Re: intentional missing prerequisites?

[Mike Shal]

On Tue, Aug 31, 2010 at 11:46 AM, Canham, Timothy K (316C)
<address@hidden> wrote:
> We have a modular make system where we would like to be allow users to add 
> and remove build targets.
>
> What I would like to be able to do is something like this:
>
> big_target: target_1 target_2 target3
>
>
> target_1:
>        do something
>
> target_2:
>        do something else
>
> and target_3 is not defined anywhere.
>
> I would like to know if there is a way to make the definition of the 
> prerequisite target optional, and not break the rule. I know I could do:
>
> target_3:
>
> and it would work, but that would require adding hundreds of them, so I'd 
> like to avoid it.
>
> Any ideas?

I used to use a rule like this to ignore missing header files:

%.h:
        @echo "  ??      $@"

The echo is just to let the user know that make couldn't find the
header, but if that header is no longer actually required then the
build will succeed. If the header is required, make should still try
to build the dependent objects, and then the compile will fail for
those.

I suppose you could try to generalize it like this:

%:
        @echo "  ??      $@"

But that might have some serious unintended side-effects. If you can
make all of these targets follow a pattern that you can wildcard it
would probably be safer (like %.target or something, and use 1.target,
2.target, etc).

-Mike