Would you just leave this blank, or not even defined?
I leave these settings undefined. In case you use those settings only in prod, I suggest defining them in dev and test only.
Well, in start you fetch those parameters from wherever they are, and then merge them, yes. AFAIK there’s no “merge env” function, so I do it by reading the top-level setting (say MyApp.Repo), adding additional info (e.g. password) into it, and putting it back with Application.put_env.
