[Freeciv-Dev] autoconf question

[Jason Dorje Short <jshort@xxxxxxxxxxxxxx>]

If I run an autoconf check for functions or headers, like

  AC_CHECK_FUNCS([strcasecmp])

or

  AC_CHECK_HEADERS([limits.h])

all this does as a result of the check is set HAVE_STRCASECMP or 
HAVE_LIMITS_H in config.h.
Of course, these values can be used within the code:

  #ifdef HAVE_LIMITS_H
  # include <limits.h>
  #endif

or

  #ifdef HAVE_STRCASECMP
    result = strcasecmp(str1, str2);
  #else
    result = strcmp(str1, str2);
  #endif

but in most cases we don't do this; there's no alternative to using the 
function or header.  So if it weren't present configure wouldn't find 
it, would continue configuring, and would succeed...and then compilation 
would fail.
These macros take an action-if-not-found argument.  I believe the 
correct configure test for most functions & headers should therefore be
  AC_CHECK_FUNCS([strcasecmp], [], AC_MSG_ERROR([no strcasecmp]))

or

  AC_CHECK_HEADERS([limits.h], [], AC_MSG_ERROR([no limits.h]))

which will cause configure to fail if the headers or functions aren't 
present.
Is this correct?  Does anyone here really know autoconf?

jason