Re: iconv.m4: avoid warning

[Eric Blake]

On 05/18/2010 03:06 AM, Bruno Haible wrote:
> Hi Eric,
> 
>> Typo in the ChangeLog; s/AM_DEFUN_ONCE/AC_DEFUN_ONCE/
> 
> Oops. Fixed now. Thanks.
> 
>>> +m4_version_prereq([2.64],[AC_DEFUN_ONCE],[AC_DEFUN])([AM_ICONV],
>>
>>  ... rather than have a version check, I'd rather see:
>>
>> m4_ifdef([AC_DEFUN_ONCE],[AC_DEFUN_ONCE],[AC_DEFUN])([AM_ICONV],
> 
> Remember that AC_DEFUN_ONCE existed all the time in autoconf, since 2.52
> or earlier, but it was not really usable before 2.64. (See autoconf/NEWS.)
> With this m4_ifdef, equivalent to an unconditional use of AC_DEFUN_ONCE,
> users of autoconf < 2.64 without gnulib would encounter warnings that
> they have not seen so far.

Good point.

> I don't see how to test for a new vs. an old definition of AC_DEFUN_ONCE.

You can use the existence of gnulib's witness macro (in 00gnulib.m4) as
the proof of a working AC_DEFUN_ONCE prior to 2.64:

m4_version_prereq([2.64],[AC_DEFUN_ONCE],
[m4_ifdef([gl_00GNULIB],[AC_DEFUN_ONCE],[AC_DEFUN])])([AM_ICONV],

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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