Fuse: "Unable to bridge Swift instance" when passing a delegate

[dfabulich]

Consider this branch of the Fuse Showcase. https://github.com/dfabulich/skipapp-showcase-fuse/tree/audio-bug-example

In dfabulich/skipapp-showcase-fuse@3b4d8c4 there's a very basic start of an audio playground.

import SwiftUI
#if canImport(SkipAV)
import SkipAV
#else
import AVKit
#endif

struct AudioPlayerPlayground: View {
    let audioPlayer = try? AVAudioPlayer(contentsOf: URL(string: "https://dare.wisc.edu/wp-content/uploads/sites/1051/2017/08/HI009clip.mp3")!)
    var body: some View {
        Text("Hello, World!")
            .task {
                logger.log("creating delegate")
                let delegate = AudioPlayerDelegate()
                logger.log("setting delegate")
                audioPlayer?.delegate = delegate
                logger.log("playing")
                audioPlayer?.play()
            }
    }
}

class AudioPlayerDelegate: NSObject, AVAudioPlayerDelegate {
    func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
        print("Finished playing")
    }
}

It builds just fine, but if you launch it on Android and navigate to the audio playground, the app will crash, with this error:

SkipBridge/BridgedTypes.swift:198: Fatal error: Unable to bridge Swift instance <AudioPlayerDelegate: 0xb40000706ae94ab0> of type: AudioPlayerDelegate

It seems like it's not possible to implement a protocol in Fuse code and pass it to transpiled Kotlin.

[marcprux]

Hmm. We do support implementing protocols (with some limitations, and some bugs like #462).

I don't think we've ever tried a Fuse implementation of AVAudioPlayerDelegate, so I'm not sure what the issue is.

Is the crash coming from when you instantiate your AudioPlayerDelegate implementation, or when it comes to assigning it to the delegate field?

[dfabulich]

It fails during assignment. I updated my branch and the sample code. The log says:

creating delegate
setting delegate
SkipBridge/BridgedTypes.swift:198: Fatal error: Unable to bridge Swift instance <AudioPlayerDelegate: 0xb40000706ae97b70> of type: AudioPlayerDelegate

[dfabulich]

You can workaround the issue by declaring the delegate twice, like this (including a workaround for #578):

#if SKIP
class AudioPlayerDelegate: NSObject, AVAudioPlayerDelegate {
    // workaround #578
    override init() { super.init() }
    func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
        print("Finished playing")
    }
}
#elseif !os(Android)
class AudioPlayerDelegate: NSObject, AVAudioPlayerDelegate {
    func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
        print("Finished playing")
    }
}
#endif

The transpiled delegate satisfies the transpiled protocol.

[dfabulich]

The workaround didn't work to workaround skiptools/skip-applovin#3 and I'm not sure why.

The workaround for #576 didn't work in this case, because the bridge generator is adding override to all of the protocol methods. (This might be a separate bug, but I can't find a reduced test case; I'm giving up trying for now, and just hoping that the fix for #576 solves all of my problems.)

e.g. RewardedView_Bridge.swift

public override func didRewardUser(for p_0: MAAd, with p_1: MAReward) {
        jniContext {
            let p_0_java = p_0.toJavaObject(options: [])!.toJavaParameter(options: [])
            let p_1_java = p_1.toJavaObject(options: [])!.toJavaParameter(options: [])
            try! Java_peer.call(method: Self.Java_didRewardUser_8_methodID, options: [], args: [p_0_java, p_1_java])
        }

method does not override any method from its superclass

[dfabulich]

Ohhhh. The bug was that I didn't add @bridgeMembers to the delegate.

This feels obvious in hindsight, but the error message was no help. I've filed skiptools/skip-bridge#104 to improve the error message.