Do not feed param_env for RPITITs impl side

compiler/rustc_ty_utils/src/assoc.rs

@@ -384,10 +384,6 @@ fn associated_type_for_impl_trait_in_impl(
         opt_rpitit_info: Some(ImplTraitInTraitData::Impl { fn_def_id: impl_fn_def_id.to_def_id() }),
     });
 
-    // Copy param_env of the containing function. The synthesized associated type doesn't have
-    // extra predicates to assume.
-    impl_assoc_ty.param_env(tcx.param_env(impl_fn_def_id));
-
     // Copy visility of the containing function.
     impl_assoc_ty.visibility(tcx.visibility(impl_fn_def_id));
 

compiler/rustc_ty_utils/src/ty.rs

@@ -130,7 +130,9 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
     // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty): I don't like this, we should
     // at least be making sure that the generics in RPITITs and their parent fn don't
     // get out of alignment, or else we do actually need to substitute these predicates.
-    if let Some(ImplTraitInTraitData::Trait { fn_def_id, .. }) = tcx.opt_rpitit_info(def_id) {
+    if let Some(ImplTraitInTraitData::Trait { fn_def_id, .. })
+    | Some(ImplTraitInTraitData::Impl { fn_def_id, .. }) = tcx.opt_rpitit_info(def_id)
+    {
         predicates = tcx.predicates_of(fn_def_id).instantiate_identity(tcx).predicates;
     }
 

tests/ui/async-await/in-trait/issue-104678.rs

@@ -1,5 +1,7 @@
 // edition:2021
 // check-pass
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+// revisions: current next
 
 #![feature(async_fn_in_trait)]
 #![allow(incomplete_features)]