Account for return-position impl Trait in trait in opt_suggest_box_span

compiler/rustc_hir_typeck/src/_match.rs

@@ -526,7 +526,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         None
                     }
                 })?;
-                let opaque_ty = self.tcx.mk_opaque(rpit_def_id, substs);
 
                 if !self.can_coerce(first_ty, expected) || !self.can_coerce(second_ty, expected) {
                     return None;
@@ -540,13 +539,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     {
                         let pred = pred.kind().rebind(match pred.kind().skip_binder() {
                             ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) => {
-                                assert_eq!(trait_pred.trait_ref.self_ty(), opaque_ty);
+                                // FIXME(rpitit): This will need to be fixed when we move to associated types
+                                assert!(matches!(
+                                    *trait_pred.trait_ref.self_ty().kind(),
+                                    ty::Alias(_, ty::AliasTy { def_id, substs, .. })
+                                    if def_id == rpit_def_id && substs == substs
+                                ));
                                 ty::PredicateKind::Clause(ty::Clause::Trait(
                                     trait_pred.with_self_ty(self.tcx, ty),
                                 ))
                             }
                             ty::PredicateKind::Clause(ty::Clause::Projection(mut proj_pred)) => {
-                                assert_eq!(proj_pred.projection_ty.self_ty(), opaque_ty);
+                                assert!(matches!(
+                                    *proj_pred.projection_ty.self_ty().kind(),
+                                    ty::Alias(_, ty::AliasTy { def_id, substs, .. })
+                                    if def_id == rpit_def_id && substs == substs
+                                ));
                                 proj_pred = proj_pred.with_self_ty(self.tcx, ty);
                                 ty::PredicateKind::Clause(ty::Clause::Projection(proj_pred))
                             }

src/test/ui/impl-trait/in-trait/box-coerce-span-in-default.rs

@@ -0,0 +1,49 @@
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+//~^ WARN the feature `return_position_impl_trait_in_trait` is incomplete
+
+struct TestA {}
+struct TestB {}
+
+impl TestTrait for TestA {
+    type Output = ();
+}
+impl TestTrait for TestB {
+    type Output = ();
+}
+
+trait TestTrait {
+    type Output;
+}
+
+impl<A, B> TestTrait for GreeterOutput<A, B>
+where
+    A: TestTrait<Output = ()>,
+    B: TestTrait<Output = ()>,
+{
+    type Output = ();
+}
+
+enum GreeterOutput<A, B>
+where
+    A: TestTrait<Output = ()>,
+    B: TestTrait<Output = ()>,
+{
+    SayHello(A),
+    SayGoodbye(B),
+}
+
+trait Greeter {
+    fn test_func(&self, func: &str) -> impl TestTrait<Output = ()> {
+        match func {
+            "SayHello" => GreeterOutput::SayHello(TestA {}),
+            "SayGoodbye" => GreeterOutput::SayGoodbye(TestB {}),
+            _ => GreeterOutput::SayHello(TestA {}),
+        }
+    }
+}
+
+fn main() {
+    println!("Hello, world!");
+}

src/test/ui/impl-trait/in-trait/box-coerce-span-in-default.stderr

@@ -0,0 +1,11 @@
+warning: the feature `return_position_impl_trait_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/box-coerce-span-in-default.rs:3:12
+   |
+LL | #![feature(return_position_impl_trait_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+