use the infcx tables to check if a closure is Copy

Fixes #28550

src/test/run-pass/issue-28550.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 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.
+
+struct A<F: FnOnce()->T,T>(F::Output);
+struct B<F: FnOnce()->T,T>(A<F,T>);
+
+// Removing Option causes it to compile.
+fn foo<T,F: FnOnce()->T>(f: F) -> Option<B<F,T>> {
+    Some(B(A(f())))
+}
+
+fn main() {
+    let v = (|| foo(||4))();
+    match v {
+        Some(B(A(4))) => {},
+        _ => unreachable!()
+    }
+}