Extending from an external `HybridObject` does not compile in Swift

[mrousavy]

What happened?

Using external types (that's structs, enums, and HybridObjects defined in another Nitro Module than your own Nitro Module) works fine when they are used as struct properties, parameters or return values.

However when you create a HybridObject that extends from a HybridObject inside an external Nitro Module, the Swift build fails.

It works fine for C++ and Kotlin.

Nitrogen CLI logs (with --logLevel="debug")

🔧  Loading nitro.json config...
🚀  Nitrogen 0.33.1 runs at ~/Projects/react-native-vision-camera-v5/packages/react-native-vision-camera
    🔍  Nitrogen found 5 specs in ./src/specs
    🔍  Nitrogen found 0 specs in ./src/specs/common-types
    🔍  Nitrogen found 2 specs in ./src/specs/frame-processors
    🔍  Nitrogen found 2 specs in ./src/specs/inputs
    🔍  Nitrogen found 4 specs in ./src/specs/instances
    🔍  Nitrogen found 1 spec in ./src/specs/metering
    🔍  Nitrogen found 8 specs in ./src/specs/outputs
    🔍  Nitrogen found 2 specs in ./src/specs/views
... omitted (private)

Nitro Specs (.nitro.ts)

// In react-native-vision-camera-v5:
export interface CameraOutput extends HybridObject<{ ios: 'swift', android: 'kotlin' }> {
  // ...
}

// In react-native-vision-camera-v5-code-scanner:
import { CameraOutput } from 'react-native-vision-camera-v5'

export interface CodeScannerOutput extends CameraOutput {
  // ...
}

Nitro Modules Version

0.33.1

Nitrogen Version

0.33.1

Operating system

MacOS

Additional information

• I have read and followed the Troubleshooting Guide.
• I created a reproduction PR to reproduce this issue here in the nitro repo. (See Contributing for more information)
• I searched for similar issues in this repository and found none.

[mrousavy]

I have added a test/repro here: #1154

The main issue is that the autogenerated -Swift.h header (generated by the Swift compiler) references the external type without importing it.
This is not the first time the Swift compiler does this, but when I try to add the import beforehand, it fails to build because some C++ types are re-defined:

I don't know why the CodeScanner module is exporting that again, but I guess it's because of the inheritance clause.

[mrousavy]

Update: I have tried to fix this by basically rewriting the whole Swift <> C++ interop structure to be C++ first, instead of Swift first: #1157

This is also blocked because of how functions work, and I am not even sure if that will work. We'll see. I also have another idea by erasing the inheritance and instead using private composition, I'll play around with that more.