HRTB WF ambiguity

[compiler-errors]

pub struct Bar
where
    for<'a> &'a mut Self:;

fn main() {}

Errors out in ambiguity:

error[E0282]: type annotations needed
 --> <source>:5:13
  |
5 |     for<'a> &'a mut Self:;
  |             ^^^^^^^^^^^^ cannot infer type for mutable reference `&'a mut Bar`
  |
note: required by a bound in `Bar`

This happens when checking that Bar is WF... so what's going on there?!

[lcnr]

that's an issue with the current coinduction handling for hrtb: https://hackmd.io/0GCBKGYCQ9a8zz_FvCWQLw#coinduction-makes-me-sad

have that as "deduplicate universes in query responses" under "initial implementation finished" in the tracking issue rust-lang/rust#107374

[lcnr]

opened it as rust-lang/rust#109764. should change the test to have revisions and be known-bug with the new solver