Support configuration on ActiveRecord::Model.

The problem: We need to be able to specify configuration in a way that
can be inherited to models that include ActiveRecord::Model. So it is
no longer sufficient to put 'top level' config on ActiveRecord::Base,
but we do want configuration specified on ActiveRecord::Base and
descendants to continue to work.

So we need something like class_attribute that can be defined on a
module but that is inherited when ActiveRecord::Model is included.

The solution: added ActiveModel::Configuration module which provides a
config_attribute macro. It's a bit specific hence I am not putting this
in Active Support or making it a 'public API' at present.

7 files changed, 308 insertions, 14 deletions

diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index d0e2a6f39c..9fc308375f 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -32,6 +32,7 @@ module ActiveModel
   autoload :AttributeMethods
   autoload :BlockValidator, 'active_model/validator'
   autoload :Callbacks
+  autoload :Configuration
   autoload :Conversion
   autoload :Dirty
   autoload :EachValidator, 'active_model/validator'
diff --git a/activemodel/lib/active_model/attribute_methods.rb b/activemodel/lib/active_model/attribute_methods.rb
index d7ec7e6ca5..71ab1501c8 100644
--- a/activemodel/lib/active_model/attribute_methods.rb
+++ b/activemodel/lib/active_model/attribute_methods.rb
@@ -61,7 +61,8 @@ module ActiveModel
     CALL_COMPILABLE_REGEXP = /\A[a-zA-Z_]\w*[!?]?\z/
 
     included do
-      class_attribute :attribute_method_matchers, :instance_writer => false
+      extend ActiveModel::Configuration
+      config_attribute :attribute_method_matchers
       self.attribute_method_matchers = [ClassMethods::AttributeMethodMatcher.new]
     end
 
diff --git a/activemodel/lib/active_model/configuration.rb b/activemodel/lib/active_model/configuration.rb
new file mode 100644
index 0000000000..1757c12ebf
--- /dev/null
+++ b/activemodel/lib/active_model/configuration.rb
@@ -0,0 +1,134 @@
+require 'active_support/concern'
+require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/class/attribute_accessors'
+
+module ActiveModel
+  # This API is for Rails' internal use and is not currently considered 'public', so
+  # it may change in the future without warning.
+  #
+  # It creates configuration attributes that can be inherited from a module down
+  # to a class that includes the module. E.g.
+  #
+  #   module MyModel
+  #     extend ActiveModel::Configuration
+  #     config_attribute :awesome
+  #     self.awesome = true
+  #   end
+  #
+  #   class Post
+  #     include MyModel
+  #   end
+  #
+  #   Post.awesome # => true
+  #
+  #   Post.awesome = false
+  #   Post.awesome    # => false
+  #   MyModel.awesome # => true
+  #
+  # We assume that the module will have a ClassMethods submodule containing methods
+  # to be transferred to the including class' singleton class.
+  #
+  # Config options can also be defined directly on a class:
+  #
+  #   class Post
+  #     extend ActiveModel::Configuration
+  #     config_attribute :awesome
+  #   end
+  #
+  # So this allows us to define a module that doesn't care about whether it is being
+  # included in a class or a module:
+  #
+  #   module Awesomeness
+  #     extend ActiveSupport::Concern
+  #
+  #     included do
+  #       extend ActiveModel::Configuration
+  #       config_attribute :awesome
+  #       self.awesome = true
+  #     end
+  #   end
+  #
+  #   class Post
+  #     include Awesomeness
+  #   end
+  #
+  #   module AwesomeModel
+  #     include Awesomeness
+  #   end
+  module Configuration #:nodoc:
+    def config_attribute(name, options = {})
+      klass = self.is_a?(Class) ? ClassAttribute : ModuleAttribute
+      klass.new(self, name, options).define
+    end
+
+    class Attribute
+      attr_reader :host, :name, :options
+
+      def initialize(host, name, options)
+        @host, @name, @options = host, name, options
+      end
+
+      def instance_writer?
+        options.fetch(:instance_writer, false)
+      end
+    end
+
+    class ClassAttribute < Attribute
+      def define
+        if options[:global]
+          host.cattr_accessor name, :instance_writer => instance_writer?
+        else
+          host.class_attribute name, :instance_writer => instance_writer?
+        end
+      end
+    end
+
+    class ModuleAttribute < Attribute
+      def class_methods
+        @class_methods ||= begin
+          if host.const_defined?(:ClassMethods, false)
+            host.const_get(:ClassMethods)
+          else
+            host.const_set(:ClassMethods, Module.new)
+          end
+        end
+      end
+
+      def define
+        host.singleton_class.class_eval <<-CODE, __FILE__, __LINE__
+          attr_accessor :#{name}
+          def #{name}?; !!#{name}; end
+        CODE
+
+        name, host = self.name, self.host
+
+        class_methods.class_eval do
+          define_method(name) { host.send(name) }
+          define_method("#{name}?") { !!send(name) }
+        end
+
+        host.class_eval <<-CODE
+          def #{name};  defined?(@#{name}) ? @#{name} : self.class.#{name}; end
+          def #{name}?; !!#{name}; end
+        CODE
+
+        if options[:global]
+          class_methods.class_eval do
+            define_method("#{name}=") { |val| host.send("#{name}=", val) }
+          end
+        else
+          class_methods.class_eval <<-CODE, __FILE__, __LINE__
+            def #{name}=(val)
+              singleton_class.class_eval do
+                remove_possible_method(:#{name})
+                define_method(:#{name}) { val }
+              end
+            end
+          CODE
+        end
+
+        host.send(:attr_writer, name) if instance_writer?
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/mass_assignment_security.rb b/activemodel/lib/active_model/mass_assignment_security.rb
index c895968f77..9b12d9d281 100644
--- a/activemodel/lib/active_model/mass_assignment_security.rb
+++ b/activemodel/lib/active_model/mass_assignment_security.rb
@@ -10,11 +10,13 @@ module ActiveModel
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_accessible_attributes
-      class_attribute :_protected_attributes
-      class_attribute :_active_authorizer
+      extend ActiveModel::Configuration
 
