It was deprecated in https://github.com/rails/rails/pull/19135.

We're now favoring `public_file_server.headers`.

1. Fix the message by wrapping the value in missing quotes and adding
the missing backtick at the end. Finally, 💄 by adding a space
inside the curly braces.

Before:

`config.public_file_server.headers = {'Cache-Control' => public,
max-age=31536000}

Now:

`config.public_file_server.headers = { 'Cache-Control' => 'public,
max-age=31536000' }`

2. Display `static_cache_control` instead of static_cache_control. This
follows what the 2 neighboring methods are doing.

3. Use strip_heredoc to improve the code formatting and readability
like the 2 neighboring methods and wrap to 80 characters.

Forgot to do it in 748b2f9c, when deprecating `serve_static_files`.

The configuration for `config.static_cache_control`, and its replacement
`config.public_file_server.headers` are implemented in Railties.

People would configure this in environment files, which is Railties domain too.

we can just reuse the parent process.  We should figure out what files
are commonly required among the test files and try to require them in
the parent so that the require time cost is amortized across the
processes.

As discussed in https://github.com/rails/rails/pull/19135#issuecomment-153385986.

Replaces `serve_static_files` to unify the static options under the `public_file_server` wing.

Deprecates `serve_static_files` accessors, but make them use the newer config internally.

`config.middleware.insert_before` changes require to restart the server 

Also added missing `.` at the EOL.

`1_valid_people_have_last_names.rb` and
`20150823202140_create_users.rb` are valid migration file name.
But `1_valid_people_have_last_names.rb` is rendered as
`********** NO FILE **********` when `rake db:migrate:status`.

Fix to this bug, this commit includes

* define some API private methdos and a Constant
  `match_to_migration_filename?`, `parse_migration_filename`, and
  `MigrationFilenameRegexp`
* use these methods in `db:migrate:status` task

Example:

These files are in `db/migrate`

* 1_valid_people_have_last_names.rb
* 20150819202140_irreversible_migration.rb
* 20150823202140_add_admin_flag_to_users.rb
* 20150823202141_migration_tests.rb
* 2_we_need_reminders.rb
* 3_innocent_jointable.rb

we can migrate all of them.

Before

```shell
$ bundle exec rake db:migrate:status

...

 Status   Migration ID    Migration Name
--------------------------------------------------
   up     001             ********** NO FILE **********
   up     002             ********** NO FILE **********
   up     003             ********** NO FILE **********
   up     20150819202140  Irreversible migration
   up     20150823202140  Add admin flag to users
   up     20150823202141  Migration tests
```

After

```shell
$ bundle exec rake db:migrate:status

...

 Status   Migration ID    Migration Name
--------------------------------------------------
   up     001             Valid people have last names
   up     002             We need reminders
   up     003             Innocent jointable
   up     20150819202140  Irreversible migration
   up     20150823202140  Add admin flag to users
   up     20150823202141  Migration tests
```

Since the sass cache is output to the `tmp/cache/sass`.

We are using the same version constraint in the database adapters so
when a new version of the adapter that doesn't work with the version of
rails is released we don't break new applications.

If `SECRET_KEY_BASE` or other `secret` gets passed as other then string
we need to raise `ArgumentError` to know that it's a wrong argument.

Closes #22072

Also move the method to the right class

`README` it is changed to `README.rdoc` in 6b126e23, it has been changed to` README.md` further 89a12c93.

[ci skip]

* If the drop task fails for a reason other than the database not
  existing, processing should end. This is indicated by a non-zero
  exit status.
* Since the backtrace is already printed to screen, we forgo
  printing it again by using an explicit call to `exit`.
* ⚠ This modifies the behavior of the db:create task slightly in
  that the stack trace is no longer printed by default. If the `--trace`
  option is used, it will print the trace _after_ the error message.

* If the create task fails for a reason other than the database already
  existing, processing should end. This is indicated by a non-zero exit
  status.
* Since the backtrace is already printed to screen, we forgo printing it
  again by using an explicit call to `exit`.
* ⚠ This modifies the behavior of the db:create task slightly in
  that the stack trace is no longer printed by default. If the `--trace`
  option is used, it will print the trace _after_ the error message.

* Previously the sqlite3 adapter could not "fail" on drop. Now an error
  is raised when no file exists.
* Also updates purge to be resilient of drop failures. This is how purge
  is expected to behave.

* Running the db:create task when the database already exists isn't
  really an error case. That is processing may proceed in this case
  because the database exists as requested. So let's validate that
  behavior with a test.
* Likewise, if the database doesn't exist when running the db:drop task
  processing may continue as the requested condition is already met.
  Thus a test.

