This is a demo code with the single purpose of reproducing a specific problem.

This project contains a Cocoa Touch Swift code built as a framework. The swift version is set to Swift Language Version = Swift 3.3.

This project uses the framework built by Compatibility project. The swift version is set to Swift Language Version = Swift 4.0.

Open Compatibility project and CMD + B it. The output will be placed in Compatibility/. Open App and CMD + B. It should already be configured to consume the .framework from the above compilation.

When Compatibility is built using Xcode 9.3 (9E145) and App is using Xcode 9.2 (9C40b), App throws the following error: Module compiled with Swift 4.1 cannot be imported in Swift 4.0.3:

Changing Swift version between all possible combinations didn't work for me. The framework had to be consumed by a project being built in the same Xcode version.