Introduce chain#prepend possible fix for #2020

lib/sidekiq/middleware/chain.rb

@@ -89,6 +89,11 @@ module Sidekiq
         entries << Entry.new(klass, *args)
       end
 
+      def prepend(klass, *args)
+        remove(klass) if exists?(klass)
+        entries.insert(0, Entry.new(klass, *args))
+      end
+
       def insert_before(oldklass, newklass, *args)
         i = entries.index { |entry| entry.klass == newklass }
         new_entry = i.nil? ? Entry.new(newklass, *args) : entries.delete_at(i)

test/test_middleware.rb

@@ -96,6 +96,15 @@ class TestMiddleware < Sidekiq::Test
       assert_equal 1, chain.count
     end
 
+    it 'correctly prepends middleware' do
+      chain = Sidekiq::Middleware::Chain.new
+      chain_entries = chain.entries
+      chain.add CustomMiddleware
+      chain.prepend YetAnotherCustomMiddleware
+      assert_equal YetAnotherCustomMiddleware, chain_entries.first.klass
+      assert_equal CustomMiddleware, chain_entries.last.klass
+    end
+
     it 'allows middleware to abruptly stop processing rest of chain' do
       recorder = []
       chain = Sidekiq::Middleware::Chain.new