regression: cycle detected when computing whether impls specialize one another

[BoxyUwU]

• https://crater-reports.s3.amazonaws.com/beta-1.79-2/beta-2024-05-11/gh/HalsekiRaika.anyid/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.79-2/beta-2024-05-11/gh/HalsekiRaika.nos/log.txt

[INFO] [stdout] error[E0391]: cycle detected when computing whether impls specialize one another
[INFO] [stdout]   --> /opt/rustwide/workdir/src/lib.rs:54:1
[INFO] [stdout]    |
[INFO] [stdout] 54 | impl<T: Identifier> PartialEq<T> for AnyId {
[INFO] [stdout]    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[INFO] [stdout]    |

[compiler-errors]

Bisecting this...

[compiler-errors]

This bisected in #122791. This crate is using specialization, which we don't stably support.

This has some interactions with specialization, and so breaks a few UI tests that I don't agree should've ever worked in the first place, and also breaks a handful of crates in a way that I don't believe is a problem.

[Mark-Simulacrum]

@compiler-errors How is that not feature gated? I don't see feature gates in the repos above and presumably it built on stable in order to regress here?

[compiler-errors]

I am mistaken then, @Mark-Simulacrum. I thought I looked at these crates, but perhaps I was looking at the wrong one.