GNU bug report logs - #8921
side stepping automake limitations with custom dependencies

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mike Frysinger <vapier <at> gentoo.org>
Subject: bug#8921: closed (Re: bug#8921: side stepping automake
 limitations with custom dependencies)
Date: Thu, 23 Jun 2011 05:45:05 +0000

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Your bug report

#8921: side stepping automake limitations with custom dependencies

which was filed against the automake package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 8921 <at> debbugs.gnu.org.

-- 
8921: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8921
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: "Ralf Wildenhues" <Ralf.Wildenhues <at> gmx.de>
To: Mike Frysinger <vapier <at> gentoo.org>
Cc: jzhang918 <at> gmail.com, 8921-done <at> debbugs.gnu.org
Subject: Re: bug#8921: side stepping automake limitations with custom
	dependencies
Date: Thu, 23 Jun 2011 07:44:41 +0200

Hi Mike,

* Mike Frysinger wrote on Thu, Jun 23, 2011 at 02:07:30AM CEST:
> ah blah, i meant automake <at> gnu.org.  i dont know how to close bugs with this e-
> mail system, so if someone could do that for me, that'd be cool ...

Write to BUG-done@...

Done.

;-)

Cheers,
Ralf

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From: Mike Frysinger <vapier <at> gentoo.org>
To: bug-automake <at> gnu.org
Cc: Jie Zhang <jzhang918 <at> gmail.com>
Subject: side stepping automake limitations with custom dependencies
Date: Wed, 22 Jun 2011 19:58:59 -0400

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i'm working on a project (urjtag) that has yacc/lex files in it.  and other 
files in the directory depend on the generated output from yacc/lex.  so the 
automake file looks something like:
libbsdl_la_SOURCES =  \
	vhdl_bison.y \
	bsdl_bison.y \
	bsdl.c       \
	bsdl_sem.c
libbsdl_flex_la_SOURCES = \
	vhdl_flex.l  \
	bsdl_flex.l

since the bison(yacc) files depend on the output of the flex(lex) files, we 
want to express the dependency:
libbsdl_flex_la-vhdl_flex.o: vhdl_bison.h
libbsdl_flex_la-bsdl_flex.o: bsdl_bison.h

but with this, we hit an ugly limitation in automake itself.  FTFM:
	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

ignoring the minor fact that a few extra objects depend on the headers than 
necessary, i get nice behavior: automake generates the compile rules for me, 
and i get to express the dependency to make so parallel builds dont fail.

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 ...
-mike

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