Fix #1759, Grape integration, adds serialization_context (#4)

* Fix #1759, Grape integration, adds serialization_context

- `serialization_context` is added in grape formatter so grape continues to render models without an explicit call to the `render` helper method
- Made it straightforward for subclasses to add other serializer options (such as `serialization_scope`).

* Updated Grape tests to include:
- paginated collections
- implicit Grape serializer (i.e. without explicit invocation of `render` helper method)

* Update Changelog with fixes.

lib/grape/formatters/active_model_serializers.rb

@@ -2,14 +2,31 @@
 #
 # Serializer options can be passed as a hash from your Grape endpoint using env[:active_model_serializer_options],
 # or better yet user the render helper in Grape::Helpers::ActiveModelSerializers
+
+require 'active_model_serializers/serialization_context'
+
 module Grape
   module Formatters
     module ActiveModelSerializers
       def self.call(resource, env)
-        serializer_options = {}
-        serializer_options.merge!(env[:active_model_serializer_options]) if env[:active_model_serializer_options]
+        serializer_options = build_serializer_options(env)
         ::ActiveModelSerializers::SerializableResource.new(resource, serializer_options).to_json
       end
+
+      def self.build_serializer_options(env)
+        ams_options = env[:active_model_serializer_options] || {}
+
+        # Add serialization context
+        ams_options.fetch(:serialization_context) do
+          request = env['grape.request']
+          ams_options[:serialization_context] = ::ActiveModelSerializers::SerializationContext.new(
+            request_url: request.url[/\A[^?]+/],
+            query_parameters: request.params
+          )
+        end
+
+        ams_options
+      end
     end
   end
 end

lib/grape/helpers/active_model_serializers.rb

@@ -1,7 +1,5 @@
 # Helpers can be included in your Grape endpoint as: helpers Grape::Helpers::ActiveModelSerializers
 
-require 'active_model_serializers/serialization_context'
-
 module Grape
   module Helpers
     module ActiveModelSerializers
@@ -11,12 +9,6 @@ module Grape
       #
       # Example: To include pagination meta data: render(posts, meta: { page: posts.page, total_pages: posts.total_pages })
       def render(resource, active_model_serializer_options = {})
-        active_model_serializer_options.fetch(:serialization_context) do
-          active_model_serializer_options[:serialization_context] = ::ActiveModelSerializers::SerializationContext.new(
-            original_url: request.url[/\A[^?]+/],
-            query_parameters: request.params
-          )
-        end
         env[:active_model_serializer_options] = active_model_serializer_options
         resource
       end