Doc specific features

[GuillaumeGomez]

This will allow gtk-rs and gstreamer-rs to remove some unneeded features. :)

I made this implementation flexible enough so we can add more build specific thing (like "test" or even "doctest").

cc @sdroege

r? @ehuss

[ehuss]

Thanks for taking a look! I'm not really sure that looking into the package metadata is really the right option, since that is a free-form area intended for external tools.

I think this will probably deserve a more general solution. There are some open issues along this line (like #2911) and a postponed RFC (rust-lang/rfcs#1956). This may require more design and planning. I think something like this will probably want to go through an RFC process.

Also, just FYI, some team members are going to be away for a while due to the holidays, so it may be a while before we can provide any more feedback.

[GuillaumeGomez]

An RFC seems a bit too much for such a thing from my point of view. However I agree that metadata might not be the best place for it. Open to suggestions!

[ehuss]

I'm going to close this for now, since this isn't an approach we want to take. In particular, we don't think Cargo should be using the package metadata. I don't have any particular suggestions for how it should work. I think the issue and RFC linked above might be a good starting point, but the relationship between command and profile is a little awkward (and the doc profile was deprecated, which we would need to resurrect). Maybe posting on internals may drum up some discussion? Or feel free to follow up on the issue tracker.

[GuillaumeGomez]

All the links you gave are stuck so I have to admit that I have lost all motivations on this... I'm surprised that profiles aren't already a thing, it's something strongly needed in a lot of places and I was hoping that since doc and doctest features were finally stabilized (even though the second needs actions on cargo that won't happen once again)...