PR libstdc++/86169 unshare COW string when non-const data() called

	PR libstdc++/86169
	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
	(basic_string::data()): Unshare string.
	* testsuite/21_strings/basic_string/operations/data/char/86169.cc:
	New.

From-SVN: r261642

libstdc++-v3/ChangeLog

 2018-06-15  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/86169
+	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
+	(basic_string::data()): Unshare string.
+	* testsuite/21_strings/basic_string/operations/data/char/86169.cc:
+	New.
+
 	* include/std/string_view (basic_string_view(const CharT*)): Remove
 	check for null pointer and add nonnull attribute.
 	(compare(const CharT*), compare(size_type, size_type, const CharT*))

libstdc++-v3/include/bits/basic_string.h

@@ -5130,7 +5130,10 @@ _GLIBCXX_END_NAMESPACE_CXX11
       */
       _CharT*
       data() noexcept
-      { return _M_data(); }
+      {
+	_M_leak();
+	return _M_data();
+      }
 #endif
 
       /**

libstdc++-v3/testsuite/21_strings/basic_string/operations/data/char/86169.cc

+// Copyright (C) 2018 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++17" }
+// { dg-do run { target c++17 } }
+
+// PR libstdc++/86169
+
+#ifndef _GLIBCXX_USE_CXX11_ABI
+# define _GLIBCXX_USE_CXX11_ABI 0
+#endif
+
+#include <string>
+#include <testsuite_hooks.h>
+
+int main()
+{
+  const std::string s0{"hello world"};
+  std::string s1 {s0};
+  char* p = s1.data();
+  *p = ' ';
+  VERIFY(s0.compare("hello world") == 0);
+}