Update "Ruby on Rails 5.2 Release Notes" Guide [ci skip]

- Add a description of major features in Rails 5.2.
- Add a reference to Pull Request/Commit to every entry in CHANGELOGs,
  note that some of them combined.
- Add section "Ruby on Rails Guides" with notable changes.
- Note that
  - Skipped this since encrypted secrets are already on the way out.
    ```
    *   Add `rails secrets:show` command.
        ([Pull Request](https://github.com/rails/rails/pull/29695))
    ```
  - Skipped this since it was backported all the way to 5-0-stable.
    ```
    *   Make Rails' test runner work better with minitest plugins.
        ([Pull Request](https://github.com/rails/rails/pull/29572))
    ```

Thanks to everyone who has been working on Rails 5.2! <3

1 files changed, 896 insertions, 47 deletions

diff --git a/guides/source/5_2_release_notes.md b/guides/source/5_2_release_notes.md
index 7b5c4b87e3..1136f3303c 100644
--- a/guides/source/5_2_release_notes.md
+++ b/guides/source/5_2_release_notes.md
@@ -7,9 +7,9 @@ Highlights in Rails 5.2:
 
 * Active Storage
 * Redis Cache Store
-* HTTP/2 Early hints support
+* HTTP/2 Early Hints
 * Credentials
-* Default Content Security Policy
+* Content Security Policy
 
 These release notes cover only the major changes. To learn about various bug
 fixes and changes, please refer to the change logs or check out the [list of
@@ -24,39 +24,130 @@ Upgrading to Rails 5.2
 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 5.1 in case you
 haven't and make sure your application still runs as expected before attempting
-an update to Rails 5.2.
-
+an update to Rails 5.2. A list of things to watch out for when upgrading is
+available in the
+[Upgrading Ruby on Rails](upgrading_ruby_on_rails.html#upgrading-from-rails-5-1-to-rails-5-2)
+guide.
 
 Major Features
 --------------
 
 ### Active Storage
 
-[README](https://github.com/rails/rails/blob/d3893ec38ec61282c2598b01a298124356d6b35a/activestorage/README.md)
+[Pull Request](https://github.com/rails/rails/pull/30020)
+
+[Active Storage](https://github.com/rails/rails/tree/5-2-stable/activestorage)
+facilitates uploading files to a cloud storage service like
+Amazon S3, Google Cloud Storage, or Microsoft Azure Storage and attaching
+those files to Active Record objects. It comes with a local disk-based service
+for development and testing and supports mirroring files to subordinate
+services for backups and migrations.
+You can read more about Active Storage in the
+[Active Storage Overview](active_storage_overview.html) guide.
 
 ### Redis Cache Store
 
 [Pull Request](https://github.com/rails/rails/pull/31134)
 
+Rails 5.2 ships with built-in Redis cache store.
+You can read more about this in the
+[Caching with Rails: An Overview](caching_with_rails.html#activesupport-cache-rediscachestore)
+guide.
 
-### HTTP/2 Early hints support
+### HTTP/2 Early Hints
 
 [Pull Request](https://github.com/rails/rails/pull/30744)
 
+Rails 5.2 supports [HTTP/2 Early Hints](https://tools.ietf.org/html/rfc8297).
+To start the server with Early Hints enabled pass `--early-hints`
+to `bin/rails server`.
 
 ### Credentials
 
 [Pull Request](https://github.com/rails/rails/pull/30067)
 
+Added `config/credentials.yml.enc` file to store production app secrets.
+It allows saving any authentication credentials for third-party services
+directly in repository encrypted with a key in the `config/master.key` file or
+the `RAILS_MASTER_KEY` environment variable.
+This will eventually replace `Rails.application.secrets` and the encrypted
+secrets introduced in Rails 5.1.
+Furthermore, Rails 5.2
+[opens API underlying Credentials](https://github.com/rails/rails/pull/30940),
+so you can easily deal with other encrypted configurations, keys, and files.
 
-### Default Content Security Policy
+### Content Security Policy
 
 [Pull Request](https://github.com/rails/rails/pull/31162)
 
-Incompatibilities
------------------
-
-ToDo
+Rails 5.2 ships with a new DSL that allows you to configure a
+[Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy)
+for your application. You can configure a global default policy and then
+override it on a per-resource basis and even use lambdas to inject per-request
+values into the header such as account subdomains in a multi-tenant application.
+
+Example global policy:
+
+```ruby
+# config/initializers/content_security_policy.rb
+Rails.application.config.content_security_policy do |policy|
+  policy.default_src :self, :https
+  policy.font_src    :self, :https, :data
+  policy.img_src     :self, :https, :data
+  policy.object_src  :none
+  policy.script_src  :self, :https
+  policy.style_src   :self, :https
+
+  # Specify URI for violation reports
+  policy.report_uri "/csp-violation-report-endpoint"
+end
+```
+
+Example controller overrides:
+
+```ruby
+# Override policy inline
+class PostsController < ApplicationController
+  content_security_policy do |p|
+    p.upgrade_insecure_requests true
+  end
+end
+
+# Using literal values
+class PostsController < ApplicationController
+  content_security_policy do |p|
+    p.base_uri "https://www.example.com"
+  end
+end
+
+# Using mixed static and dynamic values
+class PostsController < ApplicationController
+  content_security_policy do |p|
+    p.base_uri :self, -> { "https://#{current_user.domain}.example.com" }
+  end
+end
+
+# Disabling the global CSP
+class LegacyPagesController < ApplicationController
+  content_security_policy false, only: :index
+end
+```
+
+To report only content violations for migrating
+legacy content using the `content_security_policy_report_only`
+configuration attribute:
+
+```ruby
+# config/initializers/content_security_policy.rb
+Rails.application.config.content_security_policy_report_only = true
+```
+
+```ruby
+# Controller override
+class PostsController < ApplicationController
+  content_security_policy_report_only only: :index
+end
+```
 
 Railties
 --------
@@ -68,36 +159,128 @@ Please refer to the [Changelog][railties] for detailed changes.
 *   Deprecate `capify!` method in generators and templates.
     ([Pull Request](https://github.com/rails/rails/pull/29493))
 
-*   Deprecated passing the environment's name as a regular argument to the
-    `rails dbconsole` and `rails console` commands.
-    ([Pull Request](https://github.com/rails/rails/pull/29358))
+*   Passing the environment's name as a regular argument to the
+    `rails dbconsole` and `rails console` commands is deprecated.
+    The `-e` option should be used instead.
+    ([Commit](https://github.com/rails/rails/commit/48b249927375465a7102acc71c2dfb8d49af8309))
 
-*   Deprecated using subclass of `Rails::Application` to start the Rails server.
+*   Deprecate using subclass of `Rails::Application` to start the Rails server.
     ([Pull Request](https://github.com/rails/rails/pull/30127))
 
-*   Deprecated `after_bundle` callback in Rails plugin templates.
+*   Deprecate `after_bundle` callback in Rails plugin templates.
     ([Pull Request](https://github.com/rails/rails/pull/29446))
 
 ### Notable changes
 
-ToDo
+*   Namespace error pages' CSS selectors to stop the styles from bleeding
+    into other pages when using Turbolinks.
+    ([Pull Request](https://github.com/rails/rails/pull/28814))
+
+*   Added a shared section to `config/database.yml` that will be loaded for
+    all environments.
+    ([Pull Request](https://github.com/rails/rails/pull/28896))
+
+*   Allow irb options to be passed from `rails console` command.
+    ([Pull Request](https://github.com/rails/rails/pull/29010))
+
+*   Add `railtie.rb` to the plugin generator.
+    ([Pull Request](https://github.com/rails/rails/pull/29576))
+
+*   Clear screenshot files in `tmp:clear` task.
+    ([Pull Request](https://github.com/rails/rails/pull/29534))
+
+*   Allow mounting the same engine several times in different locations.
+    ([Pull Request](https://github.com/rails/rails/pull/29662))
+
+*   Load environment file in `dbconsole` command.
+    ([Pull Request](https://github.com/rails/rails/pull/29725))
+
+*   Skip unused components when running `bin/rails app:update`.
+    If the initial app generation skipped Action Cable, Active Record etc.,
+    the update task honors those skips too.
+    ([Pull Request](https://github.com/rails/rails/pull/29645))
+
+*   Allow passing a custom connection name to the `rails dbconsole`
+    command when using a 3-level database configuration.
+    Example: `bin/rails dbconsole -c replica`.
+    ([Commit](https://github.com/rails/rails/commit/1acd9a6464668d4d54ab30d016829f60b70dbbeb))
+
+*   Properly expand shortcuts for environment's name running the `console`
+    and `dbconsole` commands.
+    ([Commit](https://github.com/rails/rails/commit/3777701f1380f3814bd5313b225586dec64d4104))
+
+*   Add `bootsnap` to default `Gemfile`.
+    ([Pull Request](https://github.com/rails/rails/pull/29313))
+
+*   Support `-` as a platform-agnostic way to run a script from stdin with
+    `rails runner`
+    ([Pull Request](https://github.com/rails/rails/pull/26343))
+
+*   Add `ruby x.x.x` version to `Gemfile` and create `.ruby-version`
+    root file containing the current Ruby version when new Rails applications
+    are created.
+    ([Pull Request](https://github.com/rails/rails/pull/30016))
+
+*   Add `--skip-action-cable` option to the plugin generator.
+    ([Pull Request](https://github.com/rails/rails/pull/30164))
+
+*   Add `git_source` to `Gemfile` for plugin generator.
+    ([Pull Request](https://github.com/rails/rails/pull/30110))
+
+*   Skip unused components when running `bin/rails` in Rails plugin.
+    ([Commit](https://github.com/rails/rails/commit/62499cb6e088c3bc32a9396322c7473a17a28640))
+
+*   Optimize indentation for generator actions.
+    ([Pull Request](https://github.com/rails/rails/pull/30166))
+
+*   Optimize routes indentation.
+    ([Pull Request](https://github.com/rails/rails/pull/30241))
+
+*   Add `--skip-yarn` option to the plugin generator.
+    ([Pull Request](https://github.com/rails/rails/pull/30238))
+
+*   Support multiple versions arguments for `gem` method of Generators.
+    ([Pull Request](https://github.com/rails/rails/pull/30323))
+
+*   Derive `secret_key_base` from the app name in development and test
+    environments.
+    ([Pull Request](https://github.com/rails/rails/pull/30067))
+
+*   Add `mini_magick` to default `Gemfile` as comment.
+    ([Pull Request](https://github.com/rails/rails/pull/30633))
+
+*   Gemfile for new apps: upgrade redis-rb from ~> 3.0 to 4.0.
+    ([Pull Request](https://github.com/rails/rails/pull/30748))
+
+*   `rails new` and `rails plugin new` get `Active Storage` by default.
+     Add ability to skip `Active Storage` with `--skip-active-storage`
+     and do so automatically when `--skip-active-record` is used.
+    ([Pull Request](https://github.com/rails/rails/pull/30101))
+
+*   Fix minitest rails plugin.
+    The custom reporters are added only if needed.
+    This will fix conflicts with others plugins.
+    ([Commit](https://github.com/rails/rails/commit/ac99916fcf7bf27bb1519d4f7387c6b4c5f0463d))
 
 Action Cable
------------
+------------
 
 Please refer to the [Changelog][action-cable] for detailed changes.
 
 ### Removals
 
 *   Removed deprecated evented redis adapter.
-    ([Commit](https://github.com/rails/rails/commit/48766e32d31))
+    ([Commit](https://github.com/rails/rails/commit/48766e32d31651606b9f68a16015ad05c3b0de2c))
 
 ### Notable changes
 
-*   Added support for `host`, `port`, `db` and `password` options in cable.yml
+*   Add support for `host`, `port`, `db` and `password` options in cable.yml
     ([Pull Request](https://github.com/rails/rails/pull/29528))
 
-*   Added support for compatibility with redis-rb gem for 4.0 version.
+*   Hash long stream identifiers when using PostgreSQL adapter.
+    ([Pull Request](https://github.com/rails/rails/pull/29297))
+
+*   Add support for compatibility with redis-rb gem for 4.0 version.
     ([Pull Request](https://github.com/rails/rails/pull/30748))
 
 Action Pack
@@ -107,38 +290,158 @@ Please refer to the [Changelog][action-pack] for detailed changes.
 
