added test

src/test/run-pass/closure_to_fn_coercion-expected-types.rs

@@ -0,0 +1,18 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// Ensure that we deduce expected argument types when a `fn()` type is expected (#41755)
+
+#![feature(closure_to_fn_coercion)]
+fn foo(f: fn(Vec<u32>) -> usize) { }
+
+fn main() {
+    foo(|x| x.len())
+}