cycle on inherent associated types in structs

[peku33]

Taken out from here: #8995 (comment) as @fmease requested.

struct Foo {
    bar: Self::Bar,
}
impl Foo {
    pub type Bar = usize;
}

was compiled successfully a couple of nighly revisions before.

Now an error is returned:

error[E0391]: cycle detected when computing predicates of `Foo`
  --> src\main.rs:5:1
   |
5  | struct Foo {
   | ^^^^^^^^^^
   |
note: ...which requires computing predicates of `Foo`...
  --> src\main.rs:5:1
   |
5  | struct Foo {
   | ^^^^^^^^^^
note: ...which requires computing inferred outlives predicates of `Foo`...
  --> src\main.rs:5:1
   |
5  | struct Foo {
   | ^^^^^^^^^^
   = note: ...which requires computing the inferred outlives predicates for items in this crate...
note: ...which requires computing type of `Foo::bar`...
  --> src\main.rs:6:5
   |
6  |     bar: Self::Bar,
   |     ^^^^^^^^^^^^^^
note: ...which requires computing normalized predicates of `Foo`...
  --> src\main.rs:5:1
   |
5  | struct Foo {
   | ^^^^^^^^^^
   = note: ...which again requires computing predicates of `Foo`, completing the cycle
note: cycle used when collecting item types in top-level module

Meta

rustc --version --verbose:

rustc 1.69.0-nightly (34e6673a0 2023-02-25)

[fmease]

Thanks for reporting!

@rustbot label T-compiler F-inherent_associated_types
@rustbot claim

[joshtriplett]

What is the current state of this issue?

[fmease]

No active work on this at the moment. This issue is non-trivial and still blocked on architectural limitations (namely, the way we lower and represent types). However, I'm continuously furthering my understanding of this subject matter by attacking closely related issues and topics (e.g., #126651).