On Wed, 12 Jul 2000, Paul D. Smith wrote:
> Date: Wed, 12 Jul 2000 17:50:57 -0400 (EDT)
> From: Paul D. Smith <[EMAIL PROTECTED]>
> To: Charles Howes <[EMAIL PROTECTED]>
> Cc: [EMAIL PROTECTED]
> Subject: Re: Circular dependency dropping error
>
> %% Charles Howes <[EMAIL PROTECTED]> writes:
>
> ch> Using make version 3.79.1, on Linux 2.2.16 with glibc-2.1.2.
>
> ch> % ls -la asdf.gif
> ch> asdf.gif
>
> ch> % make asdf.png
> ch> make: *** No rule to make target `asdf.png'. Stop.
>
> This is correct, right?
No, there is a rule for %.png <- %.ppm, and a rule for %.ppm <- %.gif.
%.png <- %.gif should have worked. This does work for %.png <- %.xpm,
as seen later, and the rules are identical.
> ch> % make asdf.ppm
> ch> make: Circular asdf.bmp <- asdf.ppm dependency dropped.
> ch> ppmtobmp < > asdf.bmp
> ch> /bin/sh: -c: line 1: syntax error near unexpected token `>'
> ch> /bin/sh: -c: line 1: `ppmtobmp < > asdf.bmp'
> ch> make: *** [asdf.bmp] Error 2
>
> I agree, this seems wrong. I would expect make, after deciding to throw
> out that circular dependency, to decide it doesn't know how to build
> asdf.ppm and give output like this:
>
> make: Circular asdf.bmp <- asdf.ppm dependency dropped.
> make: *** No rule to make target `asdf.ppm'. Stop.
>
> rather than failing with an incorrect value. I'll look into this.
>
> ch> % giftopnm asdf.gif | ppmtoxpm > asdf.xpm
> ch> % rm asdf.gif
> ch> % make asdf.png
> ch> make: Circular asdf.xpm <- asdf.ppm dependency dropped.
> ch> xpmtoppm < asdf.xpm > asdf.ppm
> ch> pnmtopng < asdf.ppm > asdf.png
> ch> rm asdf.ppm
>
> This is correct, right?
Yes. This should also have happened with asdf.png <- asdf.gif, but
here it's asdf.png <- asdf.xpm.
> ch> Anyway, yes, perhaps I'm stretching 'make' too far, but I'm strongly
> ch> encouraged by the fact that this works some of the time!
>
> As far as I can tell, make works all the time when it should work. What
> is broken is that in some situations where make can't do what you want,
> it will try to do something bogus instead of just printing an error.
>
> Am I correct here, or am I missing something?
It's actually doing the right thing about half the time. I guess the
code determining which dependency to drop is picking an arbitrary
dependency, instead of useless dependencies.
A dependency graph is easy to parse when it's a tree; in this makefile
it's a graph with loops, but any graph can be turned into a tree if the
right parts get dropped. (If the wrong parts get dropped, you get two
graphs instead of one, and then you can't get there from here.)
--
Charles Howes -- [EMAIL PROTECTED]
