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Spurious local ambiguity error after empty $($ident),* #34030
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In theory there is no ambiguity because an ident can't start with |
@durka: the error is spurious; this is definitely a bug. The issue is purely when the repeating group is empty. Hence |
Fixes rust-lang#24189. Fixes rust-lang#26444. Fixes rust-lang#27832. Fixes rust-lang#34030. Fixes rust-lang#35650. Fixes rust-lang#39964. Fixes the 4th comment in rust-lang#40569. Fixes the issue blocking rust-lang#40984.
…seyfried Only match a fragment specifier the if it starts with certain tokens. When trying to match a fragment specifier, we first predict whether the current token can be matched at all. If it cannot be matched, don't bother to push the Earley item to `bb_eis`. This can fix a lot of issues which otherwise requires full backtracking (#42838). In this PR the prediction treatment is not done for `:item`, `:stmt` and `:tt`, but it could be expanded in the future. Fixes #24189. Fixes #26444. Fixes #27832. Fixes #34030. Fixes #35650. Fixes #39964. Fixes the 4th comment in #40569. Fixes the issue blocking #40984.
In this case, it should be looking for an ident or a
/
, in which there is no ambiguity.All channels are affected.
This is affecting my ability to write macros accepting generics using angle brackets, e.g.
$ty:ident<$($x:ident),*>
, with a supporting pattern to turnFoo
intoFoo<>
.May be related to #24827.
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