Consider adding a Mac Catalyst build option

[ronaldoussoren]

Feature or enhancement

Support the "Mac Catalyst" flavour of macOS binaries on recentish version of macOS

Pitch

MacOS currently has two ways to build "native" applications:

1. The macOS binaries used from macOS 10.0, for ease of reference I'll call these "Cocoa"
2. MacCatalyst binaries that link to (a subset) of the frameworks used on iOS, but recompiled for macOS

The latter have access to some interesting system APIs that former cannot use, such as the HomeKit framework. The current builds are "Cocoa" builds.

Previous discussion

There is no previous discussion of Python forums. This issue was triggered by an issue on PyObjC's tracker ronaldoussoren/pyobjc#501.

[ronaldoussoren]

I have no short-term plans to work on this, and haven't assessed the impact of this on the codebase

Doing this seriously likely requires some coordination with the PyPA and PyPI maintainers as this would effectively be a new platform: I expect that a Mac Catalyst build cannot use C-extensions (and hence binary wheels) for the current "Cocoa" variant.

That said, I have done no research on this beyond noticing that "Cocoa" binaries cannot load "Catalyst" libraries/frameworks, and that this is an intentional limitation (there is some support for loading "Cocoa" into "Catalyst" though).

[johnzhou721]

With a similar structure for ''embedded framework'' builds just like iOS, I've started the work on this:
beeware/Python-Apple-support#280 (the actual patch is at freakboy3742#8)