Add new Style/ClassMethodsDefinitions cop

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#8451](https://github.com/rubocop-hq/rubocop/issues/8451): Add new `Style/RedundantSelfAssignment` cop. ([@fatkodima][])
 * [#8562](https://github.com/rubocop-hq/rubocop/pull/8562): Add new `Style/KeywordParametersOrder` cop. ([@fatkodima][])
+* [#8381](https://github.com/rubocop-hq/rubocop/pull/8381): Add new `Style/ClassMethodsDefinitions` cop. ([@fatkodima][])
 * [#8474](https://github.com/rubocop-hq/rubocop/pull/8474): Add new `Lint/DuplicateRequire` cop. ([@fatkodima][])
 * [#8472](https://github.com/rubocop-hq/rubocop/issues/8472): Add new `Lint/UselessMethodDefinition` cop. ([@fatkodima][])
 * [#8531](https://github.com/rubocop-hq/rubocop/issues/8531): Add new `Lint/EmptyFile` cop. ([@fatkodima][])

config/default.yml

@@ -2671,6 +2671,16 @@ Style/ClassMethods:
   VersionAdded: '0.9'
   VersionChanged: '0.20'
 
+Style/ClassMethodsDefinitions:
+  Description: 'Enforces using `def self.method_name` or `class << self` to define class methods.'
+  StyleGuide: '#def-self-class-methods'
+  Enabled: false
+  VersionAdded: '0.89'
+  EnforcedStyle:  def_self
+  SupportedStyles:
+    - def_self
+    - self_class
+
 Style/ClassVars:
   Description: 'Avoid the use of class variables.'
   StyleGuide: '#no-class-vars'

docs/modules/ROOT/pages/cops.adoc

@@ -345,6 +345,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#styleclassandmodulechildren[Style/ClassAndModuleChildren]
 * xref:cops_style.adoc#styleclasscheck[Style/ClassCheck]
 * xref:cops_style.adoc#styleclassmethods[Style/ClassMethods]
+* xref:cops_style.adoc#styleclassmethodsdefinitions[Style/ClassMethodsDefinitions]
 * xref:cops_style.adoc#styleclassvars[Style/ClassVars]
 * xref:cops_style.adoc#stylecollectionmethods[Style/CollectionMethods]
 * xref:cops_style.adoc#stylecolonmethodcall[Style/ColonMethodCall]

docs/modules/ROOT/pages/cops_style.adoc

@@ -1087,6 +1087,97 @@ end
 
 * https://rubystyle.guide#def-self-class-methods
 
+== Style/ClassMethodsDefinitions
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Disabled
+| Yes
+| Yes
+| 0.89
+| -
+|===
+
+This cop enforces using `def self.method_name` or `class << self` to define class methods.
+
+=== Examples
+
+==== EnforcedStyle: def_self (default)
+
+[source,ruby]
+----
+# bad
+class SomeClass
+  class << self
+    attr_accessor :class_accessor
+
+    def class_method
+      # ...
+    end
+  end
+end
+
+# good
+class SomeClass
+  def self.class_method
+    # ...
+  end
+
+  class << self
+    attr_accessor :class_accessor
+  end
+end
+
+# good - contains private method
+class SomeClass
+  class << self
+    attr_accessor :class_accessor
+
+    private
+
+    def private_class_method
+      # ...
+    end
+  end
+end
+----
+
+==== EnforcedStyle: self_class
+
+[source,ruby]
+----
+# bad
+class SomeClass
+  def self.class_method
+    # ...
+  end
+end
+
+# good
+class SomeClass
+  class << self
+    def class_method
+      # ...
+    end
+  end
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| EnforcedStyle
+| `def_self`
+| `def_self`, `self_class`
+|===
+
+=== References
+
+* https://rubystyle.guide#def-self-class-methods
+
 == Style/ClassVars
 
 |===

lib/rubocop.rb

@@ -116,6 +116,7 @@
 require_relative 'rubocop/cop/mixin/uncommunicative_name'
 require_relative 'rubocop/cop/mixin/unused_argument'
 require_relative 'rubocop/cop/mixin/visibility_help'
+require_relative 'rubocop/cop/mixin/comments_help' # relies on visibility_help
 
 require_relative 'rubocop/cop/utils/format_string'
 
@@ -389,6 +390,7 @@
 require_relative 'rubocop/cop/style/class_and_module_children'
 require_relative 'rubocop/cop/style/class_check'
 require_relative 'rubocop/cop/style/class_methods'
+require_relative 'rubocop/cop/style/class_methods_definitions'
 require_relative 'rubocop/cop/style/class_vars'
 require_relative 'rubocop/cop/style/collection_methods'
 require_relative 'rubocop/cop/style/colon_method_call'

lib/rubocop/cop/layout/class_structure.rb

@@ -134,6 +134,7 @@ module Layout
       #
       # @see https://rubystyle.guide#consistent-classes
       class ClassStructure < Cop
+        include CommentsHelp
         include VisibilityHelp
 
