37913 added the possibility to deeply merge configurations by grouping
them within a shared section. This powerful alternative was not reflected
in any documentation, which made my team think it was not possible until
I found out this feature after looking at the source code.

This patch reflects this change in the documentation so that it is
easier for other developers to know about this behavior.

Add `config.active_storage.web_image_content_types` to allow applications
to add content types (like `image/webp`) in which variants can be processed,
instead of letting those images be converted to the fallback PNG format.

Co-Authored-By: NEileen M. Uchitelle <eileencodes@users.noreply.github.com>

`url_for` will now use "https://" as the default protocol when
`Rails.application.config.force_ssl` is set to true.

Action Mailer already behaves this way, effectively.  This commit
extends that behavior application-wide.

Closes #23543.

    - adds the option `metadata_table` to a database connection

* require, require_relative, load by double quotes

We're getting rid of all single quote usage, unless it serves a specific purpose, as per the general style guide.

This PR adds `image/webp` to the default array of variable content
types. Without this commit if we want to "handle" webp images
overwriting `config.active_storage.variable_content_types` was
necessary.

This allows deprecation messages to be matched by substring, symbol (treated as
substring), or regular expression. If a warning is matched, the behaviors
configured for disallowed deprecations will be used. The default behavior for
disallowed deprecation warnings is `:raise`.

Also adds `ActiveSupport::Deprecation.allow` for thread-local, block level ignoring of deprecation warnings which would otherwise be disallowed by ActiveSupport::Deprecation.disallowed_warnings.

While trying to fix #16433, we made the middleware deletions always
happen at the end. While this works for the case of deleting the
Rack::Runtime middleware, it makes operations like the following
misbehave.

```ruby
gem "bundler", "< 1.16"

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
end

require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = __dir__
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  middleware.insert_after ActionDispatch::Session::CookieStore, ::Rails::Rack::Logger, config.log_tags
  middleware.delete ::Rails::Rack::Logger
end

require "minitest/autorun"
require "rack/test"

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_returns_success
    get "/"
    assert last_response.ok?
  end

  private
    def app
      Rails.application
    end
end
```

In the case ☝️  the ::Rails::Rack::Logger would be deleted instead of
moved, because the order of middleware stack building execution will be:

```ruby
[:insert, ActionDispatch::Session::CookieStore, [::Rails::Rack::Logger]]
[:delete, ::Rails::Rack::Logger, [config.log_tags]]
```

This is pretty surprising and hard to reason about behaviour, unless you
go spelunking into the Rails configuration code.

I have a few solutions in mind and all of them have their drawbacks.

1. Introduce a `Rails::Configuration::MiddlewareStackProxy#delete!` that
delays the deleted operations. This will make `#delete` to be executed
in order. The drawback here is backwards incompatible behavior and a new
public method.

2. Just revert to the old operations. This won't allow people to delete
the `Rack::Runtime` middleware.

3. Legitimize the middleware moving with the new `#move_after` and
`#move_before` methods. This does not breaks any backwards
compatibility, but includes 2 new methods to the middleware stack.

I have implemented `3.` in this pull request.

Happy holidays! 🎄

This commit copies info from
https://github.com/rails/rails/pull/33145
([an excellent changelog](https://github.com/rails/rails/blob/6-0-stable/railties/CHANGELOG.md)) to
our guides.

Closes https://github.com/rails/rails/issues/36959
Not sure whether there is a need mentioning `config.hosts` in the "Upgrading to Rails 6.0" guide
since it is configured to work in the development environment by default and we guide how to deal
with "blocked host" issue, see:
https://github.com/rails/rails/blob/6-0-stable/actionpack/lib/action_dispatch/middleware/templates/rescues/blocked_host.html.erb

I would like to backport this to `6-0-stable` so users will be able to
find info about `ActionDispatch::HostAuthorization` middleware and how
to configure it.

Give credit to @gsamokovarov since I copied the info from the changelog. <3

[bogdanvlviv, Genadi Samokovarov]

According to the guide guidelines, all words except for prepositions,
conjunctions, internal articles, and forms of the verb "to be" should be
capitalized. This commit fixes some titles.

Some code examples were missing the language used for code highlighting.

* https://github.com/guard/listen/releases/tag/v3.2.0
* https://github.com/guard/listen/issues/465
* `listen` removed the unmaintained `ruby_dep` dependency, which
  incorrectly shows warnings when running on TruffleRuby.

I changed `load_defaults` to `config.load_defaults` in the guide
to emphasize its context,
sorted headers "With 'x.x'" in descending and rephrased them
to "With 'x.x', it includes previous versions' new defaults"
and documented the method on https://api.rubyonrails.org.

    class SensitiveJob < ApplicationJob
      self.log_arguments = false

      def perform(my_sensitive_argument)
      end
    end

When dealing with sensitive arugments as password and tokens it is
now possible to configure the job to not put the sensitive argument
in the logs.

Closes #34438.

Add configuration option to turn off drawing of Active Storage routes.

Assigning to a collection of attachments appends rather than replacing, as in 5.2. Existing 5.2 apps that rely on this behavior will no longer break when they're upgraded to 6.0.

For apps generated on 6.0 or newer, assigning replaces the existing attachments in the collection. #attach should be used to add new attachments to the collection without removing existing ones.

I expect that we'll deprecate the old behavior in 6.1.

Closes #36374.

The robots.txt site is moved permanently to https URL.

I changed return value of `ActionDispatch::Response#content_type` in #36034.
But this change seems to an obstacle to upgrading. https://github.com/rails/rails/pull/36034#issuecomment-498795893

Therefore, I restored the behavior of `ActionDispatch::Response#content_type`
to 5.2 and deprecated old behavior. Also, made it possible to control the
behavior with the config.

Ref: bcf370d6, 06ab7b27.

'Week day' has a specific meaning in English -- see https://en.wiktionary.org/wiki/weekday for details -- that is not meant here.  'Day of week' is more appropriate.

[ci skip]

[skip ci] The default value of config.active_record.collection_cache_versioning without loading Railtie is false

Please check https://github.com/rails/rails/pull/36260#discussion_r283266942 for reference.

[Vishal Telangre, bogdanvlviv]