[patch, libstdc++] In debug mode, diagnose empty initializer_list in min/max/minmax

[Eelis <eelis at eelis dot net>]

The std::min, std::max, and std::minmax overloads that take a std::initializer_list all require that the list is not empty. The attached patch adds debug mode checks for this.

Thanks,

Eelis

Index: libstdc++-v3/include/debug/formatter.h
===================================================================
--- libstdc++-v3/include/debug/formatter.h	(revision 233636)
+++ libstdc++-v3/include/debug/formatter.h	(working copy)
@@ -87,6 +87,8 @@
     __msg_splice_bad,
     __msg_splice_other,
     __msg_splice_overlap,
+    // std::initializer_list checks
+    __msg_empty_init_list,
     // iterator checks
     __msg_init_singular,
     __msg_init_copy_singular,
Index: libstdc++-v3/src/c++11/debug.cc
===================================================================
--- libstdc++-v3/src/c++11/debug.cc	(revision 233636)
+++ libstdc++-v3/src/c++11/debug.cc	(working copy)
@@ -139,6 +139,8 @@
     "attempt to splice an iterator from a different container",
     "splice destination %1.name;"
     " occurs within source range [%2.name;, %3.name;)",
+    // std::initializer_list checks
+    "%1;(): empty initializer_list",
     // iterator checks
     "attempt to initialize an iterator that will immediately become singular",
     "attempt to copy-construct an iterator from a singular iterator",
Index: libstdc++-v3/include/debug/macros.h
===================================================================
--- libstdc++-v3/include/debug/macros.h	(revision 233636)
+++ libstdc++-v3/include/debug/macros.h	(working copy)
@@ -69,6 +69,12 @@
 		      ._M_iterator(_First, #_First)			\
 		      ._M_iterator(_Last, #_Last))
 
+// Verify that the initializer_list is non-empty.
+#define __glibcxx_check_non_empty_init_list(_List)			\
+_GLIBCXX_DEBUG_VERIFY(_List.size() != 0,				\
+		      _M_message(__gnu_debug::__msg_empty_init_list)	\
+		      ._M_string(__func__))
+
 /** Verify that we can insert into *this with the iterator _Position.
  *  Insertion into a container at a specific position requires that
  *  the iterator be nonsingular, either dereferenceable or past-the-end,
Index: libstdc++-v3/include/debug/debug.h
===================================================================
--- libstdc++-v3/include/debug/debug.h	(revision 233636)
+++ libstdc++-v3/include/debug/debug.h	(working copy)
@@ -62,6 +62,7 @@
 
 # define __glibcxx_requires_cond(_Cond,_Msg)
 # define __glibcxx_requires_valid_range(_First,_Last)
+# define __glibcxx_requires_non_empty_init_list(_List)
 # define __glibcxx_requires_sorted(_First,_Last)
 # define __glibcxx_requires_sorted_pred(_First,_Last,_Pred)
 # define __glibcxx_requires_sorted_set(_First1,_Last1,_First2)
@@ -99,6 +100,8 @@
 # define __glibcxx_requires_cond(_Cond,_Msg) _GLIBCXX_DEBUG_VERIFY(_Cond,_Msg)
 # define __glibcxx_requires_valid_range(_First,_Last)	\
   __glibcxx_check_valid_range(_First,_Last)
+# define __glibcxx_requires_non_empty_init_list(_List)	\
+  __glibcxx_check_non_empty_init_list(_List)
 # define __glibcxx_requires_non_empty_range(_First,_Last)	\
   __glibcxx_check_non_empty_range(_First,_Last)
 # define __glibcxx_requires_sorted(_First,_Last)	\
Index: libstdc++-v3/include/bits/stl_algo.h
===================================================================
--- libstdc++-v3/include/bits/stl_algo.h	(revision 233636)
+++ libstdc++-v3/include/bits/stl_algo.h	(working copy)
@@ -3452,25 +3452,37 @@
     _GLIBCXX14_CONSTEXPR
     inline _Tp
     min(initializer_list<_Tp> __l)
-    { return *std::min_element(__l.begin(), __l.end()); }
+    {
+      __glibcxx_requires_non_empty_init_list(__l);
+      return *std::min_element(__l.begin(), __l.end());
+    }
 
