Auto merge of #135057 - compiler-errors:project-unconstrained, r=oli-obk

Project to `TyKind::Error` when there are unconstrained non-lifetime (ty/const) impl params

It splits the `enforce_impl_params_are_constrained` function into lifetime/non-lifetime, and queryfies the latter. We can then use the result of the latter query (`Result<(), ErrorGuaranteed>`) to intercept projection and constrain the projected type to `TyKind::Error`, which ensures that we leak no ty or const vars to places that don't expect them, like `normalize_erasing_regions`.

The reason we split `enforce_impl_params_are_constrained` into two parts is because we only error for *lifetimes* if the lifetime ends up showing up in any of the associated types of the impl (e.g. we allow `impl<'a> Foo { type Assoc = (); }`). However, in order to compute the `type_of` query for the anonymous associated type of an RPITIT, we need to do trait solving (in `query collect_return_position_impl_trait_in_trait_tys`). That would induce cycles. Luckily, it turns out for lifetimes we don't even care about if they're unconstrained, since they're erased in all contexts that we are trying to fix ICEs. So it's sufficient to keep this check separated out of the query.

I think this is a bit less invasive of an approach compared to #127973. The major difference between this PR and that PR is that we queryify the check instead of merging it into the `explicit_predicates_of` query, and we use the result to taint just projection goals, rather than trait goals too. This doesn't require a lot of new tracking in `ItemCtxt` and `GenericPredicates`, and it also seems to not require any other changes to typeck like that PR did.

Fixes #123141
Fixes #125874
Fixes #126942
Fixes #127804
Fixes #130967

r? oli-obk

compiler/rustc_middle/src/query/mod.rs

@@ -1716,6 +1716,11 @@ rustc_queries! {
         ensure_forwards_result_if_red
     }
 
+    query enforce_impl_non_lifetime_params_are_constrained(key: LocalDefId) -> Result<(), ErrorGuaranteed> {
+        desc { |tcx| "checking that `{}`'s generics are constrained by the impl header", tcx.def_path_str(key) }
+        ensure_forwards_result_if_red
+    }
+
     // The `DefId`s of all non-generic functions and statics in the given crate
     // that can be reached from outside the crate.
     //