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Auto merge of #118118 - spastorino:do-not-erase-late-bound-regions-on-iat, r=compiler-errors

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Do not erase late bound regions when selecting inherent associated types

In the fix for #97156 we would want the following code:

```rust
#![feature(inherent_associated_types)]
#![allow(incomplete_features)]

struct Foo<T>(T);

impl Foo<fn(&'static ())> {
    type Assoc = u32;
}

trait Other {}
impl Other for u32 {}

// FIXME(inherent_associated_types): Avoid emitting two diagnostics (they only differ in span).
// FIXME(inherent_associated_types): Enhancement: Spruce up the diagnostic by saying something like
// "implementation is not general enough" as is done for traits via
// `try_report_trait_placeholder_mismatch`.

fn bar(_: Foo<for<'a> fn(&'a ())>::Assoc) {}
//~^ ERROR mismatched types
//~| ERROR mismatched types

fn main() {}
```

to fail with ...

```
error[E0220]: associated type `Assoc` not found for `Foo<for<'a> fn(&'a ())>` in the current scope
  --> tests/ui/associated-inherent-types/issue-109789.rs:18:36
   |
4  | struct Foo<T>(T);
   | ------------- associated item `Assoc` not found for this struct
...
18 | fn bar(_: Foo<for<'a> fn(&'a ())>::Assoc) {}
   |                                    ^^^^^ associated item not found in `Foo<for<'a> fn(&'a ())>`
   |
   = note: the associated type was found for
           - `Foo<fn(&'static ())>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0220`.
```

This PR fixes the ICE we are currently getting "was a subtype of Foo<Binder(fn(&ReStatic ()), [])> during selection but now it is not"

Also fixes #112631

r? `@lcnr`
This commit is contained in:
bors 2023-11-27 17:11:35 +00:00
commit b4c4664167
5 changed files with 128 additions and 117 deletions
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13
compiler/rustc_trait_selection/src/traits/project.rs
View file

@ -1454,7 +1454,18 @@ pub fn compute_inherent_assoc_ty_args<'a, 'b, 'tcx>(
// Infer the generic parameters of the impl by unifying the
// impl type with the self type of the projection.
let self_ty = alias_ty.self_ty();
let mut self_ty = alias_ty.self_ty();
if !selcx.infcx.next_trait_solver() {
self_ty = normalize_with_depth_to(
selcx,
param_env,
cause.clone(),
depth + 1,
self_ty,
obligations,
);
}
match selcx.infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, impl_ty, self_ty) {
Ok(mut ok) => obligations.append(&mut ok.obligations),
Err(_) => {