Combine nested publishers leak

Development Core Libraries
8

Hey guys @Max_Desiatov @Joseph_Heck.

Even though its been almost a month of inactivity on this topic I came with a little update on it which it was worth mentioning in my opinion. As the project in which I discovered the problems in the first place could not wait for this bug to be fixed, I went ahead and tried to replicate the same problem in a small side project to investigate this problem some more. My intention was to create a small core data provider class which would expose an API to fetch and persist some data. The only difference between this one and the provider used in the main project is using NSPersistentContainer's performBackgroundTask closure to perform the operation instead of NSManagedObjectContext's perform as it is in the main project. Here's my implementation of the fetch:

func load<Entity: CoreDataMappable>(entitiesOfClass entityClass: Entity.Type) -> AnyPublisher<[Entity], Error> {
    Future<[Entity], Error> { [weak self] promise in
        guard let self = self else { return }
        self.persistentContainer.performBackgroundTask { _ in
            do {
                let results = try self.findAll(Entity.CDEntity.self).map { $0.wrapped() }
                promise(.success(results))
            } catch {
                promise(.failure(error))
            }
        }
    }.eraseToAnyPublisher()
}

Had it not be a problem😒, I'd say I successfully managed to reproduce the leaks in my side project. At this point I became really curious and interested to see Apple's Combine implementation of Future. Of course that was not possible but the closest I could get was the OpenCombine library on Github, whose author of its Future publisher implementation is (if I'm not wrong :sweat_smile:) @Max_Desiatov himself.
Now, most likely Apple's implementation of Future is different from OpenCombine's. Nevertheless after I replaced Apple's Future in the above load function with Max's Future, surprise, no more leaks. Nothing else changed besides the implementation of Future and the AnyCancellable subscription for it.

What is your opinion on this? Could this be a bug of Combine or I could still be doing something wrong which makes Combine's Future leak. The specific instance which leaks is Future<,>.Conduit.

Thank you for your support.

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