Hello Ralf,
> > Any BSD system must include `<sys/types.h>` in order for the test
> > code to deliver a trustworthy answer. As always this header must
> > precede `<sys/socket.h>` on any BSD system.
>
> The test should be using AC_INCLUDES_DEFAULT, no? That takes care of
> sys/types.h:
>
> AC_CHECK_MEMBERS([struct sockaddr.sa_len], , ,
> [AC_INCLUDES_DEFAULT
> [#include <sys/socket.h>
> ]])
No, the use of AC_INCLUDES_DEFAULT is not very appropriate in gnulib.
AC_INCLUDES_DEFAULT was a useful catch-all before gnulib, for common
functions and types that different systems defined in different header files.
In gnulib:
1. We have an extensive documentation which functions are defined in which
header files [1] and which header files have which problems [2], so
we don't need a catch-all any more.
2. We need the precise information. Assume that above test with succeed
because of <stdint.h> or <unistd.h>, not because of <sys/types.h>, on
some other platform. We need to know this, because then gnulib's
sys_socket.in.h needs to include <stdint.h> or <unistd.h>, which it
doesn't do now. It is good if a wrong configure test result alerts us
that something is missing, rather than if programs like inetutils
would not compile on specific platforms - which is harder to debug
(use of "gcc -E" and similar).
Also, AC_INCLUDES_DEFAULT does not include <stdbool.h>, <signal.h>,
<sys/socket.h>, and others. So it's fallacious to think that
AC_INCLUDES_DEFAULT can be reliably used for any purpose. It's better
if people learn to look up POSIX and the gnulib documentation.
Currently gnulib has 23 uses of AC_INCLUDES_DEFAULT, compared to 293 uses
of AC_LANG_PROGRAM and 125 uses of AC_CHECK_HEADERS. It would be possible
to eliminate all uses of AC_INCLUDES_DEFAULT, but it is not high priority.
Bruno
[1]
http://www.gnu.org/software/gnulib/manual/html_node/Function-Substitutes.html
[2]
http://www.gnu.org/software/gnulib/manual/html_node/Header-File-Substitutes.html
--
In memoriam Hendrik Nicolaas Werkman
<http://en.wikipedia.org/wiki/Hendrik_Nicolaas_Werkman>
