libstdc++/71320 Add or remove file permissions correctly

	PR libstdc++/71320
	* src/filesystem/ops.cc (permissions(const path&, perms, error_code&)):
	Add or remove permissions according to perms argument.
	* testsuite/experimental/filesystem/operations/permissions.cc: New
	test.

From-SVN: r237136

libstdc++-v3/ChangeLog

+2016-06-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/71320
+	* src/filesystem/ops.cc (permissions(const path&, perms, error_code&)):
+	Add or remove permissions according to perms argument.
+	* testsuite/experimental/filesystem/operations/permissions.cc: New
+	test.
+
 2016-06-05  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
 	Protect allocator-overloads of tuple-from-tuple constructors

libstdc++-v3/src/filesystem/ops.cc

@@ -1084,6 +1084,28 @@ fs::permissions(const path& p, perms prms)
 
 void fs::permissions(const path& p, perms prms, error_code& ec) noexcept
 {
+  const bool add = is_set(prms, perms::add_perms);
+  const bool remove = is_set(prms, perms::remove_perms);
+  if (add && remove)
+    {
+      ec = std::make_error_code(std::errc::invalid_argument);
+      return;
+    }
+
+  prms &= perms::mask;
+
+  if (add || remove)
+    {
+      auto st = status(p, ec);
+      if (ec)
+	return;
+      auto curr = st.permissions();
+      if (add)
+	prms |= curr;
+      else
+	prms = curr & ~prms;
+    }
+
 #if _GLIBCXX_USE_FCHMODAT
   if (::fchmodat(AT_FDCWD, p.c_str(), static_cast<mode_t>(prms), 0))
 #else

libstdc++-v3/testsuite/experimental/filesystem/operations/permissions.cc

+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++11 -lstdc++fs" }
+// { dg-require-filesystem-ts "" }
+
+// 15.26 Permissions [fs.op.permissions]
+
+#include <experimental/filesystem>
+#include <fstream>
+#include <testsuite_fs.h>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  bool test __attribute__((unused)) = true;
+  using perms = std::experimental::filesystem::perms;
+
+  auto p = __gnu_test::nonexistent_path();
+  std::ofstream{p.native()};
+  VERIFY( exists(p) );
+  permissions(p, perms::owner_all);
+  VERIFY( status(p).permissions() == perms::owner_all );
+  permissions(p, perms::group_read | perms::add_perms);
+  VERIFY( status(p).permissions() == (perms::owner_all | perms::group_read) );
+  permissions(p, perms::group_read | perms::remove_perms);
+  VERIFY( status(p).permissions() == perms::owner_all );
+
+  remove(p);
+}
+
+int
+main()
+{
+  test01();
+}