Clean up meta handling.

lib/active_model/serializer/adapter/json_api.rb

@@ -6,6 +6,7 @@ module ActiveModel
         autoload :PaginationLinks
         autoload :FragmentCache
         autoload :Link
+        autoload :Meta
         autoload :Deserialization
 
         # TODO: if we like this abstraction and other API objects to it,
@@ -157,7 +158,7 @@ module ActiveModel
           links = links_for(serializer)
           resource_object[:links] = links if links.any?
 
-          meta = serializer.meta
+          meta = meta_for(serializer)
           resource_object[:meta] = meta unless meta.nil?
 
           resource_object
@@ -220,6 +221,10 @@ module ActiveModel
         def pagination_links_for(serializer, options)
           JsonApi::PaginationLinks.new(serializer.object, options[:serialization_context]).serializable_hash(options)
         end
+
+        def meta_for(serializer)
+          Meta.new(serializer).as_json
+        end
       end
     end
   end

lib/active_model/serializer/adapter/json_api/meta.rb

@@ -0,0 +1,29 @@
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class Meta
+          def initialize(serializer)
+            @object = serializer.object
+            @scope = serializer.scope
+
+            # Use the return value of the block unless it is nil.
+            if serializer._meta.respond_to?(:call)
+              @value = instance_eval(&serializer._meta)
+            else
+              @value = serializer._meta
+            end
+          end
+
+          def as_json
+            @value
+          end
+
+          protected
+
+          attr_reader :object, :scope
+        end
+      end
+    end
+  end
+end