Add new Rails/MailerName cop

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New features
 
+* [#281](https://github.com/rubocop-hq/rubocop-rails/pull/281): Add new `Rails/MailerName` cop. ([@fatkodima][])
 * [#246](https://github.com/rubocop-hq/rubocop-rails/issues/246): Add new `Rails/PluckInWhere` cop. ([@fatkodima][])
 * [#17](https://github.com/rubocop-hq/rubocop-rails/issues/17): Add new `Rails/NegateInclude` cop. ([@fatkodima][])
 * [#278](https://github.com/rubocop-hq/rubocop-rails/pull/278): Add new `Rails/Pluck` cop. ([@eugeneius][])

config/default.yml

@@ -325,6 +325,14 @@ Rails/LinkToBlank:
  Enabled: true
  VersionAdded: '0.62'
 
+Rails/MailerName:
+ Description: 'Mailer should end with `Mailer` suffix.'
+ StyleGuide: 'https://rails.rubystyle.guide/#mailer-name'
+ Enabled: 'pending'
+ VersionAdded: '2.7'
+ Include:
+ - app/mailers/**/*.rb
+
 Rails/NegateInclude:
  Description: 'Prefer `collection.exclude?(obj)` over `!collection.include?(obj)`.'
  Enabled: 'pending'

docs/modules/ROOT/pages/cops.adoc

@@ -38,6 +38,7 @@
 * xref:cops_rails.adoc#railsinverseof[Rails/InverseOf]
 * xref:cops_rails.adoc#railslexicallyscopedactionfilter[Rails/LexicallyScopedActionFilter]
 * xref:cops_rails.adoc#railslinktoblank[Rails/LinkToBlank]
+* xref:cops_rails.adoc#railsmailername[Rails/MailerName]
 * xref:cops_rails.adoc#railsnegateinclude[Rails/NegateInclude]
 * xref:cops_rails.adoc#railsnotnullcolumn[Rails/NotNullColumn]
 * xref:cops_rails.adoc#railsoutput[Rails/Output]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -1894,6 +1894,56 @@ link_to 'Click here', url, target: '_blank', rel: 'noreferrer'
 * https://html.spec.whatwg.org/multipage/links.html#link-type-noopener
 * https://html.spec.whatwg.org/multipage/links.html#link-type-noreferrer
 
+== Rails/MailerName
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 2.7
+| -
+|===
+
+This cop enforces that mailer names end with `Mailer` suffix.
+
+Without the `Mailer` suffix it isn't immediately apparent what's a mailer
+and which views are related to the mailer.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+class User < ActionMailer::Base
+end
+
+class User < ApplicationMailer
+end
+
+# good
+class UserMailer < ActionMailer::Base
+end
+
+class UserMailer < ApplicationMailer
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| Include
+| `app/mailers/**/*.rb`
+| Array
+|===
+
+=== References
+
+* https://rails.rubystyle.guide/#mailer-name
+
 == Rails/NegateInclude
 
 |===

lib/rubocop/cop/rails/mailer_name.rb

@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+module RuboCop
+ module Cop
+ module Rails
+ # This cop enforces that mailer names end with `Mailer` suffix.
+ #
+ # Without the `Mailer` suffix it isn't immediately apparent what's a mailer
+ # and which views are related to the mailer.
+ #
+ # @example
+ # # bad
+ # class User < ActionMailer::Base
+ # end
+ #
+ # class User < ApplicationMailer
+ # end
+ #
+ # # good
+ # class UserMailer < ActionMailer::Base
+ # end
+ #
+ # class UserMailer < ApplicationMailer
+ # end
+ #
+ class MailerName < Cop
+ MSG = 'Mailer should end with `Mailer` suffix.'
+
+ def_node_matcher :mailer_base_class?, <<~PATTERN
+ {
+ (const (const nil? :ActionMailer) :Base)
+ (const nil? :ApplicationMailer)
+ }
+ PATTERN
+
+ def_node_matcher :class_definition?, <<~PATTERN
+ (class $(const _ !#mailer_suffix?) #mailer_base_class? ...)
+ PATTERN
+
+ def_node_matcher :class_new_definition?, <<~PATTERN
+ (send (const nil? :Class) :new #mailer_base_class?)
+ PATTERN
+
+ def on_class(node)
+ class_definition?(node) do |name_node|
+ add_offense(name_node)
+ end
+ end
+
+ def on_send(node)
+ return unless class_new_definition?(node)
+
+ casgn_parent = node.each_ancestor(:casgn).first
+ return unless casgn_parent
+
+ name = casgn_parent.children[1]
+ add_offense(casgn_parent, location: :name) unless mailer_suffix?(name)
+ end
+
+ def autocorrect(node)
+ lambda do |corrector|
+ if node.casgn_type?
+ name = node.children[1]
+ corrector.replace(node.loc.name, "#{name}Mailer")
+ else
+ name = node.children.last
+ corrector.replace(node.source_range, "#{name}Mailer")
+ end
+ end
+ end
+
+ private
+
+ def mailer_suffix?(mailer_name)
+ mailer_name.to_s.end_with?('Mailer')
+ end
+ end
+ end
+ end
+end

lib/rubocop/cop/rails_cops.rb

@@ -40,6 +40,7 @@
 require_relative 'rails/inverse_of'
 require_relative 'rails/lexically_scoped_action_filter'
 require_relative 'rails/link_to_blank'
+require_relative 'rails/mailer_name'
 require_relative 'rails/negate_include'
 require_relative 'rails/not_null_column'
 require_relative 'rails/output'

spec/rubocop/cop/rails/mailer_name_spec.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::MailerName do
+ subject(:cop) { described_class.new }
+
+ ['ActionMailer::Base', 'ApplicationMailer'].each do |base|
+ context 'when regular class definition' do
+ it 'registers an offense and corrects when name without suffix' do
+ expect_offense(<<~RUBY)
+ class User < #{base}
+ ^^^^ Mailer should end with `Mailer` suffix.
+ end
+ RUBY
+
+ expect_correction(<<~RUBY)
+ class UserMailer < #{base}
+ end
+ RUBY
+ end
+
+ it 'does not register an offense when name with suffix' do
+ expect_no_offenses(<<~RUBY)
+ class UserMailer < #{base}
+ end
+ RUBY
+ end
+ end
+
+ context 'when `Class.new` definition' do
+ it 'registers an offense and corrects when name without suffix' do
+ expect_offense(<<~RUBY)
+ User = Class.new(#{base})
+ ^^^^ Mailer should end with `Mailer` suffix.
+ RUBY
+
+ expect_correction(<<~RUBY)
+ UserMailer = Class.new(#{base})
+ RUBY
+ end
+
+ it 'does not register an offense when name with suffix' do
+ expect_no_offenses(<<~RUBY)
+ UserMailer = Class.new(#{base})
+ RUBY
+ end
+ end
+ end
+end