MONGOID-5422 - Configuration DSL should not require an argument to its block (Rails parity)

[johnnyshields]

This PR removes the need for |config| arg in Mongoid.configure. It makes it more terse and consistent with Rails.application.configure. The change is fully backwards compatible.

This syntax is now possible:

  Mongoid.configure do
    # can call methods by themselves:
    connect_to("mongoid_test")

    # `config` is defined internally, so this also works here:
    config.connect_to("mongoid_test")

    # must use `config.variable =` when assigning variables
    config.preload_models = true

Previous syntax (still supported):

  Mongoid.configure do |config|
    config.connect_to("mongoid_test")
    config.preload_models = true

To do this magic, like Rails, it uses instance_exec. For variable assignment, in the block, you need to use self.variable = "foo" (otherwise its a local variable.) To get around this, we introduce a method config that returns self, which is also what Rails does:

Rails.application.configure do
  config.cache_classes = true

Note this only affects assigning with =, so other methods work fine (such as connect_to in example above. (I now fully grok why Puma's config DSL uses only methods and not variable assignment.) Most IDEs will warn about local variable assignment in the block.

[p-mongo]

If you can adjust the tests to correctly restore config options everything else looks good.

[johnnyshields]

Done > using config_override now

[p-mongo]

The release notes addition will conflict with #5396.

[Neilshweky]

This is awesome! My one question is that it looks like config is now delegating to self. That means you could probably do something like:

Mongoid.configure do
  self.preload_models = true
end

Or even:

Mongoid.configure do
  preload_models = true
end

Two questions:

1. Is that true?
2. Does rails behave that way as well?

[johnnyshields]

@Neilshweky the behavior here is the same as Rails:

Mongoid.configure do
  self.preload_models = true # can do this
  config.preload_models = true # can also do this, because there is now a magic `config` method which returns self

  preload_models = true # cannot do this, because its a local variable assignment  
end

[johnnyshields]

@p-mongo release note conflict resolved; ready to merge.

[p-mongo]

Please do not add version numbers to release notes like this, it makes backporting changes more difficult and the release notes already specify the version they are for.

[johnnyshields]

Thanks @p-mongo for getting this one to the finish line!