Rollup merge of #67131 - Centril:item-merge, r=petrochenkov

Merge `TraitItem` & `ImplItem into `AssocItem`

In this PR we:

- Merge `{Trait,Impl}Item{Kind?}` into `AssocItem{Kind?}` as discussed in https://github.com/rust-lang/rust/issues/65041#issuecomment-538105286.

   - This is done by using the cover grammar of both forms.

   - In particular, it requires that we syntactically allow (under `#[cfg(FALSE)]`):

      - `default`ness on `trait` items,

      - `impl` items without a body / definition (`const`, `type`, and `fn`),

      - and associated `type`s in `impl`s with bounds, e.g., `type Foo: Ord;`.

   - The syntactic restrictions are replaced by semantic ones in `ast_validation`.

- Move syntactic restrictions around C-variadic parameters from the parser into `ast_validation`:

    - `fn`s in all contexts now syntactically allow `...`,

    - `...` can occur anywhere in the list syntactically (`fn foo(..., x: usize) {}`),

    - and `...` can be the sole parameter (`fn foo(...) {}`.

r? @petrochenkov

1 files changed, 2 insertions, 6 deletions

diff --git a/src/libsyntax/util/node_count.rs b/src/libsyntax/util/node_count.rs
index a64fec70961..3db9955d304 100644
--- a/src/libsyntax/util/node_count.rs
+++ b/src/libsyntax/util/node_count.rs
@@ -73,13 +73,9 @@ impl<'ast> Visitor<'ast> for NodeCounter {
         self.count += 1;
         walk_fn(self, fk, fd, s)
     }
-    fn visit_trait_item(&mut self, ti: &TraitItem) {
+    fn visit_assoc_item(&mut self, ti: &AssocItem) {
         self.count += 1;
-        walk_trait_item(self, ti)
-    }
-    fn visit_impl_item(&mut self, ii: &ImplItem) {
-        self.count += 1;
-        walk_impl_item(self, ii)
+        walk_assoc_item(self, ti)
     }
     fn visit_trait_ref(&mut self, t: &TraitRef) {
         self.count += 1;