11 files changed, 90 insertions, 28 deletions
diff --git a/guides/assets/stylesheets/main.css b/guides/assets/stylesheets/main.css
index cd355b1d1a..2657a84a91 100644
--- a/guides/assets/stylesheets/main.css
+++ b/guides/assets/stylesheets/main.css
@@ -283,8 +283,12 @@ body {
 #header .wrapper, #topNav .wrapper, #feature .wrapper {padding-left: 1em; max-width: 960px;}
 #feature .wrapper {max-width: 640px; padding-right: 23em; position: relative; z-index: 0;}
 
+@media screen and (max-width: 960px) {
+  #container .wrapper { padding-right: 23em; }
+}
+
 @media screen and (max-width: 800px) {
-  #feature .wrapper { padding-right: 0; }
+  #feature .wrapper, #container .wrapper { padding-right: 0; }
 }
 
 /* Links
diff --git a/guides/rails_guides/levenshtein.rb b/guides/rails_guides/levenshtein.rb
index c48af797fa..2213ef754d 100644
--- a/guides/rails_guides/levenshtein.rb
+++ b/guides/rails_guides/levenshtein.rb
@@ -12,8 +12,8 @@ module RailsGuides
       n = s.length
       m = t.length
 
-      return m if (0 == n)
-      return n if (0 == m)
+      return m if 0 == n
+      return n if 0 == m
 
       d = (0..m).to_a
       x = nil
diff --git a/guides/source/action_mailer_basics.md b/guides/source/action_mailer_basics.md
index 6c5f03ab38..37cbf3f53d 100644
--- a/guides/source/action_mailer_basics.md
+++ b/guides/source/action_mailer_basics.md
@@ -422,6 +422,21 @@ use the rendered text for the text part. The render command is the same one used
 inside of Action Controller, so you can use all the same options, such as
 `:text`, `:inline` etc.
 
+If you would like to render a template located outside of the default `app/views/mailer_name/` directory, you can apply the `prepend_view_path`, like so:
+
+```ruby
+class UserMailer < ApplicationMailer
+  prepend_view_path "custom/path/to/mailer/view"
+  
+  # This will try to load "custom/path/to/mailer/view/welcome_email" template
+  def welcome_email
+    # ...
+  end
+end
+```
+
+You can also consider using the [append_view_path](https://guides.rubyonrails.org/action_view_overview.html#view-paths) method.
+
 #### Caching mailer view
 
 You can perform fragment caching in mailer views like in application views using the `cache` method.
diff --git a/guides/source/active_record_callbacks.md b/guides/source/active_record_callbacks.md
index 5b06ff78bb..5946acb412 100644
--- a/guides/source/active_record_callbacks.md
+++ b/guides/source/active_record_callbacks.md
@@ -319,6 +319,14 @@ class Order < ApplicationRecord
 end
 ```
 
+As the proc is evaluated in the context of the object, it is also possible to write this as:
+
+```ruby
+class Order < ApplicationRecord
+  before_save :normalize_card_number, if: Proc.new { paid_with_card? }
+end
+```
+
 ### Multiple Conditions for Callbacks
 
 When writing conditional callbacks, it is possible to mix both `:if` and `:unless` in the same callback declaration:
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md
index a2890b9b7a..91cc175095 100644
--- a/guides/source/active_record_querying.md
+++ b/guides/source/active_record_querying.md
@@ -1277,16 +1277,6 @@ class Article < ApplicationRecord
 end
 ```
 
-This is exactly the same as defining a class method, and which you use is a matter of personal preference:
-
-```ruby
-class Article < ApplicationRecord
-  def self.published
-    where(published: true)
-  end
-end
-```
-
 Scopes are also chainable within scopes:
 
 ```ruby
diff --git a/guides/source/active_storage_overview.md b/guides/source/active_storage_overview.md
index 6933717c2b..1c15d075b9 100644
--- a/guides/source/active_storage_overview.md
+++ b/guides/source/active_storage_overview.md
@@ -174,7 +174,7 @@ google:
 Add the [`google-cloud-storage`](https://github.com/GoogleCloudPlatform/google-cloud-ruby/tree/master/google-cloud-storage) gem to your `Gemfile`:
 
