I have a Swift Package that builds both an AppKit and a UIKit library, and code completion works great for AppKit code, but does not work in any of the UIKit files - regardless of the target selected on the top of the IDE.
This Swift Package in turn is consumed by an AppKit sample, and a UIKit sample, code completion works just fine on both of those projects. It is just the shared Swift Package that fails to work with iOS APIs.
I have tried removing mac as a platform in `Package.swift`, and wiping out my DerivedData for the project, but it does not make a difference, completion still is completely busted for code living inside the Swift Package.
The code is open source, under the MIT license, if anyone wants to look at the setup: