Tell Carthage to build dependency using Swift 3.2.2 (NOT Swift 4.0)

Question

I have a project written in Swift 3.2.2 and compiled using XCode 9.1

I have a dependency which is built using Carthage using this command:

carthage update --platform iOS

The issue is that Carthage builds the dependency using Swift 4.0 (instead of Swift 3.2.2)

Module compiled with Swift 4.0 cannot be imported in Swift 3.2.2

How do I tell Carthage to build my dependency using Swift 3.2.2 so that it can be used in my project?

I don't want to upgrade my project to Swift 4.0 quite yet.

Xcode 9.1 has support for both Swift 3 and Swift 4. So how do I tell Carthage to use Swift 3 when compiling the dependency? I don't want to tell it to use an earlier version of XCode (which I don't have anymore)

Answer 1

You say:

1. your project is compiling in Swift 3.2.2
2. your dependency, once resolved and downloaded with Carthage, will be compiling in Swift 4 (since its Build Setting was configured in that way)

with those conditions will be impossible for you resolving the issue: you can't mix Swift 3 and 4 due to this: https://github.com/Carthage/Carthage/issues/1978

The only thing you can do, for (eventually) fixing the situation is:

---

Scenario 1

1. you should find a previous version of the library which is building in Swift 3.2~, if exists

2. on your Cartfile you specify that specific version, eg:

   github "yourDependency" == x.y.z

---

Scenario 2

1. launch carthage update --platform iOS
2. enter inside your dependency folder (Carthage/Checkouts/yourDependency) and open the .xcodeproj in order to modify manually this option:

3. then you might have tons of building problems due to the fact that you are producing a language regression, you can try to fix them (depending by the library if is small or not, it could be possible).

4. if you have solved the dependencies, then launch:

   carthage build --platform iOS

5. try to compile your project...