 ### Removals
 
-*   Removed deprecated `ActionController::ParamsParser::ParseError`.
-    ([Commit](https://github.com/rails/rails/commit/e16c765ac6d))
+*   Remove deprecated `ActionController::ParamsParser::ParseError`.
+    ([Commit](https://github.com/rails/rails/commit/e16c765ac6dcff068ff2e5554d69ff345c003de1))
 
 ### Deprecations
 
-*   Deprecated `#success?`, `#missing?` and `#error?` aliases of
+*   Deprecate `#success?`, `#missing?` and `#error?` aliases of
     `ActionDispatch::TestResponse`.
     ([Pull Request](https://github.com/rails/rails/pull/30104))
 
 ### Notable changes
 
-ToDo
+*   Add `action_controller_api` and `action_controller_base` load hooks to be
+    called in `ActiveSupport.on_load`.
+    ([Pull Request](https://github.com/rails/rails/pull/28402))
+
+*   Add support for recyclable cache keys with fragment caching.
+    ([Pull Request](https://github.com/rails/rails/pull/29092))
+
+*   Change the cache key format for fragments to make it easier to debug key
+    churn.
+    ([Pull Request](https://github.com/rails/rails/pull/29092))
+
+*   AEAD encrypted cookies and sessions with GCM.
+    ([Pull Request](https://github.com/rails/rails/pull/28132))
+
+*   `driven_by` now registers poltergeist and capybara-webkit.
+    ([Pull Request](https://github.com/rails/rails/pull/29315))
+
+*   Fallback `ActionController::Parameters#to_s` to `Hash#to_s`.
+    ([Pull Request](https://github.com/rails/rails/pull/29630))
+
+*   Protect from forgery by default.
+    ([Pull Request](https://github.com/rails/rails/pull/29742))
+
+*   Make `take_failed_screenshot` work within engine.
+    ([Pull Request](https://github.com/rails/rails/pull/30421))
+
+*   Enforce signed/encrypted cookie expiry server side.
+    ([Pull Request](https://github.com/rails/rails/pull/30121))
+
+*   Cookies `:expires` option supports `ActiveSupport::Duration` object.
+    ([Pull Request](https://github.com/rails/rails/pull/30121))
+
+*   Use Capybara registered `:puma` server config.
+    ([Pull Request](https://github.com/rails/rails/pull/30638))
+
+*   Simplify cookies middleware with key rotation support.
+    ([Pull Request](https://github.com/rails/rails/pull/29716))
+
+*   Add ability to enable Early Hints for HTTP/2.
+    ([Pull Request](https://github.com/rails/rails/pull/30744))
+
+*   Add headless chrome support to System Tests.
+    ([Pull Request](https://github.com/rails/rails/pull/30876))
+
+*   Add `:allow_other_host` option to `redirect_back` method.
+    ([Pull Request](https://github.com/rails/rails/pull/30850))
+
+*   Make `assert_recognizes` to traverse mounted engines.
+    ([Pull Request](https://github.com/rails/rails/pull/22435))
+
+*   Add DSL for configuring Content-Security-Policy header.
+    ([Pull Request](https://github.com/rails/rails/pull/31162),
+    [Commit](https://github.com/rails/rails/commit/619b1b6353a65e1635d10b8f8c6630723a5a6f1a),
+    [Commit](https://github.com/rails/rails/commit/4ec8bf68ff92f35e79232fbd605012ce1f4e1e6e))
+
+*   Fix optimized url helpers when using relative url root.
+    ([Pull Request](https://github.com/rails/rails/pull/31261))
+
+*   Register most popular audio/video/font mime types supported by modern
+    browsers.
+    ([Pull Request](https://github.com/rails/rails/pull/31251))
+
+*   Changed the default system test screenshot output from `inline` to `simple`.
+    ([Commit](https://github.com/rails/rails/commit/9d6e288ee96d6241f864dbf90211c37b14a57632))
+
+*   Add headless firefox support to System Tests.
+    ([Pull Request](https://github.com/rails/rails/pull/31365))
+
+*   Add secure `X-Download-Options` and `X-Permitted-Cross-Domain-Policies` to
+    default headers set.
+    ([Commit](https://github.com/rails/rails/commit/5d7b70f4336d42eabfc403e9f6efceb88b3eff44))
+
+*   Changed the system tests to set Puma as default server only when the
+    user haven't specified manually another server.
+    ([Pull Request](https://github.com/rails/rails/pull/31384))
+
+*   Add `Referrer-Policy` header to default headers set.
+    ([Commit](https://github.com/rails/rails/commit/428939be9f954d39b0c41bc53d85d0d106b9d1a1))
+
+*   Matches behavior of `Hash#each` in `ActionController::Parameters#each`.
+    ([Pull Request](https://github.com/rails/rails/pull/27790))
+
+*   Add support for automatic nonce generation for Rails UJS.
+    ([Commit](https://github.com/rails/rails/commit/b2f0a8945956cd92dec71ec4e44715d764990a49))
+
+*   Update the default HSTS max-age value to 31536000 seconds (1 year)
+    to meet the minimum max-age requirement for https://hstspreload.org/.
+    ([Commit](https://github.com/rails/rails/commit/30b5f469a1d30c60d1fb0605e84c50568ff7ed37))
+
+*   Add alias method `to_hash` to `to_h` for `cookies`.
+    Add alias method `to_h` to `to_hash` for `session`.
+    ([Commit](https://github.com/rails/rails/commit/50a62499e41dfffc2903d468e8b47acebaf9b500))
 
 Action View
--------------
+-----------
 
 Please refer to the [Changelog][action-view] for detailed changes.
 
 ### Removals
 
-*   Removed deprecated Erubis ERB handler.
-    ([Commit](https://github.com/rails/rails/commit/7de7f12fd14))
+*   Remove deprecated Erubis ERB handler.
+    ([Commit](https://github.com/rails/rails/commit/7de7f12fd140a60134defe7dc55b5a20b2372d06))
 
 ### Deprecations
 
-*   Deprecated `image_alt` helper which used to add default alt text to
+*   Deprecate `image_alt` helper which used to add default alt text to
     the images generated by `image_tag`.
     ([Pull Request](https://github.com/rails/rails/pull/30213))
 
 ### Notable changes
 
-ToDo
+*   Update `distance_of_time_in_words` helper to display better error messages
+    for bad input.
+    ([Pull Request](https://github.com/rails/rails/pull/20701))
+
+*   Add `:json` type to `auto_discovery_link_tag` to support
+    [JSON Feeds](https://jsonfeed.org/version/1).
+    ([Pull Request](https://github.com/rails/rails/pull/29158))
+
+*   Generate field ids in `collection_check_boxes` and
+    `collection_radio_buttons`.
+    ([Pull Request](https://github.com/rails/rails/pull/29412))
+
+*   Fix issues with scopes and engine on `current_page?` method.
+    ([Pull Request](https://github.com/rails/rails/pull/29503))
+
+*   Add `srcset` option to `image_tag` helper.
+    ([Pull Request](https://github.com/rails/rails/pull/29349))
+
+*   Fix issues with `field_error_proc` wrapping `optgroup` and
+    select divider `option`.
+    ([Pull Request](https://github.com/rails/rails/pull/31088))
+
+*   Change `form_with` to generates ids by default.
+    ([Commit](https://github.com/rails/rails/commit/260d6f112a0ffdbe03e6f5051504cb441c1e94cd))
+
+*   Add `preload_link_tag` helper.
+    ([Pull Request](https://github.com/rails/rails/pull/31251))
+
+*   Allow the use of callable objects as group methods for grouped selects.
+    ([Pull Request](https://github.com/rails/rails/pull/31578))
 
