Possible problem with AC_CHECK_TYPES

[Peter Eisentraut]

A configure.in contains a test for 'union semun':

AC_CHECK_TYPES([union semun], [], [],
[#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>])

This generates in essence the following code:

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

int
main()
{
    if ((union semun *) 0)
        return 0;

    if (sizeof (union semun))
        return 0;

    return 0;
}

Using "Intel(R) C++ Compiler for 32-bit applications, Version 7.1" (which
also serves as a C compiler), this only draws a warning, not an error, if
'union semun' doesn't exist:

config.c(8): warning #279: controlling expression is constant
      if ((union semun *) 0)
          ^

config.c(11): warning #70: incomplete type is not allowed
      if (sizeof (union semun))

Thus, all tests for structs and unions of this kind generate false
positives.

Is this compiler justified in doing so and/or should the Autoconf test be
adjusted to cover this problem?

-- 
Peter Eisentraut   address@hidden