Re: PR 58148 patch

[François Dumont <frs dot dumont at gmail dot com>]

On 08/26/2013 10:40 PM, Paolo Carlini wrote:
> On 08/26/2013 09:44 PM, François Dumont wrote:
> > Hi
> >
> >     The problem exposed in PR 58148 is quite trivial, 
> > std::common_type cannot find a result when instantiated with char* 
> > and const wchar_t*. The attached patch will fix this problem by 
> > dealing with a std::common_type resolution failure even if the 
> > drawback is that following call won't be detected as an invalid one 
> > anymore:
> >
> >   std::vector<int> v;
> >   ....
> >   v.insert(v.begin(), reinterpret_cast<char*>(v.data() + 1), 
> > reinterpret_cast<char*>(v.data() + 5)); // Expected failure
> For the time being I think we should simply live with this. To be 
> honest, I think that at this level even the very idea of using 
> common_type (and relying on the very recent sfinae-friendly feature) 
> is a bit too much, I would just return true if the type of 
> addressof(*__other) != container::pointer (modulo const). Thus have a 
> __foreign_iterator_aux4 taking two container::const_pointer and a fall 
> back always returning true.
>
> Paolo.
    As you seem to be more concern by the usage of experimental 
std::common_type than by the usage of const volatile void*I would like 
to propose the attached patch. No more usage of common_type but still 
able to detect weird issues.

Tested under Linux x86_64 debug mode.

2013-08-27  François Dumont  <fdumont@gcc.gnu.org>

    PR libstdc++/58148
    * include/bits/functions.h: Use const volatile void* as common
    type rather than result of std::common_type. Add a fallback method
    if conversion to const volatile void* is not possible.
    * testsuite/23_containers/vector/modifiers/insert/58148.cc: New.

Ok to commit ?

François


Index: include/debug/functions.h
===================================================================
--- include/debug/functions.h	(revision 201966)
+++ include/debug/functions.h	(working copy)
@@ -36,7 +36,7 @@
 #include <bits/move.h>                    // for __addressof and addressof
 #if __cplusplus >= 201103L
 # include <bits/stl_function.h>		  // for less and greater_equal
-# include <type_traits>			  // for common_type
+# include <type_traits>			  // for is_lvalue_reference and __and_
 #endif
 #include <debug/formatter.h>
 
@@ -172,19 +172,16 @@
     }
 
 #if __cplusplus >= 201103L
+  // Default implementation.
   template<typename _Iterator, typename _Sequence,
-	   typename _InputIterator,
-	   typename _PointerType1,
-	   typename _PointerType2>
+	   typename _InputIterator>
     inline bool
     __foreign_iterator_aux4(const _Safe_iterator<_Iterator, _Sequence>& __it,
 			    _InputIterator __other,
-			    _PointerType1, _PointerType2)
+			    const volatile void*, const volatile void*)
     {
-      typedef typename std::common_type<_PointerType1,
-					_PointerType2>::type _PointerType;
-      constexpr std::less<_PointerType> __l{};
-      constexpr std::greater_equal<_PointerType> __ge{};
+      constexpr std::less<const volatile void*> __l{};
+      constexpr std::greater_equal<const volatile void*> __ge{};
 
       return (__l(std::addressof(*__other),
 		  std::addressof(*(__it._M_get_sequence()->_M_base().begin())))
@@ -192,7 +189,16 @@
 		      std::addressof(*(__it._M_get_sequence()->_M_base().end()
 				       - 1)) + 1));
     }
-			  
+
+  // Fallback when one of the address type cannot be implicitely casted to const
+  // volatile void*.
+  template<typename _Iterator, typename _Sequence,
+	   typename _InputIterator>
+    inline bool
+    __foreign_iterator_aux4(const _Safe_iterator<_Iterator, _Sequence>&,
+			    _InputIterator, ...)
+    { return true; }
+
   template<typename _Iterator, typename _Sequence, typename _InputIterator>
     inline bool
     __foreign_iterator_aux3(const _Safe_iterator<_Iterator, _Sequence>& __it,
@@ -223,7 +229,7 @@
 			    std::false_type)
     { return true; }
 #endif
-			   
+
   /** Checks that iterators do not belong to the same sequence. */
   template<typename _Iterator, typename _Sequence, typename _OtherIterator>
     inline bool
Index: testsuite/23_containers/vector/modifiers/insert/58148.cc
===================================================================
--- testsuite/23_containers/vector/modifiers/insert/58148.cc	(revision 0)
+++ testsuite/23_containers/vector/modifiers/insert/58148.cc	(revision 0)
@@ -0,0 +1,35 @@
+// Copyright (C) 2013 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" }
+// { dg-do compile }
+
+#include <vector>
+
+void
+test01()
+{
+  std::vector<wchar_t> v;
+  char c = 'a';
+  v.insert(v.begin(), &c, &c);
+}
+
+int main()
+{
+  test01();
+  return 0;
+}