Introduce ApplicationRecord, an Active Record layer supertype

It's pretty common for folks to monkey patch `ActiveRecord::Base` to
work around an issue or introduce extra functionality. Instead of
shoving even more stuff in `ActiveRecord::Base`, `ApplicationRecord` can
hold all those custom work the apps may need.

Now, we don't wanna encourage all of the application models to inherit
from `ActiveRecord::Base`, but we can encourage all the models that do,
to inherit from `ApplicationRecord`.

Newly generated applications have `app/models/application_record.rb`
present by default. The model generators are smart enough to recognize
that newly generated models have to inherit from `ApplicationRecord`,
but only if it's present.

7 files changed, 29 insertions, 1 deletions

diff --git a/railties/lib/rails/generators/rails/app/app_generator.rb b/railties/lib/rails/generators/rails/app/app_generator.rb
index 889154494d..9997cf3b35 100644
--- a/railties/lib/rails/generators/rails/app/app_generator.rb
+++ b/railties/lib/rails/generators/rails/app/app_generator.rb
@@ -293,6 +293,12 @@ module Rails
         end
       end
 
+      def delete_application_record_skipping_active_record
+        if options[:skip_active_record]
+          remove_file 'app/models/application_record.rb'
+        end
+      end
+
       def delete_active_record_initializers_skipping_active_record
         if options[:skip_active_record]
           remove_file 'config/initializers/active_record_belongs_to_required_by_default.rb'
diff --git a/railties/lib/rails/generators/rails/app/templates/app/models/application_record.rb b/railties/lib/rails/generators/rails/app/templates/app/models/application_record.rb
new file mode 100644
index 0000000000..10a4cba84d
--- /dev/null
+++ b/railties/lib/rails/generators/rails/app/templates/app/models/application_record.rb
@@ -0,0 +1,3 @@
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+end
diff --git a/railties/lib/rails/generators/rails/plugin/templates/app/models/application_record.rb.tt b/railties/lib/rails/generators/rails/plugin/templates/app/models/application_record.rb.tt
new file mode 100644
index 0000000000..8aa3de78f1
--- /dev/null
+++ b/railties/lib/rails/generators/rails/plugin/templates/app/models/application_record.rb.tt
@@ -0,0 +1,6 @@
+<%= wrap_in_modules <<-rb.strip_heredoc
+  class ApplicationRecord < ActiveRecord::Base
+    self.abstract_class = true
+  end
+rb
+%>
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 25e749ac14..87e28288ee 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -228,6 +228,7 @@ module ApplicationTests
     end
 
     test "the application can be eager loaded even when there are no frameworks" do
+      FileUtils.rm_rf("#{app_path}/app/models/application_record.rb")
       FileUtils.rm_rf("#{app_path}/config/environments")
       add_to_config <<-RUBY
         config.eager_load = true
diff --git a/railties/test/application/rake_test.rb b/railties/test/application/rake_test.rb
index 0da0928b48..1b009e0742 100644
--- a/railties/test/application/rake_test.rb
+++ b/railties/test/application/rake_test.rb
@@ -98,7 +98,7 @@ module ApplicationTests
     end
 
     def test_code_statistics_sanity
-      assert_match "Code LOC: 7     Test LOC: 0     Code to Test Ratio: 1:0.0",
+      assert_match "Code LOC: 10     Test LOC: 0     Code to Test Ratio: 1:0.0",
         Dir.chdir(app_path){ `bin/rake stats` }
     end
 
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index dd2e931c5c..3f2ac3d2b6 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -334,6 +334,7 @@ class AppGeneratorTest < Rails::Generators::TestCase
     run_generator [destination_root, "--skip-active-record"]
     assert_no_file "config/database.yml"
     assert_no_file "config/initializers/active_record_belongs_to_required_by_default.rb"
+    assert_no_file "app/models/application_record.rb"
     assert_file "config/application.rb", /#\s+require\s+["']active_record\/railtie["']/
     assert_file "test/test_helper.rb" do |helper_content|
       assert_no_match(/fixtures :all/, helper_content)
diff --git a/railties/test/generators/model_generator_test.rb b/railties/test/generators/model_generator_test.rb
index e1722b84b3..fb502ec0c5 100644
--- a/railties/test/generators/model_generator_test.rb
+++ b/railties/test/generators/model_generator_test.rb
@@ -35,6 +35,17 @@ class ModelGeneratorTest < Rails::Generators::TestCase
     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 < ActiveRecord::Base/