False positive in Naming/ClassAndModuleCamelCase when using module_parent

[pdobb]

Naming/ClassAndModuleCamelCase: Use CamelCase for classes and modules. (https://rubystyle.guide#camelcase-classes)

Now that Zeitwerk is out, I prefer defining classes in a single line -- namespace and all.

# OLD (Bad)
namespace MyModule
  class MyPrimaryClass
  end
end

# NEW (Good)
class MyModule::MyPrimaryClass
end

Sometimes, however, I want to be able to define a minor, sibling class on the current namespace without creating a new file.

# Old Way (Bad -- non-collapsed namespace/class)
namespace MyModule
  # Defines: MyModule::MyPrimaryClass (Good)
  class MyPrimaryClass
  end
 
  # Defines: MyModule::MySiblingClass (Good)
  class MySiblingClass
  end
end

# New Way (Good -- collapsed namespace/class)
class MyModule::MyPrimaryClass
  # Bad
  # - Don't want this, because it defines a sub-class, not a sibling class: 
  #   MyModule::MyPrimaryClass::MySiblingClass
  class MySiblingClass
  end

  # Good
  # - Defines the intended sibling class: MyModule::MySiblingClass
  class module_parent::MySiblingClass
  end
end

---

Expected behavior

The Naming/ClassAndModuleCamelCase cop should allow module_parent::MySiblingClass since this is valid syntax that produces the wanted result and since module_parent is a class method and is not (nor is intended to be) a constant name.

Perhaps the cop can allow a few keywords that aren't camel-cased as part of a class name? Namely module_parent. (I'm not sure if others would be relevant here.)

This fix, if accepted, might add the following to the documentation for this cop:

# good
class module_parent::MyClass
end

Actual behavior

Offense raised on this line class module_parent::MySiblingClass:

Naming/ClassAndModuleCamelCase: Use CamelCase for classes and modules. (https://rubystyle.guide#camelcase-classes)

Steps to reproduce the problem

1. Define:

# app/models/my_module/my_primary_class.rb
class MyModule::MyPrimaryClass
  class module_parent::MySiblingClass
  end
end

2. Run: rubocop app/models/my_module/my_primary_class.rb

RuboCop version

$ [bundle exec] rubocop -V
0.84.0 (using Parser 2.7.1.2, rubocop-ast 0.0.3, running on ruby 2.6.6 x86_64-darwin19)