Re: [PATCH] {master} aclocal: deprecate ACLOCAL_AMFLAGS, trace AC_CONFIG_MACRO_DIR instead

[Stefano Lattarini]

On 07/02/2012 02:26 PM, Ralf Corsepius wrote:
> On 06/30/2012 08:30 PM, Stefano Lattarini wrote:
>> Maintaining ACLOCAL_AMFLAGS in the Makefile.am to pass extra flags
>> to aclocal is (and have always been) quite of an hack.  For example,
>> autoreconf is forced to grep Makefile.am to honour those flags.  But
>> this is a bad obsolescent behaviour; in fact, the autotools have moved
>> consistently in the past years from custom grepping of Makefile.am and
>> configure.ac to tracing of m4 macro calls, which is more consistent,
>> more reliable and more flexible.
>>
>> And when autoreconf is not used, the developer is forced to add *by hand*
>> the flags specified by ACLOCAL_AMFLAGS to the aclocal calls not triggered
>> by make rebuild rules; here lie again more duplication and more chances
>> for errors.
>>
>> Moreover, ACLOCAL_AMFLAGS has only two typical use cases:
>>
>>    - to instruct aclocal to look for extra macro definition in a local
>>      directory (as with "ACLOCAL_AMFLAGS = -I m4"); and
>>
>>    - to further instruct aclocal to copy in that local directory the
>>      required third-party .m4 files found in the system-wide directory
>>      (as with "ACLOCAL_AMFLAGS = -I m4 --install").
>>
>> The first use case can be better covered if aclocal can instead trace and
>> honours call to the AC_CONFIG_MACRO_DIR autoconf macro; and the second
>> use case shouldn't be considered really legitimate, as it is quite (and
>> subtly) brittle (see automake bug#9037).
> 
> ACLOCAL_AMFLAGS is able to take sequences of  "-I's".
> 
> Will your AC_CONFIG_MACRO_DIR be able handle such cases?
> 
No; and I think there is no compelling reason to support multiple local
m4 macro dirs in a build system setup.

But I recognize I might be proven wrong, so here's a sketch of how I
plan to proceed in this case.

Once we start warning about ACLOCAL_AMFLAGS (in Automake 1.14), people
that were using multiple '-I' option there will see that the new semantics
don't support their setup anymore.  So they'll either adjust such setup,
or, if that turns out to be impossible, will write to bug-automake to
complain.  If their complain turns out to be legitimate, we will add a
new autoconf macro 'AM_EXTRA_LOCAL_M4_DIRS' (say), that aclocal will
trace and use to adjust its search path accordingly.

How does this sound?

Regards,
  Stefano