non_lifetime_binders: fix ICE in lint opaque-hidden-inferred-bound

[fmease]

Opaque types like impl for<T> Trait<T> would previously lead to an ICE.

r? @compiler-errors

[fmease]

Not entirely sure if we should instantiate with fresh vars instead 😅

[compiler-errors]

placeholders i guess are fine since we don't solve regions at all

[fmease]

I couldn't craft a test that involves non-lifetime binders & triggers opaque_hidden_inferred_bound since higher-ranked hidden types aren't supported yet. E.g., impl for<T> Trait<T, Assoc = Tait<T>> errors out early.

[compiler-errors]

what does it error with?

[fmease]

(with -Zverbose)

error[E0792]: non-defining opaque type use in defining scope
  --> experiment.rs:21:28
   |
21 | () -> impl for<T> Trait<T, Assoc = Tait<T>> {
   |                            ^^^^^^^^^^^^^^^ argument `^"T"` is not a generic parameter
   |
note: for this opaque type
  --> experiment.rs:17:24
   |
17 | type Tait<T: ?Sized> = impl Duh<T>;
   |                        ^^^^^^^^^^^

error[E0792]: expected generic type parameter, found `!1_"T"`
  --> experiment.rs:22:5
   |
17 | type Tait<T: ?Sized> = impl Duh<T>;
   |           - this generic parameter must be used with a generic type parameter
...
22 |     42
   |     ^^

[compiler-errors]

oh oh right

[fmease]

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=4d06b9342a949d9adfa2d9a365dc5731

[compiler-errors]

r=me when green

[matthiaskrgr]

does this fix #108814 ?

[fmease]

Nope, it doesn't. This PR only fixes code containing opaque types with non-lifetime binders.

[fmease]

@bors r=compiler-errors

[bors]

📌 Commit 3f0a327 has been approved by compiler-errors

It is now in the queue for this repository.