Rollup merge of #66197 - Centril:transparent-ast, r=varkor

Push `ast::{ItemKind, ImplItemKind}::OpaqueTy` hack down into lowering

We currently have a hack in the form of `ast::{ItemKind, ImplItemKind}::OpaqueTy` which is constructed literally when you write `type Alias = impl Trait;` but not e.g. `type Alias = Vec<impl Trait>;`. Per https://github.com/rust-lang/rfcs/pull/2515, this needs to change to allow `impl Trait` in nested positions.  This PR achieves this change for the syntactic aspect but not the semantic one, which will require changes in lowering and def collection. In the interim, `TyKind::opaque_top_hack` is introduced to avoid knock-on changes in lowering, collection, and resolve. These hacks can then be removed and fixed one by one until the desired semantics are supported.

r? @varkor

1 files changed, 0 insertions, 20 deletions

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index f154b7bde98..ef65a744e83 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1255,19 +1255,6 @@ impl<'a> State<'a> {
                 self.s.word(";");
                 self.end(); // end the outer ibox
             }
-            ast::ItemKind::OpaqueTy(ref bounds, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "type"));
-                self.print_ident(item.ident);
-                self.word_space("= impl");
-                self.print_generic_params(&generics.params);
-                self.end(); // end the inner ibox
-
-                self.print_where_clause(&generics.where_clause);
-                self.s.space();
-                self.print_type_bounds(":", bounds);
-                self.s.word(";");
-                self.end(); // end the outer ibox
-            }
             ast::ItemKind::Enum(ref enum_definition, ref params) => {
                 self.print_enum_def(
                     enum_definition,
@@ -1620,13 +1607,6 @@ impl<'a> State<'a> {
             ast::ImplItemKind::TyAlias(ref ty) => {
                 self.print_associated_type(ii.ident, None, Some(ty));
             }
-            ast::ImplItemKind::OpaqueTy(ref bounds) => {
-                self.word_space("type");
-                self.print_ident(ii.ident);
-                self.word_space("= impl");
-                self.print_type_bounds(":", bounds);
-                self.s.word(";");
-            }
             ast::ImplItemKind::Macro(ref mac) => {
                 self.print_mac(mac);
                 match mac.delim {