Flow's Sync driver does not handle nested callbacks

[renatomassaro]

I've noticed a nested flow was not executing on_success or on_done callbacks, even though it ran successfully. Actually, only the first flow would execute.

    case get_flow() do
      {flow, 1} ->
        __driver__().execute_success(flow)
        Process.delete(:heflow)
      _ ->
        :ok

The case above led me to believe only the flow with counter 1 was being executed. Counter is not documented so I'm assuming it's a stack counter.

I've tried adding a handler for {flow, n}, and updating the :heflow process with {pid, n - 1}, similar to how it's defined on __finish__:

  def __finish__ do
    case get_flow() do
      {_, 1} ->
        Process.delete(:heflow)
      {flow, n} ->
        Process.put(:heflow, {flow, n - 1})
      nil ->
        :ok
    end
  end

No luck. By doing so, Flow enters on an infinite loop waiting for the synchronous receive. Async works fine (no need for any change). May need a couple tweaks on the Manager or how the Driver works, but since nothing is documented it's hard to spot what without going "all in".

[renatomassaro]

Hit this bug again on a non-nested callback. on_success, on_done and on_fail callbacks are completely ignored on Synchronous driver (haven't tested with async but it probably would work).