Add if/unless support to attributes.

Author: beauby

lib/active_model/serializer/attribute.rb

@@ -1,13 +1,24 @@
 module ActiveModel
   class Serializer
-    Attribute = Struct.new(:name, :key, :block) do
+    Attribute = Struct.new(:name, :key, :block, :condition_type, :condition) do
       def value(serializer)
         if block
           serializer.instance_eval(&block)
         else
           serializer.read_attribute_for_serialization(name)
         end
       end
+
+      def include?(serializer)
+        case condition_type
+        when :if
+          serializer.send(condition)
+        when :unless
+          !serializer.send(condition)
+        else
+          true
+        end
+      end
     end
   end
 end

lib/active_model/serializer/attributes.rb

@@ -7,6 +7,8 @@ module Attributes
         with_options instance_writer: false, instance_reader: false do |serializer|
           serializer.class_attribute :_attributes_data # @api private
           self._attributes_data ||= {}
+          serializer.class_attribute :_attributes_conditions # @api private
+          self._attributes_conditions ||= {}
         end
 
         autoload :Attribute
@@ -16,6 +18,7 @@ module Attributes
         def attributes(requested_attrs = nil, reload = false)
           @attributes = nil if reload
           @attributes ||= self.class._attributes_data.values.each_with_object({}) do |attr, hash|
+            next unless attr.include?(self)
             next unless requested_attrs.nil? || requested_attrs.include?(attr.key)
             hash[attr.key] = attr.value(self)
           end
@@ -53,7 +56,16 @@ def attributes(*attrs)
         #     end
         def attribute(attr, options = {}, &block)
           key = options.fetch(:key, attr)
-          _attributes_data[attr] = Attribute.new(attr, key, block)
+          condition_type =
+            if options.key?(:if)
+              :if
+            elsif options.key?(:unless)
+              :unless
+            else
+              :none
+            end
+          condition = options[condition_type]
+          _attributes_data[attr] = Attribute.new(attr, key, block, condition_type, condition)
         end
 
         # @api private