Use bound vars for GAT params in param_env in check_type_bounds #87900
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
r? @nagisa (rust-highfive has picked a reviewer for you, use r? to override) |
rust-highfive
added
the
S-waiting-on-review
b-naber
reviewed
Aug 10, 2021
| // the *trait* with the generic associated type parameters. | ||
| let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id); | ||
| // - `impl_trait_ref` would be `<(A, B) as Foo<u32>> | ||
| // - `impl_ty_substs` would be `[A, B, ^0.0]` |
There was a problem hiding this comment.
Can you please use C instead of ^0.0 here? This might be unnecessarily confusing to someone reading that comment?
|
I'm not a great reviewer for this. Is there anybody else who could review this? |
|
r? rust-lang/compiler-team |
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
nikomatsakis
approved these changes
Aug 23, 2021
|
@bors r+ |
|
📌 Commit b017077 has been approved by |
bors
added
S-waiting-on-bors
|
☀️ Test successful - checks-actions |
Noratrieb
added a commit
to Noratrieb/rust
that referenced
this pull request
Mar 28, 2023
…d, r=jackh726
Correctly substitute GAT's type used in `normalize_param_env` in `check_type_bounds`
Given:
```rust
trait Foo {
type Assoc<T>: PartialEq<Self::Assoc<i32>>;
}
impl Foo for () {
type Assoc<T> = Wrapper<T>;
}
struct Wrapper<T>(T);
impl<T> PartialEq<Wrapper<i32>> for Wrapper<T> { }
```
We add an additional predicate in the `normalize_param_env` in `check_type_bounds` that is used to normalize the GAT's bounds to check them in the impl. Problematically, though, that predicate is constructed to be `for<^0> <() as Foo>::Assoc<^0> => Wrapper<T>`, instead of `for<^0> <() as Foo>::Assoc<^0> => Wrapper<^0>`.
That means `Self::Assoc<i32>` in the bounds that we're checking normalizes to `Wrapper<T>`, instead of `Wrapper<i32>`, and so the bound `Self::Assoc<T>: PartialEq<Self::Assoc<i32>>` normalizes to `Wrapper<T>: PartialEq<Wrapper<T>>`, which does not hold.
Fixes this by properly substituting the RHS of that normalizes predicate that we add to the `normalize_param_env`. That means the bound is properly normalized to `Wrapper<T>: PartialEq<Wrapper<i32>>`, which *does* hold.
---
The second commit in this PR just cleans up some substs stuff and some naming.
r? `@jackh726` cc rust-lang#87900
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes #87429