Implement ActiveJob-style set, fixes #2780

The `set` method allows the user to dynamically override worker options without having to drop down to the Sidekiq::Client API, e.g.

    MyWorker.set(queue: 'foo').perform_async(1)

lib/sidekiq/worker.rb

@@ -50,6 +50,11 @@ module Sidekiq
         raise ArgumentError, "Do not call .delay_until on a Sidekiq::Worker class, call .perform_at"
       end
 
+      def set(options)
+        Thread.current[:sidekiq_worker_set] = options
+        self
+      end
+
       def perform_async(*args)
         client_push('class' => self, 'args' => args)
       end
@@ -97,7 +102,13 @@ module Sidekiq
 
       def client_push(item) # :nodoc:
         pool = Thread.current[:sidekiq_via_pool] || get_sidekiq_options['pool'] || Sidekiq.redis_pool
-        Sidekiq::Client.new(pool).push(item.stringify_keys)
+        hash = if Thread.current[:sidekiq_worker_set]
+          x, Thread.current[:sidekiq_worker_set] = Thread.current[:sidekiq_worker_set], nil
+          x.stringify_keys.merge(item.stringify_keys)
+        else
+          item.stringify_keys
+        end
+        Sidekiq::Client.new(pool).push(hash)
       end
 
     end

test/test_client.rb

@@ -191,4 +191,42 @@ class TestClient < Sidekiq::Test
       conn.verify
     end
   end
+
+  describe 'Sidekiq::Worker#set' do
+    class SetWorker
+      include Sidekiq::Worker
+      sidekiq_options queue: :foo, 'retry': 12
+    end
+
+    def setup
+      Sidekiq.redis {|c| c.flushdb }
+    end
+
+    it 'allows option overrides' do
+      q = Sidekiq::Queue.new('bar')
+      assert_equal 0, q.size
+      assert SetWorker.set(queue: :bar).perform_async(1)
+      job = q.first
+      assert_equal 'bar', job['queue']
+      assert_equal 12, job['retry']
+    end
+
+    it 'handles symbols and strings' do
+      q = Sidekiq::Queue.new('bar')
+      assert_equal 0, q.size
+      assert SetWorker.set('queue' => 'bar', :retry => 11).perform_async(1)
+      job = q.first
+      assert_equal 'bar', job['queue']
+      assert_equal 11, job['retry']
+
+      q.clear
+      assert SetWorker.perform_async(1)
+      assert_equal 0, q.size
+
+      q = Sidekiq::Queue.new('foo')
+      job = q.first
+      assert_equal 'foo', job['queue']
+      assert_equal 12, job['retry']
+    end
+  end
 end