Allow multiple includes of Dry::Configurable

[timriley]

Instead of raising AlreadyIncludedError (now removed), update the method undef code in .included to handle already-undefined methods gracefully.

Allowing Dry::Configurable to be included multiple times across subclasses now allows for uses cases like a subclass adjusting various extension settings, e.g. config_class.

[flash-gordon]

Now that these lines are reachable, things are more tricky. include and prepend work differently, include will add a module to the ancestors' chain only once, whereas prepend does it every time. We should keep this in mind

[timriley]

Good call. I'll look to expand the testing to cover a few more possible edge cases before I mark this ready for a final review.

[timriley]

Done in Expand tests

[timriley]

@flash-gordon FYI, this is the reason for this PR: hanami/hanami@86db090 (#1430)

Dry::System::Provider::Source already includes Dry::Configurable, providing a generic config object, which is fine in most circumstances. For the Hanami's DB provider source, however, we have fairly advanced config needs, so I want to provide a custom config API. By re-including Dry::Configurable and providing the config_class: option, we can now do that.

How does that feel to you?

I thought about adding a dedicated API to Provider::Source for specifying a custom config class, but that felt like overkill when I'm not sure how widely it will be needed, and our needs for the DB provider can be taken care of by a straightforward include. One downside of this approach is that it presumes knowledge of Provider::Source's internals (i.e. that it uses Dry::Configurable), but given the close relationship between Hanami and dry-rb, I think we can manage this.

[timriley]

@flash-gordon I've expanded the tests to make sure nothing surprising happens with the multiple prepended #initialize methods. See the last commit above. It all looks good to me, things work as they should.

Given this, are you happy to see this be merged? Thanks again for checking!