Synced 4.2 release notes with the latest commits.

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.

1 files changed, 80 insertions, 27 deletions

diff --git a/guides/source/4_2_release_notes.md b/guides/source/4_2_release_notes.md
index 8c5abb54ea..2729ca6588 100644
--- a/guides/source/4_2_release_notes.md
+++ b/guides/source/4_2_release_notes.md
@@ -62,8 +62,17 @@ Please refer to the [Changelog][railties] for detailed changes.
 * The `rails application` command has been removed without replacement.
   ([Pull Request](https://github.com/rails/rails/pull/11616))
 
+### Deprecations
+
+* Deprecated `Rails::Rack::LogTailer` without replacement.
+  ([Commit](https://github.com/rails/rails/commit/84a13e019e93efaa8994b3f8303d635a7702dbce))
+
 ### Notable changes
 
+* Introduced `--skip-gems` option in the app generator to skip gems such as
+  `turbolinks` and `coffee-rails` that does not have their own specific flags.
+  ([Commit](https://github.com/rails/rails/commit/10565895805887d4faf004a6f71219da177f78b7))
+
 * Introduced `bin/setup` script to bootstrap an application.
   ([Pull Request](https://github.com/rails/rails/pull/15189))
 
@@ -97,6 +106,15 @@ Please refer to the [Changelog][action-pack] for detailed changes.
 
 ### Notable changes
 
+* `render nothing: true` or rendering a `nil` body no longer add a single space
+  padding to the response body.
+  ([Pull Request](https://github.com/rails/rails/pull/14883))
+
+* Introduced the `always_permitted_parameters` option to configure which
+  parameters are permitted globally. The default value of this configuration is
+  `['controller', 'action']`.
+  ([Pull Request](https://github.com/rails/rails/pull/15933))
+
 * The `*_filter` family methods has been removed from the documentation. Their
   usage are discouraged in favor of the `*_action` family methods:
 
@@ -159,6 +177,10 @@ Please refer to the [Changelog][action-view] for detailed changes.
 
 ### Notable changes
 
+* The form helpers no longer generate a `<div>` element with inline CSS around
+  the hidden fields.
+  ([Pull Request](https://github.com/rails/rails/pull/14738))
+
 
 Action Mailer
 -------------
@@ -167,6 +189,10 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
 
 ### Notable changes
 
+* Added the `show_previews` configuration option for enabling mailer previews
+  outside of the development environment.
+  ([Pull Request](https://github.com/rails/rails/pull/15970))
+
 
 Active Record
 -------------
@@ -177,6 +203,9 @@ for detailed changes.
 
 ### Removals
 
+* Removed `cache_attributes` and friends. All attributes are cached.
+  ([Pull Request](https://github.com/rails/rails/pull/15429))
+
 * Removed deprecated method `ActiveRecord::Base.quoted_locking_column`.
   ([Pull Request](https://github.com/rails/rails/pull/15612))
 
@@ -184,9 +213,6 @@ for detailed changes.
   `proper_table_name` instance method on `ActiveRecord::Migration` instead.
   ([Pull Request](https://github.com/rails/rails/pull/15512))
 
-* Removed `cache_attributes` and friends. All attributes are cached.
-  ([Pull Request](https://github.com/rails/rails/pull/15429))
-
 * Removed unused `:timestamp` type. Transparently alias it to `:datetime`
   in all cases. Fixes inconsistencies when column types are sent outside of
   `ActiveRecord`, such as for XML Serialization.
@@ -194,13 +220,19 @@ for detailed changes.
 
 ### Deprecations
 
-* Deprecated returning `nil` from `column_for_attribute` when no column exists.
-  It will return a null object in Rails 5.0
-  ([Pull Request](https://github.com/rails/rails/pull/15878))
+* Deprecated broken support for automatic detection of counter caches on
+  `has_many :through` associations. You should instead manually specify the
+  counter cache on the `has_many` and `belongs_to` associations for the through
+  records.
+  ([Pull Request](https://github.com/rails/rails/pull/15754))
 
 * Deprecated `serialized_attributes` without replacement.
   ([Pull Request](https://github.com/rails/rails/pull/15704))
 
+* Deprecated returning `nil` from `column_for_attribute` when no column exists.
+  It will return a null object in Rails 5.0
+  ([Pull Request](https://github.com/rails/rails/pull/15878))
+
 * Deprecated using `.joins`, `.preload` and `.eager_load` with associations that
   depends on the instance state (i.e. those defined with a scope that takes an
   argument) without replacement.
@@ -216,21 +248,39 @@ for detailed changes.
   is not fully possible because the Ruby range does not support excluded
   beginnings.
 
