Don't enable YJIT in development and test environments

Development and test environment tend to reload code and redefine methods (e.g. mocking),
hence YJIT isn't generally faster in these environments.

Co-Authored-By: Jean Boussier <[email protected]>

Author: aliismayilov

guides/source/configuring.md

@@ -60,6 +60,8 @@ Below are the default values associated with each target version. In cases of co
 
 #### Default Values for Target Version 8.1
 
+- [`config.yjit`](#config-yjit): `!Rails.env.local?`
+
 #### Default Values for Target Version 8.0
 
 - [`Regexp.timeout`](#regexp-timeout): `1`
@@ -644,6 +646,7 @@ deploying to a memory constrained environment you may want to set this to `false
 | --------------------- | -------------------- |
 | (original)            | `false`              |
 | 7.2                   | `true`               |
+| 8.1                   | `!Rails.env.local?`  |
 
 ### Configuring Assets
 

railties/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Don't enable YJIT in development and test environments
+
+    Development and test environment tend to reload code and redefine methods (e.g. mocking),
+    hence YJIT isn't generally faster in these environments.
+
+    *Ali Ismayilov*, *Jean Boussier*
+
 *   Only include PermissionsPolicy::Middleware if policy is configured.
 
     *Petrik de Heus*

railties/lib/rails/application/configuration.rb

@@ -348,6 +348,11 @@ def load_defaults(target_version)
           Regexp.timeout ||= 1 if Regexp.respond_to?(:timeout=)
         when "8.1"
           load_defaults "8.0"
+
+          # Development and test environment tend to reload code and
+          # redefine methods (e.g. mocking), hence YJIT isn't generally
+          # faster in these environments.
+          self.yjit = !Rails.env.local?
         else
           raise "Unknown version #{target_version.to_s.inspect}"
         end

tools/rail_inspector/lib/rail_inspector/configuring/check/framework_defaults.rb

@@ -21,6 +21,8 @@ def check
 
               next if defaults_file_content.include? app_config
 
+              next if config == "self.yjit"
+
               add_error(config)
             end
           end