[postgis-devel] Geos 3.7.0 / autoconf question

[John Harvey]

Hi strk,

On Thu, Sep 27, 2018 at 11:23 AM Sandro Santilli <strk at kbt.io> wrote:

> > if the autoconf dependency is a hard dependency for 2.64, or if it would
> be
> > reasonably okay to build with autoconf 2.63.
>
> In the top-level configure.ac we are requesting 2.52 as a dependency,
> but I see macros/* are raising that:
>
>   $ grep PREREQ configure.ac macros/*
>   configure.ac:AC_PREREQ([2.52])
>   macros/ax_check_compile_flag.m4:[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX
> and AS_VAR_IF
>   macros/libtool.m4:# LT_PREREQ(VERSION)
>   macros/libtool.m4:m4_defun([LT_PREREQ],
>   macros/libtool.m4:[AC_PREREQ([2.62])dnl We use
> AC_PATH_PROGS_FEATURE_CHECK
>
> From the comment in ax_check_compile_flag.m4 it would sound like
> something would break with anyting < 2.64 (not recognizing support
> for some compiler flags?). It is likely that you can still build
> without those compiler flags passed, but you may not obtain the same
> results as we're basing our tests on.
>

Understood.  I guess I'm trying to figure out if 2.64 was just picked
because it was an important release, or if it was something specifically
relevant to the toolchain for geos.  I can see that the the origin of the
file for the geos code was updated from 2.59 to 2.64 with this patch in
2015:
http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=commitdiff;h=1a869696e4129279f7b99c3f9052717354b79a86

I found a page that said that 2.64 was important because the behavior of
some functionality changed with regards to compilation handling and headers:
https://autotools.io/forwardporting/autoconf.html
However, I'm not sure if that's relevant to geos 3.7, or if it's just a
thing that was taken because it was upstream.

I'm sorry if this sounds like an irrelevant question but if 2.64 is a hard
requirement, the consequence is that CentOS 6 becomes essentially "not
compilable out of the box", and this has a cascading impact on PostGIS 2.5
which is dependent on geos 3.7.  CentOS 6 is still in support until 2020,
so it would be a shame to require a custom-built toolchain not available
via RPM if it wasn't truly necessary.  I figured it would be worth the
question.

Maybe a better question would be-- is there a way I can test my compilation
of geos 3.7.0 on CentOS 6 with autoconf 2.63 to validate that it seems to
be working correctly?

In any case it looks like our top-level requirement is too low,
> for libtool to work ... Do you feel like sending a patch to clean
> things up ?
>

I'd be happy to try to patch whatever's needed.  Are you just asking me to
bump up configure.ac from 2.52 to 2.64 and libtool.m4 from 2.62 to 2.64?
Or, do I need to do a deeper dive into libtool?

Thanks!
  -John Harvey
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