extend comment

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -304,6 +304,11 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
 
     fn normalize(self, infcx: &InferCtxt<'tcx>) -> Vec<traits::PredicateObligation<'tcx>> {
         // Do not normalize `wf` obligations with the new solver.
+        //
+        // The current deep normalization routine with the new solver does not
+        // handle ambiguity and the new solver correctly deals with unnnormalized goals.
+        // If the user relies on normalized types, e.g. for `fn implied_outlives_bounds`,
+        // it is their responsibility to normalize while avoiding ambiguity.
         if infcx.next_trait_solver() {
             return self.out;
         }