[PATCH] PR libstdc++/83598 don't modify flags passed to std::basic_regex constructors

[Jonathan Wakely]

The standard requires that std::regex("", f).flags() == f so we
shouldn't modify the flags passed to the constructor. We can just
remove the code that does so, because the _Compiler class repeats the
code to conditionally set ECMAScript in the flags anyway, so there's
no need to do so for the value stored in the basic_regex::_M_flags
member.

        PR libstdc++/83598
        * include/bits/regex.h (basic_regex): Don't modify flags passed to
        constructors.
        * testsuite/28_regex/basic_regex/ctors/83598.cc: New test.

Tested powerpc64le-linux, committed to trunk. Backports to follow.


commit 77e90ec38484e73ae4afc80ae552859a9e3a95e1
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Dec 27 20:00:56 2017 +0000

    PR libstdc++/83598 don't modify flags passed to std::basic_regex 
constructors
    
            PR libstdc++/83598
            * include/bits/regex.h (basic_regex): Don't modify flags passed to
            constructors.
            * testsuite/28_regex/basic_regex/ctors/83598.cc: New test.

diff --git a/libstdc++-v3/include/bits/regex.h 
b/libstdc++-v3/include/bits/regex.h
index 74c5100b524..0d97d535e2a 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -756,9 +756,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       template<typename _FwdIter>
        basic_regex(_FwdIter __first, _FwdIter __last, locale_type __loc,
                    flag_type __f)
-       : _M_flags((__f & (ECMAScript | basic | extended | awk | grep | egrep))
-                  ? __f : (__f | ECMAScript)),
-       _M_loc(std::move(__loc)),
+       : _M_flags(__f), _M_loc(std::move(__loc)),
        _M_automaton(__detail::__compile_nfa<_Rx_traits>(
          std::move(__first), std::move(__last), _M_loc, _M_flags))
        { }
@@ -773,9 +771,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       template<typename, typename, typename, bool>
        friend class __detail::_Executor;
 
-      flag_type              _M_flags;
-      locale_type          _M_loc;
-      _AutomatonPtr      _M_automaton;
+      flag_type                _M_flags;
+      locale_type      _M_loc;
+      _AutomatonPtr    _M_automaton;
     };
 
 #if __cpp_deduction_guides >= 201606
diff --git a/libstdc++-v3/testsuite/28_regex/basic_regex/ctors/83598.cc 
b/libstdc++-v3/testsuite/28_regex/basic_regex/ctors/83598.cc
new file mode 100644
index 00000000000..b958dfbe42f
--- /dev/null
+++ b/libstdc++-v3/testsuite/28_regex/basic_regex/ctors/83598.cc
@@ -0,0 +1,37 @@
+// Copyright (C) 2017 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-do run { target c++11 } }
+
+#include <regex>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  // PR libstdc++83598
+  std::regex r1(".", std::regex_constants::syntax_option_type{});
+  VERIFY(r1.flags() == std::regex_constants::syntax_option_type{});
+  std::regex r2(".", std::regex_constants::icase);
+  VERIFY(r2.flags() == std::regex_constants::icase);
+}
+
+int
+main()
+{
+  test01();
+}