[Bug c++/43167] New: Warnings should not be disabled when instantiating templates defined in system headers

["ian at airs dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Consider this C++ code:

#include <vector>
#include <numeric>
#include <inttypes.h>

int64_t sum(const std::vector<int64_t>& values) {
  return std::accumulate(values.begin(), values.end(), 0);
}

I'm using mainline.  When I compile this with -Wconversion I get no warning. 
When I compile it with -Wconversion -Wsystem-headers I get

In file included from ../install/include/c++/4.5.0/numeric:63:0,
                 from /home/iant/foo1.cc:2:
../install/include/c++/4.5.0/bits/stl_numeric.h: In function ?_Tp
std::accumulate(_InputIterator, _InputIterator, _Tp) [with _InputIterator =
__gnu_cxx::__normal_iterator<const long long int*, std::vector<long long int>
>, _Tp = int]?:
/home/iant/foo1.cc:6:55:   instantiated from here
../install/include/c++/4.5.0/bits/stl_numeric.h:122:2: warning: conversion to
?int? from ?long long int? may alter its value

This warning indicates a problem with user code.  It is being disabled because
the template is defined in a system header.  That is incorrect in this sort of
case.  When a template is instantiated, we should issue warnings as
appropriate, even if the template is defined in a system header.


-- 
           Summary: Warnings should not be disabled when instantiating
                    templates defined in system headers
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ian at airs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43167