Relax the complete-type checks that are happening under __invokable<Fp, Args...> to only check Fp, and not Args... . This should be sufficient to give the desired high quality diagnostics under both bind and function. And this allows a test reported by Rich E on cfe-dev to pass. Tracked by <rdar://problem/11880602>.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@160285 91177308-0d34-0410-b5e6-96231b3b80d8

include/type_traits

@@ -2853,7 +2853,7 @@ __invoke(_Fp&& __f, _Args&& ...__args)
 
 template <class _Fp, class ..._Args>
 struct __invokable_imp
-    : private __check_complete<_Fp, _Args...>
+    : private __check_complete<_Fp>
 {
     typedef decltype(
             __invoke(_VSTD::declval<_Fp>(), _VSTD::declval<_Args>()...)

test/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/F_incomplete.pass.cpp

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <functional>
+
+// class function<R(ArgTypes...)>
+
+// template<class F> function(F);
+
+// Allow incomplete argument types in the __is_callable check
+
+#include <functional>
+
+struct X{
+	typedef std::function<void(X&)> callback_type;
+	virtual ~X() {}
+private:
+	callback_type _cb;
+};
+
+int main()
+{
+}