Propagate mutability from arguments to local bindings in async fn

src/test/ui/async-await/mutable-arguments.rs

@@ -0,0 +1,10 @@
+// edition:2018
+// run-pass
+
+#![feature(async_await)]
+
+async fn foo(n: u32, mut vec: Vec<u32>) {
+    vec.push(n);
+}
+
+fn main() {}