Fix Ruby 2.7 warnings on MiddlewareStackProxy

Especially this is caused on `config.app_middleware.insert_after` in our
code base:

2b9edb777b/activerecord/lib/active_record/railtie.rb (L88-L90)
2b9edb777b/activerecord/lib/active_record/migration.rb (L556-L557)

actionpack/lib/action_dispatch/middleware/stack.rb

@@ -90,8 +90,13 @@ module ActionDispatch
     end
 
     def unshift(klass, *args, &block)
-      middlewares.unshift(build_middleware(klass, args, block))
+      middlewares.unshift(
+        build_middleware(klass, args, block) do |app|
+          klass.new(app, *args, &block)
         end
+      )
+    end
+    ruby2_keywords(:unshift) if respond_to?(:ruby2_keywords, true)
 
     def initialize_copy(other)
       self.middlewares = other.middlewares.dup
@@ -99,8 +104,14 @@ module ActionDispatch
 
     def insert(index, klass, *args, &block)
       index = assert_index(index, :before)
-      middlewares.insert(index, build_middleware(klass, args, block))
+      middlewares.insert(
+        index,
+        build_middleware(klass, args, block) do |app|
+          klass.new(app, *args, &block)
         end
+      )
+    end
+    ruby2_keywords(:insert) if respond_to?(:ruby2_keywords, true)
 
     alias_method :insert_before, :insert
 
@@ -108,12 +119,14 @@ module ActionDispatch
       index = assert_index(index, :after)
       insert(index + 1, *args, &block)
     end
+    ruby2_keywords(:insert_after) if respond_to?(:ruby2_keywords, true)
 
     def swap(target, *args, &block)
       index = assert_index(target, :before)
       insert(index, *args, &block)
       middlewares.delete_at(index + 1)
     end
+    ruby2_keywords(:swap) if respond_to?(:ruby2_keywords, true)
 
     def delete(target)
       middlewares.delete_if { |m| m.klass == target }

railties/lib/rails/configuration.rb

@@ -41,34 +41,39 @@ module Rails
       end
 
       def insert_before(*args, &block)
-        @operations << [__method__, args, block]
+        @operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
+      ruby2_keywords(:insert_before) if respond_to?(:ruby2_keywords, true)
 
       alias :insert :insert_before
 
       def insert_after(*args, &block)
-        @operations << [__method__, args, block]
+        @operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
+      ruby2_keywords(:insert_after) if respond_to?(:ruby2_keywords, true)
 
       def swap(*args, &block)
-        @operations << [__method__, args, block]
+        @operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
+      ruby2_keywords(:swap) if respond_to?(:ruby2_keywords, true)
 
       def use(*args, &block)
-        @operations << [__method__, args, block]
+        @operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
+      ruby2_keywords(:use) if respond_to?(:ruby2_keywords, true)
 
       def delete(*args, &block)
-        @delete_operations << [__method__, args, block]
+        @delete_operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
 
       def unshift(*args, &block)
-        @operations << [__method__, args, block]
+        @operations << -> middleware { middleware.send(__method__, *args, &block) }
       end
+      ruby2_keywords(:unshift) if respond_to?(:ruby2_keywords, true)
 
       def merge_into(other) #:nodoc:
-        (@operations + @delete_operations).each do |operation, args, block|
+        (@operations + @delete_operations).each do |operation|
-          other.send(operation, *args, &block)
+          operation.call(other)
         end
 
         other