Re: AX_COMPARE_VERSION in configure.ac

[Rik]

On 11/09/2012 09:16 AM, Juan Pablo Carbajal wrote:
> Hi Rik,
>
> I noticed that (thx JordiGH for hg classes) you simplified
> configure.ac with the m4 macro AX_COMPARE_VERSION
> $ hg annotate configure.ac -ucdqv | grep AX_
>            rik a44ff4f0a20b Mon Aug 13 15:43:49 2012 -0700:
> AX_COMPARE_VERSION([$gxx_version], [lt], [3.5],
>            rik a44ff4f0a20b Mon Aug 13 15:43:49 2012 -0700:
> AX_COMPARE_VERSION([$gcc_version], [lt], [3],
>
> $ hg log -r a44ff4f0a20b
> changeset:   15170:a44ff4f0a20b
> user:        Rik <address@hidden>
> date:        Mon Aug 13 15:43:49 2012 -0700
> summary:     Add AX_COMPARE_VERSION.m4 macro m4/ dir to make configure.ac 
> simple
>
>
> I am learning autotools and I was trying to find out why... I couldn't
> find that macro but on the gnu autoconf-archive documentation
> http://www.gnu.org/software/autoconf-archive/ax_compare_version.html
>
> I found AS_VERSION_COMPARE in the autoconf manual
> http://www.gnu.org/software/autoconf/manual/autoconf.html
>
> Should we change for this macro? The change is very simple (just
> remove the [lt] parameter).
>
> Also the AX_ macro shouldn't not as it is used now (unless is wrongly
> documented...though it doesn't work for me!) since it cannot take
> variables only strings. The AS_ macro can resolve variables.
>
I think of the AX_ macros as the library that Autoconf should have had. 
Autoconf has many useful macros built-in, but a lot of testing still
requires going beyond these and writing shell script fragments, m4 scripts,
or nested Autoconf macros.  The AX_ series helps cut down the number of
times one has to go and write new macros. 

In this particular case, AX_COMPARE_VERSION is more powerful than
AS_VERSION_COMPARE in that it supports a greater number of comparisons (not
just the three <, >, =) and can compare against minor numbers only. 
Incidentally, AX_COMPARE_VERSION does resolve variables which is why the
current code is working.  The documentation may be a little difficult to
understand, but what it is trying to say is that the operation argument OP
cannot be a variable.  This means I chose the less-than operation, [lt],
when I wrote configure.ac.  I can't write

OP="lt"
AX_COMPARE_VERSION([$VER1], [$OP], [$VER2])

I think we should leave the code as it is.

--Rik