Use double quotes more consistenly in doc and error messages

For better or worse, the Rails guide settled on double quotes
and a large part of the community also use rubocop which enforce
them by default.

So we might as well try to follow that style when providing code
snippets in the documentation or error messages.

Fix: rails#49822

I certainly didn't get them all, but consistency should be significantly
improved.

Author: byroot

actionpack/lib/action_controller/template_assertions.rb

@@ -4,8 +4,8 @@ module ActionController
   module TemplateAssertions # :nodoc:
     def assert_template(options = {}, message = nil)
       raise NoMethodError,
-        "assert_template has been extracted to a gem. To continue using it,
-        add `gem 'rails-controller-testing'` to your Gemfile."
+        'assert_template has been extracted to a gem. To continue using it,
+        add `gem "rails-controller-testing"` to your Gemfile.'
     end
   end
 end

actionpack/lib/action_dispatch/middleware/templates/rescues/_source.html.erb

@@ -29,7 +29,7 @@
         </table>
       </div>
       <%- unless self.error_highlight_available? -%>
-        <p class="error_highlight_tip">Tip: You may want to add <code>gem 'error_highlight', '&gt;= 0.4.0'</code> into your Gemfile, which will display the fine-grained error location.</p>
+        <p class="error_highlight_tip">Tip: You may want to add <code>gem "error_highlight", "&gt;= 0.4.0"</code> into your Gemfile, which will display the fine-grained error location.</p>
       <%- end -%>
     </div>
   <% end %>

actionpack/lib/action_dispatch/testing/test_process.rb

@@ -30,8 +30,8 @@ def file_fixture_upload(path, mime_type = nil, binary = false)
 
     def assigns(key = nil)
       raise NoMethodError,
-        "assigns has been extracted to a gem. To continue using it,
-        add `gem 'rails-controller-testing'` to your Gemfile."
+        'assigns has been extracted to a gem. To continue using it,
+        add `gem "rails-controller-testing"` to your Gemfile.'
     end
 
     def session

activemodel/lib/active_model/secure_password.rb

@@ -41,7 +41,7 @@ module ClassMethods
       #
       # To use +has_secure_password+, add bcrypt (~> 3.1.7) to your Gemfile:
       #
-      #   gem 'bcrypt', '~> 3.1.7'
+      #   gem "bcrypt", "~> 3.1.7"
       #
       # ==== Examples
       #

activestorage/lib/active_storage/transformers/image_processing_transformer.rb

@@ -5,7 +5,7 @@
 rescue LoadError
   raise LoadError, <<~ERROR.squish
     Generating image variants require the image_processing gem.
-    Please add `gem 'image_processing', '~> 1.2'` to your Gemfile.
+    Please add `gem "image_processing", "~> 1.2"` to your Gemfile.
   ERROR
 end
 

activesupport/lib/active_support/railtie.rb

@@ -89,7 +89,7 @@ class Railtie < Rails::Railtie # :nodoc:
       begin
         TZInfo::DataSource.get
       rescue TZInfo::DataSourceNotFound => e
-        raise e.exception "tzinfo-data is not present. Please add gem 'tzinfo-data' to your Gemfile and run bundle install"
+        raise e.exception('tzinfo-data is not present. Please add gem "tzinfo-data" to your Gemfile and run bundle install')
       end
       require "active_support/core_ext/time/zones"
       Time.zone_default = Time.find_zone!(app.config.time_zone)

activesupport/lib/active_support/xml_mini.rb

@@ -12,7 +12,7 @@ module ActiveSupport
   # = \XmlMini
   #
   # To use the much faster libxml parser:
-  #   gem 'libxml-ruby'
+  #   gem "libxml-ruby"
   #   XmlMini.backend = 'LibXML'
   module XmlMini
     extend self

guides/source/3_1_release_notes.md

@@ -37,18 +37,18 @@ The following changes are meant for upgrading your application to Rails 3.1.3, t
 Make the following changes to your `Gemfile`.
 
 ```ruby
-gem 'rails', '= 3.1.3'
-gem 'mysql2'
+gem "rails", "= 3.1.3"
+gem "mysql2"
 
 # Needed for the new asset pipeline
 group :assets do
-  gem 'sass-rails',   "~> 3.1.5"
-  gem 'coffee-rails', "~> 3.1.1"
-  gem 'uglifier',     ">= 1.0.3"
+  gem "sass-rails",   "~> 3.1.5"
+  gem "coffee-rails", "~> 3.1.1"
+  gem "uglifier",     ">= 1.0.3"
 end
 
 # jQuery is the default JavaScript library in Rails 3.1
-gem 'jquery-rails'
+gem "jquery-rails"
 ```
 
 #### config/application.rb

guides/source/4_2_release_notes.md

@@ -179,7 +179,7 @@ change your code to use the explicit form (`render file: "foo/bar"`) instead.
 
 `respond_with` and the corresponding class-level `respond_to` have been moved
 to the [responders](https://github.com/plataformatec/responders) gem. Add
-`gem 'responders', '~> 2.0'` to your `Gemfile` to use it:
+`gem "responders", "~> 2.0"` to your `Gemfile` to use it:
 
 ```ruby
 # app/controllers/users_controller.rb
@@ -445,7 +445,7 @@ Please refer to the [Changelog][action-pack] for detailed changes.
 ### Removals
 
 *   `respond_with` and the class-level `respond_to` have been removed from Rails and
-    moved to the `responders` gem (version 2.0). Add `gem 'responders', '~> 2.0'`
+    moved to the `responders` gem (version 2.0). Add `gem "responders", "~> 2.0"`
     to your `Gemfile` to continue using these features.
     ([Pull Request](https://github.com/rails/rails/pull/16526),
      [More Details](https://guides.rubyonrails.org/v4.2/upgrading_ruby_on_rails.html#responders))

guides/source/action_view_overview.md

@@ -152,7 +152,7 @@ It's similar to Builder but is used to generate JSON, instead of XML.
 If you don't have it, you can add the following to your `Gemfile`:
 
 ```ruby
-gem 'jbuilder'
+gem "jbuilder"
 ```
 
 A Jbuilder object named `json` is automatically made available to templates with