is blocked by:

• SR-14575 Frameworks built from Swift packages lack a Headers folder

Issue Description:

When the Xcode target (such as Application) has a transitive dependency to the Swift Package, such as it is importing a dynamic framework that is importing Swift Package that has public @objc interface, such as a delegate protocol, we can’t build the target due to Objective-C module failure.

Reproducible project is at https://github.com/niw/swift_package_objc_module_failure.

Error message you will see is like this.

<module-includes>:2:9: note: in file included from <module-includes>:2:
#import "Headers/TestFramework-Swift.h"
        ^
/Users/niw/Library/Developer/Xcode/DerivedData/Test-gcmgljtjqifdtzbblkpxoahggxkj/Build/Products/Debug-iphonesimulator/TestFramework.framework/Headers/TestFramework-Swift.h:192:9: error: module 'TestPackage' not found
@import TestPackage;
        ^
<unknown>:0: error: could not build Objective-C module 'TestFramework'

In this example, the dependency is like this.

Application target (Test)
→ Dynamic Framework target (TestFramework)
→ Swift Package (TestPackage)

Since if the middle dynamic link library is using Swift package or not is unrelated to both the application target owner and package owner, all Swift packages that have @objc can have this issue.
Therefore, currently basically @objc can't be use feely in Swift Package.

A few observations:

• This is caused by missing -Xcc -module-map-file for swift -frontend for the transitive Swift package dependency used for the Swift files in the application target.

• This is not happening if the module that Swift Package provided is written in Objective-C.