Noise packages Racket & Chez Scheme boot files1 for all the
platforms it supports. Originally, that was just x86-64 and arm64
macOS, but when I added iOS support, that extended to include arm64
iOS. These boot files take up about 45MB for each arch+os pair and
the way I originally distributed them was placing them all in a boot
folder and adding them to the resources list for the core Noise
target.
That worked fine, but it seemed like a waste to lug around an extra 90MB
of data that would never be used inside my iOS apps. Looking at the
PackageDescription docs, there doesn't appear to be a way to filter
resources by platform. There is an exclude property on Targets,
which I tried to use by making the Package.swift script manipulate the
target at runtime, but I couldn't figure out a way to get that working
with cross-compilation.
Next, I tried writing a SwiftPM build tool plugin to remove files based on the target platform, but plugin execution is sandboxed and I couldn't figure out a way to move the boot files out of the package context2.
Finally, I settled on just making separate targets for macOS and iOS. Each target contains its respective boot files and the main target conditionally depends on the platform-specific targets. I really wanted to avoid this approach because it's somewhat ugly and it means I have to manually wire things around that the build system should be able to do for me, but, for now, this seems like the most sensible approach.