Testing how swiftLanguageModes/swiftLanguageVersions in SwiftPM behaves.

Usage

1. Pick which tools version you want to test.

   The repo comes with several Package.swift variants, written for different tools versions. Pick the one you want to test by copying/renaming it to Package.swift. For example:

   cp Package-4.2.swift Package.swift

   Note: The filenames deliberately do not follow the SwiftPM convention to provide different manifests to different compiler versions (e.g. Package@swift-5.11.swift). This makes it clear that Package.swift is always the chosen manifest, and it allows you to test old manifest versions with modern compiler versions.

2. Check out the swiftLanguageModes/swiftLanguageVersions argument in your chosen Package.swift. Comment in/out different values in the array to test different combinations.

3. Run swift run to run the program. It will print both the compiler version and language mode with which it was compiled.

Results

All of these were compiled with the Swift 6.1 compiler.

Package-4.2.swift

Swift compiler 6.0 or later
Swift language mode 4

Package-5.11.swift

Swift compiler 6.0 or later
Swift language mode 5

Package-6.0.swift with swiftLanguageModes: [.v5]

Swift compiler 6.0 or later
Swift language mode 5

Package-6.0.swift with swiftLanguageModes: [.v5, .v6]

Swift compiler 6.0 or later
Swift language mode 6 or later