Xcode 9 : Module compiled with Swift 3.1 cannot be imported in Swift 4.0

After updating to Xcode 9, I tried to build one of my projects.

I use the FacebookLogin pod. I have a compiler error in FacebookLogin/LoginButton.swift

@testable import FacebookCore
❌ Module compiled with Swift 3.1 cannot be imported in Swift 4.0

In my target's build settings, the Swift language version is set to Swift 3.2.

I guess I need to wait for Facebook to update their pod ? Or any other suggestion ?

Thanks !

Update:

Solution also tested and working in Swift 5 and Xcode 11.

Original:

I would like to add that if you are using Carthage to compile a module in Swift 3.2 you should go to a terminal and run:

sudo xcode-select --switch /Applications/Xcode-beta.app/Contents/Developer

To use the Xcode 9 command line tools, then you can run:

carthage update NameOfTheLibrary --platform iOS --no-use-binaries

This will compile the library with your current command line tools, it can be a bit slow but now the project should build.

Note

To revert and use your stable Xcode command line tools simply run:

sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer

Xcode 9 comes with a Swift 4 compiler that understands both Swift 3.2 and swift 4, it even lets you mix and match between the 2 versions. Unfortunately, other versions aren't supported.

Even if you set your language to Swift 3.2, it uses the Swift 4 compiler.

If you're using cocoapods, you can add this to the end of your pod file to force the pods to use Swift 3.2 or 4.0:

post_install do |installer|
    installer.pods_project.targets.each do |target|
        target.build_configurations.each do |config|
            config.build_settings['SWIFT_VERSION'] = '3.2'
        end
    end
end

Alternatively, you could put the files from the pod directly into your project temporarily, until FacebookLogin is updated to Swift 3.2 or 4.

Note: Edited based on Matt's feedback

Maybe you can clean the target before you build it. It works fine for me.

I ran into the same issue on Xcode 9 Beta 3, which pointing to 'Alamofire' and tried a few different solutions, the easiest one i found is

1. CMD+SHIFT+K to clean the build
2. Restart Xcode 9 <-- make sure you do this step, that's critical. `

Doing a "clean build folder" and restarting Xcode 9 cleaned up the error for me. Also the error didn't stop the app from running on my device or the simulator.

goto xcode DerivedData directory then remove all file inside it and recompile your project . it work for me .

and default DerivedData directory is :~/Library/Developer/Xcode/DerivedData.

If using Carthage , Open terminal and;

carthage update --platform iOS --no-use-binaries

If using Pod , Open terminal and;

pod update

(Also if don't work in pod, you can change SWIFT_VERSION in podfile Ex:

config.build_settings['SWIFT_VERSION'] = '3.2'

)

After;

Open Xcode and use;

Command+Option+Shift+K

It works for me.

1.Clean your project in Xcode 8

2.Build or run your project in Xcode 9

I cleaned the project in Xcode 9, and then run the app, it works.

I had the same problem with Xcode 9 GM and this solved my problem: Remove it from the project and drag it again into "Embedded Binaries".

Clean Build Folder

Cmd + option + shift + K

I have

pod 'FBSDKCoreKit'
pod 'FBSDKLoginKit'
pod 'FBSDKShareKit'

in my project and import FBSDKLoginKit, after cleaning the target i didn't have any issue

Since the pod you are using is in swift and is a beta pod, it is likely that you would have some issues with the swift 4 compiler, you should use the objective-c version of the pod for the time being

If you use from Pod:

1. In Podfile comment FacebookLogin pod
2. >pod install
3. In Podfile uncomment FacebookLogin pod
4. >pod install
5. Run again your project

For my case - the actual pod referenced a static zip with prebuilt binaries targeting swift 3.1. So only solution is to rebuild the framework with source from xcode 9.

https://github.com/AudioKit/AudioKit/issues/980