Merge pull request #652 from rails/rm-mechanism

Require applications to have reloading enabled in the managed environ…

Author: fxn

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Next Release
 
+* Require applications to have reloading enabled in the managed environments.
+
 ## 2.1.1
 
 * Avoid -I rubylibdir with default-gem bundler

README.md

@@ -65,6 +65,16 @@ automatically add `./bin` to your `PATH` when you `cd` into your application.
 Simply create an `.envrc` file with the command `PATH_add bin` in your
 Rails directory.
 
+### Enable reloading
+
+Spring reloads application code, and therefore needs the application to have
+reloading enabled.
+
+Please, make sure `config.cache_classes` is `false` in the environments that
+Spring manages. That setting is typically configured in
+`config/environments/*.rb`. In particular, make sure it is `false` for the
+`test` environment.
+
 ### Usage
 
 For this walkthrough I've generated a new Rails application, and run
@@ -257,12 +267,10 @@ run through Spring, set the `DISABLE_SPRING` environment variable.
 
 ## Class reloading
 
-Spring uses Rails' class reloading mechanism
-(`ActiveSupport::Dependencies`) to keep your code up to date between
-test runs. This is the same mechanism which allows you to see changes
-during development when you refresh the page. However, you may never
-have used this mechanism with your `test` environment before, and this
-can cause problems.
+Spring uses Rails' class reloading mechanism to keep your code up to date
+between test runs. This is the same mechanism which allows you to see changes
+during development when you refresh the page. However, you may never have used
+this mechanism with your `test` environment before, and this can cause problems.
 
 It's important to realise that code reloading means that the constants
 in your application are *different objects* after files have changed:

lib/spring/application.rb

@@ -95,22 +95,17 @@ def preload
         raise "Spring only supports Rails >= 5.2.0"
       end
 
-      # config/environments/test.rb will have config.cache_classes = true. However
-      # we want it to be false so that we can reload files. This is a hack to
-      # override the effect of config.cache_classes = true. We can then actually
-      # set config.cache_classes = false after loading the environment.
-      Rails::Application.initializer :initialize_dependency_mechanism, group: :all do
-        # Rails 7 dropped classic mode, and this setter does not exist anymore.
-        if ActiveSupport::Dependencies.respond_to?(:mechanism=)
-          ActiveSupport::Dependencies.mechanism = :load
+      Rails::Application.initializer :ensure_reloading_is_enabled, group: :all do
+        if Rails.application.config.cache_classes
+          raise <<-MSG.strip_heredoc
+            Spring reloads, and therefore needs the application to have reloading enabled.
+            Please, set config.cache_classes to false in config/environments/#{Rails.env}.rb.
+          MSG
         end
       end
 
       require Spring.application_root_path.join("config", "environment")
 
-      @original_cache_classes = Rails.application.config.cache_classes
-      Rails.application.config.cache_classes = false
-
       disconnect_database
 
       @preloaded = :success
@@ -195,14 +190,6 @@ def serve(client)
         # Load in the current env vars, except those which *were* changed when Spring started
         env.each { |k, v| ENV[k] ||= v }
 
-        # requiring is faster, so if config.cache_classes was true in
-        # the environment's config file, then we can respect that from
-        # here on as we no longer need constant reloading.
-        if @original_cache_classes
-          ActiveSupport::Dependencies.mechanism = :require
-          Rails.application.config.cache_classes = true
-        end
-
         connect_database
         srand
 

test/support/acceptance_test.rb

@@ -121,6 +121,15 @@ def without_gem(name)
         refute_output_includes "bin/rails runner ''", stderr: 'Running via Spring preloader in process'
       end
 
+      test "raises if config.cache_classes is true" do
+        config_path = app.path("config/environments/development.rb")
+        config = File.read(config_path)
+        config.sub!(/config.cache_classes\s*=\s*false/, "config.cache_classes = true")
+        File.write(config_path, config)
+
+        assert_failure "bin/rails runner 1", stderr: "Please, set config.cache_classes to false"
+      end
+
       test "test changes are picked up" do
         assert_speedup do
           assert_success app.spring_test_command, stdout: "0 failures"