Deprecate ActiveSupport::Configurable

This proposal is based on a [code review comment][]:

> I think we should deprecate and remove this module. It is only used
> once inside the framework, in a place that perhaps don't even need it
> anymore and I don't think it adds much for our users. They would be
> better served with their own config object that is just a hash.

To achieve this outcome, replace the only internal occurrence of
`ActiveSupport::Configurable` with a [class_attribute][]. Similarly,
replace [config_accessor][] calls with class- and instance-level calls
to [delegate][] for the readers and writers.

[code review comment]: rails#53796 (comment)
[class_attribute]: https://edgeapi.rubyonrails.org/classes/Class.html#method-i-class_attribute
[config_accessor]: https://edgeapi.rubyonrails.org/classes/ActiveSupport/Configurable/ClassMethods.html#method-i-config_accessor
[delegate]: https://edgeapi.rubyonrails.org/classes/Module.html#method-i-delegate

Author: seanpdoyle

actionmailer/lib/action_mailer/railtie.rb

@@ -73,12 +73,6 @@ class Railtie < Rails::Railtie # :nodoc:
       app.config.paths["test/mailers/previews"].concat(options.preview_paths)
     end
 
-    initializer "action_mailer.compile_config_methods" do
-      ActiveSupport.on_load(:action_mailer) do
-        config.compile_methods! if config.respond_to?(:compile_methods!)
-      end
-    end
-
     config.after_initialize do |app|
       options = app.config.action_mailer
 

actionpack/lib/abstract_controller/asset_paths.rb

@@ -7,8 +7,10 @@ module AssetPaths # :nodoc:
     extend ActiveSupport::Concern
 
     included do
-      config_accessor :asset_host, :assets_dir, :javascripts_dir,
-        :stylesheets_dir, :default_asset_host_protocol, :relative_url_root
+      singleton_class.delegate :asset_host, :asset_host=, :assets_dir, :assets_dir=, :javascripts_dir, :javascripts_dir=,
+        :stylesheets_dir, :stylesheets_dir=, :default_asset_host_protocol, :default_asset_host_protocol=, :relative_url_root, :relative_url_root=, to: :config
+      delegate :asset_host, :asset_host=, :assets_dir, :assets_dir=, :javascripts_dir, :javascripts_dir=,
+        :stylesheets_dir, :stylesheets_dir=, :default_asset_host_protocol, :default_asset_host_protocol=, :relative_url_root, :relative_url_root=, to: :config
     end
   end
 end

actionpack/lib/abstract_controller/base.rb

@@ -3,7 +3,6 @@
 # :markup: markdown
 
 require "abstract_controller/error"
-require "active_support/configurable"
 require "active_support/descendants_tracker"
 require "active_support/core_ext/module/anonymous"
 require "active_support/core_ext/module/attr_internal"
@@ -47,7 +46,7 @@ class Base
     # Returns the formats that can be processed by the controller.
     attr_internal :formats
 
-    include ActiveSupport::Configurable
+    class_attribute :config, instance_predicate: false, default: ActiveSupport::OrderedOptions.new
     extend ActiveSupport::DescendantsTracker
 
     class << self
@@ -65,6 +64,7 @@ def inherited(klass) # :nodoc:
         unless klass.instance_variable_defined?(:@abstract)
           klass.instance_variable_set(:@abstract, false)
         end
+        klass.config = ActiveSupport::InheritableOptions.new(config)
         super
       end
 
@@ -128,6 +128,10 @@ def controller_path
         @controller_path ||= name.delete_suffix("Controller").underscore unless anonymous?
       end
 
+      def configure # :nodoc:
+        yield config
+      end
+
       # Refresh the cached action_methods when a new action_method is added.
       def method_added(name)
         super
@@ -201,6 +205,10 @@ def self.supports_path?
       true
     end
 
+    def config # :nodoc:
+      @_config ||= self.class.config.inheritable_copy
+    end
+
     def inspect # :nodoc:
       "#<#{self.class.name}:#{'%#016x' % (object_id << 1)}>"
     end

actionpack/lib/abstract_controller/caching.rb

@@ -32,13 +32,16 @@ def cache_configured?
     included do
       extend ConfigMethods
 
-      config_accessor :default_static_extension
+      singleton_class.delegate :default_static_extension, :default_static_extension=, to: :config
+      delegate :default_static_extension, :default_static_extension=, to: :config
       self.default_static_extension ||= ".html"
 
-      config_accessor :perform_caching
+      singleton_class.delegate :perform_caching, :perform_caching=, to: :config
+      delegate :perform_caching, :perform_caching=, to: :config
       self.perform_caching = true if perform_caching.nil?
 
