Ruby on Rails 7.2 Release Notes

Highlights in Rails 7.2:

Development containers configuration for applications.
Add browser version guard by default.
Make Ruby 3.1 the new minimum version.
Default Progressive Web Application (PWA) files.
Add omakase RuboCop rules by default.
Add GitHub CI workflow by default to new applications.
Add Brakeman by default to new applications.
Set a new default for the Puma thread count.
Prevent jobs from being scheduled within transactions.
Per transaction commit and rollback callbacks.
Enable YJIT by default if running Ruby 3.3+.
New design for the Rails guides.
Setup jemalloc in default Dockerfile to optimize memory allocation.
Suggest puma-dev configuration in bin/setup.

These release notes cover only the major changes. To learn about various bug fixes and changes, please refer to the changelogs or check out the list of commits in the main Rails repository on GitHub.

1. Upgrading to Rails 7.2

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 7.1 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 7.2. A list of things to watch out for when upgrading is available in the Upgrading Ruby on Rails guide.

2. Major Features

2.1. Development containers configuration for applications

A development container (or dev container for short) allows you to use a container as a full-featured development environment.

Rails 7.2 adds the ability to generate a development container configuration for your application. This configuration includes a .devcontainer folder with a Dockerfile, a docker-compose.yml file, and a devcontainer.json file.

By default, the dev container contains the following:

A Redis container for use with Kredis, Action Cable, etc.
A database (SQLite, Postgres, MySQL or MariaDB)
A Headless Chrome container for system tests
Active Storage configured to use the local disk and with preview features working

To generate a new application with a development container, you can run:

$ rails new myapp --devcontainer

For existing applications, a devcontainer command is now available:

$ rails devcontainer

For more information, see the Getting Started with Dev Containers guide.

2.2. Add browser version guard by default

Rails now adds the ability to specify the browser versions that will be allowed to access all actions (or some, as limited by only: or except:).

Only browsers matched in the hash or named set passed to versions: will be blocked if they're below the versions specified.

This means that all other unknown browsers, as well as agents that aren't reporting a user-agent header, will be allowed access.

A browser that's blocked will by default be served the file in public/406-unsupported-browser.html with a HTTP status code of "406 Not Acceptable".

Examples:

class ApplicationController < ActionController::Base
  # Allow only browsers natively supporting webp images, web push, badges, import maps, CSS nesting + :has
  allow_browser versions: :modern
end

class ApplicationController < ActionController::Base
  # All versions of Chrome and Opera will be allowed, but no versions of "internet explorer" (ie). Safari needs to be 16.4+ and Firefox 121+.
  allow_browser versions: { safari: 16.4, firefox: 121, ie: false }
end

class MessagesController < ApplicationController
  # In addition to the browsers blocked by ApplicationController, also block Opera below 104 and Chrome below 119 for the show action.
  allow_browser versions: { opera: 104, chrome: 119 }, only: :show
end

Newly generated applications have this guard set in ApplicationController.

For more information, see the allow_browser documentation.

2.3. Make Ruby 3.1 the new minimum version

Until now, Rails only dropped compatibility with older Rubies on new majors version. We are changing this policy because it causes us to keep compatibility with long unsupported versions of Ruby or to bump the Rails major version more often, and to drop multiple Ruby versions at once when we bump the major.

We will now drop Ruby versions that are end-of-life on minor Rails versions at the time of the release.

For Rails 7.2, Ruby 3.1 is the new minimum version.

2.4. Default Progressive Web Application (PWA) files

In preparation to better supporting the creation of PWA applications with Rails, we now generate default PWA files for the manifest and service worker, which are served from app/views/pwa and can be dynamically rendered through ERB. Those files are mounted explicitly at the root with default routes in the generated routes file.

For more information, see the pull request adding the feature.

2.5. Add omakase RuboCop rules by default

Rails applications now come with RuboCop configured with a set of rules from rubocop-rails-omakase by default.

Ruby is a beautifully expressive language that not only tolerates many different dialects, but celebrates their diversity. It was never meant as a language to be written exclusively in a single style across all libraries, frameworks, or applications. If you or your team has developed a particular house style that brings you joy, you should cherish that.

This collection of RuboCop styles is for those who haven't committed to any specific dialect already. Who would just like to have a reasonable starting point, and who will benefit from some default rules to at least start a consistent approach to Ruby styling.

These specific rules aren't right or wrong, but merely represent the idiosyncratic aesthetic sensibilities of Rails' creator. Use them whole, use them as a starting point, use them as inspiration, or however you see fit.

2.6. Add GitHub CI workflow by default to new applications

Rails now adds a default GitHub CI workflow file to new applications. This will get especially newcomers off to a good start with automated scanning, linting, and testing. We find that a natural continuation for the modern age of what we've done since the start with unit tests.

It's of course true that GitHub Actions are a commercial cloud product for private repositories after you've used the free tokens. But given the relationship between GitHub and Rails, the overwhelming default nature of the platform for newcomers, and the value of teaching newcomers good CI habits, we find this to be an acceptable trade-off.

