Use explicit spring boot loader (#39225)

railties/CHANGELOG.md

+*   Use explicit `config/boot_with_spring.rb` boot file for bin/rails and bin/rake, which allows us to restrict Spring loading
+    to only test and development, and everywhere to be able to skip spring by passing UNSPRUNG=1 as an env variable.
+
+    *DHH*
+
 *   The `classic` autoloader starts its deprecation cycle.
 
     New Rails projects are strongly discouraged from using `classic`, and we recommend that existing projects running on `classic` switch to `zeitwerk` mode when upgrading. Please check the [_Upgrading Ruby on Rails_](https://guides.rubyonrails.org/upgrading_ruby_on_rails.html) guide for tips.

railties/lib/rails/generators/app_base.rb

@@ -429,9 +429,9 @@ def generate_bundler_binstub
         end
       end
 
-      def generate_spring_binstubs
+      def generate_spring_binstub
         if bundle_install? && spring_install?
-          bundle_command("exec spring binstub --all")
+          bundle_command("exec spring binstub")
         end
       end
 

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -347,6 +347,11 @@ def create_boot_file
         template "config/boot.rb"
       end
 
+      def create_boot_with_spring_file
+        return if options[:skip_spring]
+        template "config/boot_with_spring.rb"
+      end
+
       def create_active_record_files
         return if options[:skip_active_record]
         build(:database_yml)
@@ -489,7 +494,7 @@ def finish_template
       end
 
       public_task :apply_rails_template, :run_bundle
-      public_task :generate_bundler_binstub, :generate_spring_binstubs
+      public_task :generate_bundler_binstub, :generate_spring_binstub
       public_task :run_webpack
 
       def run_after_bundle_callbacks

railties/lib/rails/generators/rails/app/templates/bin/rails.tt

 APP_PATH = File.expand_path('../config/application', __dir__)
+<% if options.skip_spring? -%>
 require_relative "../config/boot"
+<% else -%>
+require_relative "../config/boot_with_spring"
+<% end -%>
 require "rails/commands"

railties/lib/rails/generators/rails/app/templates/bin/rake.tt

+<% if options.skip_spring? -%>
 require_relative "../config/boot"
+<% else -%>
+require_relative "../config/boot_with_spring"
+<% end -%>
 require "rake"
 Rake.application.run

railties/lib/rails/generators/rails/app/templates/config/boot_with_spring.rb.tt

+if ENV["UNSPRUNG"].nil? && (ENV["RAILS_ENV"].nil? || ENV["RAILS_ENV"] == "development" || ENV["RAILS_ENV"] == "test")
+  begin
+    load File.expand_path("../../bin/spring", __FILE__)
+  rescue LoadError => e
+    raise unless e.message.include?("spring")
+  end
+end
+
+require_relative "boot"

railties/test/generators/app_generator_test.rb

@@ -1066,7 +1066,7 @@ def test_after_bundle_callback
       template
     end
 
-    sequence = ["git init", "install", "binstubs bundler", "exec spring binstub --all", "webpacker:install", "echo ran after_bundle"]
+    sequence = ["git init", "install", "binstubs bundler", "exec spring binstub", "webpacker:install", "echo ran after_bundle"]
     @sequence_step ||= 0
     ensure_bundler_first = -> command, options = nil do
       assert_equal sequence[@sequence_step], command, "commands should be called in sequence #{sequence}"