 Action Mailer
 -------------
@@ -147,35 +450,399 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
 
 ### Notable changes
 
-ToDo
+*   Allow Action Mailer classes to configure their delivery job.
+    ([Pull Request](https://github.com/rails/rails/pull/29457))
+
+*   Add `assert_enqueued_email_with` test helper.
+    ([Pull Request](https://github.com/rails/rails/pull/30695))
+
+*   Bring back proc with arity of 1 in `ActionMailer::Base.default` proc
+    since it was supported in Rails 5.0 but not deprecated.
+    ([Pull Request](https://github.com/rails/rails/pull/30391))
 
 Active Record
 -------------
 
 Please refer to the [Changelog][active-record] for detailed changes.
 
-ToDo
+### Removals
+
+*   Remove deprecated `#migration_keys`.
+    ([Pull Request](https://github.com/rails/rails/pull/30337))
+
+*   Remove deprecated support to `quoted_id` when typecasting
+    an Active Record object.
+    ([Commit](https://github.com/rails/rails/commit/82472b3922bda2f337a79cef961b4760d04f9689))
+
+*   Remove deprecated argument `default` from `index_name_exists?`.
+    ([Commit](https://github.com/rails/rails/commit/8f5b34df81175e30f68879479243fbce966122d7))
+
+*   Remove deprecated support to passing a class to `:class_name`
+    on associations.
+    ([Commit](https://github.com/rails/rails/commit/e65aff70696be52b46ebe57207ebd8bb2cfcdbb6))
+
+*   Remove deprecated methods `initialize_schema_migrations_table` and
+    `initialize_internal_metadata_table`.
+    ([Commit](https://github.com/rails/rails/commit/c9660b5777707658c414b430753029cd9bc39934))
+
+*   Remove deprecated method `supports_migrations?`.
+    ([Commit](https://github.com/rails/rails/commit/9438c144b1893f2a59ec0924afe4d46bd8d5ffdd))
+
+*   Remove deprecated method `supports_primary_key?`.
+    ([Commit](https://github.com/rails/rails/commit/c56ff22fc6e97df4656ddc22909d9bf8b0c2cbb1))
+
+*   Remove deprecated method
+    `ActiveRecord::Migrator.schema_migrations_table_name`.
+    ([Commit](https://github.com/rails/rails/commit/7df6e3f3cbdea9a0460ddbab445c81fbb1cfd012))
+
+*   Remove deprecated argument `name` from `#indexes`.
+    ([Commit](https://github.com/rails/rails/commit/d6b779ecebe57f6629352c34bfd6c442ac8fba0e))
+
+*   Remove deprecated arguments from `#verify!`.
+    ([Commit](https://github.com/rails/rails/commit/9c6ee1bed0292fc32c23dc1c68951ae64fc510be))
+
+*   Remove deprecated configuration `.error_on_ignored_order_or_limit`.
+    ([Commit](https://github.com/rails/rails/commit/e1066f450d1a99c9a0b4d786b202e2ca82a4c3b3))
+
+*   Remove deprecated method `#scope_chain`.
+    ([Commit](https://github.com/rails/rails/commit/ef7784752c5c5efbe23f62d2bbcc62d4fd8aacab))
+
+*   Remove deprecated method `#sanitize_conditions`.
+    ([Commit](https://github.com/rails/rails/commit/8f5413b896099f80ef46a97819fe47a820417bc2))
 
 ### Deprecations
 
-ToDo
+*   Deprecate `supports_statement_cache?`.
+    ([Pull Request](https://github.com/rails/rails/pull/28938))
+
+*   Deprecate passing arguments and block at the same time to
+    `count` and `sum` in `ActiveRecord::Calculations`.
+    ([Pull Request](https://github.com/rails/rails/pull/29262))
+
+*   Deprecate delegating to `arel` in `Relation`.
+    ([Pull Request](https://github.com/rails/rails/pull/29619))
+
+*   Deprecate `set_state` method in `TransactionState`.
+    ([Commit](https://github.com/rails/rails/commit/608ebccf8f6314c945444b400a37c2d07f21b253))
+
+*   Deprecate `expand_hash_conditions_for_aggregates` without replacement.
+    ([Commit](https://github.com/rails/rails/commit/7ae26885d96daee3809d0bd50b1a440c2f5ffb69))
 