2.7. Add Brakeman by default to new applications

Brakeman is a great way to prevent common security vulnerabilities in Rails from going into production.

New applications come with Brakeman installed and combined with the GitHub CI workflow, it will run automatically on every push.

2.8. Set a new default for the Puma thread count

Rails changed the default number of threads in Puma from 5 to 3.

Due to the nature of well-optimized Rails applications, with quick SQL queries and slow 3rd-party calls running via jobs, Ruby can spend a significant amount of time waiting for the Global VM Lock (GVL) to release when the thread count is too high, which is hurting latency (request response time).

After careful consideration, investigation, and based on battle-tested experience from applications running in production, we decided that a default of 3 threads is a good balance between concurrency and performance.

You can follow a very detailed discussion about this change in the issue.

2.9. Prevent jobs from being scheduled within transactions

A common mistake with Active Job is to enqueue jobs from inside a transaction, causing them to potentially be picked and ran by another process, before the transaction is committed, which result in various errors.

Topic.transaction do
  topic = Topic.create

  NewTopicNotificationJob.perform_later(topic)
end

Now Active Job will automatically defer the enqueuing to after the transaction is committed, and drop the job if the transaction is rolled back.

Various queue implementations can chose to disable this behavior, and users can disable it, or force it on a per job basis:

class NewTopicNotificationJob < ApplicationJob
  self.enqueue_after_transaction_commit = :never
end

2.10. Per transaction commit and rollback callbacks

This is now possible due to a new feature that allows registering transaction callbacks outside of a record.

ActiveRecord::Base.transaction now yields an ActiveRecord::Transaction object, which allows registering callbacks on it.

Article.transaction do |transaction|
  article.update(published: true)

  transaction.after_commit do
    PublishNotificationMailer.with(article: article).deliver_later
  end
end

ActiveRecord::Base.current_transaction was also added to allow to register callbacks on it.

Article.current_transaction.after_commit do
  PublishNotificationMailer.with(article: article).deliver_later
end

And finally, ActiveRecord.after_all_transactions_commit was added, for code that may run either inside or outside a transaction and needs to perform work after the state changes have been properly persisted.

def publish_article(article)
  article.update(published: true)

  ActiveRecord.after_all_transactions_commit do
    PublishNotificationMailer.with(article: article).deliver_later
  end
end

See #51474 and #51426 for more information:

2.11. Enable YJIT by default if running Ruby 3.3+

YJIT is Ruby's JIT compiler that is available in CRuby since Ruby 3.1. It can provide significant performance improvements for Rails applications, offering 15-25% latency improvements.

In Rails 7.2, YJIT is enabled by default if running Ruby 3.3 or newer.

You can disable YJIT by setting:

Rails.application.config.yjit = false

2.12. New design for the Rails guides

When Rails 7.0 landed in December 2021, it came with a fresh new homepage and a new boot screen. The design of the guides, however, has remained largely untouched since 2009 - a point which hasn’t gone unnoticed (we heard your feedback).

With all of the work right now going into removing complexity from the Rails framework and making the documentation consistent, clear, and up-to-date, it was time to tackle the design of the guides and make them equally modern, simple, and fresh.

We worked with UX designer John Athayde to take the look and feel of the homepage and transfer that over to the Rails guides to make them clean, sleek, and up-to-date.

The layout will remain the same, but from today you will see the following changes reflected in the guides:

Cleaner, less busy design.
Fonts, color scheme, and logo more consistent with the home page.
Updated iconography.
Simplified navigation.
Sticky "Chapters" navbar when scrolling.

See the announcement blog post for some before/after images.

Remove deprecated Rails::Generators::Testing::Behaviour.
Remove deprecated Rails.application.secrets.
Remove deprecated Rails.config.enable_dependency_loading.
Remove deprecated find_cmd_and_exec console helper.
Remove support for oracle, sqlserver, and JRuby specific database adapters from the new and db:system:change rails commands.
Remove config.public_file_server.enabled option from the generators.

3.2. Deprecations

3.3. Notable changes

Add RuboCop with rules from rubocop-rails-omakase by default in both new applications and plugins.
Add Brakeman with default configuration for security checks in new applications.
Add GitHub CI files for Dependabot, Brakeman, RuboCop, and running tests by default for new applications and plugins.
YJIT is now enabled by default for new applications running on Ruby 3.3+.
Generate a .devcontainer folder for running the application in a container with Visual Studio Code.
```
$ rails new myapp --devcontainer
```
Introduce Rails::Generators::Testing::Assertions#assert_initializer to test initializers.
System tests now use Headless Chrome by default for new applications.
Support the BACKTRACE environment variable to turn off backtrace cleaning in normal server runnings. Previously, this was only available for testing.
Add default Progressive Web App (PWA) files for the manifest and service worker, served from app/views/pwa, and make them dynamically renderable through ERB.

