A high impact bug because a lot of common traits use a `Self`
substitution by default. Should be backported to beta.
There was a check for this which wasn't catching all cases, it was made
more robust.
Fixes#49376Fixes#50626
r? @petrochenkov
Also move the check for not having type parameters into ast_validation.
I was not sure what to do with compile-fail/issue-23046.rs: The issue looks like
maybe the bounds actually played a role in triggering the ICE, but that seems
unlikely given that the compiler seems to entirely ignore them. However, I
couldn't find a testcase without the bounds, so I figured the best I could do is
to just remove the bounds and make sure at least that keeps working.
After this change, impl Trait existentials are
desugared to a new `abstract type` definition
paired with a set of lifetimes to apply.
In-scope generics are included as parents of the
`abstract type` generics. Parent regions are
replaced with static, and parent regions
referenced in the `impl Trait` type are duplicated
at the end of the `abstract type`'s generics.
We already disallowed them to be in the arg list, such as
Fn(impl Debug), but now we disallow Fn() -> impl Debug.
Also remove the ImplTraitContext argument from the function
lower_parenthesized_parameter_data as it is now unused.
Comment out part of test run-pass/impl-trait/xcrate.rs that now fails.
