How to fix “SWIFT_VERSION '3.0' is unsupported, supported versions are: 4.0, 4.2, 5.0” error in Xcode 10.2?

Question

I\'m trying to run downloaded from app, try to open in Xcode and have an error:

\" Showing Recent Messages
:-1: SWIFT_VERSION \'3.0\' is unsu

Answer 1

It seems that the app might have an old Swift version code like Swift 3.0 in your case. In the release of Xcode version 10.2 has launched Swift 5.0 version. Xcode 10.2 does not support compiler for Swift 3.0 version. You can change compiler from Build Settings -> Swift Compiler - Language -> Swift Language Version -> Change it to Swift 5. If your code is compatible with that language version then it will run the code without error.

However, the Swift 3 compatibility mode will not be supported in the Swift 5 compiler. Swift 4.2 is the last release of Swift to support Swift 3 mode. There are important changes to both the surface of the language and the interior of its implementation in the releases following Swift 3 that will be the basis of future (and lasting) source and binary stability.

Refer below link for more details. https://developer.apple.com/documentation/xcode_release_notes/xcode_10_2_release_notes/swift_5_release_notes_for_xcode_10_2

If you really wish to run the app which has older Swift version code than you must have to use an older version of Xcode. You can use Xcode version 10.1, it's compiler having support for Swift 3.0 version.

Another alternative way is to migrate your old Swift code to the new version of the Swift version. You can migrate you Swift 3.0 to Swift 4.0 in Xcode 10.1 version.

For migration guide refer to this https://swift.org/migration-guide-swift4/