Re: Change a target within Makefile?

[Taylor Hutt]

> My question is very similar to this:
>
https://stackoverflow.com/questions/31443920/remove-target-from-makecmdgoals
>
> When a particular flag is set, I want to do something extra.
> I know this is hard, but please forgive me to repeat a similar question
> in case somebody in the list may know something.

<snip>

> Then, I hope the following would happen.
>
> $ make x.a
>    -> create x.a
>
>
> $ make x.a GENERATE_B_AS_WELL=1
>    -> create x.b as well as x.a
>

As you have a specific flag, you can make 'x.a' dependent on a
conditionalized version of x.b.  The example below makes a simple
mapping to conditionally include 'x.b' in the prerequisites of 'x.a'
based on the value of 'GENERATE_B_AS_WELL'.

_MAP_x_b_1 := x.b
_MAP_x_b_0 :=

x.b:
@echo "$@ is up-to-date";

x.a: $(_MAP_x_b_$(GENERATE_B_AS_WELL))
@echo "$@ is up-to-date";

It is left as an excercise in robustness to ensure
'GENERATE_B_AS_WELL' is always in {0, 1}.

On Wed, Jul 24, 2024 at 4:35 AM Paul Smith <psmith@gnu.org> wrote:

> On Wed, 2024-07-24 at 18:44 +0900, Masahiro Yamada wrote:
> > ifdef GENERATE_B_AS_WELL
> > # When this flag is set, we want to generate %.b as well.
> > # I know I cannot update MAKECMDGOALS...
> > MAKECMDGOALS := $(patsubst %.a, %.b, $(MAKECMDGOALS))
> > endif
> >
> >
> > %.a:
> >         touch
> >
> > %.b: %.a
> >         cp $< $@
>
> > Then, I hope the following would happen.
> >
> >
> > $ make x.a
> >    -> create x.a
> >
> >
> > $ make x.a GENERATE_B_AS_WELL=1
> >    -> create x.b as well as x.a
>
>
> Your example output cannot be generated by this makefile, so it's
> confusing as to what exactly you want to happen.
>
> However, doesn't something like this work:
>
>     a_prereq =
>     ifdef GENERATE_B_AS_WELL
>     a_prereq = %.b
>     endif
>
>     %a: $(a_prereq)
>             touch $@
>
>     %.b: %.a
>             cp $< $@
>
>

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