 ### Notable changes
 
-ToDo
+*   When calling the dynamic fixture accessor method with no arguments, it now
+    returns all fixtures of this type. Previously this method always returned
+    an empty array.
+    ([Pull Request](https://github.com/rails/rails/pull/28692))
+
+*   Fix inconsistency with changed attributes when overriding
+    Active Record attribute reader.
+    ([Pull Request](https://github.com/rails/rails/pull/28661))
+
+*   Support Descending Indexes for MySQL.
+    ([Pull Request](https://github.com/rails/rails/pull/28773))
+
+*   Fix `bin/rails db:forward` first migration.
+    ([Commit](https://github.com/rails/rails/commit/b77d2aa0c336492ba33cbfade4964ba0eda3ef84))
+
+*   Raise error `UnknownMigrationVersionError` on the movement of migrations
+    when the current migration does not exist.
+    ([Commit](https://github.com/rails/rails/commit/bb9d6eb094f29bb94ef1f26aa44f145f17b973fe))
+
+*   Add type caster to `RuntimeReflection#alias_name`.
+    ([Pull Request](https://github.com/rails/rails/pull/28961))
+
+*   Respect `SchemaDumper.ignore_tables` in rake tasks for
+    databases structure dump.
+    ([Pull Request](https://github.com/rails/rails/pull/29077))
+
+*   Add `ActiveRecord::Base#cache_version` to support recyclable cache keys via
+    the new versioned entries in `ActiveSupport::Cache`. This also means that
+    `ActiveRecord::Base#cache_key` will now return a stable key that
+    does not include a timestamp any more.
+    ([Pull Request](https://github.com/rails/rails/pull/29092))
+
+*   Loading model schema from database is now thread-safe.
+    ([Pull Request](https://github.com/rails/rails/pull/29216))
+
+*   Prevent creation of bind param if casted value is nil.
+    ([Pull Request](https://github.com/rails/rails/pull/29282))
+
+*   Use bulk INSERT to insert fixtures for better performance.
+    ([Pull Request](https://github.com/rails/rails/pull/29504))
+
+*   Fix destroying existing object does not work well when optimistic locking
+    enabled and `locking_column` is null in the database.
+    ([Pull Request](https://github.com/rails/rails/pull/28926))
+
+*   `ActiveRecord::Persistence#touch` does not work well
+    when optimistic locking enabled and `locking_column`,
+    without default value, is null in the database.
+    ([Pull Request](https://github.com/rails/rails/pull/28914))
+
+*   Merging two relations representing nested joins no longer transforms
+    the joins of the merged relation into LEFT OUTER JOIN.
+    ([Pull Request](https://github.com/rails/rails/pull/27063))
+
+*   Previously, when building records using a `has_many :through` association,
+    if the child records were deleted before the parent was saved,
+    they would still be persisted. Now, if child records are deleted
+    before the parent is saved on a `has_many :through` association,
+    the child records will not be persisted.
+    ([Pull Request](https://github.com/rails/rails/pull/29593))
+
+*   Query cache was unavailable when entering the `ActiveRecord::Base.cache`
+    block without being connected.
+    ([Pull Request](https://github.com/rails/rails/pull/29609))
+
+*   Fix transactions to apply state to child transactions.
+    Previously, if you had a nested transaction and the outer transaction was
+    rolledback, the record from the inner transaction would still be marked
+    as persisted. It was fixed by applying the state of the parent
+    transaction to the child transaction when the parent transaction is
+    rolledback. This will correctly mark records from the inner transaction
+    as not persisted.
+    ([Commit](https://github.com/rails/rails/commit/0237da287eb4c507d10a0c6d94150093acc52b03))
+
+*   Fix eager loading/preloading association with scope including joins.
+    ([Pull Request](https://github.com/rails/rails/pull/29413))
+
+*   Prevent errors raised by `sql.active_record` notification subscribers
+    from being converted into `ActiveRecord::StatementInvalid` exceptions.
+    ([Pull Request](https://github.com/rails/rails/pull/29692))
+
+*   Skip query caching when working with batches of records
+    (`find_each`, `find_in_batches`, `in_batches`).
+    ([Commit](https://github.com/rails/rails/commit/b83852e6eed5789b23b13bac40228e87e8822b4d))
+
+*   Change sqlite3 boolean serialization to use 1 and 0.
+    SQLite natively recognizes 1 and 0 as true and false, but does not natively
+    recognize 't' and 'f' as was previously serialized.
+    ([Pull Request](https://github.com/rails/rails/pull/29699))
+
+*   `Relation#joins` is no longer affected by the target model's
+    `current_scope`, with the exception of `unscoped`.
+    ([Commit](https://github.com/rails/rails/commit/5c71000d086cc42516934415b79380c2224e1614))
+
+*   Values constructed using multi-parameter assignment will now use the
+    post-type-cast value for rendering in single-field form inputs.
+    ([Commit](https://github.com/rails/rails/commit/1519e976b224871c7f7dd476351930d5d0d7faf6))
+
+*   Fix `unscoped(where: [columns])` removing the wrong bind values.
+    ([Pull Request](https://github.com/rails/rails/pull/29780))
+
+*   When a `has_one` association is destroyed by `dependent: destroy`,
+    `destroyed_by_association` will now be set to the reflection, matching the
+    behaviour of `has_many` associations.
+    ([Pull Request](https://github.com/rails/rails/pull/29855))
+
+*   Fix `COUNT(DISTINCT ...)` with `ORDER BY` and `LIMIT`
+    to keep the existing select list.
+    ([Pull Request](https://github.com/rails/rails/pull/29848))
+
+*   `ApplicationRecord` is no longer generated when generating models. If you
+    need to generate it, it can be created with `rails g application_record`.
+    ([Pull Request](https://github.com/rails/rails/pull/29916))
+
+*   `Relation#or` now accepts two relations who have different values for
+    `references` only, as `references` can be implicitly called by `where`.
+    ([Commit](https://github.com/rails/rails/commit/ea6139101ccaf8be03b536b1293a9f36bc12f2f7))
+
+*   When using `Relation#or`, extract the common conditions and
+    put them before the OR condition.
+    ([Pull Request](https://github.com/rails/rails/pull/29950))
+
+*   Add `binary` fixture helper method.
+    ([Pull Request](https://github.com/rails/rails/pull/30073))
+
+*   Ensure `sum` honors `distinct` on `has_many :through` associations.
+    ([Commit](https://github.com/rails/rails/commit/566f1fd068711dfe557bef63406f8dd6d41d473d))
+
+*   Automatically guess the inverse associations for STI.
+    ([Pull Request](https://github.com/rails/rails/pull/23425))
+
+*   Add new error class `LockWaitTimeout` which will be raised
+    when lock wait timeout exceeded.
+    ([Pull Request](https://github.com/rails/rails/pull/30360))
+
+*   Update payload names for `sql.active_record` instrumentation to be
+    more descriptive.
+    ([Pull Request](https://github.com/rails/rails/pull/30619))
+
+*   Use given algorithm while removing index from database.
