Assert that obligations are empty before deeply normalizing

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

@@ -60,6 +60,9 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
     ty: Ty<'tcx>,
 ) -> Result<Vec<OutlivesBound<'tcx>>, NoSolution> {
     let normalize_op = |ty| -> Result<_, NoSolution> {
+        // We must normalize the type so we can compute the right outlives components.
+        // for example, if we have some constrained param type like `T: Trait<Out = U>`,
+        // and we know that `&'a T::Out` is WF, then we want to imply `U: 'a`.
         let ty = ocx
             .deeply_normalize(&ObligationCause::dummy(), param_env, ty)
             .map_err(|_| NoSolution)?;