SwiftPM packages linked into static libraries (bug)

Hey! I seem to have ran into a bug with the SwiftPM package integration for static libraries. When a static library depends on an SDK (e.g. Foundation, UIKit, …) all SwiftPM packages will also be linked into it. Adding other types of dependencies doesn’t seem to have any impact. It seems like it’s only when a static library depends on both a SwiftPM package and an SDK that the issue occurs.

In my case it caused just over 3000 duplicate symbol errors. As both my app and static library target linked with Alamofire from SwiftPM 😅

I was able to reproduce with latest master. See an example using this small modification of the SPM test fixture:

name: SPM
packages:
  Codability:
    url: https://github.com/yonaskolb/Codability
    majorVersion: 0.2.1
localPackages:
 - ../../.. #XcodeGen itself
targets:
  App:
    type: application
    platform: iOS
    sources: [SPM]
    scheme: {}
    dependencies:
      - package: Codability
      - target: StaticLibrary
  StaticLibrary:
    type: library.static
    platform: iOS
    sources: StaticLibrary
    dependencies:
      - package: Codability
      - sdk: UIKit.framework # <- the addition

Screenshot

Start with the SPM test fixture and its modified YAML, reproducing the App and StaticLibrary targets with Codability and UIKit.framework dependencies. Trace the generated Xcode project and verify that the SwiftPM package is not linked redundantly into the static library, eliminating the duplicate symbol errors.