From e0f80558716372902b2eda1e43ab2e169bfb3669 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 21 May 2025 18:07:29 +0000
Subject: [PATCH] Fix FnOnce impl for AsyncFn/AsyncFnMut closures in new solver

---
 .../src/solve/assembly/structural_traits.rs       |  2 +-
 .../async-closures/async-fn-mut-impl-fn-once.rs   | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/async-await/async-closures/async-fn-mut-impl-fn-once.rs

diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 2a2b462a36c..26ad72bea80 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -327,7 +327,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
                 // always be called once. It additionally implements `Fn`/`FnMut`
                 // only if it has no upvars referencing the closure-env lifetime,
                 // and if the closure kind permits it.
-                if closure_kind != ty::ClosureKind::FnOnce && args.has_self_borrows() {
+                if goal_kind != ty::ClosureKind::FnOnce && args.has_self_borrows() {
                     return Err(NoSolution);
                 }
 
diff --git a/tests/ui/async-await/async-closures/async-fn-mut-impl-fn-once.rs b/tests/ui/async-await/async-closures/async-fn-mut-impl-fn-once.rs
new file mode 100644
index 00000000000..59d034953d7
--- /dev/null
+++ b/tests/ui/async-await/async-closures/async-fn-mut-impl-fn-once.rs
@@ -0,0 +1,15 @@
+//@ edition:2021
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+fn call_once<F>(_: impl FnOnce() -> F) {}
+
+fn main() {
+    let mut i = 0;
+    let c = async || {
+        i += 1;
+    };
+    call_once(c);
+}