Re: implicit rules

[Noel Yap]

I see.  You wouldn't happen to have a patch that'll allow make to use the 
implicit rule for the former example, would you?

Thanks,
Noel

Boris Kolpackov wrote:

> I will start from the second example:
>
> Noel Yap <address@hidden> writes:
>
>
> > But if it's changed to:
> >
> > .PHONY: all
> > all: aoeu/aoeu.mk
> >
> > %.mk: %.m
> >         cp $(<) $(@)
> >
> > %/.:
> >         mkdir -p $(@)
> >
> > aoeu/aoeu.mk: aoeu.m | aoeu/.
> >
> >
> > The output becomes:
> >
> > $ gmake
> > mkdir -p aoeu/.
>
>
> If you run this with 'make -r -d' you will see that make 
> didn't find any rules for 'aoeu/aoeu.mk'. The reason why
> make didn't complain about it is because make has this
> habit of imagining that targets "somehow" get updated.
>
> If I run my -bk-patched make with --no-implicit-phony flag
> I get the following:
>
> make: *** No rule to make target `aoeu/aoeu.mk', needed by `all'.  Stop.
>
> See
>
> http://mail.gnu.org/archive/html/help-make/2004-02/msg00028.html
>
> for more information.
>
> Now let's go to your first example which is quite interesting:
>
>
> > .PHONY: all
> > all: aoeu/aoeu.mk
> >
> > %.mk: %.mk
> >         cp $(<) $(@)
> >
> > %/.:
> >         mkdir -p $(@)
> >
> > aoeu/aoeu.mk: aoeu.mk | aoeu/.
> >
> >
> > The output is:
> >
> > $ gmake
> > gmake: Circular aoeu/aoeu.mk <- aoeu/aoeu.mk dependency dropped.
> > gmake: Circular aoeu.mk <- aoeu.mk dependency dropped.
> > mkdir -p aoeu/.
> > cp aoeu.mk aoeu/aoeu.mk
>
>
> Again, let's run 'make -r -d' on it. Here is the relevant part of 
> the output:
>
> Considering target file `all'.
>  File `all' does not exist.
>   Considering target file `aoeu/aoeu.mk'.
>    File `aoeu/aoeu.mk' does not exist.
>    Looking for an implicit rule for `aoeu/aoeu.mk'.
>    Trying pattern rule with stem `aoeu'.
>    Trying rule prerequisite `aoeu/aoeu.mk'.
>    Found an implicit rule for `aoeu/aoeu.mk'.
>
> Here make found satisfying implicit rule which looks like this:
>
> aoeu/aoeu.mk: aoeu/aoeu.mk
>         cp $(<) $(@)
>
> But then make drops circular dependency:
>
> make: Circular aoeu/aoeu.mk <- aoeu/aoeu.mk dependency dropped.
>
> Which makes this rules looks like this:
>
> aoeu/aoeu.mk:
>         cp $(<) $(@)
>
> And, finally, make adds dependencies that you specified by hand:
>
>
> aoeu/aoeu.mk: aoeu.mk | aoeu/.
>         cp $(<) $(@)
>
> Now $< is bound to 'aoeu.mk', $@ - to 'aoeu/aoeu.mk' and you get
>
>
> > cp aoeu.mk aoeu/aoeu.mk.
>
>
> The funny part is that you would expect '%.mk' to end up in $<
> but because make dropped it 'aoeu.mk' took its place which
> happened to be what you actually wanted.
>
>
> hth,
> -boris
>
>
>
>
>
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