[PATCH] PR libstdc++/79162 disambiguate assignment from string_view

[Jonathan Wakely]

This fixes a new ambiguity in C++17 mode introduced by string_view
support in basic_string.

	PR libstdc++/79162
	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Replace
	with a constrained template.
	[!_GLIBCXX_USE_CXX11_ABI]
	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Likewise.
	* testsuite/21_strings/basic_string/cons/char/79162.cc: New test.
	* testsuite/21_strings/basic_string/cons/wchar_t/79162.cc: New test.

Tested ppc64le-linux, committed to trunk.

-------------- next part --------------
commit 14b75fa34a68bfbc60fc20685bcb19e152b4cc56
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Mar 14 13:47:12 2017 +0000

    PR libstdc++/79162 disambiguate assignment from string_view
    
    	PR libstdc++/79162
    	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
    	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Replace
    	with a constrained template.
    	[!_GLIBCXX_USE_CXX11_ABI]
    	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Likewise.
    	* testsuite/21_strings/basic_string/cons/char/79162.cc: New test.
    	* testsuite/21_strings/basic_string/cons/wchar_t/79162.cc: New test.

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 981ffc5..b6693c4 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -758,9 +758,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  @brief  Set value to string constructed from a string_view.
        *  @param  __sv  A string_view.
        */
-      basic_string&
-      operator=(__sv_type __sv)
-      {	return this->assign(__sv); }
+      template<typename _Tp>
+	_If_sv<_Tp, basic_string&>
+	operator=(_Tp __sv)
+	{ return this->assign(__sv); }
 
       /**
        *  @brief  Convert to a string_view.
@@ -3560,9 +3561,10 @@ _GLIBCXX_END_NAMESPACE_CXX11
        *  @brief  Set value to string constructed from a string_view.
        *  @param  __sv  A string_view.
        */
-      basic_string&
-      operator=(__sv_type __sv)
-      { return this->assign(__sv); }
+      template<typename _Tp>
+	_If_sv<_Tp, basic_string&>
+	operator=(_Tp __sv)
+	{ return this->assign(__sv); }
 
       /**
        *  @brief  Convert to a string_view.
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/79162.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/79162.cc
new file mode 100644
index 0000000..0afbe11
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/79162.cc
@@ -0,0 +1,28 @@
+// 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-options "-std=gnu++17" }
+// { dg-do compile { target c++1z } }
+
+#include <string>
+
+void
+test01()
+{
+  std::string s;
+  s = {"abc", 1};
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/79162.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/79162.cc
new file mode 100644
index 0000000..0afbe11
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/79162.cc
@@ -0,0 +1,28 @@
+// 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-options "-std=gnu++17" }
+// { dg-do compile { target c++1z } }
+
+#include <string>
+
+void
+test01()
+{
+  std::string s;
+  s = {"abc", 1};
+}