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Re: side stepping automake limitations with custom dependencies


From: Ralf Wildenhues
Subject: Re: side stepping automake limitations with custom dependencies
Date: Thu, 23 Jun 2011 07:52:37 +0200

Hi Mike,

* Mike Frysinger wrote on Thu, Jun 23, 2011 at 02:08:50AM CEST:
>       http://sources.redhat.com/automake/automake.html#Extending
>       [quote]
>       Note that Automake does not make any distinction between rules with
>       commands and rules that only specify dependencies. So it is not possible
>       to append new dependencies to an automake-defined target without
>       redefining the entire rule.
>       [/quote]
> 
> i happened to notice though that automake only parses exact semantic matches. 
>  
> it cannot handle going through variables.  so i tried out:
> $(libbsdl_la_OBJECTS): bsdl_bison.h vhdl_bison.h

> is this an undocumented feature ?  or a bug that'll get fixed at some point ? 
>  
> we've been using this for a few years now without problems, but past behavior 
> does not guarantee future behavior ...

I'd say there are two undocumented bits involved here: the name of the
_OBJECTS variable, and the fact that automake only parses exact matches.
Both are exploited in several user packages, esp. the latter one is,
because in many cases there is no better way.

I'd say that for any of those to change, it would require at least a
major version bump, a big announcement, and most importantly, a
documented replacement mechanism that works for all use cases.  And
maybe even an upgrade path that warns users about their current code.
I don't see that happening anytime soon.  The replacement mechanism
would obviously have to be the first thing, to allow smooth migration.

The only thing that keeps me from setting current behavior in stone is
that it is sooo unintuitive and ugly.

Cheers,
Ralf



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