Xcode 8 Swift Update with Error "Use Legacy Swift Language Version"

“Use Legacy Swift Language Version” (SWIFT_VERSION) is required to be configured correctly for targets which use Swift.

Xcode 8 seems to be wrongfully displaying a nonexistent ("phantom", if you will) No. There's a trivial fix for this:

1. Click the tiny arrow next to SWIFT_VERSION to toggle the drop-down list.
2. Set the values for Debug and Release to Yes.
3. Set the values for Debug and Release back to No.

The image below was taken just after setting Debug to No. Xcode shows that both Debug and Release are set to No, however SWIFT_VERSION reads <Multiple Values>:

From this, I can only conclude that it is a bug; and that some value (or more probably a null value) is being misrepresented as No.

Use Legacy Swift Language Version - Xcode 8.2

Found work around. I went through each target (and project settings, so both in the project and target) in my project, toggled the "Use Legacy Swift Language Version" from "No" to "Yes" and back to "No" for each. The project then built again.

Xcode 8 Beta 3 Use Legacy Swift issue

I have been ignoring this problem for a while now and just working on other stuff in the meantime - I finally found the solution to my problem.

Since my project is Objective-C I figured maybe one of the Pods I am using was using Swift, I checked each Pod and none of them were.

The final solution was that my Core Data model was set to generate code in Swift even though I have been manually generating them in the File > New > NSManagedObjectSubclass menu. All I had to do was switch it to Objective-C.

“Swift Language Version” (SWIFT_VERSION) is required to be configured correctly for targets which use Swift

In the navigator selection bar, click the magnifying glass, then search for "SWIFT_VERSION" You will find the places in the project where you can adjust the swift version accordingly.

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