rubocop-style-compact_nesting

A RuboCop plugin that enforces a hybrid module/class nesting style:

• All namespace segments are collapsed onto a single module line using ::.
• When the innermost definition in a wrapper chain is a class, that class is nested separately inside the compact module wrapper.
• When the chain is entirely modules, every segment is collapsed into a single compact module A::B::C wrapping the body directly.

Canonical form

module A::B::C
  class D
    # ...
  end
end

Examples

# bad
module A
  module B
    class C
      # ...
    end
  end
end

# good
module A::B
  class C
    # ...
  end
end

# bad
class A::B::C
  # ...
end

# good
module A::B
  class C
    # ...
  end
end

# good (no namespace)
class Foo
  # ...
end

# bad
module A
  module B
    module C
    end
  end
end

# good (module-only chain collapses to one compact module)
module A::B::C
end

Installation

# Gemfile
gem 'rubocop-style-compact_nesting', require: false

# .rubocop.yml
plugins:
  - rubocop-style-compact_nesting

The plugin disables Style/ClassAndModuleChildren by default because that cop enforces the opposite layout. If you want it back, re-enable it in your own config:

Style/ClassAndModuleChildren:
  Enabled: true

Requires RuboCop >= 1.72 and Ruby >= 3.1.

Rules

Style/CompactModuleNesting

• Detects chains of wrapper modules whose body is a single nested module/class ending in a class, and rewrites them to one compact outer module A::B::C with a separately nested innermost class D.
• Rewrites class A::B::C to module A::B; class C; end; end.
• Collapses pure module-only chains into a single compact module A::B::C wrapping the body directly.
• Flags (without autocorrect) files that define more than one top-level module/class.
• Ignores bare top-level classes/modules with no namespace.
• Ignores wrapper modules whose body contains anything besides a single nested definition (e.g. constants, methods, or sibling classes).

License

MIT