevent potential conflicts with UFCS from parsing
correctly for the near term.
This commit is contained in:
Without Boats 2016-12-09 10:54:05 -08:00
parent 6a495f71ff
commit 90f6219f49
1 changed files with 17 additions and 0 deletions
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17
src/libsyntax/parse/parser.rs
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@ -4377,6 +4377,23 @@ impl<'a> Parser<'a> {
return Ok(where_clause);
}
// This is a temporary hack.
//
// We are considering adding generics to the `where` keyword as an alternative higher-rank
// parameter syntax (as in `where<'a>` or `where<T>`. To avoid that being a breaking
// change, for now we refuse to parse `where < (ident | lifetime) (> | , | :)`.
if token::Lt == self.token {
let ident_or_lifetime = self.look_ahead(1, |t| t.is_ident() || t.is_lifetime());
if ident_or_lifetime {
let gt_comma_or_colon = self.look_ahead(2, |t| {
*t == token::Gt || *t == token::Comma || *t == token::Colon
});
if gt_comma_or_colon {
return Err(self.fatal("TODO How to even explain this error?"));
}
}
}
let mut parsed_something = false;
loop {
let lo = self.span.lo;