Package Manager Swift and Xcode are orthogonal. That is, you cannot expect Package.swift to compile in Xcode; it just won't work. Instead, while Xcode does not support the package manager, you need to have two different assemblies: one with the package manager and one with Xcode.
, Swift, Package.swift , , :
swift build
Xcode Xcode, , Package.swift. Siren.git, - Xcode.