Add new Rails/DefaultScope cop

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#283](https://github.com/rubocop-hq/rubocop-rails/pull/283): Add new `Rails/FindById` cop. ([@fatkodima][])
 * [#276](https://github.com/rubocop-hq/rubocop-rails/pull/276): Add new `Rails/RenderPlainText` cop. ([@fatkodima][])
+* [#76](https://github.com/rubocop-hq/rubocop-rails/issues/76): Add new `Rails/DefaultScope` cop. ([@fatkodima][])
 * [#275](https://github.com/rubocop-hq/rubocop-rails/pull/275): Add new `Rails/MatchRoute` cop. ([@fatkodima][])
 * [#271](https://github.com/rubocop-hq/rubocop-rails/pull/271): Add new `Rails/RenderInline` cop. ([@fatkodima][])
 * [#281](https://github.com/rubocop-hq/rubocop-rails/pull/281): Add new `Rails/MailerName` cop. ([@fatkodima][])

config/default.yml

@@ -153,6 +153,12 @@ Rails/Date:
     - strict
     - flexible
 
+Rails/DefaultScope:
+  Description: 'Avoid use of `default_scope`.'
+  StyleGuide: 'https://rails.rubystyle.guide#avoid-default-scope'
+  Enabled: false
+  VersionAdded: '2.7'
+
 Rails/Delegate:
   Description: 'Prefer delegate method for delegations.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -17,6 +17,7 @@
 * xref:cops_rails.adoc#railscontenttag[Rails/ContentTag]
 * xref:cops_rails.adoc#railscreatetablewithtimestamps[Rails/CreateTableWithTimestamps]
 * xref:cops_rails.adoc#railsdate[Rails/Date]
+* xref:cops_rails.adoc#railsdefaultscope[Rails/DefaultScope]
 * xref:cops_rails.adoc#railsdelegate[Rails/Delegate]
 * xref:cops_rails.adoc#railsdelegateallowblank[Rails/DelegateAllowBlank]
 * xref:cops_rails.adoc#railsdynamicfindby[Rails/DynamicFindBy]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -740,6 +740,45 @@ date.in_time_zone
 | `strict`, `flexible`
 |===
 
+== Rails/DefaultScope
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Disabled
+| Yes
+| No
+| 2.7
+| -
+|===
+
+This cop looks for uses of `default_scope`.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+default_scope -> { where(hidden: false) }
+
+# good
+scope :published, -> { where(hidden: false) }
+
+# bad
+def self.default_scope
+  where(hidden: false)
+end
+
+# good
+def self.published
+  where(hidden: false)
+end
+----
+
+=== References
+
+* https://rails.rubystyle.guide#avoid-default-scope
+
 == Rails/Delegate
 
 |===

lib/rubocop/cop/rails/default_scope.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop looks for uses of `default_scope`.
+      #
+      # @example
+      #   # bad
+      #   default_scope -> { where(hidden: false) }
+      #
+      #   # good
+      #   scope :published, -> { where(hidden: false) }
+      #
+      #   # bad
+      #   def self.default_scope
+      #     where(hidden: false)
+      #   end
+      #
+      #   # good
+      #   def self.published
+      #     where(hidden: false)
+      #   end
+      #
+      class DefaultScope < Cop
+        MSG = 'Avoid use of `default_scope`. It is better to use explicitly named scopes.'
+
+        def_node_matcher :method_call?, <<~PATTERN
+          (send nil? :default_scope ...)
+        PATTERN
+
+        def_node_matcher :class_method_definition?, <<~PATTERN
+          (defs _ :default_scope args ...)
+        PATTERN
+
+        def_node_matcher :eigenclass_method_definition?, <<~PATTERN
+          (sclass (self) $(def :default_scope args ...))
+        PATTERN
+
+        def on_send(node)
+          add_offense(node, location: :selector) if method_call?(node)
+        end
+
+        def on_defs(node)
+          add_offense(node, location: :name) if class_method_definition?(node)
+        end
+
+        def on_sclass(node)
+          eigenclass_method_definition?(node) { |default_scope| add_offense(default_scope, location: :name) }
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -19,6 +19,7 @@
 require_relative 'rails/content_tag'
 require_relative 'rails/create_table_with_timestamps'
 require_relative 'rails/date'
+require_relative 'rails/default_scope'
 require_relative 'rails/delegate'
 require_relative 'rails/delegate_allow_blank'
 require_relative 'rails/dynamic_find_by'

spec/rubocop/cop/rails/default_scope_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::DefaultScope do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense when calling `default_scope` within class' do
+    expect_offense(<<~RUBY)
+      class Post < ApplicationRecord
+        default_scope -> { where(hidden: false) }
+        ^^^^^^^^^^^^^ Avoid use of `default_scope`. It is better to use explicitly named scopes.
+      end
+    RUBY
+  end
+
+  it 'registers an offense when defining `default_scope` as class method' do
+    expect_offense(<<~RUBY)
+      class Post < ApplicationRecord
+        def self.default_scope
+                 ^^^^^^^^^^^^^ Avoid use of `default_scope`. It is better to use explicitly named scopes.
+        end
+      end
+    RUBY
+  end
+
+  it 'registers an offense when defining `default_scope` as eigenclass method' do
+    expect_offense(<<~RUBY)
+      class Post < ApplicationRecord
+        class << self
+          def default_scope
+              ^^^^^^^^^^^^^ Avoid use of `default_scope`. It is better to use explicitly named scopes.
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when defining `default_scope` instance method' do
+    expect_no_offenses(<<~RUBY)
+      class Post < ApplicationRecord
+        def default_scope
+        end
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when calling `default_scope` on local variable receiver' do
+    expect_no_offenses(<<~RUBY)
+      foo.default_scope
+    RUBY
+  end
+end