-      config_accessor :enable_fragment_cache_logging
+      singleton_class.delegate :enable_fragment_cache_logging, :enable_fragment_cache_logging=, to: :config
+      delegate :enable_fragment_cache_logging, :enable_fragment_cache_logging=, to: :config
       self.enable_fragment_cache_logging = false
 
       class_attribute :_view_cache_dependencies, default: []

actionpack/lib/abstract_controller/logger.rb

@@ -9,7 +9,8 @@ module Logger # :nodoc:
     extend ActiveSupport::Concern
 
     included do
-      config_accessor :logger
+      singleton_class.delegate :logger, :logger=, to: :config
+      delegate :logger, :logger=, to: :config
       include ActiveSupport::Benchmarkable
     end
   end

actionpack/lib/action_controller/metal/request_forgery_protection.rb

@@ -71,32 +71,39 @@ module RequestForgeryProtection
     included do
       # Sets the token parameter name for RequestForgery. Calling
       # `protect_from_forgery` sets it to `:authenticity_token` by default.
-      config_accessor :request_forgery_protection_token
+      singleton_class.delegate :request_forgery_protection_token, :request_forgery_protection_token=, to: :config
+      delegate :request_forgery_protection_token, :request_forgery_protection_token=, to: :config
       self.request_forgery_protection_token ||= :authenticity_token
 
       # Holds the class which implements the request forgery protection.
-      config_accessor :forgery_protection_strategy
+      singleton_class.delegate :forgery_protection_strategy, :forgery_protection_strategy=, to: :config
+      delegate :forgery_protection_strategy, :forgery_protection_strategy=, to: :config
       self.forgery_protection_strategy = nil
 
       # Controls whether request forgery protection is turned on or not. Turned off by
       # default only in test mode.
-      config_accessor :allow_forgery_protection
+      singleton_class.delegate :allow_forgery_protection, :allow_forgery_protection=, to: :config
+      delegate :allow_forgery_protection, :allow_forgery_protection=, to: :config
       self.allow_forgery_protection = true if allow_forgery_protection.nil?
 
       # Controls whether a CSRF failure logs a warning. On by default.
-      config_accessor :log_warning_on_csrf_failure
+      singleton_class.delegate :log_warning_on_csrf_failure, :log_warning_on_csrf_failure=, to: :config
+      delegate :log_warning_on_csrf_failure, :log_warning_on_csrf_failure=, to: :config
       self.log_warning_on_csrf_failure = true
 
       # Controls whether the Origin header is checked in addition to the CSRF token.
-      config_accessor :forgery_protection_origin_check
+      singleton_class.delegate :forgery_protection_origin_check, :forgery_protection_origin_check=, to: :config
+      delegate :forgery_protection_origin_check, :forgery_protection_origin_check=, to: :config
       self.forgery_protection_origin_check = false
 
       # Controls whether form-action/method specific CSRF tokens are used.
-      config_accessor :per_form_csrf_tokens
+      singleton_class.delegate :per_form_csrf_tokens, :per_form_csrf_tokens=, to: :config
+      delegate :per_form_csrf_tokens, :per_form_csrf_tokens=, to: :config
       self.per_form_csrf_tokens = false
 
       # The strategy to use for storing and retrieving CSRF tokens.
-      config_accessor :csrf_token_storage_strategy
+      singleton_class.delegate :csrf_token_storage_strategy, :csrf_token_storage_strategy=, to: :config
+      delegate :csrf_token_storage_strategy, :csrf_token_storage_strategy=, to: :config
       self.csrf_token_storage_strategy = SessionStore.new
 
       helper_method :form_authenticity_token

actionpack/lib/action_controller/railtie.rb

@@ -93,12 +93,6 @@ class Railtie < Rails::Railtie # :nodoc:
       end
     end
 
-    initializer "action_controller.compile_config_methods" do
-      ActiveSupport.on_load(:action_controller) do
-        config.compile_methods! if config.respond_to?(:compile_methods!)
-      end
-    end
-
     initializer "action_controller.request_forgery_protection" do |app|
       ActiveSupport.on_load(:action_controller_base) do
         if app.config.action_controller.default_protect_from_forgery

activesupport/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Deprecate `ActiveSupport::Configurable`
+
+    *Sean Doyle*
+
 *   `nil.to_query("key")` now returns `key`.
 
     Previously it would return `key=`, preventing round tripping with `Rack::Utils.parse_nested_query`.

activesupport/lib/active_support.rb

@@ -91,6 +91,10 @@ module ActiveSupport
   autoload :SafeBuffer, "active_support/core_ext/string/output_safety"
   autoload :TestCase
 
+  include Deprecation::DeprecatedConstantAccessor
+
+  deprecate_constant :Configurable, "class_attribute :config, default: {}", deprecator: ActiveSupport.deprecator
+
   def self.eager_load!
     super