- Auto-generating content from the filename of an image is not suitable
  alternative text; alt text that isn't fully considered can be
  distracting and fatiguing for screen readers users (blind, low vision,
  dyslexic people).
- Setting a filename fallback short circuits screen reader default
  behavior and configuration for blank descriptions.
- Setting poor defaults also creates false negatives for accessibility
  linting and testing software, that makes it harder to improve
  application accessibility.

***

- After this change, if authors leave images without alt text, screen
  readers will fallback to default behavior for missing alt text.
- Also with this change, Automated linting and testing tools will
  correctly generate warnings.

[Fixes #30096]

If clear it before the test, the mail of the last executed test will not
be correctly cleared.

Therefore, executing the test with seed below will result in an error.

```
./bin/test -w --seed 55480
Run options: --seed 55480

# Running:

...........................................................................................................................................................F

Failure:
MailDeliveryTest#test_does_not_increment_the_deliveries_collection_on_error [/home/yaginuma/program/rails/master_y_yagi/rails/actionmailer/test/delivery_methods_test.rb:221]:
--- expected
+++ actual
@@ -1 +1 @@
-[]
+[#<Mail::Message:47011389364640, Multipart: false, Headers: <Date: Mon, 14 Aug 2017 07:48:40 +0900>, <From: test-sender@test.com>, <To: test-receiver@test.com>, <Message-ID: <5990d748ea5b2_29342ac1af8bcf40886f7@yaginuma.mail>>, <Subject: Test Subject>, <Mime-Version: 1.0>, <Content-Type: text/plain>, <Content-Transfer-Encoding: 7bit>>]

bin/test test/delivery_methods_test.rb:216
```

This reverts commit 3420a145, reversing
changes made to afb66a5a.

Setting delivery_job on a mailer class will cause MessageDelivery to use
the specified job instead of ActionMailer::DeliveryJob:

    class MyMailer < ApplicationMailer
      self.delivery_job = MyCustomDeliveryJob

      ...
    end

".. with __dir__ we can restore order in the Universe." - by @fxn

Related to 5b8738c2

This will avoid to the test fail when running in isolation because the
message generated is nil.

`ActionMailer::Base.delivery_method` is already defined in
https://github.com/rails/rails/blob/master/actionmailer/test/parameterized_test.rb#L13

Adding durations to `Time` instances is perfectly okay.

Currently `ActiveSupport::Duration` implicitly converts to a seconds
value when used in a calculation except for the explicit examples of
addition and subtraction where the duration is the receiver, e.g:

    >> 2 * 1.day
    => 172800

This results in lots of confusion especially when using durations
with dates because adding/subtracting a value from a date treats
integers as a day and not a second, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 2 * 1.day
    => Mon, 10 Apr 2490

To fix this we're implementing `coerce` so that we can provide a
deprecation warning with the intent of removing the implicit coercion
in Rails 5.2, e.g:

    >> 2 * 1.day
    DEPRECATION WARNING: Implicit coercion of ActiveSupport::Duration
    to a Numeric is deprecated and will raise a TypeError in Rails 5.2.
    => 172800

In Rails 5.2 it will raise `TypeError`, e.g:

    >> 2 * 1.day
    TypeError: ActiveSupport::Duration can't be coerced into Integer

This is the same behavior as with other types in Ruby, e.g:

    >> 2 * "foo"
    TypeError: String can't be coerced into Integer
    >> "foo" * 2
    => "foofoo"

As part of this deprecation add `*` and `/` methods to `AS::Duration`
so that calculations that keep the duration as the receiver work
correctly whether the final receiver is a `Date` or `Time`, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 1.day * 2
    => Fri, 03 Mar 2017

Fixes #27457.

Needed for testing of parameterized mailers

Currently use two variables to restore `delivery_method`, but the order
of restoring the values is incorrect and does not restore is correctly.

Offer the option to use parameterization for shared processing of headers and ivars

we call them only in the tests

(I personally prefer writing one string in one line no matter how long it is, though)

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

A few have been left for aesthetic reasons, but have made a pass
and removed most of them.

Note that if the method `foo` returns an array, `foo << 1`
is a regular push, nothing to do with assignments, so
no self required.

Implement naive partial caching mechanism.

Add test for LogSubscriber

Use ActionView::Base#log_payload to store log_subscriber's payload, so we can pass cache result into it.

Fixed tests

Remove useless settings

Check if #log_payload exists before calling it. Because other classes also includes CacheHelper but don't have is attribute

Use @log_payload_for_partial_reder instead of #log_payload to carry ActionView's payload.

Update test's hash syntax

Add configuration to enable/disable fragment caching logging

Remove unless test and add new test to ensure cache info won't effect next rendering's log

Move :enable_fragment_cache_logging config from ActionView to ActionPack

Apply new config to tests

Update actionview's changelog

Update configuration guide

Improve actionview's changelog

Refactor PartialRenderer#render and log tests

Mute subscriber's log instead of disabling instrumentation.

Fix typo, remove useless comment and use new hash syntax

Improve actionpack's log_subscriber test

Fix rebase mistake

Apply new config to all caching intstrument actions

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

Follows the same pattern as controllers and jobs. Exceptions raised in
delivery jobs (enqueued by `#deliver_later`) are also delegated to the
mailer's rescue_from handlers, so you can handle the DeserializationError
raised by delivery jobs:

```ruby
class MyMailer < ApplicationMailer
  rescue_from ActiveJob::DeserializationError do
    …
  end
```

ActiveSupport::Rescuable polish:
* Add the `rescue_with_handler` class method so exceptions may be
  handled at the class level without requiring an instance.
* Rationalize `exception.cause` handling. If no handler matches the
  exception, fall back to the handler that matches its cause.
* Handle exceptions raised elsewhere. Pass `object: …` to execute
  the `rescue_from` handler (e.g. a method call or a block to
  instance_exec) against a different object. Defaults to `self`.