rust-analyzer: fix parsing of trait bound polarity and for-binders #145199
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The rustc AST allows both `for<>` binders and `?` polarity
modifiers in trait bounds, but they are parsed in a specific
order and validated for correctness:
1. `for<>` binder is parsed first.
2. Polarity modifiers (`?`, `!`) are parsed second.
3. The parser validates that binders and polarity modifiers
do not conflict:
```rust
if let Some(binder_span) = binder_span {
match modifiers.polarity {
BoundPolarity::Maybe(polarity_span) => {
// Error: "for<...> binder not allowed with ? polarity"
}
}
}
```
This implies:
- `for<> ?Sized` → Valid syntax. Invalid semantics.
- `?for<> Sized` → Invalid syntax.
However, rust-analyzer incorrectly had special-case logic that
allowed `?for<>` as valid syntax. This fix removes that incorrect
special case, making rust-analyzer reject `?for<> Sized` as a
syntax error, matching rustc behavior.
This has caused confusion in other crates (such as syn) which
rely on these files to implement correct syntax evaluation.
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rustbot has assigned @Mark-Simulacrum. Use |
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rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead. cc @rust-lang/rust-analyzer |
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This is a r-a-only change, so please instead submit this PR against the r-a repository. |
I don't think this is true. I think my commit message just triggered the bot. This is a change to the parser crate which is hosted in this repo. I'm not sure the best way to improve my commit message. |
To clarify, rust-analyzer is a subtree of this repository, but it is not a git submodule (because that has annoying UX issue). It is in fact sync'd between this repo and rust-analyzer with https://github.com/rust-lang/josh-sync. You can see an example sync such as #144887. Please refer to https://rustc-dev-guide.rust-lang.org/external-repos.html?highlight=josh#external-dependencies-subtrees. I.e. the bot message is correct. |
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In any case, I'll roll a rust-analyzer reviewer, if the r-a reviewer is fine reviewing/accepting it on the r-l/r repo side then disregard the above. r? rust-analyzer |
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Please send rust-analyzer-only PRs to https://github.com/rust-lang/rust-analyzer/. |
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The rustc AST allows both
for<>binders and?polarity modifiers in trait bounds, but they are parsed in a specific order and validated for correctness:This implies:
for<> ?Sized→ Valid syntax. Invalid semantics.?for<> Sized→ Invalid syntax.However, rust-analyzer incorrectly had special-case logic that allowed
?for<>as valid syntax. This fix removes that incorrect special case, making rust-analyzer reject?for<> Sizedas a syntax error, matching rustc behavior.This has caused confusion in other crates (such as syn) which rely on these files to implement correct syntax evaluation.