+    ([Pull Request](https://github.com/rails/rails/pull/24199))
+
+*   Passing a `Set` to `Relation#where` now behaves the same as passing
+    an array.
+    ([Commit](https://github.com/rails/rails/commit/9cf7e3494f5bd34f1382c1ff4ea3d811a4972ae2))
+
+*   PostgreSQL `tsrange` now preserves subsecond precision.
+    ([Pull Request](https://github.com/rails/rails/pull/30725))
+
+*   Fix `COUNT(DISTINCT ...)` for `GROUP BY` with `ORDER BY` and `LIMIT`.
+    ([Commit](https://github.com/rails/rails/commit/5668dc6b1863ef43be8f8ef0fb1d5db913085fb3))
+
+*   MySQL: Don't lose `auto_increment: true` in the `db/schema.rb`.
+    ([Commit](https://github.com/rails/rails/commit/9493d4553569118b2a85da84fd3a8ba2b5b2de76))
+
+*   Fix longer sequence name detection for serial columns.
+    ([Pull Request](https://github.com/rails/rails/pull/28339))
+
+*   Fix `bin/rails db:setup` and `bin/rails db:test:prepare` create wrong
+    ar_internal_metadata's data for a test database.
+    ([Pull Request](https://github.com/rails/rails/pull/30579))
+
+*   Raises when calling `lock!` in a dirty record.
+    ([Commit](https://github.com/rails/rails/commit/63cf15877bae859ff7b4ebaf05186f3ca79c1863))
+
+*   Fixed a bug where column orders for an index weren't written to
+    `db/schema.rb` when using the sqlite adapter.
+    ([Pull Request](https://github.com/rails/rails/pull/30970))
+
+*   Fix `bin/rails db:migrate` with specified `VERSION`.
+    `bin/rails db:migrate` with empty VERSION behaves as without `VERSION`.
+    Check a format of `VERSION`: Allow a migration version number
+    or name of a migration file. Raise error if format of `VERSION` is invalid.
+    Raise error if target migration doesn't exist.
+    ([Pull Request](https://github.com/rails/rails/pull/30714))
+
+*   Add new error class `StatementTimeout` which will be raised
+    when statement timeout exceeded.
+    ([Pull Request](https://github.com/rails/rails/pull/31129))
+
+*   `update_all` will now pass its values to `Type#cast` before passing them to
+    `Type#serialize`. This means that `update_all(foo: 'true')` will properly
+    persist a boolean.
+    ([Commit](https://github.com/rails/rails/commit/68fe6b08ee72cc47263e0d2c9ff07f75c4b42761))
+
+*   Require raw SQL fragments to be explicitly marked when used in
+    relation query methods.
+    ([Commit](https://github.com/rails/rails/commit/a1ee43d2170dd6adf5a9f390df2b1dde45018a48),
+    [Commit](https://github.com/rails/rails/commit/e4a921a75f8702a7dbaf41e31130fe884dea93f9))
+
+*   Add `#up_only` to database migrations for code that is only relevant when
+    migrating up, e.g. populating a new column.
+    ([Pull Request](https://github.com/rails/rails/pull/31082))
+
+*   Add new error class `QueryCanceled` which will be raised
+    when canceling statement due to user request.
+    ([Pull Request](https://github.com/rails/rails/pull/31235))
+
+*   Don't allow scopes to be defined which conflict with instance methods
+    on `Relation`.
+    ([Pull Request](https://github.com/rails/rails/pull/31179))
+
+*   Add support for PostgreSQL operator classes to `add_index`.
+    ([Pull Request](https://github.com/rails/rails/pull/19090))
+
+*   Fix conflicts `counter_cache` with `touch: true` by optimistic locking.
+    ([Pull Request](https://github.com/rails/rails/pull/31405))
+
+*   Log database query callers.
+    ([Pull Request](https://github.com/rails/rails/pull/26815),
+    [Pull Request](https://github.com/rails/rails/pull/31519),
+    [Pull Request](https://github.com/rails/rails/pull/31690))
+
+*   Undefine attribute methods on descendants when resetting column information.
+    ([Pull Request](https://github.com/rails/rails/pull/31475))
+
+*   Using subselect for `delete_all` with `limit` or `offset`.
+    ([Commit](https://github.com/rails/rails/commit/9e7260da1bdc0770cf4ac547120c85ab93ff3d48))
+
+*   Fix `count(:all)` to correctly work `distinct` with custom SELECT list.
+    ([Commit](https://github.com/rails/rails/commit/c6cd9a59f200863ccfe8ad1d9c5a8876c39b9c5c))
+
+*   Fix to invoke callbacks when using `update_attribute`.
+    ([Commit](https://github.com/rails/rails/commit/732aa34b6e6459ad66a3d3ad107cfff75cc45160))
+
+*   Use `count(:all)` in `HasManyAssociation#count_records` to prevent invalid
+    SQL queries for association counting.
+    ([Pull Request](https://github.com/rails/rails/pull/27561))
+
+*   Fixed inconsistency with `first(n)` when used with `limit()`.
+    The `first(n)` finder now respects the `limit()`, making it consistent
+    with `relation.to_a.first(n)`, and also with the behavior of `last(n)`.
+    ([Pull Request](https://github.com/rails/rails/pull/27597))
+
+*   Fix nested `has_many :through` associations on unpersisted parent instances.
+    ([Commit](https://github.com/rails/rails/commit/027f865fc8b262d9ba3ee51da3483e94a5489b66))
+
+*   Take into account association conditions when deleting through records.
+    ([Commit](https://github.com/rails/rails/commit/ae48c65e411e01c1045056562319666384bb1b63))
+
+*   Don't allow destroyed object mutation after `save` or `save!` is called.
+    ([Commit](https://github.com/rails/rails/commit/562dd0494a90d9d47849f052e8913f0050f3e494))
+
+*   Fix relation merger issue with `left_outer_joins`.
+    ([Pull Request](https://github.com/rails/rails/pull/27860))
+
+*   Support for PostgreSQL foreign tables.
+    ([Pull Request](https://github.com/rails/rails/pull/31549))
+
+*   Clear the transaction state when an Active Record object is duped.
+    ([Pull Request](https://github.com/rails/rails/pull/31751))
+
+*   Fix `count(:all)` with eager loading and having an order other than
+    the driving table.
+    ([Commit](https://github.com/rails/rails/commit/ebc09ed9ad9a04338138739226a1a92c7a2707ee))
+
+*   Fix not expanded problem when passing an Array object as argument
+    to the where method using `composed_of` column.
+    ([Pull Request](https://github.com/rails/rails/pull/31724))
+
+*   PostgreSQL: Allow pg-1.0 gem to be used with Active Record.
+    ([Pull Request](https://github.com/rails/rails/pull/31671))
+
+*   Make `reflection.klass` raise if `polymorphic?` not to be misused.
+    ([Commit](https://github.com/rails/rails/commit/63fc1100ce054e3e11c04a547cdb9387cd79571a))
+
+*   Fix `#columns_for_distinct` of MySQL and PostgreSQL to make
+    `ActiveRecord::FinderMethods#limited_ids_for` use correct primary key values
+    even if `ORDER BY` columns include other table's primary key.
+    ([Commit](https://github.com/rails/rails/commit/851618c15750979a75635530200665b543561a44))
+
+*   Fix that after commit callbacks on update does not triggered
+    when optimistic locking is enabled.
+    ([Commit](https://github.com/rails/rails/commit/7f9bd034c485c2425ae0164ff5d6374834e3aa1d))
+
+*   Fix `dependent: :destroy` issue for has_one/belongs_to relationship where
+    the parent class was getting deleted when the child was not.
+    ([Commit](https://github.com/rails/rails/commit/b0fc04aa3af338d5a90608bf37248668d59fc881))
 
