Implement LWG2664 and update its status

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@284310 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/experimental/filesystem/class.path/path.member/path.append.pass.cpp

@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03
+
+// <experimental/filesystem>
+
+// class path
+
+// path& operator/=(path const&)
+// path operator/(path const&, path const&)
+
+
+#define _LIBCPP_DEBUG 0
+#define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : (void)::AssertCount++)
+int AssertCount = 0;
+
+#include <experimental/filesystem>
+#include <type_traits>
+#include <string_view>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+#include "count_new.hpp"
+#include "filesystem_test_helper.hpp"
+
+namespace fs = std::experimental::filesystem;
+
+int main()
+{
+  using namespace fs;
+  {
+    path lhs("//foo");
+    path rhs("/bar");
+    assert(AssertCount == 0);
+    lhs /= rhs;
+    assert(AssertCount == 0);
+  }
+  {
+    path lhs("//foo");
+    path rhs("/bar");
+    assert(AssertCount == 0);
+    (void)(lhs / rhs);
+    assert(AssertCount == 0);
+  }
+  {
+    path lhs("//foo");
+    path rhs("//bar");
+    assert(AssertCount == 0);
+    lhs /= rhs;
+    assert(AssertCount == 1);
+    AssertCount = 0;
+  }
+  {
+    path lhs("//foo");
+    path rhs("//bar");
+    assert(AssertCount == 0);
+    (void)(lhs / rhs);
+    assert(AssertCount == 1);
+  }
+  // FIXME The same error is not diagnosed for the append(Source) and
+  // append(It, It) overloads.
+}