strerror_r requires non-null buffer pointer

[ashtum]

According to the documentation, in the non-allocating overload of message, we can pass a nullptr for buffer when len is 0.

If len is 0, nothing is copied, but the function still returns buffer. Note that when len is 0, buffer may be nullptr

Compiling the following generates -Wnonnull warnings, because buffer parameter in strerror_r signature is marked as non-null:
https://godbolt.org/z/sdbvfY7vo

#include <boost/system.hpp>

int main()
{
  boost::system::error_code ec;
  ec.message(nullptr, 0);
}

In file included from /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/generic_category.hpp:14,
                 from /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/error_condition.hpp:14,
                 from /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/error_code.hpp:15,
                 from /opt/compiler-explorer/libs/boost_1_84_0/boost/system/error_code.hpp:13,
                 from /opt/compiler-explorer/libs/boost_1_84_0/boost/system.hpp:10,
                 from <source>:1:
In function 'const char* boost::system::detail::generic_error_category_message(int, char*, std::size_t)',
    inlined from 'const char* boost::system::detail::system_error_category_message(int, char*, std::size_t)' at /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/system_category_message.hpp:62:42,
    inlined from 'const char* boost::system::error_code::message(char*, std::size_t) const' at /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/error_code.hpp:311:57,
    inlined from 'int main()' at <source>:6:13:
/opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/generic_category_message.hpp:42:41: warning: argument 2 null where non-null expected [-Wnonnull]
   42 |     return strerror_r_helper( strerror_r( ev, buffer, len ), buffer );
      |                               ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
In file included from /opt/compiler-explorer/gcc-13.3.0/include/c++/13.3.0/cstring:42,
                 from /opt/compiler-explorer/libs/boost_1_84_0/boost/system/detail/generic_category_message.hpp:15:
/usr/include/string.h: In function 'int main()':
/usr/include/string.h:444:14: note: in a call to function 'char* strerror_r(int, char*, size_t)' declared 'nonnull'
  444 | extern char *strerror_r (int __errnum, char *__buf, size_t __buflen)
      |              ^~~~~~~~~~
Compiler returned: 0

[ashtum]

https://github.com/boostorg/system/actions/runs/9338190106/job/25703151871?pr=122#step:4:3

  sudo apt-get update
  sudo apt-get -y install g++-11
  shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
  env:
    UBSAN_OPTIONS: print_stacktrace=1
Get:1 file:/etc/apt/apt-mirrors.txt Mirrorlist [142 B]
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Fetched 10.6 MB in 1s (7192 kB/s)
Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
clang-11 is already the newest version (1:11.0.0-2~ubuntu20.04.1).
The following additional packages will be installed:
  fonts-mathjax libjs-mathjax
Suggested packages:
  fonts-mathjax-extras fonts-stix libjs-mathjax-doc
The following NEW packages will be installed:
  clang-11-doc clang-11-examples fonts-mathjax libclang-11-dev libjs-mathjax
  python3-clang-11

This doesn't make any sense, why it tries to install clang-11!

[pdimov]

I'll take care of it.

[pdimov]

Can you please make the following changes:

• rebase on develop to pick up the new ci.yml
• remove the changes to generic_category_test and system_category_test
• remove the inclusion of core/ignore_unused.hpp and the uses of boost::ignore_unused

Thanks.