make serialization_context available in link

lib/active_model_serializers/adapter/json_api.rb

@@ -467,7 +467,7 @@ def relationships_for(serializer, requested_associations, include_slice)
       #   }.reject! {|_,v| v.nil? }
       def links_for(serializer)
         serializer._links.each_with_object({}) do |(name, value), hash|
-          result = Link.new(serializer, value).as_json
+          result = Link.new(serializer, value, instance_options).as_json
           hash[name] = result if result
         end
       end

lib/active_model_serializers/adapter/json_api/link.rb

@@ -41,11 +41,12 @@ class JsonApi
       class Link
         include SerializationContext::UrlHelpers
 
-        def initialize(serializer, value)
+        def initialize(serializer, value, adapter_options)
           @_routes ||= nil # handles warning
           # actionpack-4.0.13/lib/action_dispatch/routing/route_set.rb:417: warning: instance variable @_routes not initialized
           @object = serializer.object
           @scope = serializer.scope
+          @context = adapter_options[:serialization_context]
           # Use the return value of the block unless it is nil.
           if value.respond_to?(:call)
             @value = instance_eval(&value)
@@ -76,7 +77,7 @@ def as_json
 
         protected
 
-        attr_reader :object, :scope
+        attr_reader :object, :scope, :context
       end
     end
   end

lib/active_model_serializers/adapter/json_api/relationship.rb

@@ -48,7 +48,7 @@ def data_for(association)
 
         def links_for(association)
           association.links.each_with_object({}) do |(key, value), hash|
-            result = Link.new(parent_serializer, value).as_json
+            result = Link.new(parent_serializer, value, serializable_resource_options).as_json
             hash[key] = result if result
           end
         end

lib/active_model_serializers/serialization_context.rb

@@ -21,7 +21,7 @@ def default_url_options
       end
     end
 
-    attr_reader :request_url, :query_parameters, :key_transform
+    attr_reader :request_url, :query_parameters, :key_transform, :url_helpers
 
     def initialize(*args)
       options = args.extract_options!