Store associated item defaultness in impl_defaultness.

clippy_lints/src/missing_inline.rs

@@ -105,7 +105,7 @@ fn check_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx hir::Item<'_>) {
                     match tit_.kind {
                         hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(..) => {},
                         hir::TraitItemKind::Fn(..) => {
-                            if tit.defaultness.has_value() {
+                            if cx.tcx.impl_defaultness(tit.id.def_id).has_value() {
                                 // trait method with default body needs inline in case
                                 // an impl is not provided
                                 let desc = "a default trait method";