Rollup merge of #34368 - petrochenkov:astqpath, r=Manishearth

The AST part of https://github.com/rust-lang/rust/pull/34365

plugin-[breaking-change] cc https://github.com/rust-lang/rust/issues/31645

src/libsyntax/ext/build.rs

@@ -830,7 +830,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     }
     fn pat_enum(&self, span: Span, path: ast::Path, subpats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
         let pat = if subpats.is_empty() {
-            PatKind::Path(path)
+            PatKind::Path(None, path)
         } else {
             PatKind::TupleStruct(path, subpats, None)
         };