 ```ruby
-gem "google-cloud-storage", "~> 1.8", require: false
+gem "google-cloud-storage", "~> 1.11", require: false
 ```
 
 ### Mirror Service
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index dfd21915b0..f9fc7044ba 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -2156,6 +2156,19 @@ This method is an alias of `Array#<<`.
 
 NOTE: Defined in `active_support/core_ext/array/prepend_and_append.rb`.
 
+### Extracting
+
+The method `extract!` removes and returns the elements for which the block returns a true value.
+If no block is given, an Enumerator is returned instead.
+
+```ruby
+numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+odd_numbers = numbers.extract! { |number| number.odd? } # => [1, 3, 5, 7, 9]
+numbers # => [0, 2, 4, 6, 8]
+```
+
+NOTE: Defined in `active_support/core_ext/array/extract.rb`.
+
 ### Options Extraction
 
 When the last argument in a method call is a hash, except perhaps for a `&block` argument, Ruby allows you to omit the brackets:
diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index 6e4f1f9648..36882fec3f 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -989,6 +989,14 @@ development:
 
 If your development database has a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the `development` section as appropriate.
 
+Advisory Locks are enabled by default on MySQL and are used to make database migrations concurrent safe. You can disable advisory locks by setting `advisory_locks` to `false`:
+
+```yaml
+production:
+  adapter: mysql2
+  advisory_locks: false
+```
+
 #### Configuring a PostgreSQL Database
 
 If you choose to use PostgreSQL, your `config/database.yml` will be customized to use PostgreSQL databases:
@@ -1001,12 +1009,13 @@ development:
   pool: 5
 ```
 
-Prepared Statements are enabled by default on PostgreSQL. You can disable prepared statements by setting `prepared_statements` to `false`:
+By default Active Record uses database features like prepared statements and advisory locks. You might need to disable those features if you're using an external connection pooler like PgBouncer:
 
 ```yaml
 production:
   adapter: postgresql
   prepared_statements: false
+  advisory_locks: false
 ```
 
 If enabled, Active Record will create up to `1000` prepared statements per database connection by default. To modify this behavior you can set `statement_limit` to a different value:
diff --git a/guides/source/contributing_to_ruby_on_rails.md b/guides/source/contributing_to_ruby_on_rails.md
index 3147b00f3b..b5e40aa40f 100644
--- a/guides/source/contributing_to_ruby_on_rails.md
+++ b/guides/source/contributing_to_ruby_on_rails.md
@@ -239,7 +239,6 @@ Now get busy and add/edit code. You're on your branch now, so you can write what
 * Include tests that fail without your code, and pass with it.
 * Update the (surrounding) documentation, examples elsewhere, and the guides: whatever is affected by your contribution.
 
-
 TIP: Changes that are cosmetic in nature and do not add anything substantial to the stability, functionality, or testability of Rails will generally not be accepted (read more about [our rationales behind this decision](https://github.com/rails/rails/pull/13771#issuecomment-32746700)).
 
 #### Follow the Coding Conventions
@@ -254,12 +253,24 @@ Rails follows a simple set of coding style conventions:
 * Prefer class << self over self.method for class methods.
 * Use `my_method(my_arg)` not `my_method( my_arg )` or `my_method my_arg`.
 * Use `a = b` and not `a=b`.
-* Use assert_not methods instead of refute.
+* Use assert\_not methods instead of refute.
 * Prefer `method { do_stuff }` instead of `method{do_stuff}` for single-line blocks.
 * Follow the conventions in the source you see used already.
 
 The above are guidelines - please use your best judgment in using them.
 
