Rollup merge of rust-lang#120322 - compiler-errors:higher-ranked-async-closures, r=oli-obk

Don't manually resolve async closures in `rustc_resolve`

There's a comment here that talks about doing this "[so] closure [args] are detected as upvars rather than normal closure arg usages", but we do upvar analysis on the HIR now:

https://github.com/rust-lang/rust/blob/cd6d8f2a04528f827ad3d399581c0f3502b15a72/compiler/rustc_passes/src/upvars.rs#L21-L29

Removing this ad-hoc logic makes it so that `async |x: &str|` now introduces an implicit binder, like regular closures.

r? ```@oli-obk```

Author: matthiaskrgr

compiler/rustc_resolve/src/late.rs

@@ -4424,35 +4424,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             ExprKind::Type(ref _type_expr, ref _ty) => {
                 visit::walk_expr(self, expr);
             }
-            // `async |x| ...` gets desugared to `|x| async {...}`, so we need to
-            // resolve the arguments within the proper scopes so that usages of them inside the
-            // closure are detected as upvars rather than normal closure arg usages.
-            //
-            // Similarly, `gen |x| ...` gets desugared to `|x| gen {...}`, so we handle that too.
-            ExprKind::Closure(box ast::Closure {
-                coroutine_kind: Some(_),
-                ref fn_decl,
-                ref body,
-                ..
-            }) => {
-                self.with_rib(ValueNS, RibKind::Normal, |this| {
-                    this.with_label_rib(RibKind::FnOrCoroutine, |this| {
-                        // Resolve arguments:
-                        this.resolve_params(&fn_decl.inputs);
-                        // No need to resolve return type --
-                        // the outer closure return type is `FnRetTy::Default`.
-
-                        // Now resolve the inner closure
-                        {
-                            // No need to resolve arguments: the inner closure has none.
-                            // Resolve the return type:
-                            visit::walk_fn_ret_ty(this, &fn_decl.output);
-                            // Resolve the body
-                            this.visit_expr(body);
-                        }
-                    })
-                });
-            }
             // For closures, RibKind::FnOrCoroutine is added in visit_fn
             ExprKind::Closure(box ast::Closure {
                 binder: ClosureBinder::For { ref generic_params, span },

tests/ui/async-await/async-closures/higher-ranked.rs

@@ -0,0 +1,12 @@
+// edition:2021
+
+#![feature(async_closure)]
+
+fn main() {
+    let x = async move |x: &str| {
+        //~^ ERROR lifetime may not live long enough
+        // This error is proof that the `&str` type is higher-ranked.
+        // This won't work until async closures are fully impl'd.
+        println!("{x}");
+    };
+}

tests/ui/async-await/async-closures/higher-ranked.stderr

@@ -0,0 +1,17 @@
+error: lifetime may not live long enough
+  --> $DIR/higher-ranked.rs:6:34
+   |
+LL |       let x = async move |x: &str| {
+   |  ____________________________-___-_^
+   | |                            |   |
+   | |                            |   return type of closure `{async closure body@$DIR/higher-ranked.rs:6:34: 11:6}` contains a lifetime `'2`
+   | |                            let's call the lifetime of this reference `'1`
+LL | |
+LL | |         // This error is proof that the `&str` type is higher-ranked.
+LL | |         // This won't work until async closures are fully impl'd.
+LL | |         println!("{x}");
+LL | |     };
+   | |_____^ returning this value requires that `'1` must outlive `'2`
+
+error: aborting due to 1 previous error
+