allow bound regions in writeback

Author: lcnr

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> {

tests/crashes/117808.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 {})
+}