Jim Bosch your suggestion would work, but I confess I lean towards going the other route:

• skip the ABC because the API is so simple
• Have exactly one task, e.g. BaseFakeSourcesTask, that adds the necessary fields when constructed and logs a warning that no sources will be added when it is run.
• Add a config flag to run the task, and if it is false then don't construct it (and hence don't add the fields)

The advantages I see are:

• It is simple, adding just one nearly trivial task
• It can be called, e.g. for testing purposes

The main disadvantages I see are:

• It is more different from the HSC code, though still not very different
• It requires every caller to add a config parameter that enables the task. But this is such a common pattern that I see it as only a minor disadvantage. And if one omitted that flag the worst that happens is a few unused fields get added to the source catalog.

Ah, that's a good point. I think Nate Lust's implementation issue with the ABC came from the fact that it was failing when constructed, but we shouldn't be constructing it when doFakes=False anyway. Hopefully he can confirm. So if we have a doFakes option, we can indeed use ABC.

So I think your original proposal works, and I'll just let you two go ahead with that (sorry about all the mixed signals, Nate Lust). I believe with the ABC approach there's no need to have a warning in BaseFakeSourcesTask.run, since we can guarantee it'll never be called.

Two small comments on the code:

• I think the __metaclass__ line needs to go after the class docstring if you want the docstring to function properly.
• Commit message should probably be changed to reflect the fact that there's no longer a dummy task, and I think the sense of "users can not" is the opposite of what was intended (maybe "not" -> "now"?).

I changed FakeSoucesTask to BaseFakeSourcesTask which is an abc. I added a configuration option to not run the fake sources by default. I eliminated the dummy class all together. This task will then not run if 1 the doFakes option is not set and 2. if the doFakes option is set, and the task is not retargeted, the task will fail as it is an abc. A user must set doFakes, and retarget the task to a subclass of BaseFakeSourcesTask

I note (for my own benefit) that this is already mentioned in the release notes. Many thanks!