Add new AttributeDefaultBlockValue cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#362](https://github.com/rubocop-hq/rubocop-rails/pull/362): Add new `Rails/WhereEquals` cop. ([@eugeneius][])
+* [#339](https://github.com/rubocop-hq/rubocop-rails/pull/339): Add new `Rails/AttributeDefaultBlockValue` cop. ([@cilim][])
 
 ### Bug fixes
 
@@ -298,3 +299,4 @@
 [@bubaflub]: https://github.com/bubaflub
 [@dvandersluis]: https://github.com/dvandersluis
 [@Tietew]: https://github.com/Tietew
+[@cilim]: https://github.com/cilim

config/default.yml

@@ -105,6 +105,13 @@ Rails/AssertNot:
   Include:
     - '**/test/**/*'
 
+Rails/AttributeDefaultBlockValue:
+  Description: 'Pass method call in block for attribute option `default`.'
+  Enabled: pending
+  VersionAdded: '2.9'
+  Include:
+    - 'models/**/*'
+
 Rails/BelongsTo:
   Description: >-
                   Use `optional: true` instead of `required: false` for

docs/modules/ROOT/pages/cops.adoc

@@ -27,6 +27,7 @@ based on the https://rails.rubystyle.guide/[Rails Style Guide].
 * xref:cops_rails.adoc#railsapplicationmailer[Rails/ApplicationMailer]
 * xref:cops_rails.adoc#railsapplicationrecord[Rails/ApplicationRecord]
 * xref:cops_rails.adoc#railsassertnot[Rails/AssertNot]
+* xref:cops_rails.adoc#railsattributedefaultblockvalue[Rails/AttributeDefaultBlockValue]
 * xref:cops_rails.adoc#railsbelongsto[Rails/BelongsTo]
 * xref:cops_rails.adoc#railsblank[Rails/Blank]
 * xref:cops_rails.adoc#railsbulkchangetable[Rails/BulkChangeTable]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -409,6 +409,68 @@ assert_not x
 | Array
 |===
 
+== Rails/AttributeDefaultBlockValue
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 2.9
+| -
+|===
+
+This cop looks for `attribute` class methods that specify a `:default` option
+which value is a method call without a block.
+It will accept all other values, such as literals and constants.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+class User < ApplicationRecord
+  attribute :confirmed_at, :datetime, default: Time.zone.now
+end
+
+# good
+class User < ActiveRecord::Base
+  attribute :confirmed_at, :datetime, default: -> { Time.zone.now }
+end
+
+# good
+class User < ActiveRecord::Base
+  attribute :role, :string, default: :customer
+end
+
+# good
+class User < ActiveRecord::Base
+  attribute :activated, :boolean, default: false
+end
+
+# good
+class User < ActiveRecord::Base
+  attribute :login_count, :integer, default: 0
+end
+
+# good
+class User < ActiveRecord::Base
+  FOO = 123
+  attribute :custom_attribute, :integer, default: FOO
+end
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| Include
+| `models/**/*`
+| Array
+|===
+
 == Rails/BelongsTo
 
 |===

lib/rubocop/cop/rails/attribute_default_block_value.rb

@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop looks for `attribute` class methods that specify a `:default` option
+      # which value is a method call without a block.
+      # It will accept all other values, such as literals and constants.
+      #
+      # @example
+      #   # bad
+      #   class User < ApplicationRecord
+      #     attribute :confirmed_at, :datetime, default: Time.zone.now
+      #   end
+      #
+      #   # good
+      #   class User < ActiveRecord::Base
+      #     attribute :confirmed_at, :datetime, default: -> { Time.zone.now }
+      #   end
+      #
+      #   # good
+      #   class User < ActiveRecord::Base
+      #     attribute :role, :string, default: :customer
+      #   end
+      #
+      #   # good
+      #   class User < ActiveRecord::Base
+      #     attribute :activated, :boolean, default: false
+      #   end
+      #
+      #   # good
+      #   class User < ActiveRecord::Base
+      #     attribute :login_count, :integer, default: 0
+      #   end
+      #
+      #   # good
+      #   class User < ActiveRecord::Base
+      #     FOO = 123
+      #     attribute :custom_attribute, :integer, default: FOO
+      #   end
+      class AttributeDefaultBlockValue < Cop
+        MSG = 'Pass method in a block to `:default` option.'
+
+        def_node_matcher :default_attribute, <<~PATTERN
+          (send nil? :attribute _ _ (hash <$#attribute ...>))
+        PATTERN
+
+        def_node_matcher :attribute, '(pair (sym :default) $_)'
+
+        def on_send(node)
+          default_attribute(node) do |attribute|
+            value = attribute.children.last
+
+            add_offense(node, location: value) if value.send_type?
+          end
+        end
+
+        def autocorrect(node)
+          expression = default_attribute(node).children.last
+
+          lambda do |corrector|
+            corrector.replace(expression, "-> { #{expression.source} }")
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -15,6 +15,7 @@
 require_relative 'rails/application_mailer'
 require_relative 'rails/application_record'
 require_relative 'rails/assert_not'
+require_relative 'rails/attribute_default_block_value'
 require_relative 'rails/belongs_to'
 require_relative 'rails/blank'
 require_relative 'rails/bulk_change_table'