Remove deprecated constant ActionDispatch::IllegalStateError.
Remove deprecated constant AbstractController::Helpers::MissingHelperError.
Remove deprecated comparison between ActionController::Parameters and Hash.
Remove deprecated Rails.application.config.action_dispatch.return_only_request_media_type_on_content_type.
Remove deprecated speaker, vibrate, and vr permissions policy directives.
Remove deprecated support to set Rails.application.config.action_dispatch.show_exceptions to true and false.

5.2. Deprecations

Deprecate Rails.application.config.action_controller.allow_deprecated_parameters_hash_equality.

Remove deprecated @rails/ujs in favor of Turbo.

6.2. Deprecations

Deprecate passing content to void elements when using tag.br type tag builders.

Remove deprecated config.action_mailer.preview_path.
Remove deprecated params via :args for assert_enqueued_email_with.

Remove deprecated Rails.application.config.active_record.suppress_multiple_database_warning.
Remove deprecated support to call alias_attribute with non-existent attribute names.
Remove deprecated name argument from ActiveRecord::Base.remove_connection.
Remove deprecated ActiveRecord::Base.clear_active_connections!.
Remove deprecated ActiveRecord::Base.clear_reloadable_connections!.
Remove deprecated ActiveRecord::Base.clear_all_connections!.
Remove deprecated ActiveRecord::Base.flush_idle_connections!.
Remove deprecated ActiveRecord::ActiveJobRequiredError.
Remove deprecated support to define explain in the connection adapter with 2 arguments.
Remove deprecated ActiveRecord::LogSubscriber.runtime method.
Remove deprecated ActiveRecord::LogSubscriber.runtime= method.
Remove deprecated ActiveRecord::LogSubscriber.reset_runtime method.
Remove deprecated ActiveRecord::Migration.check_pending method.
Remove deprecated support to passing SchemaMigration and InternalMetadata classes as arguments to ActiveRecord::MigrationContext.
Remove deprecated behavior to support referring to a singular association by its plural name.
Remove deprecated TestFixtures.fixture_path.
Remove deprecated support to ActiveRecord::Base#read_attribute(:id) to return the custom primary key value.
Remove deprecated support to passing coder and class as second argument to serialize.
Remove deprecated #all_foreign_keys_valid? from database adapters.
Remove deprecated ActiveRecord::ConnectionAdapters::SchemaCache.load_from.
Remove deprecated ActiveRecord::ConnectionAdapters::SchemaCache#data_sources.
Remove deprecated #all_connection_pools.
Remove deprecated support to apply #connection_pool_list, #active_connections?, #clear_active_connections!, #clear_reloadable_connections!, #clear_all_connections! and #flush_idle_connections! to the connections pools for the current role when the role argument isn't provided.
Remove deprecated ActiveRecord::ConnectionAdapters::ConnectionPool#connection_klass.
Remove deprecated #quote_bound_value.
Remove deprecated support to quote ActiveSupport::Duration.
Remove deprecated support to pass deferrable: true to add_foreign_key.
Remove deprecated support to pass rewhere to ActiveRecord::Relation#merge.
Remove deprecated behavior that would rollback a transaction block when exited using return, break or throw.

8.2. Deprecations

Deprecate Rails.application.config.active_record.allow_deprecated_singular_associations_name
Deprecate Rails.application.config.active_record.commit_transaction_on_non_local_return

Remove deprecated config.active_storage.replace_on_assign_to_many.
Remove deprecated config.active_storage.silence_invalid_content_types_warning.

Remove deprecated ActiveSupport::Notifications::Event#children and ActiveSupport::Notifications::Event#parent_of?.
Remove deprecated support to call the following methods without passing a deprecator:
- deprecate
- deprecate_constant
- ActiveSupport::Deprecation::DeprecatedObjectProxy.new
- ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new
- ActiveSupport::Deprecation::DeprecatedConstantProxy.new
- assert_deprecated
- assert_not_deprecated
- collect_deprecations
Remove deprecated ActiveSupport::Deprecation delegation to instance.
Remove deprecated SafeBuffer#clone_empty.
Remove deprecated #to_default_s from Array, Date, DateTime and Time.
Remove deprecated :pool_size and :pool_timeout options for the cache storage.
Remove deprecated support for config.active_support.cache_format_version = 6.1.
Remove deprecated constants ActiveSupport::LogSubscriber::CLEAR and ActiveSupport::LogSubscriber::BOLD.
Remove deprecated support to bolding log text with positional boolean in ActiveSupport::LogSubscriber#color.
Remove deprecated config.active_support.disable_to_s_conversion.
Remove deprecated config.active_support.remove_deprecated_time_with_zone_name.
Remove deprecated config.active_support.use_rfc4122_namespaced_uuids.
Remove deprecated support to passing Dalli::Client instances to MemCacheStore.

Remove deprecated primitive serializer for BigDecimal arguments.
Remove deprecated support to set numeric values to scheduled_at attribute.
Remove deprecated :exponentially_longer value for the :wait in retry_on.

12.2. Deprecations

Deprecate Rails.application.config.active_job.use_big_decimal_serialize.