fix: Properly lower SelfOnly predicates
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Few nits and one comment.
crates/hir-ty/src/lower.rs
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| db: &'db dyn HirDatabase, | ||
| type_alias: TypeAliasId, | ||
| ) -> (EarlyBinder<'db, Clauses<'db>>, Diagnostics) { | ||
| ) -> (EarlyBinder<'db, Clauses<'db>>, u32, Diagnostics) { |
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Return a struct? The role of the u32 isn't clear from the outside.
crates/hir-ty/src/lower.rs
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| self.predicates.get().map_bound(|it| &it.as_slice()[self.own_predicates_start as usize..]) | ||
| } | ||
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| /// Returns the predicates, minus the implicit `Self: Trait` predicate for a trait. |
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crates/hir-ty/src/lower.rs
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| let diagnostics = create_diagnostics(ctx.diagnostics); | ||
| let assoc_ty_bounds_start = predicates.len() as u32; | ||
| predicates.extend(assoc_ty_bounds); |
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This will mean query_own() will get the assoc type bounds from the parent as well, which isn't what we want. I think you'll need to have two assoc_ty_bounds_starts.
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Oh, right. I'm messing up bounds from parents here 😅
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Fixes #19339
In the following code:
And we have some trait bounds like
Self: Foo<Assoc1 = Bar, Assoc2: Baz>, rustc considers<Self as Foo>::Assoc1 = Baras a self bound<Self as Foo>::Assoc2: Bazas a non-self boundhttps://github.com/rust-lang/rust/blob/00f49d22042dce59561b36eb075bbf5e343c23c4/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs#L547-L668
As I have previously stated in some FIXME comment 😅, we and rustc has a bit different predicates lowering implementation: rustc lowers them multiple times with granular filtering options, while we lower them as little as possible.
I think our current implementation makes sense for memory usages and we don't need much granular filtering options like rustc (yet) so I just reordered those assoc item bounds at the end of the predicates and discern them by range.