Assert that various types have the right amount of generic args and fix the sites that used the wrong amount

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -93,7 +93,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         def_id: DefId,
     ) {
         let tcx = self.infcx.tcx;
-        let trait_ref = ty::TraitRef { def_id, substs: tcx.mk_substs_trait(ty, &[]) };
+        let trait_ref = tcx.mk_trait_ref(def_id, ty, &[]);
         self.register_obligation(Obligation {
             cause,
             recursion_depth: 0,