ActiveSupport::Configurable default value option

Sometimes it can be very strange or long have to define default values
for config accessors as blocks, specially when config is a simple value
like 1, true, :symbol. This commit adds the ability to specify those
values by just passing a ` default` option when defining the accessor.

It also makes config accessor's interface similar to other Rails
methods like `class_attribute`, which also has the instance_reader,
instance_writer and instance_accessor options.

activesupport/lib/active_support/configurable.rb

@@ -94,17 +94,19 @@ module ActiveSupport
       #   User.new.allowed_access = true # => NoMethodError
       #   User.new.allowed_access        # => NoMethodError
       #
-      # Also you can pass a block to set up the attribute with a default value.
+      # Also you can pass <tt>default</tt> or a block to set up the attribute with a default value.
       #
       #   class User
       #     include ActiveSupport::Configurable
+      #     config_accessor :allowed_access, default: false
       #     config_accessor :hair_colors do
       #       [:brown, :black, :blonde, :red]
       #     end
       #   end
       #
+      #   User.allowed_access # => false
       #   User.hair_colors # => [:brown, :black, :blonde, :red]
-      def config_accessor(*names, instance_reader: true, instance_writer: true, instance_accessor: true) # :doc:
+      def config_accessor(*names, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil) # :doc:
         names.each do |name|
           raise NameError.new("invalid config attribute name") unless /\A[_A-Za-z]\w*\z/.match?(name)
 
@@ -118,7 +120,8 @@ module ActiveSupport
             class_eval reader, __FILE__, reader_line if instance_reader
             class_eval writer, __FILE__, writer_line if instance_writer
           end
-          send("#{name}=", yield) if block_given?
+
+          send("#{name}=", block_given? ? yield : default)
         end
       end
       private :config_accessor

activesupport/test/configurable_test.rb

@@ -50,7 +50,7 @@ class ConfigurableActiveSupport < ActiveSupport::TestCase
     assert_not_respond_to instance, :baz=
   end
 
-  test "configuration accessors can take a default value" do
+  test "configuration accessors can take a default value as a block" do
     parent = Class.new do
       include ActiveSupport::Configurable
       config_accessor :hair_colors, :tshirt_colors do
@@ -62,6 +62,15 @@ class ConfigurableActiveSupport < ActiveSupport::TestCase
     assert_equal [:black, :blue, :white], parent.tshirt_colors
   end
 
+  test "configuration accessors can take a default value as an option" do
+    parent = Class.new do
+      include ActiveSupport::Configurable
+      config_accessor :foo, default: :bar
+    end
+
+    assert_equal :bar, parent.foo
+  end
+
   test "configuration hash is available on instance" do
     instance = Parent.new
     assert_equal :bar, instance.config.foo