Value for SWIFT_VERSION cannot be empty

Select your app target then goto build setting, search for swift set the swift language version from the dropdown.

In case there is anybody else reading through this thread who has this same problem but was unable to solve it using the above answers, this may help:

If you have a data model, you need to check that when you click on the data model, click on an entity, and bring up the file inspector, the "Code Generation" Language is properly set. In my case my whole app was written Objective-C, but was set here to Swift for some reason. This is another reason that Error will show up in the Issue Navigator.

It's very important to clear the build folder after changing Code Generation Language. This can be done by pressing Command-Shift-K or by clicking Product->Clean Build Folder in the menu at the top of the screen.

Check out this link for a picture of where to find the "Code Generation" option I'm talking about.

Model.xcdatamodeld->File Inspector->Code Generation

Update for Xcode 10.2

1. Go to --> Build Setting

2. Select All + Combined or All + Levels underneath the Build Settings

3. And Finally on the search bar, on the right hand side search for "Swift Language Version"

You need to search for every "PRODUCT_NAME =" There needs to be a " SWIFT_VERSION = "4.2"; " after everyone. eg. also PRODUCT_NAME = "$(TARGET_NAME)";enter code here

Still, after all of that, if you're still at lost, you can add a SWIFT_VERSION directly the project file:

        80B11AAAAAAAAAAAAAAAC3E5D8 /* Debug */ = {
        isa = XCBuildConfiguration;
        baseConfigurationReference = DF5...040;
        buildSettings = {
            ...
            PRODUCT_MODULE_NAME = react-native-some-module;
            ...
            SWIFT_VERSION = "4.2";
        };
        name = Debug;
    };

Repeat for both the Debug and Release targets. That had me hop over this issue.

If you are using Ionic with Cordova and you got here because of this error do this:

In your config.xml add

<platform name="ios">
        <preference name="UseSwiftLanguageVersion" value="5" />

You may need to remove the resource for ios and re-add it to make it work.

cordova platform remove ios
cordova platform add ios

Cheers!

I use circle ci to run tests and generate app previews on testFlight I was having this issue and was able to fix this issue by setting the SWIFT_VERSION under ios/{your_project_name}.xcodeproj/project.pcxproj.

1. Search for SWIFT_VERSION under this file and COPY IT

    13B07F941A680F5B00A75B9A /* Debug */ = {
            isa = XCBuildConfiguration;
            baseConfigurationReference = 8F6A6E403A1DCB019B5AB844 /* Pods-heartland_charter_s_34954.debug.xcconfig */;
            buildSettings = {
                ...
                PRODUCT_NAME = heartland_charter_s_34954;
                SWIFT_OPTIMIZATION_LEVEL = "-Onone";
                SWIFT_VERSION = 5.0; // Copy this line
                ...
            };
            name = Debug;
        };

2. Search for PRODUCT_NAME and paste the SWIFT_VERSION just under each PRODUCT_NAME block, provided that it is not already there

        13B07F951A680F5B00A75B9A /* Release */ = {
            isa = XCBuildConfiguration;
            baseConfigurationReference = CF85766339BED655A366B986 /* Pods-heartland_charter_s_34954.release.xcconfig */;
            buildSettings = {
                ...
                PRODUCT_NAME = "$(TARGET_NAME)";
                SWIFT_VERSION = 5.0; // Add it here
                ...
            };
            name = Release;
        };

3. pod install and re run the app

For a Cordova app add the following line in config.xml

<preference name="SwiftVersion" value="5.3"/>