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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 11:24:33 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121029 Thunderbird/16.0.2

On 11/12/2012 08:42 AM, Nick Bowler wrote:
> On 2012-11-09 15:53 -0700, Eric Blake wrote:
>> Too many legacy tools exist for us to unilaterally quit supporting
>> AC_CONFIG_MACRO_DIR - it is feasible for someone to want their
>> package to bootstrap with both automake 1.13 and libtool 2.4.2,
>> where the newer automake will only trace the new style of multiple
>> directory listings, but the older libtool does a sed and settles
>> on the one use of the old name.  So, we let both macros forward
>> to a new tracing macro, which also has the benefit of sanitizing
>> calls into one directory per trace; we also ensure that the old
>> macro is always traced, and appears at most once and before any
>> use of the new macro.
> If the goal is compatibility with existing behaviour of libtool,
> then we must allow multiple invocations of AC_CONFIG_MACRO_DIR and
> they must emit AC_CONFIG_MACRO_DIR_TRACE in the reverse order.

No, existing use of libtool was intended to honor only the first
AC_CONFIG_MACRO_DIR, but due to a bug, actually honored only the last.
It does NOT honor multiple directories, so anyone actually _using_
AC_CONFIG_MACRO_DIR with existing libtool could only successfully use it
once.  The new code in autoconf enforces that usage, since anything else
is confusing.

>>From the look of things, this patch intentionally breaks such
> invocations, which currently work (since AC_CONFIG_MACRO_DIR
> doesn't do anything).

Yes, it DOES do something - it tells libtool where to install files, and
libtool needs to install files in the FIRST directory, not the last.  So
this change is indeed intentional.

> I still maintain that we should not touch this macro at all.

We haven't done anything to this macro except for hardening it up to
detect invalid usage.

>  No
> released version of libtool requires AC_CONFIG_MACRO_DIR to be used
> in

Yes it does - libtoolize warns noisily if you didn't use
AC_CONFIG_MACRO_DIR in, so people have been adding it
because of libtool's warnings.

>  Any package targeting compatibility with as-yet-
> unreleased versions of automake (read: such packages are by definition
> new developments) and old versions of libtool can simply elide the
> macro from their, and things will work.

Yes, they will work (because the message from libtool was a warning, not
an error), but silence is better than warnings.  Hence my goal of
allowing the macro to continue to be used in a manner which will shut up
older libtoolize warnings.

Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library

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