Auto merge of #122500 - petrochenkov:deleg, r=fmease

delegation: Support renaming, and async, const, extern "ABI" and C-variadic functions

Also allow delegating to functions with opaque types (`impl Trait`).
The delegation item will refer to the original opaque type from the callee, fresh opaque type won't be created, which seems like a reasonable behavior.
(Such delegation items will cause query cycles when used in trait impls, but it can be fixed later.)

Part of https://github.com/rust-lang/rust/issues/118212.

1 files changed, 5 insertions, 5 deletions

diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 84ecd0a0de5..ed51710564a 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -686,6 +686,8 @@ impl<'a> Parser<'a> {
             (None, self.parse_path(PathStyle::Expr)?)
         };
 
+        let rename = if self.eat_keyword(kw::As) { Some(self.parse_ident()?) } else { None };
+
         let body = if self.check(&token::OpenDelim(Delimiter::Brace)) {
             Some(self.parse_block()?)
         } else {
@@ -695,11 +697,9 @@ impl<'a> Parser<'a> {
         let span = span.to(self.prev_token.span);
         self.psess.gated_spans.gate(sym::fn_delegation, span);
 
-        let ident = path.segments.last().map(|seg| seg.ident).unwrap_or(Ident::empty());
-        Ok((
-            ident,
-            ItemKind::Delegation(Box::new(Delegation { id: DUMMY_NODE_ID, qself, path, body })),
-        ))
+        let ident = rename.unwrap_or_else(|| path.segments.last().unwrap().ident);
+        let deleg = Delegation { id: DUMMY_NODE_ID, qself, path, rename, body };
+        Ok((ident, ItemKind::Delegation(Box::new(deleg))))
     }
 
     fn parse_item_list<T>(