It is related with https://github.com/rack/rack/commit/7b66d2cdb80a4d6b44fa8c61d92e25fbbda1f152

Refactor connection handler

In #18721 we removed the discard key from the session hash used to flash
messages and that broke compatibility with Rails 4 applications because they
try to map in the discarded flash messages and it returns nil.

Fixes #24726.

[skip ci]

BoomerAPI is not used anywhere, so removed it!

Release notes: Add a note about `use_transactional_tests` in the deprecated section of Active Record notes [ci skip]

- It was originally added in 83b4e907 and partially
  removed in 05d89410.

Array#split refactoring for case with block

Dont call each when calling body on response to fix #23964

Fixes #23964

Release notes: Add a note about `use_transactional_tests` in the deprecated section of Active Record notes [ci skip]

- Followup of PR #19282.

Fix failures due to transactions

We are erroring due to nested transaction failures from mysql on test_migrate_clears_schema_cache_afterward test.
Disable transactions for this test.

Fixes #24391

Fix broken links in 'Ruby on Rails 2.3 Release Notes' [ci skip]

In 5.0 we use bind parameters for limit and offset, while in 4.2 we used
the values directly. The code as it was written assumed that limit and
offset worked as `LIMIT ? OFFSET ?`. Both Oracle and SQL Server have a
different syntax, where the offset is stated before the limit. We
delegate this behavior to the connection adapter so that these adapters
are able to determine how the bind parameters are flattened based on
what order their specification has the various clauses appear.

Fixes #24775

Calculating -------------------------------------
              before    26.319k i/100ms
               after    29.414k i/100ms
-------------------------------------------------
              before    350.623k (± 1.6%) i/s -      1.763M
               after    416.227k (± 1.4%) i/s -      2.088M

Comparison:
               after:   416226.8 i/s
              before:   350622.8 i/s - 1.19x slower

Fix link in 'Configuring Rails Applications' [ci skip]

Fix link in 'Ruby on Rails 3.0 Release Notes' [ci skip]

Fix markdown syntax in 'Ruby on Rails 2.2 Release Notes' [ci skip]

[ci skip] Release notes: Add PR #24866 to release notes

Implement helpers proxy in controller instance level

Active Model: Improve CHANGELOG and documentation for `validates_acceptance_of` [ci skip]

Expand on Action Mailer Fragment caching tests

- Improve CHANGELOG entry for #18439.
- The documentation is updated as per changes in PR #18439 to the
  `accept` option.
- The explanation about the virtual attribute is moved at the end so
  that the arity of `accept` option is explained first.
- Added a note that `message` can also be passed to `validates_acceptance_of`.

Followup of #18322

It is a common pattern in the Rails community that when people want to
:xa
use any kind of helper that is defined inside app/helpers they includes
the helper module inside the controller like:

    module UserHelper
      def my_user_helper
        # ...
      end
    end

    class UsersController < ApplicationController
      include UserHelper

      def index
        render inline: my_user_helper
      end
    end

This has problem because the helper can't access anything that is
defined in the view level context class.

Also all public methods of the helper become available in the controller
what can lead to undesirable methods being routed and behaving as
actions.

Also if you helper depends on other helpers or even Action View helpers
you need to include each one of these dependencies in your controller
otherwise your helper is not going to work.

We already have a helpers proxy at controller class level but that proxy
doesn't have access to the instance variables defined in the
controller.

With this new instance level helper proxy users can reuse helpers in the
controller without having to include the modules and with access to
instance variables defined in the controller.

    class UsersController < ApplicationController
      def index
        render inline: helpers.my_user_helper
      end
    end

Change to use a more realistic example [ci skip]

delegate encode_with instead of to_yaml, which is deprecated

Change to use a more realistic example and not giving the impression that destroy_all is preferred way to destroy related records.
This example just wants to demonstrate callback behaviour.

[ci skip]