@CasePathable fails to compile when nested in private type

[pietrasm]

Describe the bug
@CasePathable generates code that fails to compile when the enum is nested in a private type.

To Reproduce

struct A {
    private struct B {
        @CasePathable
        enum C {}
        // Expanded Macro
        extension A.B.C: CasePaths.CasePathable, CasePaths.CasePathIterable { // 🛑 Error: 'B' is inaccessible due to 'private' protection level
        }
    }
}

Expected behavior
Successful compilation.

Environment

• swift-case-paths 1.5.6
• Xcode 16.0
• Swift 6.0
• OS: iOS 18.0.1

Additional context
Relaxing private to fileprivate can be used as a workaround.

[mbrandonw]

Hi @pietrasm, unfortunately I'm not sure there is anything we can do to fix this. Our macro is merely expanding an "extension macro" to add some conformances to the C type, and Swift is interpreting that to mean extension A.B.C. I think for now using fileprivate is a good workaround, or you can add the conformances yourself and then the macro will skip them:

@CasePathable
enum C: CasePathable, CasePathIterable {}

Since this isn't an issue with the library I am going to convert it to a discussion. Please feel free to continue the conversation over there! And if you have the time I recommend filing an issue with Apple because it does seem like something that should be allowed.

[pietrasm]

Hi @mbrandonw, I suspected this might be a swift issue. I have just reported it: swiftlang/swift#77023

Also, thanks for pointing out that manually conforming the type could be used as a workaround as well.