Activity Stub Injection in Workflow Implementation

[rmanibus]

Temporal is discouraging the use if Dependency Injection for Workflow class, because

Dependency Injection into Workflow Instances is a direct way to cause changes that are incompatible with the persisted histories

However, I believe there is some room to allow injection of Activity stubs (and all other type of temporal stubs).

This way we could move all the options in build time configuration and simplify the workflow implementation from this:

    private final FileProcessingActivities activities;

    public FileProcessingWorkflowImpl() {
        this.activities = Workflow.newActivityStub(
                FileProcessingActivities.class,
                ActivityOptions.newBuilder()
                        .setStartToCloseTimeout(Duration.ofHours(1))
                        .build());
    }

to this:

    private final FileProcessingActivities activities;

   @Inject
    public FileProcessingWorkflowImpl(FileProcessingActivities activities) {
        this.activities = activities
    }

or even:

    @Inject
    private FileProcessingActivities activities;

I don't think that we can leverage arc for this. I think the best solution would be to scan the constructor parameters / annotated fields using jandex and create the workflow instance accordingly.