   template<typename _Tp, typename _Compare>
     _GLIBCXX14_CONSTEXPR
     inline _Tp
     min(initializer_list<_Tp> __l, _Compare __comp)
-    { return *std::min_element(__l.begin(), __l.end(), __comp); }
+    {
+      __glibcxx_requires_non_empty_init_list(__l);
+      return *std::min_element(__l.begin(), __l.end(), __comp);
+    }
 
   template<typename _Tp>
     _GLIBCXX14_CONSTEXPR
     inline _Tp
     max(initializer_list<_Tp> __l)
-    { return *std::max_element(__l.begin(), __l.end()); }
+    {
+      __glibcxx_requires_non_empty_init_list(__l);
+      return *std::max_element(__l.begin(), __l.end());
+    }
 
   template<typename _Tp, typename _Compare>
     _GLIBCXX14_CONSTEXPR
     inline _Tp
     max(initializer_list<_Tp> __l, _Compare __comp)
-    { return *std::max_element(__l.begin(), __l.end(), __comp); }
+    {
+      __glibcxx_requires_non_empty_init_list(__l);
+      return *std::max_element(__l.begin(), __l.end(), __comp);
+    }
 
   template<typename _Tp>
     _GLIBCXX14_CONSTEXPR
@@ -3477,6 +3489,7 @@
     inline pair<_Tp, _Tp>
     minmax(initializer_list<_Tp> __l)
     {
+      __glibcxx_requires_non_empty_init_list(__l);
       pair<const _Tp*, const _Tp*> __p =
 	std::minmax_element(__l.begin(), __l.end());
       return std::make_pair(*__p.first, *__p.second);
@@ -3487,6 +3500,7 @@
     inline pair<_Tp, _Tp>
     minmax(initializer_list<_Tp> __l, _Compare __comp)
     {
+      __glibcxx_requires_non_empty_init_list(__l);
       pair<const _Tp*, const _Tp*> __p =
 	std::minmax_element(__l.begin(), __l.end(), __comp);
       return std::make_pair(*__p.first, *__p.second);
Index: libstdc++-v3/testsuite/25_algorithms/max/debug/empty_neg.cc
===================================================================
--- libstdc++-v3/testsuite/25_algorithms/max/debug/empty_neg.cc	(revision 0)
+++ libstdc++-v3/testsuite/25_algorithms/max/debug/empty_neg.cc	(working copy)
@@ -0,0 +1,34 @@
+// 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" }
+// { dg-do run { xfail *-*-* } }
+
+#define _GLIBCXX_DEBUG
+
+#include <algorithm>
+
+void test01()
+{
+  std::max<int>({}); // error: empty initializer_list
+}
+
+int main()
+{
+  test01();
+  return 0;
+}
Index: libstdc++-v3/testsuite/25_algorithms/min/debug/empty_neg.cc
===================================================================
--- libstdc++-v3/testsuite/25_algorithms/min/debug/empty_neg.cc	(revision 0)
+++ libstdc++-v3/testsuite/25_algorithms/min/debug/empty_neg.cc	(working copy)
@@ -0,0 +1,34 @@
+// 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" }
+// { dg-do run { xfail *-*-* } }
+
+#define _GLIBCXX_DEBUG
+
+#include <algorithm>
+
+void test01()
+{
+  std::min<int>({}); // error: empty initializer_list
+}
+
+int main()
+{
+  test01();
+  return 0;
+}
Index: libstdc++-v3/testsuite/25_algorithms/minmax/debug/empty_neg.cc
===================================================================
--- libstdc++-v3/testsuite/25_algorithms/minmax/debug/empty_neg.cc	(revision 0)
+++ libstdc++-v3/testsuite/25_algorithms/minmax/debug/empty_neg.cc	(working copy)
@@ -0,0 +1,34 @@
+// 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" }
+// { dg-do run { xfail *-*-* } }
+
+#define _GLIBCXX_DEBUG
+
+#include <algorithm>
+
+void test01()
+{
+  std::minmax<int>({}); // error: empty initializer_list
+}
+
+int main()
+{
+  test01();
+  return 0;
+}