-      class_attribute :_mass_assignment_sanitizer
+      config_attribute :_accessible_attributes
+      config_attribute :_protected_attributes
+      config_attribute :_active_authorizer
+
+      config_attribute :_mass_assignment_sanitizer
       self.mass_assignment_sanitizer = :logger
     end
 
@@ -56,7 +58,7 @@ module ActiveModel
     # You can specify your own sanitizer object eg. MySanitizer.new.
     # See <tt>ActiveModel::MassAssignmentSecurity::LoggerSanitizer</tt> for example implementation.
     #
-    # 
+    #
     module ClassMethods
       # Attributes named in this macro are protected from mass-assignment
       # whenever attributes are sanitized before assignment. A role for the
@@ -70,13 +72,13 @@ module ActiveModel
       #
       #   class Customer
       #     include ActiveModel::MassAssignmentSecurity
-      #   
+      #
       #     attr_accessor :name, :email, :logins_count
-      #   
+      #
       #     attr_protected :logins_count
       #     # Suppose that admin can not change email for customer
-      #     attr_protected :logins_count, :email, :as => :admin 
-      #   
+      #     attr_protected :logins_count, :email, :as => :admin
+      #
       #     def assign_attributes(values, options = {})
       #       sanitize_for_mass_assignment(values, options[:as]).each do |k, v|
       #         send("#{k}=", v)
@@ -99,7 +101,7 @@ module ActiveModel
       #   customer.name          # => "David"
       #   customer.email # => nil
       #   customer.logins_count    # => nil
-      #   
+      #
       #   customer.email = "c@d.com"
       #   customer.email # => "c@d.com"
       #
diff --git a/activemodel/lib/active_model/serializers/json.rb b/activemodel/lib/active_model/serializers/json.rb
index c845440120..63ab8e7edc 100644
--- a/activemodel/lib/active_model/serializers/json.rb
+++ b/activemodel/lib/active_model/serializers/json.rb
@@ -10,8 +10,9 @@ module ActiveModel
 
       included do
         extend ActiveModel::Naming
+        extend ActiveModel::Configuration
 
-        class_attribute :include_root_in_json
+        config_attribute :include_root_in_json
         self.include_root_in_json = true
       end
 
diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index 8ed392abca..1779efd526 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -42,9 +42,9 @@ module ActiveModel
   #
   module Validations
     extend ActiveSupport::Concern
-    include ActiveSupport::Callbacks
 
     included do
+      extend ActiveModel::Callbacks
       extend ActiveModel::Translation
 
       extend  HelperMethods
@@ -53,7 +53,8 @@ module ActiveModel
       attr_accessor :validation_context
       define_callbacks :validate, :scope => :name
 
