[libcxx] Fix PR 22468 - std::function<void()> does not accept non-void-returning functions

Summary:
The bug can be found here: http://llvm.org/bugs/show_bug.cgi?id=22468

`__invoke_void_return_wrapper` is needed to properly handle calling a function that returns a value but where the std::function return type is void. Without this '-Wsystem-headers' will cause `function::operator()(...)` to not compile. 

Reviewers: eugenis, K-ballo, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D7444

llvm-svn: 228705

1 files changed, 57 insertions, 0 deletions

diff --git a/libcxx/include/__functional_base_03 b/libcxx/include/__functional_base_03
index 22c06add90f..65502778666 100644
--- a/libcxx/include/__functional_base_03
+++ b/libcxx/include/__functional_base_03
@@ -995,6 +995,63 @@ struct __invoke_return2
                                                     _VSTD::declval<_A2>())) type;
 };
 
+template <class _Ret>
+struct __invoke_void_return_wrapper
+{
+    template <class _Fn>
+    static _Ret __call(_Fn __f)
+    {
+        return __invoke(__f);
+    }
+
+    template <class _Fn, class _A0>
+    static _Ret __call(_Fn __f, _A0& __a0)
+    {
+        return __invoke(__f, __a0);
+    }
+
+    template <class _Fn, class _A0, class _A1>
+    static _Ret __call(_Fn __f, _A0& __a0, _A1& __a1)
+    {
+        return __invoke(__f, __a0, __a1);
+    }
+
+    template <class _Fn, class _A0, class _A1, class _A2>
+    static _Ret __call(_Fn __f, _A0& __a0, _A1& __a1, _A2& __a2)
+    {
+        return __invoke(__f, __a0, __a1, __a2);
+    }
+};
+
+
+template <>
+struct __invoke_void_return_wrapper<void>
+{
+    template <class _Fn>
+    static void __call(_Fn __f)
+    {
+        __invoke(__f);
+    }
+
+    template <class _Fn, class _A0>
+    static void __call(_Fn __f, _A0& __a0)
+    {
+        __invoke(__f, __a0);
+    }
+
+    template <class _Fn, class _A0, class _A1>
+    static void __call(_Fn __f, _A0& __a0, _A1& __a1)
+    {
+        __invoke(__f, __a0, __a1);
+    }
+
+    template <class _Fn, class _A0, class _A1, class _A2>
+    static void __call(_Fn __f, _A0& __a0, _A1& __a1, _A2& __a2)
+    {
+        __invoke(__f, __a0, __a1, __a2);
+    }
+};
+
 template <class _Tp>
 class _LIBCPP_TYPE_VIS_ONLY reference_wrapper
     : public __weak_result_type<_Tp>