-    The current solution of incrementing the beginning is not correct
-    and is now deprecated. For subtypes where we don't know how to increment
-    (e.g. `#succ` is not defined) it will raise an `ArgumentError` for ranges with
-    excluding beginnings.
+  The current solution of incrementing the beginning is not correct
+  and is now deprecated. For subtypes where we don't know how to increment
+  (e.g. `#succ` is not defined) it will raise an `ArgumentError` for ranges with
+  excluding beginnings.
 
-    ([Commit](https://github.com/rails/rails/commit/91949e48cf41af9f3e4ffba3e5eecf9b0a08bfc3))
-
-* Deprecated broken support for automatic detection of counter caches on
-  `has_many :through` associations. You should instead manually specify the
-  counter cache on the `has_many` and `belongs_to` associations for the through
-  records.
-  ([Pull Request](https://github.com/rails/rails/pull/15754))
+  ([Commit](https://github.com/rails/rails/commit/91949e48cf41af9f3e4ffba3e5eecf9b0a08bfc3))
 
 ### Notable changes
 
+* Added a `:required` option to singular associations, which defines a
+  presence validation on the association.
+  ([Pull Request](https://github.com/rails/rails/pull/16056))
+
+* Introduced `ActiveRecord::Base#validate!` that raises `RecordInvalid` if the
+  record is invalid.
+  ([Pull Request](https://github.com/rails/rails/pull/8639))
+
+* `ActiveRecord::Base#reload` now behaves the same as `m = Model.find(m.id)`,
+  meaning that it no longer retains the extra attributes from custom `select`s.
+  ([Pull Request](https://github.com/rails/rails/pull/15866))
+
+* Introduced the `bin/rake db:purge` task to empty the database for the current
+  environment.
+  ([Commit](https://github.com/rails/rails/commit/e2f232aba15937a4b9d14bd91e0392c6d55be58d))
+
+* `ActiveRecord::Dirty` now detects in-place changes to mutable values.
+  Serialized attributes on ActiveRecord models will no longer save when
+  unchanged. This also works with other types such as string columns and
+  json columns on PostgreSQL.
+  (Pull Requests [1](https://github.com/rails/rails/pull/15674),
+  [2](https://github.com/rails/rails/pull/15786),
+  [3](https://github.com/rails/rails/pull/15788))
+
 * Added support for `#pretty_print` in `ActiveRecord::Base` objects.
   ([Pull Request](https://github.com/rails/rails/pull/15172))
 
@@ -259,9 +309,6 @@ for detailed changes.
 * Added support for user-created range types in PostgreSQL adapter.
   ([Commit](https://github.com/rails/rails/commit/4cb47167e747e8f9dc12b0ddaf82bdb68c03e032))
 
-* Added a `:required` option to singular associations, which defines a
-  presence validation on the association.
-  ([Pull Request](https://github.com/rails/rails/pull/16056))
 
 Active Model
 ------------
@@ -275,6 +322,14 @@ Please refer to the [Changelog][active-model] for detailed changes.
 
 ### Notable changes
 
+* Introduced `undo_changes` method in `ActiveModel::Dirty` to restore the
+  changed (dirty) attributes to their previous values.
+  ([Pull Request](https://github.com/rails/rails/pull/14861))
+
+* `has_secure_password` now verifies that the given password is less than 72
+  characters if validations are enabled.
+  ([Pull Request](https://github.com/rails/rails/pull/15708))
+
 * Introduced `#validate` as an alias for `#valid?`.
   ([Pull Request](https://github.com/rails/rails/pull/14456))
 
@@ -302,20 +357,18 @@ Please refer to the [Changelog][active-support] for detailed changes.
 
 ### Notable changes
 
+* Added `Hash#transform_values` and `Hash#transform_values!` to simplify a
+  common pattern where the values of a hash must change, but the keys are left
+  the same.
+  ([Pull Request](https://github.com/rails/rails/pull/15819))
+
 * The `humanize` inflector helper now strips any leading underscores.
   ([Commit](https://github.com/rails/rails/commit/daaa21bc7d20f2e4ff451637423a25ff2d5e75c7))
 
-* Added `SecureRandom::uuid_v3` and `SecureRandom::uuid_v5`.
-  ([Pull Request](https://github.com/rails/rails/pull/12016))
-
 * Introduce `Concern#class_methods` as an alternative to `module ClassMethods`,
   as well as `Kernel#concern` to avoid the `module Foo; extend ActiveSupport::Concern; end`
   boilerplate. ([Commit](https://github.com/rails/rails/commit/b16c36e688970df2f96f793a759365b248b582ad))
 
-* Added `Hash#transform_values` and `Hash#transform_values!` to simplify a
-  common pattern where the values of a hash must change, but the keys are left
-  the same.
-  ([Pull Request](https://github.com/rails/rails/pull/15819))
 
 Credits
 -------