fix ICE in writeback due to bound regions

compiler/rustc_hir_typeck/src/writeback.rs

@@ -1003,8 +1003,10 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Resolver<'cx, 'tcx> {
     }
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        debug_assert!(!r.is_bound(), "Should not be resolving bound region.");
-        self.fcx.tcx.lifetimes.re_erased
+        match r.kind() {
+            ty::ReBound(..) => r,
+            _ => self.fcx.tcx.lifetimes.re_erased,
+        }
     }
 
     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {

compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

@@ -100,9 +100,9 @@ where
         } else if let Err(guar) = infcx.tcx.check_potentially_region_dependent_goals(root_def_id) {
             Err(guar)
         } else {
-            Err(infcx
-                .dcx()
-                .delayed_bug(format!("errors selecting obligation during MIR typeck: {errors:?}")))
+            Err(infcx.dcx().delayed_bug(format!(
+                "errors selecting obligation during MIR typeck: {name} {root_def_id:?} {errors:?}"
+            )))
         }
     })?;
 

tests/ui/traits/next-solver/writeback-predicate-bound-region.rs

@@ -0,0 +1,14 @@
+//@ edition: 2024
+//@ check-pass
+//@ compile-flags: -Znext-solver
+
+// This previously ICE'd during writeback when resolving
+// the stalled coroutine predicate due to its bound lifetime.
+
+trait Trait<'a> {}
+impl<'a, T: Send> Trait<'a> for T {}
+
+fn is_trait<T: for<'a> Trait<'a>>(_: T) {}
+fn main() {
+    is_trait(async {})
+}