Correct handling of arguments in async fn

src/test/ui/async-await/argument-patterns.rs

@@ -0,0 +1,30 @@
+// edition:2018
+// run-pass
+
+#![allow(unused_variables)]
+#![deny(unused_mut)]
+#![feature(async_await)]
+
+type A = Vec<u32>;
+
+async fn a(n: u32, mut vec: A) {
+    vec.push(n);
+}
+
+async fn b(n: u32, ref mut vec: A) {
+    vec.push(n);
+}
+
+async fn c(ref vec: A) {
+    vec.contains(&0);
+}
+
+async fn d((a, mut b): (A, A)) {
+    b.push(1);
+}
+
+async fn f((ref mut a, ref b): (A, A)) {}
+
+async fn g(((ref a, ref mut b), (ref mut c, ref d)): ((A, A), (A, A))) {}
+
+fn main() {}