Hide some follow-up errors

Author: oli-obk

compiler/rustc_hir_analysis/src/impl_wf_check.rs

@@ -86,6 +86,8 @@ fn enforce_impl_params_are_constrained(
     let impl_predicates = tcx.predicates_of(impl_def_id);
     let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).map(ty::EarlyBinder::instantiate_identity);
 
+    impl_trait_ref.error_reported()?;
+
     let mut input_parameters = cgp::parameters_for_impl(tcx, impl_self_ty, impl_trait_ref);
     cgp::identify_constrained_generic_params(
         tcx,

tests/ui/traits/issue-78372.stderr

@@ -55,12 +55,6 @@ LL | impl<T> DispatchFromDyn<Smaht<U, MISC>> for T {}
    = help: add `#![feature(dispatch_from_dyn)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0378]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures
-  --> $DIR/issue-78372.rs:3:1
-   |
-LL | impl<T> DispatchFromDyn<Smaht<U, MISC>> for T {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
 error[E0038]: the trait `Foo` cannot be made into an object
   --> $DIR/issue-78372.rs:12:17
    |
@@ -88,6 +82,12 @@ LL |     fn foo(self: Smaht<Self, T>);
    = note: type of `self` must be `Self` or a type that dereferences to it
    = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
+error[E0378]: the trait `DispatchFromDyn` may only be implemented for a coercion between structures
+  --> $DIR/issue-78372.rs:3:1
+   |
+LL | impl<T> DispatchFromDyn<Smaht<U, MISC>> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: aborting due to 8 previous errors
 
 Some errors have detailed explanations: E0038, E0307, E0378, E0412, E0658.