Stop creating ApplicationRecord on model generation

When generating models, we created ApplicationRecord in the default
location if no file existed there.  That was annoying for people who
moved it to somewhere else in the autoload path.  At this point, the
vast majority of apps should have either run the upgrade script or
generated a model since upgrading.  For those that haven't the error
message after generating a new model should be helpful:

   NameError: uninitialized constant ApplicationRecord

To ease friction in that case, this also adds a generator for
ApplicationRecord.

activerecord/CHANGELOG.md

+*   ApplicationRecord is no longer generated when generating models.  If you
+    need to generate it, it can be created with `rails g application_record`.
+
+    *Lisa Ugray*
+
 *   Fix `COUNT(DISTINCT ...)` with `ORDER BY` and `LIMIT` to keep the existing select list.
 
     *Ryuta Kamizono*

activerecord/lib/rails/generators/active_record/application_record/application_record_generator.rb

+# frozen_string_literal: true
+
+require "rails/generators/active_record"
+
+module ActiveRecord
+  module Generators # :nodoc:
+    class ApplicationRecordGenerator < ::Rails::Generators::Base # :nodoc:
+      source_root File.expand_path("templates", __dir__)
+
+      # FIXME: Change this file to a symlink once RubyGems 2.5.0 is required.
+      def create_application_record
+        template "application_record.rb", application_record_file_name
+      end
+
+      private
+
+        def application_record_file_name
+          @application_record_file_name ||= if namespaced?
+                                              "app/models/#{namespaced_path}/application_record.rb"
+                                            else
+                                              "app/models/application_record.rb"
+                                            end
+        end
+    end
+  end
+end

activerecord/lib/rails/generators/active_record/model/model_generator.rb

@@ -23,13 +23,11 @@ def create_migration_file
       end
 
       def create_model_file
-        generate_application_record
         template "model.rb", File.join("app/models", class_path, "#{file_name}.rb")
       end
 
       def create_module_file
         return if regular_class_path.empty?
-        generate_application_record
         template "module.rb", File.join("app/models", "#{class_path.join('/')}.rb") if behavior == :invoke
       end
 
@@ -41,31 +39,10 @@ def attributes_with_index
           attributes.select { |a| !a.reference? && a.has_index? }
         end
 
-        # FIXME: Change this file to a symlink once RubyGems 2.5.0 is required.
-        def generate_application_record
-          if behavior == :invoke && !application_record_exist?
-            template "application_record.rb", application_record_file_name
-          end
-        end
-
         # Used by the migration template to determine the parent name of the model
         def parent_class_name
           options[:parent] || "ApplicationRecord"
         end
-
-        def application_record_exist?
-          file_exist = nil
-          in_root { file_exist = File.exist?(application_record_file_name) }
-          file_exist
-        end
-
-        def application_record_file_name
-          @application_record_file_name ||= if mountable_engine?
-            "app/models/#{namespaced_path}/application_record.rb"
-          else
-            "app/models/application_record.rb"
-          end
-        end
     end
   end
 end

railties/lib/rails/generators/rails/application_record/application_record_generator.rb

+# frozen_string_literal: true
+
+module Rails
+  module Generators
+    class ApplicationRecordGenerator < Base # :nodoc:
+      hook_for :orm, required: true, desc: "ORM to be invoked"
+    end
+  end
+end

railties/test/generators/application_record_generator_test.rb

+require "generators/generators_test_helper"
+require "rails/generators/rails/application_record/application_record_generator"
+
+class ApplicationRecordGeneratorTest < Rails::Generators::TestCase
+  include GeneratorsTestHelper
+
+  def test_application_record_skeleton_is_created
+    run_generator
+    assert_file "app/models/application_record.rb" do |record|
+      assert_match(/class ApplicationRecord < ActiveRecord::Base/, record)
+      assert_match(/self\.abstract_class = true/, record)
+    end
+  end
+end

railties/test/generators/model_generator_test.rb

@@ -6,14 +6,6 @@ class ModelGeneratorTest < Rails::Generators::TestCase
   include GeneratorsTestHelper
   arguments %w(Account name:string age:integer)
 
