From 41501d1ae708f6977d957b61f797fda15ce33f0b Mon Sep 17 00:00:00 2001
From: Tim Shen <timshen@google.com>
Date: Thu, 22 Sep 2016 03:15:58 +0000
Subject: [PATCH] re PR libstdc++/77641 (std::variant copy-initialization fails
 for type with non-trivial constexpr ctor)

	PR libstdc++/77641
	* include/std/variant (_Variant_storage::_Variant_storage):
	Change _Variant_storage's union to be default constructible.
	* testsuite/20_util/variant/compile.cc: New test.

From-SVN: r240340
---
 libstdc++-v3/ChangeLog                        |  7 +++++
 libstdc++-v3/include/std/variant              | 29 ++++++++++++-------
 .../testsuite/20_util/variant/compile.cc      |  9 ++++++
 3 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 7e7c3468c2a..0de2044de14 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2016-09-22  Tim Shen  <timshen@google.com>
+
+	PR libstdc++/77641
+	* include/std/variant (_Variant_storage::_Variant_storage):
+	Change _Variant_storage's union to be default constructible.
+	* testsuite/20_util/variant/compile.cc: New test.
+
 2016-09-21  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
 	PR libstdc++/77288
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 7dbb533dd83..013884bb23e 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -296,15 +296,9 @@ namespace __variant
     {
       constexpr _Variant_storage() = default;
 
-      template<typename... _Args>
-	constexpr _Variant_storage(in_place_index_t<0>, _Args&&... __args)
-	: _M_first(in_place<0>, forward<_Args>(__args)...)
-	{ }
-
-      template<size_t _Np, typename... _Args,
-	       typename = enable_if_t<0 < _Np && _Np < sizeof...(_Rest) + 1>>
+      template<size_t _Np, typename... _Args>
 	constexpr _Variant_storage(in_place_index_t<_Np>, _Args&&... __args)
-	: _M_rest(in_place<_Np - 1>, forward<_Args>(__args)...)
+	: _M_union(in_place<_Np>, forward<_Args>(__args)...)
 	{ }
 
       ~_Variant_storage() = default;
@@ -313,14 +307,27 @@ namespace __variant
       _M_storage() const
       {
 	return const_cast<void*>(
-	  static_cast<const void*>(std::addressof(_M_first._M_storage)));
+	  static_cast<const void*>(std::addressof(_M_union._M_first._M_storage)));
       }
 
-      union
+      union _Union
       {
+	constexpr _Union() {};
+
+	template<typename... _Args>
+	  constexpr _Union(in_place_index_t<0>, _Args&&... __args)
+	  : _M_first(in_place<0>, forward<_Args>(__args)...)
+	  { }
+
+	template<size_t _Np, typename... _Args,
+		 typename = enable_if_t<0 < _Np && _Np < sizeof...(_Rest) + 1>>
+	  constexpr _Union(in_place_index_t<_Np>, _Args&&... __args)
+	  : _M_rest(in_place<_Np - 1>, forward<_Args>(__args)...)
+	  { }
+
 	_Uninitialized<__storage<_First>> _M_first;
 	_Variant_storage<_Rest...> _M_rest;
-      };
+      } _M_union;
     };
 
   template<typename _Derived, bool __is_trivially_destructible>
diff --git a/libstdc++-v3/testsuite/20_util/variant/compile.cc b/libstdc++-v3/testsuite/20_util/variant/compile.cc
index b57d356d301..99f980a72db 100644
--- a/libstdc++-v3/testsuite/20_util/variant/compile.cc
+++ b/libstdc++-v3/testsuite/20_util/variant/compile.cc
@@ -403,3 +403,12 @@ void test_void()
   v = 3;
   v = "asdf";
 }
+
+void test_pr77641()
+{
+  struct X {
+    constexpr X() { }
+  };
+
+  constexpr std::variant<X> v1 = X{};
+}
-- 
2.30.2