Do binder folding eagerly in bound_coroutine_hidden_types

I refuse to fix this in the old solver; its lazy instantiation of
binders will be the end of me.

2 files changed, 8 insertions, 35 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs b/compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs
index 51a3298a90b..80c31831462 100644
--- a/compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs
@@ -6,7 +6,7 @@ use rustc_hir::{def_id::DefId, Movability, Mutability};
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::traits::solve::Goal;
 use rustc_middle::ty::{
-    self, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
+    self, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
 };
 use rustc_span::sym;
 
@@ -73,8 +73,8 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
 
         ty::CoroutineWitness(def_id, args) => Ok(ecx
             .tcx()
-            .coroutine_hidden_types(def_id)
-            .map(|bty| replace_erased_lifetimes_with_bound_vars(tcx, bty.instantiate(tcx, args)))
+            .bound_coroutine_hidden_types(def_id)
+            .map(|bty| bty.instantiate(tcx, args))
             .collect()),
 
         // For `PhantomData<T>`, we pass `T`.
@@ -93,26 +93,6 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
     }
 }
 
-pub(in crate::solve) fn replace_erased_lifetimes_with_bound_vars<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    ty: Ty<'tcx>,
-) -> ty::Binder<'tcx, Ty<'tcx>> {
-    let mut counter = 0;
-    let ty = tcx.fold_regions(ty, |r, current_depth| match r.kind() {
-        ty::ReErased => {
-            let br = ty::BoundRegion { var: ty::BoundVar::from_u32(counter), kind: ty::BrAnon };
-            counter += 1;
-            ty::Region::new_bound(tcx, current_depth, br)
-        }
-        // All free regions should be erased here.
-        r => bug!("unexpected region: {r:?}"),
-    });
-    let bound_vars = tcx.mk_bound_variable_kinds_from_iter(
-        (0..counter).map(|_| ty::BoundVariableKind::Region(ty::BrAnon)),
-    );
-    ty::Binder::bind_with_vars(ty, bound_vars)
-}
-
 #[instrument(level = "debug", skip(ecx), ret)]
 pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
     ecx: &EvalCtxt<'_, 'tcx>,
@@ -240,13 +220,8 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         // impl Copy/Clone for CoroutineWitness where T: Copy/Clone forall T in coroutine_hidden_types
         ty::CoroutineWitness(def_id, args) => Ok(ecx
             .tcx()
-            .coroutine_hidden_types(def_id)
-            .map(|bty| {
-                replace_erased_lifetimes_with_bound_vars(
-                    ecx.tcx(),
-                    bty.instantiate(ecx.tcx(), args),
-                )
-            })
+            .bound_coroutine_hidden_types(def_id)
+            .map(|bty| bty.instantiate(ecx.tcx(), args))
             .collect()),
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 51fc223a5d1..557fc99a536 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -14,7 +14,7 @@ use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData};
 use rustc_middle::ty::{
     self, GenericArgs, GenericArgsRef, GenericParamDefKind, ToPolyTraitRef, ToPredicate,
-    TraitPredicate, Ty, TyCtxt, TypeVisitableExt,
+    TraitPredicate, Ty, TyCtxt,
 };
 use rustc_span::def_id::DefId;
 
@@ -1438,10 +1438,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
                 ty::CoroutineWitness(def_id, args) => {
                     let tcx = self.tcx();
-                    stack.extend(tcx.coroutine_hidden_types(def_id).map(|bty| {
-                        let ty = bty.instantiate(tcx, args);
-                        debug_assert!(!ty.has_bound_regions());
-                        ty
+                    stack.extend(tcx.bound_coroutine_hidden_types(def_id).map(|bty| {
+                        self.infcx.enter_forall_and_leak_universe(bty.instantiate(tcx, args))
                     }))
                 }