Make fns from other crates with RPITIT work

compiler/rustc_hir/src/definitions.rs

@@ -404,8 +404,12 @@ impl DefPathData {
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
 
+            // We use this name when collecting `ModChild`s.
+            // FIXME this could probably be removed with some refactoring to the name resolver.
+            ImplTraitAssocTy => Some(kw::Empty),
+
             Impl | ForeignMod | CrateRoot | Use | GlobalAsm | ClosureExpr | Ctor | AnonConst
-            | ImplTrait | ImplTraitAssocTy => None,
+            | ImplTrait => None,
         }
     }
 

compiler/rustc_ty_utils/src/assoc.rs

@@ -328,6 +328,9 @@ fn impl_associated_item_for_impl_trait_in_trait(
     // `opt_local_def_id_to_hir_id` with `None`.
     impl_assoc_ty.opt_local_def_id_to_hir_id(None);
 
+    // Copy span of the opaque.
+    impl_assoc_ty.def_ident_span(Some(span));
+
     impl_assoc_ty.associated_item(ty::AssocItem {
         name: kw::Empty,
         kind: ty::AssocKind::Type,
@@ -342,6 +345,9 @@ fn impl_associated_item_for_impl_trait_in_trait(
     // extra predicates to assume.
     impl_assoc_ty.param_env(tcx.param_env(impl_fn_def_id));
 
+    // Copy visility of the containing function.
+    impl_assoc_ty.visibility(tcx.visibility(impl_fn_def_id));
+
     // Copy impl_defaultness of the containing function.
     impl_assoc_ty.impl_defaultness(tcx.impl_defaultness(impl_fn_def_id));
 

tests/ui/impl-trait/in-trait/foreign.rs

@@ -1,5 +1,7 @@
 // check-pass
 // aux-build: rpitit.rs
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 extern crate rpitit;