How do I diagnose and fix 'Module compiled with Swift X cannot be imported by the Swift Y compiler' in Swift/Xcode?

When you encounter the error message 'Module compiled with Swift X cannot be imported by the Swift Y compiler', it indicates that there is a mismatch between the version of the Swift compiler used to compile a module and the version currently being used to build your project. This is a common issue when working with Swift packages or libraries, especially if you're using multiple versions of Xcode or if you've recently updated Xcode or the Swift toolchain.

Diagnosing the Issue

To diagnose this error, consider the following steps:

• Check the compiled module version by reviewing the Swift version compatibility in the Xcode project settings.
• Ensure all dependencies are compiled with the same version of Swift.
• Clean the build folder by selecting Product > Clean Build Folder in Xcode.
• Rebuild the project to see if the issue resolves.

Resolving the Issue

To fix this error, follow these solutions:

1. Update your project settings to use the current Swift version.
2. If you're using CocoaPods, make sure to run pod install to ensure all pods are built with the right Swift version.
3. Recheck all dependencies to ensure they are built with the correct compiler version.
4. If necessary, delete derived data through Xcode > Preferences > Locations > click on the arrow next to Derived Data and remove the content.

Example Code Snippet

    // Example: Basic Swift function
    func helloWorld() {
        print("Hello, World!")
    }