Give GeneratedAttributeMethods module a name

[shioyama]

Summary

Currently, inspecting the ancestors of an AR class gives you something like this:

=> [User (call 'User.connection' to establish a connection),
 User::GeneratedAssociationMethods,
 #<ActiveRecord::AttributeMethods::GeneratedAttributeMethods:0x000055ace0f05b08>,
 ApplicationRecord(abstract),
 ApplicationRecord::GeneratedAssociationMethods,
 #<ActiveRecord::AttributeMethods::GeneratedAttributeMethods:0x000055ace093c460>,
 ActiveRecord::Base,
 [...]

The second and fifth objects that appear in this list (after the model class itself) are instances of the ActiveRecord::AttributeMethods::GeneratedAttributeMethods module builder, included into every AR class to hold the class' attribute methods. These are extremely important modules for AR classes, probably the most important type of module in their ancestors, and they appear very prominently at the top of this list. But in their current form, most Rails developers probably have no idea what they are actually doing or why they are even there.

This is not helped by the fact that the generated association methods module is given its own name under the model namespace, in the case above, User::GeneratedAssociationMethods.

This PR brings some consistency and clarity to this situation by creating a constant under the model namespace to capture these generated attribute methods, so that the ancestor list above becomes:

=> [User (call 'User.connection' to establish a connection),
 User::GeneratedAssociationMethods,
 User::GeneratedAttributeMethods,
 ApplicationRecord(abstract),
 ApplicationRecord::GeneratedAssociationMethods,
 ApplicationRecord::GeneratedAttributeMethods,
 ActiveRecord::Base,
 [...]

Now, rather than an instance of a module builder class, the AR model gets a (private) named module User::GeneratedAttributeMethods, which is much more readable and approachable than before, and which follows the same pattern as User::GeneratedAssociationMethods. Also, since this applies to all AR models, the parent class' attribute methods also appear in this form as ApplicationRecord::GeneratedAttributeMethods, and we eliminate all anonymous instances in model ancestors.

Other Information

In addition to the change above, I have also renamed the previously-named ActiveRecord::AttributeMethods::GeneratedAttributeMethods to ActiveRecord::AttributeMethods::GeneratedAttributeMethodsBuilder, to emphasize that this is not a module but a module builder (class). Currently this is a point of inconsistency between generated association methods and generated attribute methods, which surely causes additional confusion to developers trying to understand how these modules work internally.

[shioyama]

I can add a changelog to this, just let me know.

[shioyama]

Related: #30836.

[shioyama]

@matthewd Pinging you because you've reviewed my PRs in the past, hope that's appropriate. This is a very small change, mostly cosmetic but I think, like #30836, important for code readability reasons.

Could you take a quick look? I'm actually planning to reference this in my RailsConf talk so would be great to get feedback! 😅

[shioyama]

@rafaelfranca Thanks for the quick merge!!!