From c1f3529c911eb252aaddb139bf54afca8475df6b Mon Sep 17 00:00:00 2001
From: Santiago Pastorino <spastorino@gmail.com>
Date: Mon, 20 Mar 2023 13:20:28 -0300
Subject: [PATCH] Always encode RPITITs

---
 compiler/rustc_metadata/src/rmeta/encoder.rs     | 8 +++++++-
 tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index ef3eda584e1..44a57770221 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1044,7 +1044,13 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
             let assoc_item = tcx.associated_item(def_id);
             match assoc_item.container {
                 ty::AssocItemContainer::ImplContainer => true,
-                ty::AssocItemContainer::TraitContainer => assoc_item.defaultness(tcx).has_value(),
+                // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty) always encode RPITITs,
+                // since we need to be able to "project" from an RPITIT associated item
+                // to an opaque when installing the default projection predicates in
+                // default trait methods with RPITITs.
+                ty::AssocItemContainer::TraitContainer => {
+                    assoc_item.defaultness(tcx).has_value() || assoc_item.opt_rpitit_info.is_some()
+                }
             }
         }
         DefKind::TyParam => {
diff --git a/tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs b/tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs
index 74df300f85a..74f7bc603aa 100644
--- a/tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs
+++ b/tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs
@@ -1,3 +1,5 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+
 #![feature(return_position_impl_trait_in_trait)]
 
 pub trait Foo {