Add caching for iOS build

[ann0see]

Has this feature been discussed and generally agreed?
No

Describe the solution you'd like
Since #2355 has been merged, we should also use caching/parallelising for the iOS build.

Describe alternatives that have been considered

/

[ann0see]

To me it seems as if parallelising isn't really needed. Probably we could use the caching logic from macOS?

@hoffie ?

[hoffie]

To me it seems as if parallelising isn't really needed

Do you think it's already being used? I've got zero experience with Xcode or xcodebuild itself, but a quick search suggests that the relevant options would be

defaults write com.apple.dt.Xcode IDEBuildOperationMaxNumberOfConcurrentCompileTasks `sysctl -n hw.ncpu`
defaults write com.apple.dt.Xcode PBXNumberOfParallelBuildSubtasks `sysctl -n hw.ncpu`

But maybe that is already the default? Do you have a way to check? If not, it seems to be possible to read it like that:

defaults read com.apple.dt.xcodebuild
defaults read com.apple.dt.Xcode

Probably we could use the caching logic from macOS?

Yes, it looks like the paths for (a)qt and pip should be the same so the same logic can be used. I guess it should still be duplicated as we would otherwise rely on iOS and macOS using the exact same versions. The cache key has to be adjusted as well, of course.

[ann0see]

Do you think it's already being used?

I think I googled it once and I think I read that it is enabled by default (I assume this to be true since the build time is not that long).

Probably caching should go in with your refactoring.

[ann0see]

@hoffie sorry to tag you here again, but this issue is still outstanding? Feel free to tag it for the next release.