-      class_attribute :_validators
+      extend ActiveModel::Configuration
+      config_attribute :_validators
       self._validators = Hash.new { |h,k| h[k] = [] }
     end
 
diff --git a/activemodel/test/cases/configuration_test.rb b/activemodel/test/cases/configuration_test.rb
new file mode 100644
index 0000000000..a172fa26a3
--- /dev/null
+++ b/activemodel/test/cases/configuration_test.rb
@@ -0,0 +1,154 @@
+require 'cases/helper'
+
+class ConfigurationOnModuleTest < ActiveModel::TestCase
+  def setup
+    @mod = mod = Module.new do
+      extend ActiveSupport::Concern
+      extend ActiveModel::Configuration
+
+      config_attribute :omg
+      self.omg = "default"
+
+      config_attribute :wtf, global: true
+      self.wtf = "default"
+
+      config_attribute :boolean
+
+      config_attribute :lol, instance_writer: true
+    end
+
+    @klass = Class.new do
+      include mod
+    end
+
+    @subklass = Class.new(@klass)
+  end
+
+  test "default" do
+    assert_equal "default", @mod.omg
+    assert_equal "default", @klass.omg
+    assert_equal "default", @klass.new.omg
+  end
+
+  test "setting" do
+    @mod.omg = "lol"
+    assert_equal "lol", @mod.omg
+  end
+
+  test "setting on class including the module" do
+    @klass.omg = "lol"
+    assert_equal "lol", @klass.omg
+    assert_equal "lol", @klass.new.omg
+    assert_equal "default", @mod.omg
+  end
+
+  test "setting on subclass of class including the module" do
+    @subklass.omg = "lol"
+    assert_equal "lol", @subklass.omg
+    assert_equal "default", @klass.omg
+    assert_equal "default", @mod.omg
+  end
+
+  test "setting on instance" do
+    assert !@klass.new.respond_to?(:omg=)
+
+    @klass.lol = "lol"
+    obj = @klass.new
+    assert_equal "lol", obj.lol
+    obj.lol = "omg"
+    assert_equal "omg", obj.lol
+    assert_equal "lol", @klass.lol
+    assert_equal "lol", @klass.new.lol
+    obj.lol = false
+    assert !obj.lol?
+  end
+
+  test "global attribute" do
+    assert_equal "default", @mod.wtf
+    assert_equal "default", @klass.wtf
+
+    @mod.wtf = "wtf"
+
+    assert_equal "wtf", @mod.wtf
+    assert_equal "wtf", @klass.wtf
+
+    @klass.wtf = "lol"
+
+    assert_equal "lol", @mod.wtf
+    assert_equal "lol", @klass.wtf
+  end
+
+  test "boolean" do
+    assert_equal false, @mod.boolean?
+    assert_equal false, @klass.new.boolean?
+    @mod.boolean = true
+    assert_equal true, @mod.boolean?
+    assert_equal true, @klass.new.boolean?
+  end
+end
+
+class ConfigurationOnClassTest < ActiveModel::TestCase
+  def setup
+    @klass = Class.new do
+      extend ActiveModel::Configuration
+
+      config_attribute :omg
+      self.omg = "default"
+
+      config_attribute :wtf, global: true
+      self.wtf = "default"
+
+      config_attribute :omg2, instance_writer: true
+      config_attribute :wtf2, instance_writer: true, global: true
+    end
+
+    @subklass = Class.new(@klass)
+  end
+
+  test "defaults" do
+    assert_equal "default", @klass.omg
+    assert_equal "default", @klass.wtf
+    assert_equal "default", @subklass.omg
+    assert_equal "default", @subklass.wtf
+  end
+
+  test "changing" do
+    @klass.omg = "lol"
+    assert_equal "lol", @klass.omg
+    assert_equal "lol", @subklass.omg
+  end
+
+  test "changing in subclass" do
+    @subklass.omg = "lol"
+    assert_equal "lol", @subklass.omg
+    assert_equal "default", @klass.omg
+  end
+
+  test "changing global" do
+    @klass.wtf = "wtf"
+    assert_equal "wtf", @klass.wtf
+    assert_equal "wtf", @subklass.wtf
+
+    @subklass.wtf = "lol"
+    assert_equal "lol", @klass.wtf
+    assert_equal "lol", @subklass.wtf
+  end
+
+  test "instance_writer" do
+    obj = @klass.new
+
+    @klass.omg2 = "omg"
+    @klass.wtf2 = "wtf"
+
+    assert_equal "omg", obj.omg2
+    assert_equal "wtf", obj.wtf2
+
+    obj.omg2 = "lol"
+    obj.wtf2 = "lol"
+
+    assert_equal "lol", obj.omg2
+    assert_equal "lol", obj.wtf2
+    assert_equal "omg", @klass.omg2
+    assert_equal "lol", @klass.wtf2
+  end
+end