Add option for class_attribute default (#29270)

* Allow a default value to be declared for class_attribute

* Convert to using class_attribute default rather than explicit setter

* Removed instance_accessor option by mistake

* False is a valid default value

* Documentation

9 files changed, 11 insertions, 22 deletions

diff --git a/actionpack/lib/abstract_controller/caching.rb b/actionpack/lib/abstract_controller/caching.rb
index 26e3f08bc1..30e3d4426c 100644
--- a/actionpack/lib/abstract_controller/caching.rb
+++ b/actionpack/lib/abstract_controller/caching.rb
@@ -37,8 +37,7 @@ module AbstractController
       config_accessor :enable_fragment_cache_logging
       self.enable_fragment_cache_logging = false
 
-      class_attribute :_view_cache_dependencies
-      self._view_cache_dependencies = []
+      class_attribute :_view_cache_dependencies, default: []
       helper_method :view_cache_dependencies if respond_to?(:helper_method)
     end
 
diff --git a/actionpack/lib/abstract_controller/helpers.rb b/actionpack/lib/abstract_controller/helpers.rb
index ef3be7af83..2e50637c39 100644
--- a/actionpack/lib/abstract_controller/helpers.rb
+++ b/actionpack/lib/abstract_controller/helpers.rb
@@ -5,11 +5,8 @@ module AbstractController
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_helpers
-      self._helpers = Module.new
-
-      class_attribute :_helper_methods
-      self._helper_methods = Array.new
+      class_attribute :_helpers, default: Module.new
+      class_attribute :_helper_methods, default: Array.new
     end
 
     class MissingHelperError < LoadError
diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index 246644dcbd..96c708f45a 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -208,8 +208,7 @@ module ActionController
       @_request.reset_session
     end
 
-    class_attribute :middleware_stack
-    self.middleware_stack = ActionController::MiddlewareStack.new
+    class_attribute :middleware_stack, default: ActionController::MiddlewareStack.new
 
     def self.inherited(base) # :nodoc:
       base.middleware_stack = middleware_stack.dup
diff --git a/actionpack/lib/action_controller/metal/conditional_get.rb b/actionpack/lib/action_controller/metal/conditional_get.rb
index eb636fa3f6..0525252c7c 100644
--- a/actionpack/lib/action_controller/metal/conditional_get.rb
+++ b/actionpack/lib/action_controller/metal/conditional_get.rb
@@ -7,8 +7,7 @@ module ActionController
     include Head
 
     included do
-      class_attribute :etaggers
-      self.etaggers = []
+      class_attribute :etaggers, default: []
     end
 
     module ClassMethods
diff --git a/actionpack/lib/action_controller/metal/etag_with_template_digest.rb b/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
index 798564db96..69c3979a0e 100644
--- a/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
+++ b/actionpack/lib/action_controller/metal/etag_with_template_digest.rb
@@ -22,8 +22,7 @@ module ActionController
     include ActionController::ConditionalGet
 
     included do
-      class_attribute :etag_with_template_digest
-      self.etag_with_template_digest = true
+      class_attribute :etag_with_template_digest, default: true
 
       ActiveSupport.on_load :action_view, yield: true do
         etag do |options|
diff --git a/actionpack/lib/action_controller/metal/flash.rb b/actionpack/lib/action_controller/metal/flash.rb
index 347fbf0e74..24d1097ebe 100644
--- a/actionpack/lib/action_controller/metal/flash.rb
+++ b/actionpack/lib/action_controller/metal/flash.rb
@@ -3,8 +3,7 @@ module ActionController #:nodoc:
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_flash_types, instance_accessor: false
-      self._flash_types = []
+      class_attribute :_flash_types, instance_accessor: false, default: []
 
       delegate :flash, to: :request
       add_flash_types(:alert, :notice)
diff --git a/actionpack/lib/action_controller/metal/helpers.rb b/actionpack/lib/action_controller/metal/helpers.rb
index 476d081239..913a4b9a04 100644
--- a/actionpack/lib/action_controller/metal/helpers.rb
+++ b/actionpack/lib/action_controller/metal/helpers.rb
@@ -53,9 +53,8 @@ module ActionController
     include AbstractController::Helpers
 
     included do
-      class_attribute :helpers_path, :include_all_helpers
-      self.helpers_path ||= []
-      self.include_all_helpers = true
+      class_attribute :helpers_path, default: []
+      class_attribute :include_all_helpers, default: true
     end
 
     module ClassMethods
diff --git a/actionpack/lib/action_controller/metal/params_wrapper.rb b/actionpack/lib/action_controller/metal/params_wrapper.rb
index a89fc1678b..68881b8402 100644
--- a/actionpack/lib/action_controller/metal/params_wrapper.rb
+++ b/actionpack/lib/action_controller/metal/params_wrapper.rb
@@ -159,8 +159,7 @@ module ActionController
     end
 
     included do
-      class_attribute :_wrapper_options
-      self._wrapper_options = Options.from_hash(format: [])
+      class_attribute :_wrapper_options, default: Options.from_hash(format: [])
     end
 
     module ClassMethods
diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index 733aca195d..23c21b0501 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -26,8 +26,7 @@ module ActionController
     RENDERERS = Set.new
 
     included do
-      class_attribute :_renderers
-      self._renderers = Set.new.freeze
+      class_attribute :_renderers, default: Set.new.freeze
     end
 
     # Used in <tt>ActionController::Base</tt>