1 files changed, 12 insertions, 16 deletions
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index b10aaad5f2a..eb3c21163ab 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -27,8 +27,7 @@ fn resolve_instance<'tcx>(
         )
     } else {
         let ty = tcx.type_of(def);
-        let item_type =
-            tcx.subst_and_normalize_erasing_regions(substs, param_env, ty.skip_binder());
+        let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, ty);
 
         let def = match *item_type.kind() {
             ty::FnDef(def_id, ..) if tcx.is_intrinsic(def_id) => {
@@ -195,21 +194,18 @@ fn resolve_associated_item<'tcx>(
             })
         }
         traits::ImplSource::Future(future_data) => {
-            if cfg!(debug_assertions) && tcx.item_name(trait_item_id) != sym::poll {
-                // For compiler developers who'd like to add new items to `Future`,
-                // you either need to generate a shim body, or perhaps return
-                // `InstanceDef::Item` pointing to a trait default method body if
-                // it is given a default implementation by the trait.
-                span_bug!(
-                    tcx.def_span(future_data.generator_def_id),
-                    "no definition for `{trait_ref}::{}` for built-in async generator type",
-                    tcx.item_name(trait_item_id)
-                )
+            if Some(trait_item_id) == tcx.lang_items().future_poll_fn() {
+                // `Future::poll` is generated by the compiler.
+                Some(Instance {
+                    def: ty::InstanceDef::Item(future_data.generator_def_id),
+                    substs: future_data.substs,
+                })
+            } else {
+                // All other methods are default methods of the `Future` trait.
+                // (this assumes that `ImplSource::Future` is only used for methods on `Future`)
+                debug_assert!(tcx.impl_defaultness(trait_item_id).has_value());
+                Some(Instance::new(trait_item_id, rcvr_substs))
             }
-            Some(Instance {
-                def: ty::InstanceDef::Item(future_data.generator_def_id),
-                substs: future_data.substs,
-            })
         }
         traits::ImplSource::Closure(closure_data) => {
             if cfg!(debug_assertions)