Allow removing LocalCache middleware in application.rb

All other middlewares can be removed from the stack in `config/application.rb`. `ActiveSupport::Cache::Strategy::LocalCache::Middleware` cannot, because it is added to the stack as an instance rather than a class, here: https://github.com/rails/rails/blob/main/railties/lib/rails/application/bootstrap.rb#L62. As a result, [this check](https://github.com/rails/rails/blob/main/actionpack/lib/action_dispatch/middleware/stack.rb#L133) fails unless you also pass the same instance. The instance is not available in `config/appliaction.rb` because `Rails.cache` has not been initialized yet (it's initialized when the middleware is set).

This means that if you want to remove the local cache middleware you have to make an initiailzer just for that. Unlike all other middlewares which can be dealt with as classes in `config/application.rb`.

The fix is to check the middleware's `name`, not `klass`, for delete operations. The name is [provided explicitly](https://github.com/rails/rails/blob/main/activesupport/lib/active_support/cache/strategy/local_cache.rb#L162) presumably for this reason.

Author: ghiculescu

actionpack/lib/action_dispatch/middleware/stack.rb

@@ -130,7 +130,7 @@ def swap(target, *args, &block)
     ruby2_keywords(:swap)
 
     def delete(target)
-      middlewares.delete_if { |m| m.klass == target }
+      middlewares.delete_if { |m| m.name == target.name }
     end
 
     def move(target, source)
@@ -180,10 +180,10 @@ def build_middleware(klass, args, block)
         Middleware.new(klass, args, block)
       end
 
-      def index_of(index)
-        raise "ActionDispatch::MiddlewareStack::FakeRuntime can not be referenced in middleware operations" if index == FakeRuntime
+      def index_of(klass)
+        raise "ActionDispatch::MiddlewareStack::FakeRuntime can not be referenced in middleware operations" if klass == FakeRuntime
 
-        if index == Rack::Runtime && @rack_runtime_deprecated
+        if klass == Rack::Runtime && @rack_runtime_deprecated
           ActiveSupport::Deprecation.warn(<<-MSG.squish)
             Rack::Runtime is removed from the default middleware stack in Rails
             and referencing it in middleware operations without adding it back
@@ -192,7 +192,7 @@ def index_of(index)
         end
 
         middlewares.index do |m|
-          m.klass == index || (@rack_runtime_deprecated && m.klass == FakeRuntime && index == Rack::Runtime)
+          m.name == klass.name || (@rack_runtime_deprecated && m.klass == FakeRuntime && klass == Rack::Runtime)
         end
       end
   end

railties/test/application/configuration_test.rb

@@ -3226,6 +3226,97 @@ class MyLogger < ::Logger
       assert_no_match(/You are running SQLite in production, this is generally not recommended/, Rails.logger.recording)
     end
 
+    test "app starts with LocalCache middleware" do
+      app "development"
+
+      assert(Rails.application.config.middleware.map(&:name).include?("ActiveSupport::Cache::Strategy::LocalCache"))
+
+      local_cache_index = Rails.application.config.middleware.map(&:name).index("ActiveSupport::Cache::Strategy::LocalCache")
+      logger_index = Rails.application.config.middleware.map(&:name).index("Rails::Rack::Logger")
+      assert local_cache_index < logger_index
+    end
+
+    test "LocalCache middleware can be moved via app config" do
+      # you can't move Rails.cache.middleware as it doesn't exist yet
+      add_to_config "config.middleware.move_after(Rails::Rack::Logger, ActiveSupport::Cache::Strategy::LocalCache)"
+
+      app "development"
+
+      local_cache_index = Rails.application.config.middleware.map(&:name).index("ActiveSupport::Cache::Strategy::LocalCache")
+      logger_index = Rails.application.config.middleware.map(&:name).index("Rails::Rack::Logger")
+      assert local_cache_index > logger_index
+    end
+
+    test "LocalCache middleware can be moved via initializer" do
+      app_file "config/initializers/move_local_cache_middleware.rb", <<~RUBY
+        Rails.application.config.middleware.move_after(Rails::Rack::Logger, Rails.cache.middleware)
+      RUBY
+
+      app "development"
+
+      local_cache_index = Rails.application.config.middleware.map(&:name).index("ActiveSupport::Cache::Strategy::LocalCache")
+      logger_index = Rails.application.config.middleware.map(&:name).index("Rails::Rack::Logger")
+      assert local_cache_index > logger_index
+    end
+
+    test "LocalCache middleware can be removed via app config" do
+      # you can't delete Rails.cache.middleware as it doesn't exist yet
+      add_to_config "config.middleware.delete(ActiveSupport::Cache::Strategy::LocalCache)"
+
+      app "development"
+
+      assert_not(Rails.application.config.middleware.map(&:name).include?("ActiveSupport::Cache::Strategy::LocalCache"))
+    end
+
+    test "LocalCache middleware can be removed via initializer" do
+      app_file "config/initializers/remove_local_cache_middleware.rb", <<~RUBY
+        Rails.application.config.middleware.delete(Rails.cache.middleware)
+      RUBY
+
+      app "development"
+
+      assert_not(Rails.application.config.middleware.map(&:name).include?("ActiveSupport::Cache::Strategy::LocalCache"))
+    end
+
+    test "custom middleware with overridden names can be added, moved, or deleted" do
+      app_file "config/initializers/add_custom_middleware.rb", <<~RUBY
+        class CustomMiddlewareOne
+          def self.name
+            "1st custom middleware"
+          end
+          def initialize(app, *args); end
+          def new(app); self; end
+        end
+
+        class CustomMiddlewareTwo
+          def initialize(app, *args); end
+          def new(app); self; end
+        end
+
+        class CustomMiddlewareThree
+          def self.name
+            "3rd custom middleware"
+          end
+          def initialize(app, *args); end
+          def new(app); self; end
+        end
+
+        Rails.application.config.middleware.use(CustomMiddlewareOne)
+        Rails.application.config.middleware.use(CustomMiddlewareTwo)
+        Rails.application.config.middleware.use(CustomMiddlewareThree)
+        Rails.application.config.middleware.move_after(CustomMiddlewareTwo, CustomMiddlewareOne)
+        Rails.application.config.middleware.delete(CustomMiddlewareThree)
+      RUBY
+
+      app "development"
+
+      custom_middleware_one = Rails.application.config.middleware.map(&:name).index("1st custom middleware")
+      custom_middleware_two = Rails.application.config.middleware.map(&:name).index("CustomMiddlewareTwo")
+      assert custom_middleware_one > custom_middleware_two
+
+      assert_nil Rails.application.config.middleware.map(&:name).index("3rd custom middleware")
+    end
+
     private
       def set_custom_config(contents, config_source = "custom".inspect)
         app_file "config/custom.yml", contents