Update asset pipeline guide

Change a to an for HTML word [ci skip]

allow '1' or true for acceptance validation.

Removing :en in favor of default locale for duration#inspect

Hi there,

i have an app without english as available locale. So i got an error when we try to inspect something like 1.day. This is done automatically when we use the dalli cache.

I would like to change the :en to ::I18n.default_locale to be sure that this is always constant and is an available locale.

Tests are all green with this change.

Calculating -------------------------------------
:locale => :en                              2.024k i/100ms
:locale => ::I18n.default_locale   2.236k i/100ms
-------------------------------------------------
:locale => :en                                  25.758k (±26.3%) i/s -    117.392k
:locale => ::I18n.default_locale       26.311k (±18.1%) i/s -    127.452k

Rack is very carefully released, we should be able to upgrade minor
versions without much effort. We are a bunch of Rails core who are also
Rack core members so there won't be any issue with that. And in case
there's something wrong, we should fix on both sides.
Even though, doesn't seem like we will have a 1.7 version, this will be
useful as an example for when we go with Rack 2.0. We should ~> 2.0.

Fix description for ActiveModel::Errors#generate_message [skip ci]

Change 'a' to 'an' for 'XML' word [ci skip]

minor grammatical fix in documentation

Better fork detection in ActiveSupport::Testing::Isolation

Remove unused AV fixtures from AP tests

Add test for AM::Validation::Callbacks with :on

Remove unused "deprecated_reload" method

When `render` was moved from ActionPack to ActionView in acc8e259,
some fixtures required by the tests were duplicated, but they are
actually only required by ActionView tests.

To give one example, `double_render` is already defined [in the AV tests](https://github.com/rails/rails/blob/72139d8d310d896db78eaec98582c7a638135102/actionview/test/actionpack/controller/render_test.rb#L407)
and is never used in the ActionPack tests.

The method was introduced in https://github.com/rails/rails/commit/66d0a0153578ce760d822580c5b8c0b726042ac2#diff-8cec05860729a3851ceb756f4dd90370R49
for the "reset_changes is deprecated" test, but this test was successively
removed in https://github.com/rails/rails/commit/37175a24bd508e2983247ec5d011d57df836c743

`before_validation` and `after_validation` from
ActiveModel::Validation::Callbacks accept an optional `:on` parameter
that was not previously documented or tested. For instance given

    before_validation :do_something, on: :create

then `object.valid?(:create)` will invoke `:do_something` while
`object.valid?` or `object.valid?(:anything_else)` will not.

Add has secure token to migration generator

Re-add section in SQL Caching [ci skip]

Fix assertion that was never run

In order to run whether the `welcome` method of the ActionMailer::Base
subclass raises an error, `message` must be called, otherwise the method
is not executed at all.

You could just replace with `def welcome; raise StandardError; end` and you
would still see a passing test.

This commit fixes the test so the assertion is actually executed, just like
any other tests in the file, where `.message` is called.

This section was accidentally removed in 4b5e4244, and partially re-added in dc14b893.

[ci skip]

No need of requiring `rbconfig`, it is by-default loaded

remove autoload HideActions, no longer exist

It's only used to grab the type for type casting purposes, and we would
like to remove the type from the columns entirely.

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11

Fix Typo SecureToken [ci skip]

I'm planning on deprecating the column argument to mirror the
deprecation in [arel].

[arel]: https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11