Sorry, I misunderstood your question.(I thought you'd like to share code between different normal Swift Targets)
As @0xTim said, it is currently not possible to share code between multiple Package.swift files.
And actually, I have the same issue here.
I have a helper function defined at
Package.Dependencyand I'd like to use it on multi package files.
Can we prefer local package and fallback to url package - #2 by Kyle-Ye
The current solution for me is to manually copy and paste the contents to different Package.swift files (Or we use a tool to manage and append the helper func to different Package.swift files)