Make nested RPITIT inherit the parent opaque's generics.

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -4,7 +4,6 @@ use hir::{
     GenericParamKind, HirId, Node,
 };
 use rustc_hir as hir;
-use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint;
@@ -143,20 +142,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::Generics {
             Some(tcx.typeck_root_def_id(def_id))
         }
         Node::Item(item) => match item.kind {
-            ItemKind::OpaqueTy(hir::OpaqueTy {
-                origin:
-                    hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
-                in_trait,
-                ..
-            }) => {
-                if in_trait {
-                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn))
-                } else {
-                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn))
-                }
-                Some(fn_def_id.to_def_id())
-            }
-            ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
+            ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
                 let parent_id = tcx.hir().get_parent_item(hir_id);
                 assert_ne!(parent_id, hir::CRATE_OWNER_ID);
                 debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);

src/test/ui/async-await/in-trait/nested-rpit.rs

@@ -0,0 +1,17 @@
+// check-pass
+// edition: 2021
+
+#![feature(async_fn_in_trait)]
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+use std::future::Future;
+use std::marker::PhantomData;
+
+trait Lockable<K, V> {
+    async fn lock_all_entries(&self) -> impl Future<Output = Guard<'_>>;
+}
+
+struct Guard<'a>(PhantomData<&'a ()>);
+
+fn main() {}