Rollup merge of #130485 - compiler-errors:impossible-types, r=BoxyUwU

Do not expect infer/bound/placeholder/error in v0 symbol mangling

Infer/bound/placeholder/error are not encounterable during codegen. Let's make sure v0 symbol mangling doesn't "accidentally" handle them.

As for aliases (namely: projections and uv consts) these may still be encounterable because of the way that we render the def paths of items. Specifically, when we have something like:

```
struct W<T>(T);

impl<T> W<T> {
    fn x() {
        fn y() {}
    }
}
```

The path of `y` is rendered like `crate_name::W<T>::x::y`. Specifically, since `y` doesn't inherit the generics of the impl, we use the *identity* substitutions for that impl. If the impl has any aliases, they will remain unnormalized if they're rigid.

r? `@BoxyUwU`

0 files changed, 0 insertions, 0 deletions