 Active Model
 ------------
 
 Please refer to the [Changelog][active-model] for detailed changes.
 
-### Removals
+### Notable changes
 
-ToDo
+*   Fix methods `#keys`, `#values` in `ActiveModel::Errors`.
+    Change `#keys` to only return the keys that don't have empty messages.
+    Change `#values` to only return the not empty values.
+    ([Pull Request](https://github.com/rails/rails/pull/28584))
 
-### Notable changes
+*   Fix regression in numericality validator when comparing Decimal and Float
+    input values with more scale than the schema.
+    ([Pull Request](https://github.com/rails/rails/pull/28584))
+
+*   Add method `#merge!` for `ActiveModel::Errors`.
+    ([Pull Request](https://github.com/rails/rails/pull/29714))
+
+*   Allow passing a Proc or Symbol to length validator options.
+    ([Pull Request](https://github.com/rails/rails/pull/30674))
+
+*   Execute `ConfirmationValidator` validation when `_confirmation`'s value
+    is `false`.
+    ([Pull Request](https://github.com/rails/rails/pull/31058))
 
-ToDo
+*   Fix to working before/after validation callbacks on multiple contexts.
+    ([Pull Request](https://github.com/rails/rails/pull/31483))
+
+*   Models using the attributes API with a proc default can now be marshalled.
+    ([Commit](https://github.com/rails/rails/commit/0af36c62a5710e023402e37b019ad9982e69de4b))
+
+*   Do not lose all multiple `:includes` with options in serialization.
+    ([Commit](https://github.com/rails/rails/commit/853054bcc7a043eea78c97e7705a46abb603cc44))
 
 Active Support
 --------------
@@ -184,35 +851,216 @@ Please refer to the [Changelog][active-support] for detailed changes.
 
 ### Removals
 
-ToDo
+*   Remove deprecated `:if` and `:unless` string filter for callbacks.
+    ([Commit](https://github.com/rails/rails/commit/c792354adcbf8c966f274915c605c6713b840548))
+
+*   Remove deprecated `halt_callback_chains_on_return_false` option.
+    ([Commit](https://github.com/rails/rails/commit/19fbbebb1665e482d76cae30166b46e74ceafe29))
 
 ### Deprecations
 
-ToDo
+*   Deprecate `Module#reachable?` method.
+    ([Pull Request](https://github.com/rails/rails/pull/30624))
+
+*   Deprecate `secrets.secret_token`.
+    ([Commit](https://github.com/rails/rails/commit/fbcc4bfe9a211e219da5d0bb01d894fcdaef0a0e))
 