+Additionally, we have [RuboCop](https://www.rubocop.org/) rules defined to codify some of our coding conventions. You can run RuboCop locally against the file that you have modified before submitting a pull request:
+
+```bash
+$ rubocop actionpack/lib/action_controller/metal/strong_parameters.rb
+Inspecting 1 file
+.
+
+1 file inspected, no offenses detected
+```
+
+For `rails-ujs` CoffeeScript and JavaScript files, you can run `npm run lint` in `actionview` folder.
+
 ### Benchmark Your Code
 
 For changes that might have an impact on performance, please benchmark your
diff --git a/guides/source/development_dependencies_install.md b/guides/source/development_dependencies_install.md
index 7a414f21fe..07538a1cb7 100644
--- a/guides/source/development_dependencies_install.md
+++ b/guides/source/development_dependencies_install.md
@@ -350,35 +350,35 @@ prerequisite for installing this package manager is that
 On macOS, you can run:
 
 ```bash
-brew install yarn
+$ brew install yarn
 ```
 
 On Ubuntu, you can run:
 
 ```bash
-curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
-echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
+$ curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
+$ echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
 
-sudo apt-get update && sudo apt-get install yarn
+$ sudo apt-get update && sudo apt-get install yarn
 ```
 
 On Fedora or CentOS, just run:
 
 ```bash
-sudo wget https://dl.yarnpkg.com/rpm/yarn.repo -O /etc/yum.repos.d/yarn.repo
+$ sudo wget https://dl.yarnpkg.com/rpm/yarn.repo -O /etc/yum.repos.d/yarn.repo
 
-sudo yum install yarn
+$ sudo yum install yarn
 ```
 
 Finally, after installing Yarn, you will need to run the following
 command inside of the `activestorage` directory to install the dependencies:
 
 ```bash
-yarn install
+$ yarn install
 ```
 
 Extracting previews, tested in Active Storage's test suite requires third-party
-applications, FFmpeg for video and muPDF for PDFs, and on macOS also XQuartz
+applications, ImageMagick for images, FFmpeg for video and muPDF for PDFs, and on macOS also XQuartz
 and Poppler. Without these applications installed, Active Storage tests will
 raise errors.
 
@@ -386,6 +386,7 @@ On macOS you can run:
 
 ```bash
 $ brew install ffmpeg
+$ brew install imagemagick
 $ brew cask install xquartz
 $ brew install mupdf-tools
 $ brew install poppler
@@ -396,6 +397,7 @@ On Ubuntu, you can run:
 ```bash
 $ sudo apt-get update
 $ sudo apt-get install ffmpeg
+$ sudo apt-get install imagemagick
 $ sudo apt-get install mupdf mupdf-tools
 ```
 
@@ -403,12 +405,23 @@ On Fedora or CentOS, just run:
 
 ```bash
 $ sudo yum install ffmpeg
+$ sudo yum install imagemagick
 $ sudo yum install mupdf
 ```
 
 FreeBSD users can just run:
 
 ```bash
+# pkg install imagemagick
 # pkg install ffmpeg
 # pkg install mupdf
 ```
+
+On Arch Linux, you can run:
+
+```bash
+$ sudo pacman -S ffmpeg
+$ sudo pacman -S imagemagick
+$ sudo pacman -S mupdf mupdf-tools
+$ sudo pacman -S poppler
+```
diff --git a/guides/source/testing.md b/guides/source/testing.md
index 01cda8e6e4..de93e1c653 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -1113,11 +1113,10 @@ end
 
 Now you can try running all the tests and they should pass.
 
-NOTE: If you followed the steps in the Basic Authentication section, you'll need to add the following to the `setup` block to get all the tests passing:
+NOTE: If you followed the steps in the Basic Authentication section, you'll need to add authorization to every request header to get all the tests passing:
 
 ```ruby
-request.headers['Authorization'] = ActionController::HttpAuthentication::Basic.
-  encode_credentials('dhh', 'secret')
+post articles_url, params: { article: { body: 'Rails is awesome!', title: 'Hello Rails' } }, headers: { Authorization: ActionController::HttpAuthentication::Basic.encode_credentials('dhh', 'secret') }
 ```
 
 ### Available Request Types for Functional Tests