-  def test_application_record_skeleton_is_created
-    run_generator
-    assert_file "app/models/application_record.rb" do |record|
-      assert_match(/class ApplicationRecord < ActiveRecord::Base/, record)
-      assert_match(/self\.abstract_class = true/, record)
-    end
-  end
-
   def test_help_shows_invoked_generators_options
     content = run_generator ["--help"]
     assert_match(/ActiveRecord options:/, content)
@@ -43,17 +35,6 @@ def test_model_with_parent_option
     assert_no_migration "db/migrate/create_accounts.rb"
   end
 
-  def test_model_with_existent_application_record
-    mkdir_p "#{destination_root}/app/models"
-    touch "#{destination_root}/app/models/application_record.rb"
-
-    Dir.chdir(destination_root) do
-      run_generator ["account"]
-    end
-
-    assert_file "app/models/account.rb", /class Account < ApplicationRecord/
-  end
-
   def test_plural_names_are_singularized
     content = run_generator ["accounts".freeze]
     assert_file "app/models/account.rb", /class Account < ApplicationRecord/

railties/test/generators/namespaced_generators_test.rb

@@ -3,6 +3,7 @@
 require "rails/generators/rails/model/model_generator"
 require "rails/generators/mailer/mailer_generator"
 require "rails/generators/rails/scaffold/scaffold_generator"
+require "rails/generators/rails/application_record/application_record_generator"
 
 class NamespacedGeneratorTestCase < Rails::Generators::TestCase
   include GeneratorsTestHelper
@@ -421,3 +422,13 @@ def test_api_scaffold_with_namespace_on_invoke
                 /module TestApp\n  class Admin::RolesControllerTest < ActionDispatch::IntegrationTest/
   end
 end
+
+class NamespacedApplicationRecordGeneratorTest < NamespacedGeneratorTestCase
+  include GeneratorsTestHelper
+  tests Rails::Generators::ApplicationRecordGenerator
+
+  def test_adds_namespace_to_application_record
+    run_generator
+    assert_file "app/models/test_app/application_record.rb", /module TestApp/, /  class ApplicationRecord < ActiveRecord::Base/
+  end
+end

railties/test/generators/plugin_generator_test.rb

@@ -679,20 +679,6 @@ def test_model_with_existent_application_record_in_mountable_engine
     assert_file "app/models/bukkits/article.rb", /class Article < ApplicationRecord/
   end
 
-  def test_generate_application_record_when_does_not_exist_in_mountable_engine
-    run_generator [destination_root, "--mountable"]
-    FileUtils.rm "#{destination_root}/app/models/bukkits/application_record.rb"
-    capture(:stdout) do
-      `#{destination_root}/bin/rails g model article`
-    end
-
-    assert_file "#{destination_root}/app/models/bukkits/application_record.rb" do |record|
-      assert_match(/module Bukkits/, record)
-      assert_match(/class ApplicationRecord < ActiveRecord::Base/, record)
-      assert_match(/self\.abstract_class = true/, record)
-    end
-  end
-
   def test_generate_application_mailer_when_does_not_exist_in_mountable_engine
     run_generator [destination_root, "--mountable"]
     FileUtils.rm "#{destination_root}/app/mailers/bukkits/application_mailer.rb"

railties/test/generators_test.rb

@@ -124,7 +124,7 @@ def test_rails_generators_help_with_builtin_information
 
   def test_rails_generators_help_does_not_include_app_nor_plugin_new
     output = capture(:stdout) { Rails::Generators.help }
-    assert_no_match(/app/, output)
+    assert_no_match(/app\W/, output)
     assert_no_match(/[^:]plugin/, output)
   end