Do the check even when the feature is not enabled

compiler/rustc_passes/src/check_const.rs

@@ -60,9 +60,7 @@ impl NonConstExpr {
 fn check_mod_const_bodies(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
     let mut vis = CheckConstVisitor::new(tcx);
     tcx.hir().visit_item_likes_in_module(module_def_id, &mut vis.as_deep_visitor());
-    if tcx.features().enabled(sym::const_trait_impl) {
-        tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckConstTraitVisitor::new(tcx));
-    }
+    tcx.hir().visit_item_likes_in_module(module_def_id, &mut CheckConstTraitVisitor::new(tcx));
 }
 
 pub(crate) fn provide(providers: &mut Providers) {
@@ -80,6 +78,8 @@ impl<'tcx> CheckConstTraitVisitor<'tcx> {
 }
 
 impl<'tcx> hir::itemlikevisit::ItemLikeVisitor<'tcx> for CheckConstTraitVisitor<'tcx> {
+    /// check for const trait impls, and errors if the impl uses provided/default functions
+    /// of the trait being implemented; as those provided functions can be non-const.
     fn visit_item(&mut self, item: &'hir hir::Item<'hir>) {
         let _: Option<_> = try {
             if let hir::ItemKind::Impl(ref imp) = item.kind {
@@ -103,6 +103,9 @@ impl<'tcx> hir::itemlikevisit::ItemLikeVisitor<'tcx> for CheckConstTraitVisitor<
                         .filter(|it| matches!(it.kind, hir::AssocItemKind::Fn { .. }))
                         .count();
 
+                    // number of trait functions unequal to functions in impl,
+                    // meaning that one or more provided/default functions of the
+                    // trait are used.
                     if trait_fn_cnt != impl_fn_cnt {
                         self.tcx
                             .sess