Module compiled with Swift 4.0 cannot be imported in Swift 4.0.1

However I have recompiled the framework using the same Xcode and it still gives me this error.

• Base SDK iOS 11.1 for both
• Swift Language Version Swift 4.0 for both
• Not using Pods/Carthage

I hope someone might know

Update:

For release versions of Xcode:

This error (and similar errors involving Swift 4.1, 4.2, etc.) will occur when opening a project with Xcode 9.1, 9.2, 9.3, 9.4, 10, etc. that uses frameworks that were built with earlier Xcode tools.

To fix the issue, update and rebuild your frameworks using Carthage ( carthage update --platform iOS), Cocoapods (pod update or pod install), or manually, with the new updated Xcode tools. The tools should be updated automatically when you update Xcode, but if not, you can follow the steps outlined below in the original answer.

You may also need to clean your project cmd + shift + k and possibly your build folder cmd + option + shift + k to get Xcode to not use cached framework builds.

In some cases you may also need to delete your derived data folder (Easily found by going to Xcode Preferences -> Locations -> Derived Data Folder (Thanks Stunner)

For beta versions of Xcode:

See original answer below and then follow steps above.

Original Answer:

You probably still have your xcodebuild tools set to Xcode 9.0 which builds with Swift 4.0 and is incompatible with Xcode 9.1 beta's Swift 4.0.1.

Check in the terminal using the command:

xcodebuild -version

Or just go into Xcode preferences -> Locations and check/change the command line tools to Xcode 9.1. You should be set then.

My issue was due to an external framework not being compiled for Swift 4.0.2. I had added this file via Carthage, so running:

carthage update --platform iOS

And then cleaning the project cmd + shift + k and build folder cmd + option + shift + k and deleting the derived data folder (merely moving it to trash works as well) worked for me.

In my case, I downloaded xCode 11 Beta version to test SwiftUI. When i run my project, i got "Module compiled with Swift 5.1 cannot be imported by the Swift 5.0.1 compiler:..." error.

To do fix this issue. i changed xCode command line tool to new xCode 11 comment line tool. After that, you can create new xcode project with SwiftUI.

Xcode -> Preferences -> Location -> XCode command Line Tool

i hope, this will help someone who want to test with new freamework :)

Install Xcode Toolchain of specific Xcode version which was working for you from here.

An Xcode toolchain includes a copy of the compiler, lldb, and other related tools needed to provide a cohesive development experience for working in a specific version of Swift.

Open Xcode's Preferences, navigate to Components > Toolchains , and select the installed Swift toolchain.

This will let you compile and run the app for now.

I hit this issue with Xcode 10 beta, which adds Swift 4.2. My issue was unrelated to Carthage or any external dependencies.

Go to YourTarget > Build Settings > Swift Language Version for all of your Xcode targets.

Mine were all set to Swift 4.

After adding a Copy Files Build Phase, I started getting the error

> :0: error: module compiled with Swift 4.1.2 cannot be imported by the Swift 4.2 compiler: /Users/user/Library/Developer/Xcode/DerivedData/MyApp-faskfrihumfcdibjxisjvbfshppp/Build/Intermediates.noindex/MyApp.build/Debug/MyAppExtension.build/Objects-normal/x86_64/MyClass~partial.swiftmodule > > Command MergeSwiftModule failed with a nonzero exit code

I then set each target's Swift Language Version to Swift 4.2, which eliminated the error.

I'm not sure why the error was occuring in the first place, though, as having all targets set to Swift 4 should be equally as valid.

In my case (Xcode 9.2):

I went to Xcode Preferences > Locations > Derived Data

I then deleted the data and did a clean build and was ok.

In my case, I used CocoaPods with plugin cocoapods-binary to prebuild libraries to binaries. After I upgrade Xcode from 10 to 11, Xcode gives me this error:

Module compiled with Swift 5.0.1 cannot be imported by the Swift 5.1 compiler

I fix it by removing the /Pods directory and running pod install.

In my case, I re-compiled the framework with whatever version it was complaining about.

To recompile, run pod update or update the carthage (which ever one you're using), and build the project.

Then search for the framework in finder. Copy-paste the theFramework.framework to your project and make sure to "Copy items if needed."Build the project again and it should work.