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From: bin@primate.wisc.edu (Brain in Neutral)
Newsgroups: comp.windows.x
Subject: Re: imake (and "unreferenced Makefile variables")
Message-ID: <2775@uakari.primate.wisc.edu>
Date: 19 Jul 90 06:21:57 GMT
References: <1990Jul18.213435.7284@cbnewsl.att.com>
Sender: bin@primate.wisc.edu
Reply-To: bin@primate.wisc.edu
Lines: 40

From article <1990Jul18.213435.7284@cbnewsl.att.com>, by siyt@cbnewsl.att.com (p.jayne):
> I've been maintaining AT&T/USL's imake since X11R3.  In R2, we
> rewrote it as a shell script and a C program.  Much of
> the template and rules set were discarded to simplify things.
> In R4, I put back most of the discarded stuff so that we
> could use contributed Imakefiles w/o hacking.  (And besides,
> some people were unhappy with the changes we made.)
> The shell script does mostly what imake.c from the tape does,
> i.e. it runs cpp through the source tree's Imakefiles.  The
> C program handles the @@ stuff and additionally strips out
> redundant and unreferenced Makefile variables and tosses extra
> blank lines.  This means you get readable Makefiles out of the deal.

Stripping out "unreferenced" Makefile variables may not be such a good
idea in certain contexts.

A lot of the X stuff creates target files from templates by running
them through cpp (using the CppScriptTarget() rule).  That rule
explicitly requires a -D for each variable you want substituted
in the template to create the target, so you *do* know which Makefile
variables are referenced in creating it.

But that's not the only way to do it.  The CppScriptTarget() is unwieldy
if you want to use 10 or 20 of the Makefile variables, say.  For that
reason (among others) I use a thing called msub (substitute from
Makefile) that looks through a Makefile, grabs all the variable
definitions, expands them (so there are no $(other-makefile-variable)
constructions in them), and then replaces any occurrances of any of
those variables in the target file with the value.  It works well
enough that I rarely use CppScriptTarget() any more.

But the implication for this discussion is:
The rule for creating targets from msub templates doesn't name any of the
Makefile variables to be substituted (doesn't have to, since any of them
can be used in the template without prior arrangment).  This means that
you can't tell, by looking at the Makefile, which variables are
referenced and which aren't!

Paul DuBois
dubois@primate.wisc.edu