More work on subdir-objects, AC_PROG_CC and AM_PROG_CC_C_O

[Stefano Lattarini]

Reference:
<http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#130>

Hello everybody, sorry for the delay.  This follow-up is looong
overdue.

On 01/14/2013 11:23 AM, Stefano Lattarini wrote:
> On 01/13/2013 10:06 PM, Nick Bowler wrote:
>> On 2013-01-13, Stefano Lattarini <address@hidden> wrote:
>>
>>> Another useful follow-up would be to move the AM_PROG_CC_C_O in a private
>>> macro (to be expanded in AC_CONFIG_COMMANDS_PRE like you did above), and
>>> make AM_PROG_CC_C_O a no-op (without runtime deprecation).  That way, we
>>> could rely on the improved semantic of having the potential '$CC' rewrite
>>> placed near the end of configure, rather than near the beginning.  WDYT?
>>
>> With AC_CONFIG_COMMANDS_PRE, AM_PROG_CC_C_O would still be required if
>> package authors want to make use of the "compile" wrapper in configure
>> tests -- essentially, configure.ac can call AM_PROG_CC_C_O to force the
>> test to happen where it is needed, rather than just before AC_OUTPUT.
>>
>> I think it'd be worthwhile to keep that working.
>>
> Ah, but the $CC rewrite has always been an undocumented hack, and relying
> on it is a bad idea.  Still, your reasoning makes it clear that changing
> that semantics abruptly might cause subtle backward-incompatibilities in
> corner-case but perfectly valid situations.  Hmmm...  I think it's better
> to follow your approach for now, and then, if and when we decide to fix
> our macros not to rewrite $CC, do so with proper NEWS and documentation
> warnings beforehand, and a viable deprecation plan.
> 
The attached patches implement Nick's suggestion on the current code
base (original patches from Nick has unfortunately gotten too much
out-of-sync with the current codebase situation).  But note that the
second (one-liner) is actually identical to the first patch originally
posted by Nick <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13378#121>,
so it's still in his name.

I plan to push these patches to maint in a couple of days if there is
no objection.

Regards,
  Stefano

0001-compile-avoid-AC_PROG_CC-messy-rewrite.patch
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0002-Use-AC_DEFUN_ONCE-to-define-AM_PROG_CC_C_O.patch
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