`ActiveJob::QueueAdapters::*` are no longer singletons

1 files changed, 29 insertions, 9 deletions

diff --git a/activejob/lib/active_job/queue_adapter.rb b/activejob/lib/active_job/queue_adapter.rb
index aa3ebdbc7b..23b5f7de75 100644
--- a/activejob/lib/active_job/queue_adapter.rb
+++ b/activejob/lib/active_job/queue_adapter.rb
@@ -14,20 +14,40 @@ module ActiveJob
       # Specify the backend queue provider. The default queue adapter
       # is the :inline queue. See QueueAdapters for more
       # information.
-      def queue_adapter=(name_or_adapter)
-        @@queue_adapter = \
-          case name_or_adapter
-          when Symbol, String
-            load_adapter(name_or_adapter)
+      def queue_adapter=(name_or_adapter_or_class)
+        case name_or_adapter_or_class
+        when Symbol, String
+          self.queue_adapter = load_adapter(name_or_adapter_or_class)
+        else
+          @@queue_adapter = if queue_adapter?(name_or_adapter_or_class)
+            name_or_adapter_or_class
+          elsif queue_adapter_class?(name_or_adapter_or_class)
+            ActiveSupport::Deprecation.warn "Passing an adapter class is deprecated " \
+            "and will be removed in Rails 5.1. Please pass an adapter name " \
+            "(.queue_adapter = :#{name_or_adapter_or_class.name.demodulize.remove('Adapter').underscore}) " \
+            "or an instance (.queue_adapter = #{name_or_adapter_or_class.name}.new) instead."
+            name_or_adapter_or_class.new
           else
-            name_or_adapter if name_or_adapter.respond_to?(:enqueue)
+            raise ArgumentError
           end
+        end
       end
 
       private
-        def load_adapter(name)
-          "ActiveJob::QueueAdapters::#{name.to_s.camelize}Adapter".constantize
-        end
+
+      QUEUE_ADAPTER_METHODS = [:enqueue, :enqueue_at].freeze
+
+      def queue_adapter?(object)
+        QUEUE_ADAPTER_METHODS.all? { |meth| object.respond_to?(meth) }
+      end
+
+      def queue_adapter_class?(object)
+        object.is_a?(Class) && QUEUE_ADAPTER_METHODS.all? { |meth| object.public_method_defined?(meth) }
+      end
+
+      def load_adapter(name)
+        "ActiveJob::QueueAdapters::#{name.to_s.camelize}Adapter".constantize.new
+      end
     end
   end
 end