         HUMANIZED_NODE_TYPE = {

lib/rubocop/cop/mixin/comments_help.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Help methods for working with nodes containing comments.
+    module CommentsHelp
+      include VisibilityHelp
+
+      def source_range_with_comment(node)
+        begin_pos, end_pos =
+          if node.def_type?
+            start_node = find_visibility_start(node) || node
+            end_node = find_visibility_end(node) || node
+            [begin_pos_with_comment(start_node),
+             end_position_for(end_node) + 1]
+          else
+            [begin_pos_with_comment(node), end_position_for(node)]
+          end
+
+        Parser::Source::Range.new(buffer, begin_pos, end_pos)
+      end
+
+      private
+
+      def end_position_for(node)
+        end_line = buffer.line_for_position(node.loc.expression.end_pos)
+        buffer.line_range(end_line).end_pos
+      end
+
+      def begin_pos_with_comment(node)
+        annotation_line = node.first_line - 1
+        first_comment = nil
+
+        processed_source.comments_before_line(annotation_line)
+                        .reverse_each do |comment|
+          if comment.location.line == annotation_line
+            first_comment = comment
+            annotation_line -= 1
+          end
+        end
+
+        start_line_position(first_comment || node)
+      end
+
+      def start_line_position(node)
+        buffer.line_range(node.loc.line).begin_pos - 1
+      end
+
+      def buffer
+        processed_source.buffer
+      end
+    end
+  end
+end

lib/rubocop/cop/style/class_methods_definitions.rb

@@ -0,0 +1,131 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop enforces using `def self.method_name` or `class << self` to define class methods.
+      #
+      # @example EnforcedStyle: def_self (default)
+      #   # bad
+      #   class SomeClass
+      #     class << self
+      #       attr_accessor :class_accessor
+      #
+      #       def class_method
+      #         # ...
+      #       end
+      #     end
+      #   end
+      #
+      #   # good
+      #   class SomeClass
+      #     def self.class_method
+      #       # ...
+      #     end
+      #
+      #     class << self
+      #       attr_accessor :class_accessor
+      #     end
+      #   end
+      #
+      #   # good - contains private method
+      #   class SomeClass
+      #     class << self
+      #       attr_accessor :class_accessor
+      #
+      #       private
+      #
+      #       def private_class_method
+      #         # ...
+      #       end
+      #     end
+      #   end
+      #
+      # @example EnforcedStyle: self_class
+      #   # bad
+      #   class SomeClass
+      #     def self.class_method
+      #       # ...
+      #     end
+      #   end
+      #
+      #   # good
+      #   class SomeClass
+      #     class << self
+      #       def class_method
+      #         # ...
+      #       end
+      #     end
+      #   end
+      #
+      class ClassMethodsDefinitions < Base
+        include ConfigurableEnforcedStyle
+        include CommentsHelp
+        include VisibilityHelp
+        extend AutoCorrector
+
+        MSG = 'Use `%<preferred>s` to define class method.'
+
+        def on_sclass(node)
+          return unless def_self_style?
+          return unless node.identifier.source == 'self'
+          return if contains_non_public_methods?(node)
+
+          def_nodes(node).each do |def_node|
+            next unless node_visibility(def_node) == :public
+
+            message = format(MSG, preferred: "def self.#{def_node.method_name}")
+            add_offense(def_node, message: message) do |corrector|
+              extract_def_from_sclass(def_node, node, corrector)
+            end
+          end
+        end
+
+        def on_defs(node)
+          return if def_self_style?
+
+          message = format(MSG, preferred: 'class << self')
+          add_offense(node, message: message)
+        end
+
+        private
+
+        def def_self_style?
+          style == :def_self
+        end
+
+        def contains_non_public_methods?(sclass_node)
+          def_nodes(sclass_node).any? { |def_node| node_visibility(def_node) != :public }
+        end
+
+        def def_nodes(sclass_node)
+          sclass_def = sclass_node.body
+          return [] unless sclass_def
+
+          if sclass_def.def_type?
+            [sclass_def]
+          elsif sclass_def.begin_type?
+            sclass_def.each_child_node(:def).to_a
+          else
+            []
+          end
+        end
+
+        def extract_def_from_sclass(def_node, sclass_node, corrector)
+          range = source_range_with_comment(def_node)
+          source = range.source.sub!(
+            "def #{def_node.method_name}",
+            "def self.#{def_node.method_name}"
+          )
+
+          corrector.insert_before(sclass_node, "#{source}\n#{indent(sclass_node)}")
+          corrector.remove(range)
+        end
+
+        def indent(node)
+          ' ' * node.loc.column
+        end
+      end
+    end
+  end
+end