[patch] Make vector::at() assertion message more useful (try #2)

[Paul Pluzhnikov <ppluzhnikov at google dot com>]

Greetings,

This is a followup to:
http://gcc.gnu.org/ml/libstdc++/2013-08/msg00096.html

Without this patch, the user on vector::at out of bounds sees:

terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check
Aborted (core dumped)

With the patch:

terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check: __n (which is 3) >= this->size() (which is 2)
Aborted (core dumped)


I am not at all sure the names I choose here are good ones. Suggestions
welcome.

I also shudder at the idea of repeating _M_range_check code in
e.g. string::at(), and elsewhere. Perhaps we need a snprintf_lite, that
only understands '%zu' and literal characters, e.g.:

  snprintf_lite(__s, sizeof(__s),
                _N("vector::_M_range_check: __n (which is %zu) >= "
                   "this->size() (which is %zu)"), __n, this->size());


[The patch also doesn't include libstdc++-v3/libsupc++/Makefile.in,
which I'll regenerate before submitting.]

[Please CC me on any replies.]

--
Paul Pluzhnikov

2013-09-04  Paul Pluzhnikov  <ppluzhnikov@google.com>

	* libstdc++-v3/config/abi/pre/gnu.ver: Add
        _ZN9__gnu_cxx13concat_size_tEPcm
	* libstdc++-v3/include/bits/stl_vector.h (_M_range_check): Print
        additional assertion details
	* libstdc++-v3/libsupc++/Makefile.am: Add support.cc
	* libstdc++-v3/libsupc++/support.cc: New
        * libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/assign_neg.cc: 
	Adjust.
	* testsuite/23_containers/vector/requirements/dr438/insert_neg.cc:
	Likewise.
	* testsuite/23_containers/vector/requirements/dr438/constructor_1_neg.cc:
	Likewise.
	* testsuite/23_containers/vector/requirements/dr438/constructor_2_neg.cc:
	Likewise.


Index: libstdc++-v3/config/abi/pre/gnu.ver
===================================================================
--- libstdc++-v3/config/abi/pre/gnu.ver	(revision 202262)
+++ libstdc++-v3/config/abi/pre/gnu.ver	(working copy)
@@ -1365,6 +1365,9 @@
     # std::get_unexpected()
     _ZSt14get_unexpectedv;
 
+    # __gnu_cxx::concat_size_t(char*, unsigned long)
+    _ZN9__gnu_cxx13concat_size_tEPcm;
+
 } GLIBCXX_3.4.19;
 
 # Symbols in the support library (libsupc++) have their own tag.
Index: libstdc++-v3/include/bits/stl_vector.h
===================================================================
--- libstdc++-v3/include/bits/stl_vector.h	(revision 202262)
+++ libstdc++-v3/include/bits/stl_vector.h	(working copy)
@@ -63,6 +63,10 @@
 #include <initializer_list>
 #endif
 
+namespace __gnu_cxx {
+  int concat_size_t(char *, size_t);
+}
+
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
@@ -791,7 +795,26 @@
       _M_range_check(size_type __n) const
       {
 	if (__n >= this->size())
-	  __throw_out_of_range(__N("vector::_M_range_check"));
+	  {
+	    const char __p[] = __N("vector::_M_range_check: __n (which is ");
+	    const char __q[] = __N(") >= this->size() (which is ");
+
+	    // Enough space for __p, __q, size and __n (in decimal).
+	    const int __alloc_size =
+	      sizeof(__p) + sizeof(__q) + 3 * 2 * sizeof(size_type) + 10;
+
+	    char *__s = static_cast<char*>(__builtin_alloca(__alloc_size));
+	    char *__ps = __s;
+	    __builtin_memcpy(__ps, __p, sizeof(__p));
+	    __ps += sizeof(__p) - 1;
+	    __ps += __gnu_cxx::concat_size_t(__ps, __n);
+	    __builtin_memcpy(__ps, __q, sizeof(__q));
+	    __ps += sizeof(__q) - 1;
+	    __ps += __gnu_cxx::concat_size_t(__ps, this->size());
+	    *(__ps++) = __N(')');
+	    *(__ps++) = '\0';
+	    __throw_out_of_range(__s);
+	  }
       }
 
     public:
Index: libstdc++-v3/libsupc++/Makefile.am
===================================================================
--- libstdc++-v3/libsupc++/Makefile.am	(revision 202262)
+++ libstdc++-v3/libsupc++/Makefile.am	(working copy)
@@ -91,6 +91,7 @@
 	pointer_type_info.cc \
 	pure.cc \
 	si_class_type_info.cc \
+	support.cc \
 	tinfo.cc \
 	tinfo2.cc \
 	vec.cc \
Index: libstdc++-v3/libsupc++/support.cc
===================================================================
--- libstdc++-v3/libsupc++/support.cc	(revision 0)
+++ libstdc++-v3/libsupc++/support.cc	(revision 0)
@@ -0,0 +1,53 @@
+// Debugging support -*- C++ -*-
+
+// Copyright (C) 2013 Free Software Foundation, Inc.
+//
+// This file is part of GCC.
+//
+// GCC 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.
+//
+// GCC 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.
+//
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+#include <bits/locale_facets.h>
+
+namespace std {
+  template<typename _CharT, typename _ValueT>
+  int
+  __int_to_char(_CharT* __bufend, _ValueT __v, const _CharT* __lit,
+                ios_base::fmtflags __flags, bool __dec);
+}
+
+namespace __gnu_cxx {
+
+// Exported routine to append decimal representation of __val to the given
+// buffer, which must be at least 21 characters long in 64-bit mode.
+// Does not NUL-terminate the output buffer.
+// Returns number of characters appended.
+  int concat_size_t(char *__buf, size_t __val)
+  {
+    // Long enough for decimal representation.
+    int __ilen = 3 * sizeof(__val);
+    char *__cs = static_cast<char*>(__builtin_alloca(__ilen));
+    int __len = std::__int_to_char(__cs + __ilen, __val,
+				   std::__num_base::_S_atoms_out,
+				   std::ios_base::dec, true);
+    __builtin_memcpy(__buf, __cs + __ilen - __len, __len);
+    return __len;
+  }
+
+}  // __gnu_cxx
Index: libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/assign_neg.cc
===================================================================
--- libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/assign_neg.cc	(revision 202262)
+++ libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/assign_neg.cc	(working copy)
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1308 }
+// { dg-error "no matching" "" { target *-*-* } 1331 }
 
 #include <vector>
 
Index: libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/insert_neg.cc
===================================================================
--- libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/insert_neg.cc	(revision 202262)
+++ libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/insert_neg.cc	(working copy)
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1349 }
+// { dg-error "no matching" "" { target *-*-* } 1372 }
 
 #include <vector>
 
Index: libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_1_neg.cc
===================================================================
--- libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_1_neg.cc	(revision 202262)
+++ libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_1_neg.cc	(working copy)
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1234 }
+// { dg-error "no matching" "" { target *-*-* } 1257 }
 
 #include <vector>
 
Index: libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_2_neg.cc
===================================================================
--- libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_2_neg.cc	(revision 202262)
+++ libstdc++-v3/testsuite/23_containers/vector/requirements/dr438/constructor_2_neg.cc	(working copy)
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1234 }
+// { dg-error "no matching" "" { target *-*-* } 1257 }
 
 #include <vector>
 #include <utility>