 ### Notable changes
 
-ToDo
+*   Add `fetch_values` for `HashWithIndifferentAccess`.
+    ([Pull Request](https://github.com/rails/rails/pull/28316))
+
+*   Add support for `:offset` to `Time#change`.
+    ([Commit](https://github.com/rails/rails/commit/851b7f866e13518d900407c78dcd6eb477afad06))
+
+*   Add support for `:offset` and `:zone`
+    to `ActiveSupport::TimeWithZone#change`.
+    ([Commit](https://github.com/rails/rails/commit/851b7f866e13518d900407c78dcd6eb477afad06))
+
+*   Pass gem name and deprecation horizon to deprecation notifications.
+    ([Pull Request](https://github.com/rails/rails/pull/28800))
+
+*   Add support for versioned cache entries. This enables the cache stores to
+    recycle cache keys, greatly saving on storage in cases with frequent churn.
+    Works together with the separation of `#cache_key` and `#cache_version`
+    in Active Record and its use in Action Pack's fragment caching.
+    ([Pull Request](https://github.com/rails/rails/pull/29092))
+
+*   Fix implicit coercion calculations with scalars and durations.
+    ([Pull Request](https://github.com/rails/rails/pull/29163),
+    [Pull Request](https://github.com/rails/rails/pull/29971))
+
+*   Add `ActiveSupport::CurrentAttributes` to provide a thread-isolated
+    attributes singleton. Primary use case is keeping all the per-request
+    attributes easily available to the whole system.
+    ([Pull Request](https://github.com/rails/rails/pull/29180))
+
+*   `#singularize` and `#pluralize` now respect uncountables for
+    the specified locale.
+    ([Commit](https://github.com/rails/rails/commit/352865d0f835c24daa9a2e9863dcc9dde9e5371a))
+
+*   Add default option to `class_attribute`.
+    ([Pull Request](https://github.com/rails/rails/pull/29270))
+
+*   Add `Date#prev_occurring` and `Date#next_occurring` to return
+    specified next/previous occurring day of week.
+    ([Pull Request](https://github.com/rails/rails/pull/26600))
+
+*   Add default option to module and class attribute accessors.
+    ([Pull Request](https://github.com/rails/rails/pull/29294))
+
+*   Cache: `write_multi`.
+    ([Pull Request](https://github.com/rails/rails/pull/29366))
+
+*   Default `ActiveSupport::MessageEncryptor` to use AES 256 GCM encryption.
+    ([Pull Request](https://github.com/rails/rails/pull/29263))
+
+*   Add `freeze_time` helper which freezes time to `Time.now` in tests.
+    ([Pull Request](https://github.com/rails/rails/pull/29681))
+
+*   Make the order of `Hash#reverse_merge!` consistent
+    with `HashWithIndifferentAccess`.
+    ([Pull Request](https://github.com/rails/rails/pull/28077))
+
+*   Add purpose and expiry support to `ActiveSupport::MessageVerifier` and
+    `ActiveSupport::MessageEncryptor`.
+    ([Pull Request](https://github.com/rails/rails/pull/29892))
+
+*   Fix modulo operations involving durations.
+    ([Commit](https://github.com/rails/rails/commit/a54e13bd2e8fb4d6aa0aebe59271699a2d62567b))
+
+*   Update `String#camelize` to provide feedback when wrong option is passed.
+    ([Pull Request](https://github.com/rails/rails/pull/30039))
+
+*   `Module#delegate_missing_to` now raises `DelegationError` if target is nil,
+    similar to `Module#delegate`.
+    ([Pull Request](https://github.com/rails/rails/pull/30191))
+
+*   Add `ActiveSupport::EncryptedFile` and
+    `ActiveSupport::EncryptedConfiguration`.
+    ([Pull Request](https://github.com/rails/rails/pull/30067))
+
+*   Add `config/credentials.yml.enc` to store production app secrets.
+    ([Pull Request](https://github.com/rails/rails/pull/30067))
+
+*   Add key rotation support to `MessageEncryptor` and `MessageVerifier`.
+    ([Pull Request](https://github.com/rails/rails/pull/29716))
+
+*   Return an instance of `HashWithIndifferentAccess` from
+    `HashWithIndifferentAccess#transform_keys`.
+    ([Pull Request](https://github.com/rails/rails/pull/30728))
+
+*   `Hash#slice` now falls back to Ruby 2.5+'s built-in definition if defined.
+    ([Commit](https://github.com/rails/rails/commit/01ae39660243bc5f0a986e20f9c9bff312b1b5f8))
+
+*   `IO#to_json` now returns the `to_s` representation, rather than
+    attempting to convert to an array. This fixes a bug where `IO#to_json`
+    would raise an `IOError` when called on an unreadable object.
+    ([Pull Request](https://github.com/rails/rails/pull/30953))
+
+*   Add same method signature for `Time#prev_day` and `Time#next_day`
+    in accordance with `Date#prev_day`, `Date#next_day`.
+    Allows pass argument for `Time#prev_day` and `Time#next_day`.
+    ([Commit](https://github.com/rails/rails/commit/61ac2167eff741bffb44aec231f4ea13d004134e))
+
+*   Add same method signature for `Time#prev_month` and `Time#next_month`
+    in accordance with `Date#prev_month`, `Date#next_month`.
+    Allows pass argument for `Time#prev_month` and `Time#next_month`.
+    ([Commit](https://github.com/rails/rails/commit/f2c1e3a793570584d9708aaee387214bc3543530))
+
+*   Add same method signature for `Time#prev_year` and `Time#next_year`
+    in accordance with `Date#prev_year`, `Date#next_year`.
+    Allows pass argument for `Time#prev_year` and `Time#next_year`.
+    ([Commit](https://github.com/rails/rails/commit/ee9d81837b5eba9d5ec869ae7601d7ffce763e3e))
+
+*   Fix acronym support in `humanize`.
+    ([Commit](https://github.com/rails/rails/commit/0ddde0a8fca6a0ca3158e3329713959acd65605d))
+
+*   Allow `Range#include?` on TWZ ranges.
+    ([Pull Request](https://github.com/rails/rails/pull/31081))
+
+*   Cache: Enable compression by default for values > 1kB.
+    ([Pull Request](https://github.com/rails/rails/pull/31147))
+
+*   Redis cache store.
+    ([Pull Request](https://github.com/rails/rails/pull/31134),
+    [Pull Request](https://github.com/rails/rails/pull/31866))
+
+*   Handle `TZInfo::AmbiguousTime` errors.
+    ([Pull Request](https://github.com/rails/rails/pull/31128))
+
+*   MemCacheStore: Support expiring counters.
+    ([Commit](https://github.com/rails/rails/commit/b22ee64b5b30c6d5039c292235e10b24b1057f6d))
+
+*   Make `ActiveSupport::TimeZone.all` return only time zones that are in
+    `ActiveSupport::TimeZone::MAPPING`.
+    ([Pull Request](https://github.com/rails/rails/pull/31176))
+
+*   Changed default behaviour of `ActiveSupport::SecurityUtils.secure_compare`,
+    to make it not leak length information even for variable length string.
+    Renamed old `ActiveSupport::SecurityUtils.secure_compare` to
+    `fixed_length_secure_compare`, and started raising `ArgumentError` in
+    case of length mismatch of passed strings.
+    ([Pull Request](https://github.com/rails/rails/pull/24510))
+
+*   Use SHA-1 to generate non-sensitive digests, such as the ETag header.
+    ([Pull Request](https://github.com/rails/rails/pull/31289),
+    [Pull Request](https://github.com/rails/rails/pull/31651))
+
+*   `assert_changes` will always assert that the expression changes,
+    regardless of `from:` and `to:` argument combinations.
+    ([Pull Request](https://github.com/rails/rails/pull/31011))
+
+*   Add missing instrumentation for `read_multi`
+    in `ActiveSupport::Cache::Store`.
+    ([Pull Request](https://github.com/rails/rails/pull/30268))
+
+*   Support hash as first argument in `assert_difference`.
+    This allows to specify multiple numeric differences in the same assertion.
+    ([Pull Request](https://github.com/rails/rails/pull/31600))
+
+*   Return all mappings for a timezone identifier in `country_zones`.
+    ([Commit](https://github.com/rails/rails/commit/cdce6a709e1cbc98fff009effc3b1b3ce4c7e8db))
+
+*   Caching: MemCache and Redis `read_multi` and `fetch_multi` speedup.
+    Read from the local in-memory cache before consulting the backend.
+    ([Commit](https://github.com/rails/rails/commit/a2b97e4ffef971607a1be8fc7909f099b6840f36))
 
 Active Job
------------
+----------
 
 Please refer to the [Changelog][active-job] for detailed changes.
 
-### Removals
+### Notable changes
+
+*   Add support for compatibility with redis-rb gem for 4.0 version.
+    ([Pull Request](https://github.com/rails/rails/pull/30748))
 
-ToDo
+*   Allow block to be passed to `ActiveJob::Base.discard_on` to allow custom
+    handling of discard jobs.
+    ([Pull Request](https://github.com/rails/rails/pull/30622))
+
+Ruby on Rails Guides
+--------------------
+
+Please refer to the [Changelog][guides] for detailed changes.
 
 ### Notable changes
 
-ToDo
+*   Add
+    [Threading and Code Execution in Rails](threading_and_code_execution.html)
+    Guide.
+    ([Pull Request](https://github.com/rails/rails/pull/27494))
+
+*   Add [Active Storage Overview](active_storage_overview.html) Guide.
+    ([Pull Request](https://github.com/rails/rails/pull/31037))
 
 Credits
 -------
 
 See the
-[full list of contributors to Rails](http://contributors.rubyonrails.org/) for
-the many people who spent many hours making Rails, the stable and robust
+[full list of contributors to Rails](http://contributors.rubyonrails.org/)
+for the many people who spent many hours making Rails, the stable and robust
 framework it is. Kudos to all of them.
 
 [railties]:       https://github.com/rails/rails/blob/5-2-stable/railties/CHANGELOG.md
@@ -224,3 +1072,4 @@ framework it is. Kudos to all of them.
 [active-model]:   https://github.com/rails/rails/blob/5-2-stable/activemodel/CHANGELOG.md
 [active-support]: https://github.com/rails/rails/blob/5-2-stable/activesupport/CHANGELOG.md
 [active-job]:     https://github.com/rails/rails/blob/5-2-stable/activejob/CHANGELOG.md
+[guides]:         https://github.com/rails/rails/blob/5-2-stable/guides/CHANGELOG.md