Add test

tests/ui/typeck/issue-116864.rs

@@ -0,0 +1,31 @@
+// compile-flags: -Znext-solver
+// check-pass
+// edition: 2021
+
+use std::future::Future;
+
+trait Baz {
+    type Param;
+}
+
+trait FnMutFut<P, R>: FnMut(P) -> Self::Future {
+    type Future: Future<Output = R>;
+}
+
+impl<P, F, FUT, R> FnMutFut<P, R> for F
+where
+    F: FnMut(P) -> FUT,
+    FUT: Future<Output = R>,
+{
+    type Future = FUT;
+}
+
+async fn foo<BAZ>(_: BAZ, mut cb: impl for<'any> FnMutFut<&'any BAZ::Param, ()>)
+where
+    BAZ: Baz<Param = i32>,
+{
+    cb(&1i32).await;
+}
+
+fn main() {
+}