Added RuboCop cops to enforce code reuse rules

These Cops enforces the code reuse rules as defined in merge request
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21254.

1 files changed, 156 insertions, 0 deletions

diff --git a/rubocop/code_reuse_helpers.rb b/rubocop/code_reuse_helpers.rb
new file mode 100644
index 00000000000..0929a55d901
--- /dev/null
+++ b/rubocop/code_reuse_helpers.rb
@@ -0,0 +1,156 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module CodeReuseHelpers
+    # Returns true for a `(send const ...)` node.
+    def send_to_constant?(node)
+      node.type == :send && node.children&.first&.type == :const
+    end
+
+    # Returns `true` if the name of the receiving constant ends with a given
+    # `String`.
+    def send_receiver_name_ends_with?(node, suffix)
+      return false unless send_to_constant?(node)
+
+      receiver_name = name_of_receiver(node)
+
+      receiver_name != suffix &&
+        receiver_name.end_with?(suffix)
+    end
+
+    # Returns the file path (as a `String`) for an AST node.
+    def file_path_for_node(node)
+      node.location.expression.source_buffer.name
+    end
+
+    # Returns the name of a constant node.
+    #
+    # Given the AST node `(const nil :Foo)`, this method will return `:Foo`.
+    def name_of_constant(node)
+      node.children[1]
+    end
+
+    # Returns true if the given node resides in app/finders or ee/app/finders.
+    def in_finder?(node)
+      in_directory?(node, 'finders')
+    end
+
+    # Returns true if the given node resides in app/models or ee/app/models.
+    def in_model?(node)
+      in_directory?(node, 'models')
+    end
+
+    # Returns true if the given node resides in app/services or ee/app/services.
+    def in_service_class?(node)
+      in_directory?(node, 'services')
+    end
+
+    # Returns true if the given node resides in app/presenters or
+    # ee/app/presenters.
+    def in_presenter?(node)
+      in_directory?(node, 'presenters')
+    end
+
+    # Returns true if the given node resides in app/serializers or
+    # ee/app/serializers.
+    def in_serializer?(node)
+      in_directory?(node, 'serializers')
+    end
+
+    # Returns true if the given node resides in app/workers or ee/app/workers.
+    def in_worker?(node)
+      in_directory?(node, 'workers')
+    end
+
+    # Returns true if the given node resides in app/controllers or
+    # ee/app/controllers.
+    def in_controller?(node)
+      in_directory?(node, 'controllers')
+    end
+
+    # Returns true if the given node resides in lib/api or ee/lib/api.
+    def in_api?(node)
+      file_path_for_node(node).start_with?(
+        File.join(ce_lib_directory, 'api'),
+        File.join(ee_lib_directory, 'api')
+      )
+    end
+
+    # Returns `true` if the given AST node resides in the given directory,
+    # relative to app and/or ee/app.
+    def in_directory?(node, directory)
+      file_path_for_node(node).start_with?(
+        File.join(ce_app_directory, directory),
+        File.join(ee_app_directory, directory)
+      )
+    end
+
+    # Returns the receiver name of a send node.
+    #
+    # For the AST node `(send (const nil :Foo) ...)` this would return
+    # `'Foo'`.
+    def name_of_receiver(node)
+      name_of_constant(node.children.first).to_s
+    end
+
+    # Yields every defined class method in the given AST node.
+    def each_class_method(node)
+      return to_enum(__method__, node) unless block_given?
+
+      # class << self
+      #   def foo
+      #   end
+      # end
+      node.each_descendant(:sclass) do |sclass|
+        sclass.each_descendant(:def) do |def_node|
+          yield def_node
+        end
+      end
+
+      # def self.foo
+      # end
+      node.each_descendant(:defs) do |defs_node|
+        yield defs_node
+      end
+    end
+
+    # Yields every send node found in the given AST node.
+    def each_send_node(node, &block)
+      node.each_descendant(:send, &block)
+    end
+
+    # Registers a RuboCop offense for a `(send)` node with a receiver that ends
+    # with a given suffix.
+    #
+    # node - The AST node to check.
+    # suffix - The suffix of the receiver name, such as "Finder".
+    # message - The message to use for the offense.
+    def disallow_send_to(node, suffix, message)
+      each_send_node(node) do |send_node|
+        next unless send_receiver_name_ends_with?(send_node, suffix)
+
+        add_offense(send_node, location: :expression, message: message)
+      end
+    end
+
+    def ce_app_directory
+      File.join(rails_root, 'app')
+    end
+
+    def ee_app_directory
+      File.join(rails_root, 'ee', 'app')
+    end
+
+    def ce_lib_directory
+      File.join(rails_root, 'lib')
+    end
+
+    def ee_lib_directory
+      File.join(rails_root, 'ee', 'lib')
+    end
+
+    def rails_root
+      File.expand_path('..', __dir__)
+    end
+  end
+end