Auto merge of #112422 - aliemjay:implied-bounds-placeholders, r=lcnr

ignore implied bounds with placeholders

given the following code:
```rust
trait Trait {
    type Ty<'a> where Self: 'a;
}

impl<T> Trait for T {
    type Ty<'a> = () where Self: 'a;
}

struct Foo<T: Trait>(T)
where
    for<'x> T::Ty<'x>: Sized;
```

when computing the implied bounds from `Foo<X>` we incorrectly get the bound `X: !x` from the normalization of ` for<'x> <X as Trait>::Ty::<'x>: Sized`. This is a a known bug! we shouldn't use the constraints that arise from normalization as implied bounds. See #109628.

Ignore these bounds for now. This should prevent later ICEs.

Fixes #112250
Fixes #107409

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -72,7 +72,7 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
         };
 
         let mut constraints = QueryRegionConstraints::default();
-        let Ok(InferOk { value, obligations }) = self
+        let Ok(InferOk { value: mut bounds, obligations }) = self
             .instantiate_nll_query_response_and_region_obligations(
                 &ObligationCause::dummy(),
                 param_env,
@@ -85,6 +85,10 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
         };
         assert_eq!(&obligations, &[]);
 
+        // Because of #109628, we may have unexpected placeholders. Ignore them!
+        // FIXME(#109628): panic in this case once the issue is fixed.
+        bounds.retain(|bound| !bound.has_placeholders());
+
         if !constraints.is_empty() {
             let span = self.tcx.def_span(body_id);
 
@@ -114,7 +118,7 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
             }
         };
 
-        value
+        bounds
     }
 
     fn implied_bounds_tys(