We are using blocks here so we have access to the environment around
them, no need for globals.

Email does not support relative links since there is no implicit host. Therefore all links inside of emails must be fully qualified URLs. All path helpers are now deprecated. When removed, the error will give early indication to developers to use `*_url` methods instead.

Currently if a developer uses a `*_path` helper, their tests and `mail_view` will not catch the mistake. The only way to see the error is by sending emails in production. Preventing sending out emails with non-working path's is the desired end goal of this PR.

Currently path helpers are mixed-in to controllers (the ActionMailer::Base acts as a controller). All `*_url` and `*_path` helpers are made available through the same module. This PR separates this behavior into two modules so we can extend the `*_path` methods to add a Deprecation to them. Once deprecated we can use this same area to raise a NoMethodError and add an informative message directing the developer to use `*_url` instead.

The module with warnings is only mixed in when a controller returns false from the newly added `supports_relative_path?`.

Paired @sgrif & @schneems

This reverts commit f632f79b, reversing
changes made to 98c7fe87.

Closes #16343

Now the default is always true.

Users still can set it using config.i18n.enforce_available_locales.

Since the rubysl-yaml gem doesn't ship with Psych by default because of
its dependency on libyaml, on Rubinius, the default engine is Syck.

However, if we want to be able to run the application safely on
different rubies, we need to make people using Rubinius rely on Psych.

See http://git.io/uuLVag for further information.

We are planning to remove mocha from our test suite because of
performance problems. To make this possible we should stop require mocha
on ActionSupport::TestCase.

This should not affect applications since users still need to add mocha
to Gemfile and this already load mocha.

Added FIXME notes to place that still need mocha removal

The Logger by default includes a guard which checks for the
logging level. By removing the custom logging guards, we can decouple
the logging guard from the logging action to be done.

This also follows the good practice listed on http://guides.rubyonrails.org/debugging_rails_applications.html#impact-of-logs-on-performance.

Added additional help messaging when there's scaffolding being generated and a migration already exists for the resource.

The user is now alerted that they are able to skip the conflicted migration file via the --skip option.

This is a convenience for loading configuration for the current Rails
environment.

With this change it will be possible to add additional options to the `option_parser` like this:

    require 'rails/commands/server'
    module Rails
      class Server < ::Rack::Server
        class Options
          def option_parser_with_open(options)
            parser = option_parser_without_open options
            parser.on('-o', '--open', 'Open in default browser') { options[:open] = true }
            parser
          end
          alias_method_chain :option_parser, :open
        end

        def start_with_open
          start_without_open do
            `open http://localhost:3000` if options[:open]
          end
        end
        alias_method_chain :start, :open
      end
    end

Also reordered some of the items to put newer ones on top (same order as
CHANGELOGs), which makes it easier to diff while we are still working on it.

adapter, fixed from #16057 [ci skip]

As we are setting notice in destroy action we should display that

For more information see https://github.com/rails/rails/pull/14044
And https://github.com/rails/jbuilder/pull/191

closes #14044

Revert "Merge pull request #15394 from morgoth/fix-automatic-maintaining-test-schema-for-sql-format"

This reverts commit 46139d33, reversing
changes made to 8f247871.

Conflicts:
	activerecord/CHANGELOG.md

Adds `config.action_mailer.preview_enabled`

This allows mail previewing to be enabled easily in non-development
environments such as staging. The default is set to true for development
so no changes should be required to existing Rails applications.

The mail preview path can still be configured using the existing
`config.action_mailer.preview_path` configuration option.

Adding this avoids devs from having to do stuff like:
https://gist.github.com/lengarvey/fa2c9bd6cdbeba96526a

Update actionmailer/CHANGELOG with new configuration.
Update configuring guide with new configuratation.
Add `config.action_mailer.preview_path` to configuring guide.

* General style fixes.
* Add changes to configuration guide.
* Add missing tests.

Closes #15942