dont expect normalization to succeed in elaborate_drops

Author: b-naber

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -272,10 +272,16 @@ where
                 let field = FieldIdx::new(i);
                 let subpath = self.elaborator.field_subpath(variant_path, field);
                 let tcx = self.tcx();
-
                 assert_eq!(self.elaborator.param_env().reveal(), Reveal::All);
-                let field_ty =
-                    tcx.normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs));
+
+                let fty = f.ty(tcx, substs);
+                let field_ty = match tcx
+                    .try_normalize_erasing_regions(self.elaborator.param_env(), f.ty(tcx, substs))
+                {
+                    Ok(f_ty) => f_ty,
+                    Err(_) => fty,
+                };
+
                 (tcx.mk_place_field(base_place, field, field_ty), subpath)
             })
             .collect()