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Re: [PATCH] AC_CONFIG_MACRO_DIRS: improve tracing and add sanity checks


From: Eric Blake
Subject: Re: [PATCH] AC_CONFIG_MACRO_DIRS: improve tracing and add sanity checks
Date: Mon, 12 Nov 2012 15:19:37 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121029 Thunderbird/16.0.2

On 11/12/2012 03:13 PM, Nick Bowler wrote:
>> If libtool will get the information in a different way, then that new 
>> way must return the same information - and that implies that autoconf 
>> now has to do something with AC_CONFIG_MACRO_DIR.
> 
> On this point, I disagree: the way to maintain compatibility is to not
> change this macro, and instead add a totally new one (which we've done:
> it's called AC_CONFIG_MACRO_DIRS with an S) that new packages can make
> use of if they want, and old packages can continue to not use.
> 
> I thought my examples already demonstrated where the proposed changes
> would cause existing, *working* configure.ac files to fail after
> updating to a version of Autoconf with the changes.

Our point is that any configure.ac with two or more AC_CONFIG_MACRO_DIR
is NOT working.  It was merely lucky that it wasn't tripping over other
problems.  But since we can't make it continue to work with the new
semantics of AC_CONFIG_MACRO_DIRS, the best we can do (and indeed, what
we DID do) is loudly flag incorrect usage as an error rather than
silently change semantics.

> The backwards-compatible way of handing AC_CONFIG_MACRO_DIR is to have
> it do exactly what it has done for the past 10 years: nothing useful.

When used exactly once, it does just that.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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