have better explanation for `relate_types`

1 files changed, 7 insertions, 3 deletions

diff --git a/compiler/rustc_middle/src/mir/tcx.rs b/compiler/rustc_middle/src/mir/tcx.rs
index f534f0f5f3c..44ae75e2de7 100644
--- a/compiler/rustc_middle/src/mir/tcx.rs
+++ b/compiler/rustc_middle/src/mir/tcx.rs
@@ -69,7 +69,7 @@ impl<'tcx> PlaceTy<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         elem: &ProjectionElem<V, T>,
         mut handle_field: impl FnMut(&Self, FieldIdx, T) -> Ty<'tcx>,
-        mut handle_opaque_cast: impl FnMut(&Self, T) -> Ty<'tcx>,
+        mut handle_opaque_cast_and_subtype: impl FnMut(&Self, T) -> Ty<'tcx>,
     ) -> PlaceTy<'tcx>
     where
         V: ::std::fmt::Debug,
@@ -110,8 +110,12 @@ impl<'tcx> PlaceTy<'tcx> {
                 PlaceTy { ty: self.ty, variant_index: Some(index) }
             }
             ProjectionElem::Field(f, fty) => PlaceTy::from_ty(handle_field(&self, f, fty)),
-            ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(handle_opaque_cast(&self, ty)),
-            ProjectionElem::Subtype(_) => PlaceTy::from_ty(self.ty),
+            ProjectionElem::OpaqueCast(ty) => {
+                PlaceTy::from_ty(handle_opaque_cast_and_subtype(&self, ty))
+            }
+            ProjectionElem::Subtype(ty) => {
+                PlaceTy::from_ty(handle_opaque_cast_and_subtype(&self, ty))
+            }
         };
         debug!("projection_ty self: {:?} elem: {:?} yields: {:?}", self, elem, answer);
         answer