fix: handle lifetime variables in projection normalization #13223
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Sep 12, 2022
fix: handle lifetime variables in projection normalization Fixes #12674 The problem is that we've been skipping the binders of normalized projections assuming they should be empty, but the assumption is unfortunately wrong. We may get back lifetime variables and should handle them before returning them as normalized projections. For those who are curious why we get those even though we treat all lifetimes as 'static, [this comment in chalk](https://github.com/rust-lang/chalk/blob/d875af0ff196dd6430b5f5fd87a640fa5ab59d1e/chalk-solve/src/infer/unify.rs#L888-L908) may be interesting. I thought using `InferenceTable` would be cleaner than the other ways as it already has the methods for canonicalization, normalizing projection, and resolving variables, so moved goal building and trait solving logic to a new `HirDatabase` query. I made it transparent query as the query itself doesn't do much work but the eventual call to `HirDatabase::trait_solve_query()` does.
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This was referenced Sep 12, 2022
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Sep 13, 2022
fixup: remove unnecessary `Option` Fixup for #13223, two things: - `normalize_projection_query()` (and consequently `HirDatabase::normalize_projection()`) never returns `None` (well, it used to when I first wrote it...), so just return `Ty` instead of `Option<Ty>` - When chalk cannot normalize projection uniquely, `normalize_trait_assoc_type()` used to return `None` before #13223, but not anymore because of the first point. I restored the behavior so its callers work as before.
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Dec 25, 2022
…r=lowr fix: handle lifetime variables in `CallableSig` query Fixes #13838 The problem is similar to #13223: we've been skipping non-empty binders, letting lifetime bound variables escape. I ended up refactoring `hir_ty::callable_sig_from_fnonce()`. Like #13223, I chose to make use of `InferenceTable` which is capable of handling variables (I feel we should always use it when we solve trait-related stuff instead of manually building obligations/queries). I couldn't make up a test that crashes without this patch (since the function I'm fixing is only used *outside* `hir-ty`, simple `hir-ty` test wouldn't cause crash), but at least I tested with my local build and made sure it doesn't crash with the code in the original issue. I'd appreciate any help to find a regression test.
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Fixes #12674
The problem is that we've been skipping the binders of normalized projections assuming they should be empty, but the assumption is unfortunately wrong. We may get back lifetime variables and should handle them before returning them as normalized projections. For those who are curious why we get those even though we treat all lifetimes as 'static, this comment in chalk may be interesting.
I thought using
InferenceTablewould be cleaner than the other ways as it already has the methods for canonicalization, normalizing projection, and resolving variables, so moved goal building and trait solving logic to a newHirDatabasequery. I made it transparent query as the query itself doesn't do much work but the eventual call toHirDatabase::trait_solve_query()does.