From 358ca0c04bc297a9d34577d19e8814b0ca2e9411 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Sun, 10 Sep 2017 23:12:33 +0000
Subject: Fix PR34298 - Allow std::function with an incomplete return type.

This patch fixes llvm.org/PR34298. Previously libc++ incorrectly evaluated
the __invokable trait via the converting constructor `function(Tp)` [with Tp = std::function]
whenever the copy constructor or copy assignment operator
was required. This patch further constrains that constructor to short
circut before evaluating the troublesome SFINAE when `Tp` matches
std::function.

The original patch is from Alex Lorenz.

llvm-svn: 312890
---
 .../func.wrap.func.con/F_incomplete.pass.cpp       | 37 +++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

(limited to 'libcxx/test/std/utilities/function.objects')

diff --git a/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/F_incomplete.pass.cpp b/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/F_incomplete.pass.cpp
index c8f4178a26b..136b15b2a2a 100644
--- a/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/F_incomplete.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/F_incomplete.pass.cpp
@@ -16,6 +16,7 @@
 // Allow incomplete argument types in the __is_callable check
 
 #include <functional>
+#include <cassert>
 
 struct X{
     typedef std::function<void(X&)> callback_type;
@@ -24,6 +25,40 @@ private:
     callback_type _cb;
 };
 
-int main()
+struct IncompleteReturnType {
+  std::function<IncompleteReturnType ()> fn;
+};
+
+
+int called = 0;
+IncompleteReturnType test_fn() {
+  ++called;
+  IncompleteReturnType I;
+  return I;
+}
+
+// See llvm.org/PR34298
+void test_pr34298()
 {
+  static_assert(std::is_copy_constructible<IncompleteReturnType>::value, "");
+  static_assert(std::is_copy_assignable<IncompleteReturnType>::value, "");
+  {
+    IncompleteReturnType X;
+    X.fn = test_fn;
+    const IncompleteReturnType& CX = X;
+    IncompleteReturnType X2 = CX;
+    assert(X2.fn);
+    assert(called == 0);
+    X2.fn();
+    assert(called == 1);
+  }
+  {
+    const IncompleteReturnType Empty;
+    IncompleteReturnType X2 = Empty;
+    assert(!X2.fn);
+  }
+}
+
+int main() {
+  test_pr34298();
 }
-- 
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