ChangesFollower.init/1 doesn't comply with GenServer spec

[dch]

It should be possible to drop an instance of ChangesFollower directly into a Supervision tree, so it can act as a normally managed Worker, but it returns a different set of tuples than expected, so this fails.

As ChangesFollower registers as a behaviour, it must comply with the GenServer spec:

 @callback init(args :: term()) ::
            {:ok, state}
            | {:ok, state, timeout() | :hibernate | {:continue, term()}}
            | :ignore
            | {:stop, reason :: any()}
          when state: any()

However its return spec is different, returning:

  @callback init(args :: term) ::
    {:ok, db :: ICouch.DB.t, state} |
    {:ok, db :: ICouch.DB.t, opts :: [option], state} |
    {:ok, db :: ICouch.DB.t, opts :: [option], state, timeout | :hibernate} |
    :ignore |
{:stop, reason :: any} when state: term

There's presumably a reason for doing it this way, but the result is that an additional GenServer-compliant behaviour needs to be wrapped around this before it can be used correctly in a standard OTP supervision tree.

Would you take a breaking change PR for ChangesFollower that deals with the extraneous items db, opts simply by removing them entirely from the returned tuple? It seems that any process spawning a ChangesFollower will already have the DB and options it passes into the worker.

I'm still working on a wrapper but how do you handle this at meetnow? It seems better to achieve this directly in ICouch.

[dch]

any comments?