Revert " Added an example to show how common secrets can be shared across multiple environments in secrets.yml"

`images` method has been deleted in 2bc48561, `create_images_directory` does nothing.

In the Rails console, the `helper` function provides a shorthand for
working with application helpers.  However, `helper` memoizes the
value of `ApplicationController#helpers`. This means that if a user
subsequently changes helper code and calls `reload!` in the console,
their code changes will not be reflected by the `helper` function,
even though the helper was, in fact, reloaded.

Since the plugin generator do not generate assets, I think manifest.js also that it unnecessary.

`shellwords` is no longer needed from #20605.

`prepare_destination` has been used in the template file for the generator,
I think it should be a public API

ref: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/test_unit/generator/templates/generator_test.rb#L8

Change the reporter to just read the option.

Pass output_inline where needed in tests.

Lets us cut the verbose and straight up duplicated setup in 3 tests down to one line.

We'd see the failures and errors reported after the run, which is needless, when we've already
reported them.

Turns:

```

.......................................S....................F

This failed

bin/rails test test/models/bunny_test.rb:14

....

Finished in 0.100886s, 1020.9583 runs/s, 1001.1338 assertions/s.

  2) Failure:
BunnyTest#test_something_failing [/Users/kasperhansen/Documents/code/collection_caching_test/test/models/bunny_test.rb:15]:
This failed

103 runs, 101 assertions, 1 failures, 0 errors, 1 skips

You have skipped tests. Run with --verbose for details.
```

Into:

```

...................S.......................................F

This failed

bin/rails test test/models/bunny_test.rb:14

......................

Finished in 0.069910s, 1473.3225 runs/s, 1444.7143 assertions/s.

103 runs, 101 assertions, 1 failures, 0 errors, 1 skips
```

When generating the url for a mounted engine through its proxy, the path should be the sum of three parts:

1. Any `SCRIPT_NAME` request header or the value of `ActionDispatch::Routing::RouteSet#relative_url_root`.
2. A prefix (the engine's mounted path).
3. The path of the named route inside the engine.

Since commit https://github.com/rails/rails/commit/44ff0313c121f528a68b3bd21d6c7a96f313e3d3, this has been broken. Step 2 has been changed to:

2. A prefix (the value of `ActionDispatch::Routing::RouteSet#relative_url_root` + the engine's mounted path).

The value of `ActionDispatch::Routing::RouteSet#relative_url_root` is taken into account in step 1 of the route generation and should be ignored when generating the mounted engine's prefix in step 2.

This commit fixes the regression by having `ActionDispatch::Routing::RouteSet#url_for` check `options[:relative_url_root]` before falling back to `ActionDispatch::Routing::RouteSet#relative_url_root`. The prefix generating code then sets `options[:relative_url_root]` to an empty string. This empty string is used instead of `ActionDispatch::Routing::RouteSet#relative_url_root` and avoids the duplicate `relative_url_root` value in the final result.

This resolves #20920 and resolves #21459

Added javascript to update the URL on mailer previews with the
currently selected email format. Reloading the page now keeps you on
your selected format rather than going back to the default html version.

Rails 4.x and earlier didn't support `Mime::Type[:FOO]`, so libraries
that support multiple Rails versions would've had to feature-detect
whether to use `Mime::Type[:FOO]` or `Mime::FOO`.

`Mime[:foo]` has been around for ages to look up registered MIME types
by symbol / extension, though, so libraries and plugins can safely
switch to that without breaking backward- or forward-compatibility.

Note: `Mime::ALL` isn't a real MIME type and isn't registered for lookup
by type or extension, so it's not available as `Mime[:all]`. We use it
internally as a wildcard for `respond_to` negotiation. If you use this
internal constant, continue to reference it with `Mime::ALL`.

Ref. efc6dd55

This reverts commit 37423e4f.

Jeremy is right that we shouldn't remove this.  The fact is that many
engines are depending on this middleware to be in the default stack.
This ties our hands and forces us to keep the middleware in the stack so
that engines will work.  To be extremely clear, I think this is another
smell of "the rack stack" that we have in place.  When manipulating
middleware, we should have meaningful names for places in the req / res
lifecycle **not** have engines depend on a particular constant be in a
particular place in the stack.  This is a weakness of the API that we
have to figure out a way to address before removing the constant.

As far as timing attacks are concerned, we can reduce the granularity
such that it isn't useful information for hackers, but is still useful
for developers.