From 1335da9d485879a99c3ba24827781c6ee6705cc6 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 11 Sep 2022 09:35:43 +0000
Subject: [PATCH] Only encode RPITIT when trait method has default body

---
 compiler/rustc_metadata/src/rmeta/encoder.rs | 14 +++++++++++++-
 src/test/ui/impl-trait/in-trait/encode.rs    |  9 +++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/impl-trait/in-trait/encode.rs

diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index f967ac9a4dc3e..5a60ea794edd8 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1036,7 +1036,6 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
         | DefKind::Static(..)
         | DefKind::TyAlias
         | DefKind::OpaqueTy
-        | DefKind::ImplTraitPlaceholder
         | DefKind::ForeignTy
         | DefKind::Impl
         | DefKind::AssocFn
@@ -1047,6 +1046,19 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
         | DefKind::AnonConst
         | DefKind::InlineConst => true,
 
+        DefKind::ImplTraitPlaceholder => {
+            let parent_def_id = tcx.impl_trait_in_trait_parent(def_id.to_def_id());
+            let assoc_item = tcx.associated_item(parent_def_id);
+            match assoc_item.container {
+                // Always encode an RPIT in an impl fn, since it always has a body
+                ty::AssocItemContainer::ImplContainer => true,
+                ty::AssocItemContainer::TraitContainer => {
+                    // Encode an RPIT for a trait only if the trait has a default body
+                    assoc_item.defaultness(tcx).has_value()
+                }
+            }
+        }
+
         DefKind::AssocTy => {
             let assoc_item = tcx.associated_item(def_id);
             match assoc_item.container {
diff --git a/src/test/ui/impl-trait/in-trait/encode.rs b/src/test/ui/impl-trait/in-trait/encode.rs
new file mode 100644
index 0000000000000..efb9f6498ba6d
--- /dev/null
+++ b/src/test/ui/impl-trait/in-trait/encode.rs
@@ -0,0 +1,9 @@
+// build-pass
+// compile-flags: --crate-type=lib
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    fn bar() -> impl Sized;
+}