Handle ForeignItem as TAIT scope.

compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs

@@ -69,6 +69,7 @@ pub(super) fn find_opaque_ty_constraints_for_tait(tcx: TyCtxt<'_>, def_id: Local
             Node::Item(it) => locator.visit_item(it),
             Node::ImplItem(it) => locator.visit_impl_item(it),
             Node::TraitItem(it) => locator.visit_trait_item(it),
+            Node::ForeignItem(it) => locator.visit_foreign_item(it),
             other => bug!("{:?} is not a valid scope for an opaque type item", other),
         }
     }
@@ -240,6 +241,12 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
         self.check(it.owner_id.def_id);
         intravisit::walk_trait_item(self, it);
     }
+    fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
+        trace!(?it.owner_id);
+        assert_ne!(it.owner_id.def_id, self.def_id);
+        // No need to call `check`, as we do not run borrowck on foreign items.
+        intravisit::walk_foreign_item(self, it);
+    }
 }
 
 pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(

tests/ui/type-alias-impl-trait/nested-in-anon-const.rs

@@ -0,0 +1,21 @@
+// Regression test for issue #119295.
+
+#![feature(type_alias_impl_trait)]
+
+type Bar<T> = T;
+type S<const A: usize> = [i32; A];
+
+extern "C" {
+    pub fn lint_me(
+        x: Bar<
+            S<
+                { //~ ERROR mismatched types
+                    type B<Z> = impl Sized;
+                    //~^ ERROR unconstrained opaque type
+                },
+            >,
+        >,
+    );
+}
+
+fn main() {}

tests/ui/type-alias-impl-trait/nested-in-anon-const.stderr

@@ -0,0 +1,20 @@
+error: unconstrained opaque type
+  --> $DIR/nested-in-anon-const.rs:13:33
+   |
+LL |                     type B<Z> = impl Sized;
+   |                                 ^^^^^^^^^^
+   |
+   = note: `B` must be used in combination with a concrete type within the same item
+
+error[E0308]: mismatched types
+  --> $DIR/nested-in-anon-const.rs:12:17
+   |
+LL | /                 {
+LL | |                     type B<Z> = impl Sized;
+LL | |
+LL | |                 },
+   | |_________________^ expected `usize`, found `()`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.