Feature request: Allow conditional targets

[osa1]

I'm wondering if there's a problem with this idea. I'd like to enable some executables/tests only when --ghcjs is used, for example. But currently this is not allowed:

if impl(ghcjs)
  executable ...
    build-depends: ...

How hard would it be to implement this? Are there any problems with this idea?

[23Skidoo]

@dcoutts, what do you think?

[luite]

You can already use the buildable: False field to disable building something, although I think you also need to pull the dependencies under the conditional to make them not affect builds with another compiler. I do agree that this construction is rather unintuitive

[23Skidoo]

I think you also need to pull the dependencies under the conditional to make them not affect builds with another compiler.

I believe that this is #1725.

[sebright]

Now that #1725 is fixed, putting buildable: False under a conditional is very similar to making the target conditional.