Rollup merge of #132612 - compiler-errors:async-trait-bounds, r=lcnr

Gate async fn trait bound modifier on `async_trait_bounds`

This PR moves `async Fn()` trait bounds into a new feature gate: `feature(async_trait_bounds)`. The general vibe is that we will most likely stabilize the `feature(async_closure)` *without* the `async Fn()` trait bound modifier, so we need to gate that separately.

We're trying to work on the general vision of `async` trait bound modifier general in: https://github.com/rust-lang/rfcs/pull/3710, however that RFC still needs more time for consensus to converge, and we've decided that the value that users get from calling the bound `async Fn()` is *not really* worth blocking landing async closures in general.

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 505586e74f1..1340558d968 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -940,7 +940,7 @@ impl<'a> Parser<'a> {
         let asyncness = if self.token.uninterpolated_span().at_least_rust_2018()
             && self.eat_keyword(kw::Async)
         {
-            self.psess.gated_spans.gate(sym::async_closure, self.prev_token.span);
+            self.psess.gated_spans.gate(sym::async_trait_bounds, self.prev_token.span);
             BoundAsyncness::Async(self.prev_token.span)
         } else if self.may_recover()
             && self.token.uninterpolated_span().is_rust_2015()
@@ -951,7 +951,7 @@ impl<'a> Parser<'a> {
                 span: self.prev_token.span,
                 help: HelpUseLatestEdition::new(),
             });
-            self.psess.gated_spans.gate(sym::async_closure, self.prev_token.span);
+            self.psess.gated_spans.gate(sym::async_trait_bounds, self.prev_token.span);
             BoundAsyncness::Async(self.prev_token.span)
         } else {
             BoundAsyncness::Normal