Re: make doesn't rebuild file when I expect it to

[Paul Smith]

On Tue, 2009-08-04 at 07:16 +0300, Dmitri Gribenko wrote:
> Here is a very simplified version of my makefile for latex.  All actual
> commands have been replaced by 'touch'.  There is a text.tex and a directory
> for images.  Images are in svg format and have to be converted to eps before
> running latex.
> 
> $ mkdir test-dir
> $ cd test-dir
> $ cat > Makefile
> text.dvi: text.tex images/image.eps
>       touch $@
>       echo === no bug ===
> 
> images/image.eps: images
> 
> .PHONY: images
> images:
>       $(MAKE) -C images
> 
> $ mkdir images
> $ cat > images/Makefile
> image.eps: image.svg
>       touch $@
> 
> $ touch text.tex images/image.svg
> 
> With these makefiles I expect that if images/image.svg is newer than text.dvi
> then text.dvi will be rebuilt if make is called in the toplevel directory.
> 
> However, consider such situation: images/image.eps is older than text.dvi, but
> images/image.svg is newer than any of them.  (Like image.svg was edited.)
> 'images' target is invoked regardless the timestamp because it is phony.  In
> the sub-make images/image.eps is updated.  But when sub-make finishes, 
> toplevel
> make doesn't see that images/image.eps is newer than text.dvi.  text.dvi is 
> not
> rebuilt.

This is expected.  Here, you are not telling make the truth.  The
top-level makefile has no commands to build the target images/image.eps.
It's built as a side-effect of the "directory" prerequisite "images".
But make doesn't know that; make sees that you have no commands in your
rule for images/image.eps, so make doesn't know that this file was
updated.

If you change your rule to contain a command line, then I believe it
will work:

        images/image.eps: images
                @:

-- 
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 Paul D. Smith <address@hidden>          Find some GNU make tips at:
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