Re: a question about why implicit rule must use the path found by directory search!!

[Paul Smith]

On Mon, 2010-09-27 at 10:06 +0330, ali hagigat wrote:
> /root> touch di4/preq1.u
> ---------------------------------
> vpath preq1.u di4
> all6: preq1.u
>       @echo "kkkkk"
> %.u: preq2
>       @echo "hhhhh"
>       @touch $@
> preq2:
>       @echo "llllll"
> ---------------------------------
> The manual says:
> 4.4.5 Directory Search and Implicit Rules
> The recipes of implicit rules normally use automatic variables as a
> matter of necessity;
> consequently they will use the file names found by directory search
> with no extra effort.
> ----------------------------------
> In the example I wrote, why 'di4/preq1.u' is not touched by '@touch $@'?
> Why the pathname found by directory search means 'di4/preq1.u' was not
> used by the automatic variable of our implicit rule($@)?

This is because of rule 4b in the search algorithm, summarized there as:

        In short, if `make' must rebuild, then the target is rebuilt
        locally, not in the directory found via directory search.

Since preq1.u is being rebuilt, it's built using the path in the
makefile (preq1.u) not the path found via directory search.  So, $@ (the
name of the target to build) is preq1.u, not di4/preq1.u.

-- 
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