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

[Adrian Bunk]

On Tue, Nov 13, 2012 at 02:44:08PM -0500, Nick Bowler wrote:
> On 2012-11-13 20:51 +0200, Adrian Bunk wrote:
> > On Tue, Nov 13, 2012 at 09:30:45AM -0500, Nick Bowler wrote:
> > > On 2012-11-13 01:12 +0200, Adrian Bunk wrote:
> > > > In the future libtool will use the result of tracing 
> > > > AC_CONFIG_MACRO_DIR_TRACE instead of grep'ing configure.ac.
> > > 
> > > So what you are saying is that this change is a "workaround" for a
> > > planned regression in libtool.  Why are we planning to regress libtool?
> > > Why can't libtool just continue to do what it's always done for packages
> > > that don't make use the new feature (AC_CONFIG_MACRO_DIRS)?
> > 
> > The cleanest solution is to handle AC_CONFIG_MACRO_DIR in autoconf,
> > without making libtool and other users like automake bother about
> > whether AC_CONFIG_MACRO_DIR or AC_CONFIG_MACRO_DIRS is present.
> > 
> > Handling that in one place is much better than having the same logic 
> > duplicated in multiple places.
> 
> Unfortunately, this "cleanest" solution of moving everything into
> Autoconf will, by definition, break any package that relies on the
> existing, longstanding behaviour that AC_CONFIG_MACRO_DIR doesn't
> actually do *anything* (OK, it can cause libtool to print fewer
> messages).
>...

Any usage of AC_CONFIG_MACRO_DIR that is following what is documented in
any released version of autoconf should continue working as before.

The implementation detail that AC_CONFIG_MACRO_DIR was not doing 
anything so far can of course change at any time.

>...
> > libtool will access the same information through a new way that has been 
> > implemented by this patch.
> 
> But the old way will have to stick around for compatibility with older
> packages that have not been updated to the New Way.  So since we have to
> keep the old way around anyway, why not just continue to use the old way
> for old packages?
>...

Wrong.

libtool does not have to support the old way of manually searching for 
AC_CONFIG_MACRO_DIR in the future, if it requires autoconf >= 2.70 it
can use the new way of tracing AC_CONFIG_MACRO_DIR_TRACE exclusively 
even for old packages.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed