Fix bug in __libcpp_db::__iterator_copy.  Add debug test for swaping lists.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@178892 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/containers/sequences/list/list.special/db_swap_1.pass.cpp b/test/containers/sequences/list/list.special/db_swap_1.pass.cpp
new file mode 100644
index 0000000..12730c2
--- /dev/null
+++ b/test/containers/sequences/list/list.special/db_swap_1.pass.cpp
@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <list>
+
+// template <class T, class Alloc>
+//   void swap(list<T,Alloc>& x, list<T,Alloc>& y);
+
+#if _LIBCPP_DEBUG2 >= 1
+#define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
+#endif
+
+#include <list>
+#include <cassert>
+
+#include <__debug>
+
+int main()
+{
+#if _LIBCPP_DEBUG2 >= 1
+    {
+        int a1[] = {1, 3, 7, 9, 10};
+        int a2[] = {0, 2, 4, 5, 6, 8, 11};
+        std::list<int> c1(a1, a1+sizeof(a1)/sizeof(a1[0]));
+        std::list<int> c2(a2, a2+sizeof(a2)/sizeof(a2[0]));
+        std::list<int>::iterator i1 = c1.begin();
+        std::list<int>::iterator i2 = c2.begin();
+        swap(c1, c2);
+        c1.erase(i2);
+        c2.erase(i1);
+        std::list<int>::iterator j = i1;
+        c1.erase(i1);
+        assert(false);
+    }
+#endif
+}