Adding Fragment Cache to AMS

It's an upgrade based on the new Cache implementation #693.
It allows to use the Rails conventions to cache
specific attributes or associations.
It's based on the Cache Composition implementation.

lib/active_model/serializer/adapter/json_api.rb

@@ -1,3 +1,5 @@
+require 'active_model/serializer/adapter/json_api/fragment_cache'
+
 module ActiveModel
   class Serializer
     class Adapter
@@ -26,15 +28,17 @@ module ActiveModel
               end
             end
           else
-            @hash = cached_object do
-              @hash[:data] = attributes_for_serializer(serializer, @options)
-              add_resource_links(@hash[:data], serializer)
-              @hash
-            end
+            @hash[:data] = attributes_for_serializer(serializer, @options)
+            add_resource_links(@hash[:data], serializer)
           end
           @hash
         end
 
+        def fragment_cache(cached_hash, non_cached_hash)
+          root = false if @options.include?(:include)
+          JsonApi::FragmentCache.new().fragment_cache(root, cached_hash, non_cached_hash)
+        end
+
         private
 
         def add_links(resource, name, serializers)
@@ -43,7 +47,7 @@ module ActiveModel
           resource[:links][name][:linkage] += serializers.map { |serializer| { type: serializer.type, id: serializer.id.to_s } }
         end
 
-        def add_link(resource, name, serializer)
+        def add_link(resource, name, serializer, val=nil)
           resource[:links] ||= {}
           resource[:links][name] = { linkage: nil }
 
@@ -76,24 +80,27 @@ module ActiveModel
           end
         end
 
-
         def attributes_for_serializer(serializer, options)
           if serializer.respond_to?(:each)
             result = []
             serializer.each do |object|
               options[:fields] = @fieldset && @fieldset.fields_for(serializer)
-              options[:required_fields] = [:id, :type]
-              attributes = object.attributes(options)
-              attributes[:id] = attributes[:id].to_s
-              result << attributes
+              result << cache_check(object) do
+                options[:required_fields] = [:id, :type]
+                attributes = object.attributes(options)
+                attributes[:id] = attributes[:id].to_s
+                result << attributes
+              end
             end
           else
             options[:fields] = @fieldset && @fieldset.fields_for(serializer)
             options[:required_fields] = [:id, :type]
-            result = serializer.attributes(options)
-            result[:id] = result[:id].to_s
+            result = cache_check(serializer) do
+              result = serializer.attributes(options)
+              result[:id] = result[:id].to_s
+              result
+            end
           end
-
           result
         end
 
@@ -124,7 +131,11 @@ module ActiveModel
             if association.respond_to?(:each)
               add_links(attrs, name, association)
             else
-              add_link(attrs, name, association)
+              if opts[:virtual_value]
+                add_link(attrs, name, nil, opts[:virtual_value])
+              else
+                add_link(attrs, name, association)
+              end
             end
 
             if options[:add_included]