libstdc++: Constrain std::make_any [PR102894]

std::make_any should be constrained so it can only be called if the
construction of the return value would be valid.

libstdc++-v3/ChangeLog:

	PR libstdc++/102894
	* include/std/any (make_any): Add SFINAE constraint.
	* testsuite/20_util/any/102894.cc: New test.

(cherry picked from commit 0c1f737a485f05c591c94b50acfb416c45a4c916)

diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any
index 16723c3a304a728480e74508e82bbf450ca78633..1428858d6001c642c4b176fe1ad076c5b8e571df 100644 (file)
--- a/libstdc++-v3/include/std/any
+++ b/libstdc++-v3/include/std/any
@@ -411,16 +411,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// Exchange the states of two @c any objects.
   inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
 
-  /// Create an any holding a @c _Tp constructed from @c __args.
+  /// Create an `any` holding a `_Tp` constructed from `__args...`.
   template <typename _Tp, typename... _Args>
-    any make_any(_Args&&... __args)
+    inline
+    enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>, _Args...>, any>
+    make_any(_Args&&... __args)
     {
       return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
     }
 
-  /// Create an any holding a @c _Tp constructed from @c __il and @c __args.
+  /// Create an `any` holding a `_Tp` constructed from `__il` and `__args...`.
   template <typename _Tp, typename _Up, typename... _Args>
-    any make_any(initializer_list<_Up> __il, _Args&&... __args)
+    inline
+    enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>,
+                                  initializer_list<_Up>&, _Args...>, any>
+    make_any(initializer_list<_Up> __il, _Args&&... __args)
     {
       return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
     }

diff --git a/libstdc++-v3/testsuite/20_util/any/102894.cc b/libstdc++-v3/testsuite/20_util/any/102894.cc
new file mode 100644 (file)
index 0000000..66ea9a0
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/any/102894.cc
@@ -0,0 +1,20 @@
+// { dg-do compile { target c++17 } }
+#include <any>
+
+template<typename T, typename = void>
+struct can_make_any
+: std::false_type
+{ };
+
+template<typename T>
+struct can_make_any<T, std::void_t<decltype(std::make_any<T>())>>
+: std::true_type
+{ };
+
+struct move_only
+{
+  move_only() = default;
+  move_only(move_only&&) = default;
+};
+
+static_assert( ! can_make_any<move_only>::value ); // PR libstdc++/102894