spec/rubocop/cop/rails/attribute_default_block_value_spec.rb

@@ -0,0 +1,138 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::AttributeDefaultBlockValue do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+  let(:message) { 'Pass method in a block to `:default` option.' }
+
+  context 'when `:default` option is last' do
+    it 'disallows method' do
+      expect_offense(<<~RUBY)
+        def bar
+        end
+
+        attribute :foo, :string, default: bar
+                                          ^^^ #{message}
+      RUBY
+    end
+
+    it 'disallows method called from other instance object' do
+      expect_offense(<<~RUBY)
+        attribute :foo, :string, default: Foo.new.bar
+                                          ^^^^^^^^^^^ #{message}
+      RUBY
+    end
+
+    it 'autocorrects `:default` method value in same row' do
+      expect_offense(<<~RUBY)
+        attribute :foo, :string, default: Foo.bar
+                                          ^^^^^^^ #{message}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        attribute :foo, :string, default: -> { Foo.bar }
+      RUBY
+    end
+
+    it 'autocorrects `:default` method value in next row' do
+      expect_offense(<<~RUBY)
+        attribute :foo, :string, limit: 1,
+                                 default: Foo.bar
+                                          ^^^^^^^ #{message}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        attribute :foo, :string, limit: 1,
+                                 default: -> { Foo.bar }
+      RUBY
+    end
+
+    it 'allows boolean false' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :boolean, default: false
+      RUBY
+    end
+
+    it 'allows boolean true' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :boolean, default: true
+      RUBY
+    end
+
+    it 'allows symbol' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :string, default: :bar
+      RUBY
+    end
+
+    it 'allows int' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :integer, default: 1
+      RUBY
+    end
+
+    it 'allows decimal' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :decimal, default: 3.14
+      RUBY
+    end
+
+    it 'allows constant' do
+      expect_no_offenses(<<~RUBY)
+        CONSTANT = :foo
+        attribute :bar, :string, default: CONSTANT
+      RUBY
+    end
+
+    it 'allows block' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :datetime, default: -> { Time.zone.now }
+      RUBY
+    end
+
+    it 'allows without default value' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :datetime
+      RUBY
+    end
+
+    it 'allows with array option' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :bar, array: FooBar.array
+      RUBY
+    end
+
+    it 'allows with range option' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :bar, range: FooBar.range
+      RUBY
+    end
+
+    it 'allows with limit option' do
+      expect_no_offenses(<<~RUBY)
+        attribute :foo, :bar, limit: FooBar.limit
+      RUBY
+    end
+  end
+
+  context 'when `:default` option is next to last' do
+    it 'disallows `:default` method value' do
+      expect_offense(<<~RUBY)
+        attribute :foo, :string, range: true, default: Foo.bar, limit: 10
+                                                       ^^^^^^^ #{message}
+      RUBY
+    end
+
+    it 'autocorrects `:default` method value' do
+      expect_offense(<<~RUBY)
+        attribute :foo, :string, default: Foo.bar, limit: 1
+                                          ^^^^^^^ #{message}
+      RUBY
+
+      expect_correction(<<~RUBY)
+        attribute :foo, :string, default: -> { Foo.bar }, limit: 1
+      RUBY
+    end
+  end
+end