Support for macOS static framework

[kjteske]

Any plans for this?

I'm guessing it would look pretty similar to other static framework implementations, I could take a stab at a PR.

[allevato]

Our rough plan for rules dealing with distributable frameworks going forward is that we'd like to unify things around Xcode 11's new .xcframework bundle format, where we'd only have to maintain a single rule implementation that would build whichever platform/architecture combinations that users are interested in.

For that reason, we'd like to avoid adding more variants of the existing implementation at this time, since we don't want to imply that they would be supported longer-term.

[kjteske]

Makes sense. Any guess on how soon that'll be?

[keith]

Here's a tracking issue for supporting distributable xcframeworks #1249

I would be happy to accept a macos_static_framework rule in the meantime, since I think that could still be desirable since unlike iOS we won't have architecture conflicts, and once the M1 transition is complete, you may want to produce a "simpler" framework than a full xcframework just for a single platform