On Fri, 23 Dec 2022, 17:06 Iain Sandoe via Libstdc++, <libstdc++@gcc.gnu.org>
wrote:

>  This is a patch for comment on the approach - tested on x86_64-darwi21
>  thoughts?
>  Iain
>
>  --- 8< ---
>
> Testing on Darwin revealed that the GLIBCXX_ZONEINFO_DIR was not doing
> quite
> the right thing (we ended up with ${withval} in the config.h file).
>
> This patch proposes revising the behaviour of the configure flag thus:
>
> --with-libstdcxx-zoneinfo-dir=
>  unspecified : Set _GLIBCXX_ZONEINFO_DIR to a default suitable for $host
>          yes : Set _GLIBCXX_ZONEINFO_DIR to a default suitable for $host
>          no  : Do not set _GLIBCXX_ZONEINFO_DIR
>

What's the use case for "no"? Enforcing a UTC-only tzdb that doesn't even
try to load the tzdata? If that's desirable, we could #ifdef huge parts of
src/c++20/tzdb.cc to make the library smaller. That might make sense for a
toolchain for embedded targets where it's known there's no need for time
zone conversions.



 /some/path  : set _GLIBCXX_ZONEINFO_DIR = "/some/path"
>
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
>
> libstdc++-v3/ChangeLog:
>
>         * acinclude.m4 (GLIBCXX_ZONEINFO_DIR): Revise configure flag
>         handling.
>         * configure: Regenerate.
>         * src/c++20/tzdb.cc: Add a comment that an unset
> _GLIBCXX_ZONEINFO_DIR
>         implies that the configuration specified that no directory should
> be
>         used.
> ---
>  libstdc++-v3/acinclude.m4      | 21 ++++++++++++++-------
>  libstdc++-v3/configure         | 28 +++++++++++++++++++---------
>  libstdc++-v3/src/c++20/tzdb.cc |  1 +
>  3 files changed, 34 insertions(+), 16 deletions(-)
>
> diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> index f73946a4918..3653822aed4 100644
> --- a/libstdc++-v3/acinclude.m4
> +++ b/libstdc++-v3/acinclude.m4
> @@ -5153,18 +5153,25 @@ AC_DEFUN([GLIBCXX_ZONEINFO_DIR], [
>    AC_ARG_WITH([libstdcxx-zoneinfo-dir],
>      AC_HELP_STRING([--with-libstdcxx-zoneinfo-dir],
>                    [the directory to search for tzdata files]),
> -    [zoneinfo_dir="${withval}"
> -     AC_DEFINE(_GLIBCXX_ZONEINFO_DIR, "${withval}",
> -       [Define if a non-default location should be used for tzdata
> files.])
> -    ],
> -    [
> +    [],[with_libstdcxx_zoneinfo_dir=yes])
> +
> +  # Pick a default when no specific path is set.
> +  if test x${with_libstdcxx_zoneinfo_dir} = xyes; then
>      case "$host" in
>        # *-*-aix*) zoneinfo_dir="/usr/share/lib/zoneinfo" ;;
> +      *-*-darwin2*) zoneinfo_dir="/usr/share/lib/zoneinfo.default" ;;
>        *) zoneinfo_dir="/usr/share/zoneinfo" ;;
>      esac
> -    ])
> -
> +  elif test x${with_libstdcxx_zoneinfo_dir} = xno; then
> +    zoneinfo_dir=none
> +  else
> +    zoneinfo_dir=${with_libstdcxx_zoneinfo_dir}
> +  fi
>    AC_MSG_NOTICE([zoneinfo data directory: ${zoneinfo_dir}])
> +  if test x${zoneinfo_dir} != xnone; then
> +    AC_DEFINE_UNQUOTED(_GLIBCXX_ZONEINFO_DIR, "${zoneinfo_dir}",
> +       [Define if a non-default location should be used for tzdata
> files.])
> +  fi
>  ])
>
>  # Macros from the top-level gcc directory.
>
> diff --git a/libstdc++-v3/src/c++20/tzdb.cc
> b/libstdc++-v3/src/c++20/tzdb.cc
> index 5f5c4199f65..c4311d0902a 100644
> --- a/libstdc++-v3/src/c++20/tzdb.cc
> +++ b/libstdc++-v3/src/c++20/tzdb.cc
> @@ -52,6 +52,7 @@
>  # endif
>  #endif
>
> +// This is a bit odd; the configure-time setting was 'no zoneinfo
> directory'
>  #ifndef _GLIBCXX_ZONEINFO_DIR
>  # define _GLIBCXX_ZONEINFO_DIR "/usr/share/zoneinfo"
>  #endif
> --
> 2.37.1 (Apple Git-137.1)
>
>