LWG 2975 ensure construct(pair<T,U>*, ...) used to construct pairs

	* include/std/scoped_allocator (__not_pair): Define SFINAE helper.
	(construct(_Tp*, _Args&&...)): Remove from overload set when _Tp is
	a specialization of std::pair.
	* testsuite/20_util/scoped_allocator/construct_pair.cc: Ensure
	pair elements are constructed correctly.

From-SVN: r261716

1 files changed, 28 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc b/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc
index 341328e487f..b34efc88798 100644
--- a/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc
+++ b/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc
@@ -73,9 +73,37 @@ test03()
   a.deallocate(ptr, 1);
 }
 
+void
+test04()
+{
+  struct X
+  {
+    using allocator_type = std::allocator<int>;
+    X() = default;
+    X(const X&) { throw 1; }
+    X(const X&, const allocator_type&) { }
+  };
+
+  struct Y
+  {
+    using allocator_type = std::allocator<int>;
+    Y() = default;
+    Y(const Y&) = delete;
+    Y(std::allocator_arg_t, const allocator_type&, const Y&) { }
+  };
+
+  using pair_type = std::pair<X, Y>;
+  std::scoped_allocator_adaptor<std::allocator<pair_type>> a;
+  auto ptr = a.allocate(1);
+  /* not const */ pair_type p;
+  a.construct(ptr, p); // LWG 2975
+  a.deallocate(ptr, 1);
+}
+
 int main()
 {
   test01();
   test02();
   test03();
+  test04();
 }