Module compiled with swift 4.0 cannot be imported in swift 3.1

Question

Apparently I have managed to build my project in Xcode 9 beta and now I only get the error

Module compiled with swift 4.0 cannot be imported in swift 3.1

When I run the project in Xcode 8. The module in my case are Alamofire. I have tried to restart Xcode but nothing happens any ideas how to solve this issue?

Answer 1

You have two options that you can do:

Clean the project and then try to re-build your solution and see if it works.

If it don´t work and you still get the same error message then do the following steps and it should work for you:

1. Open your podfile and remove Alamofire
2. Run pod update
3. Re-add Alamofire to your podfile
4. Run pod update
5. When this is done, clean your project and run it

Answer 2

Same problem here but using Carthage. And here is the answer:

• rm -rf ~/Library/Caches/org.carthage.CarthageKit/DerivedData
• delete the Carthage folder for the project
• Update Carthage: carthage update --platform iOS

And voilà!

Answer 3

I had the same problem and cleaning the build folder helped:

Command+Option+Shift+K

or

Product -> Option+Clean

Answer 4

只是删除派生数据为我工作，无需再次安装Pod

Answer 5

I met this problem in a project where dependency is managed by Carthage. In my case, I didn't set command line tool in xcode (Type in xcodebuild -version, you will know whether you set it up or not), so first step is to go to XCode --> Preference --> Locations then select the xcode you want to serve as command line tool. Then you can follow the steps that @Domsware mentioned above to rebuild all frameworks you are gonna use.

===============================================

Same problem here but using Carthage. And here is the answer:

rm -rf ~/Library/Caches/org.carthage.CarthageKit/DerivedData
delete the Carthage folder for the project
Update Carthage: carthage update --platform iOS

===============================================

Then don't forget to delete old links under 'Linked frameworks and libraries' and drag all frameworks from /Carthage folder under you project to 'Linked frameworks and libraries'.

Then voilà!

For those who are using CocoaPods, I suspect (Disclaimer: I didn't encounter this problem in project where CocoaPods is the dependency manager) the solution would be run the following command in terminal:

$ pod deintegrate
$ pod clean
$ pod install

where you might need to install 'deintegrate' and 'clean' tool for CocoaPod

$ sudo gem install cocoapods-deintegrate cocoapods-clean

more details see post How to remove CocoaPods from a project?

Answer 6

Add following lines at the end of your pod file:

post_install do |installer|
    print "Setting the default SWIFT_VERSION to 4.0\n"
    installer.pods_project.build_configurations.each do |config|
        config.build_settings['SWIFT_VERSION'] = '4.0'
    end

    installer.pods_project.targets.each do |target|
        if ['SomeTarget-iOS', 'SomeTarget-watchOS'].include? "#{target}"
            print "Setting #{target}'s SWIFT_VERSION to 3.0\n"
            target.build_configurations.each do |config|
                config.build_settings['SWIFT_VERSION'] = '3.0'
            end
        else
            print "Setting #{target}'s SWIFT_VERSION to Undefined (Xcode will automatically resolve)\n"
            target.build_configurations.each do |config|
                config.build_settings.delete('SWIFT_VERSION')
            end
        end
    end
end