Add new rails Schema Comment cop

CHANGELOG.md

@@ -483,3 +483,4 @@
 [@johnsyweb]: https://github.com/johnsyweb
 [@theunraveler]: https://github.com/theunraveler
 [@pirj]: https://github.com/pirj
+[@vitormd]: https://github.com/vitormd

changelog/new_schema_comment_cop.md

@@ -0,0 +1 @@
+* [#568](https://github.com/rubocop/rubocop-rails/issues/568): Add `Rails/SchemaComment` cop. ([@vitormd][])

config/default.yml

@@ -733,6 +733,13 @@ Rails/SaveBang:
   AllowedReceivers: []
   SafeAutoCorrect: false
 
+Rails/SchemaComment:
+  Description: >-
+    This cop enforces the use of the `comment` option when adding a new table or column
+    to the database during a migration.
+  Enabled: false
+  VersionAdded: '2.13'
+
 Rails/ScopeArgs:
   Description: 'Checks the arguments of ActiveRecord scopes.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -97,6 +97,7 @@ based on the https://rails.rubystyle.guide/[Rails Style Guide].
 * xref:cops_rails.adoc#railssafenavigation[Rails/SafeNavigation]
 * xref:cops_rails.adoc#railssafenavigationwithblank[Rails/SafeNavigationWithBlank]
 * xref:cops_rails.adoc#railssavebang[Rails/SaveBang]
+* xref:cops_rails.adoc#railsschemacomment[Rails/SchemaComment]
 * xref:cops_rails.adoc#railsscopeargs[Rails/ScopeArgs]
 * xref:cops_rails.adoc#railsshorti18n[Rails/ShortI18n]
 * xref:cops_rails.adoc#railsskipsmodelvalidations[Rails/SkipsModelValidations]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -4503,6 +4503,40 @@ Service::Mailer::update
 
 * https://rails.rubystyle.guide#save-bang
 
+== Rails/SchemaComment
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Disabled
+| Yes
+| No
+| 2.13
+| -
+|===
+
+This cop enforces the use of the `comment` option when adding a new table or column
+to the database during a migration.
+
+=== Examples
+
+[source,ruby]
+----
+# bad (no comment for a new column or table)
+add_column :table, :column, :integer
+
+create_table :table do |t|
+  t.type :column
+end
+
+# good
+add_column :table, :column, :integer, comment: 'Number of offenses'
+
+create_table :table, comment: 'Table of offenses data' do |t|
+  t.type :column, comment: 'Number of offenses'
+end
+----
+
 == Rails/ScopeArgs
 
 |===

lib/rubocop/cop/mixin/active_record_migrations_helper.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # A mixin to extend cops for Active Record features
+    module ActiveRecordMigrationsHelper
+      extend NodePattern::Macros
+
+      RAILS_ABSTRACT_SCHEMA_DEFINITIONS = %i[
+        bigint binary boolean date datetime decimal float integer json string
+        text time timestamp virtual
+      ].freeze
+      RAILS_ABSTRACT_SCHEMA_DEFINITIONS_HELPERS = %i[
+        column references belongs_to primary_key numeric
+      ].freeze
+      POSTGRES_SCHEMA_DEFINITIONS = %i[
+        bigserial bit bit_varying cidr citext daterange hstore inet interval
+        int4range int8range jsonb ltree macaddr money numrange oid point line
+        lseg box path polygon circle serial tsrange tstzrange tsvector uuid xml
+      ].freeze
+      MYSQL_SCHEMA_DEFINITIONS = %i[
+        blob tinyblob mediumblob longblob tinytext mediumtext longtext
+        unsigned_integer unsigned_bigint unsigned_float unsigned_decimal
+      ].freeze
+
+      def_node_matcher :create_table_with_block?, <<~PATTERN
+        (block
+          (send nil? :create_table ...)
+          (args (arg _var))
+          _)
+      PATTERN
+    end
+  end
+end

lib/rubocop/cop/rails/create_table_with_timestamps.rb

@@ -41,16 +41,11 @@ module Rails
       #     t.datetime :updated_at, default: -> { 'CURRENT_TIMESTAMP' }
       #   end
       class CreateTableWithTimestamps < Base
+        include ActiveRecordMigrationsHelper
+
         MSG = 'Add timestamps when creating a new table.'
         RESTRICT_ON_SEND = %i[create_table].freeze
 
-        def_node_matcher :create_table_with_block?, <<~PATTERN
-          (block
-            (send nil? :create_table ...)
-            (args (arg _var))
-            _)
-        PATTERN
-
         def_node_matcher :create_table_with_timestamps_proc?, <<~PATTERN
           (send nil? :create_table (sym _) ... (block-pass (sym :timestamps)))
         PATTERN

lib/rubocop/cop/rails/schema_comment.rb

@@ -0,0 +1,104 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop enforces the use of the `comment` option when adding a new table or column
+      # to the database during a migration.
+      #
+      # @example
+      #   # bad (no comment for a new column or table)
+      #   add_column :table, :column, :integer
+      #
+      #   create_table :table do |t|
+      #     t.type :column
+      #   end
+      #
+      #   # good
+      #   add_column :table, :column, :integer, comment: 'Number of offenses'
+      #
+      #   create_table :table, comment: 'Table of offenses data' do |t|
+      #     t.type :column, comment: 'Number of offenses'
+      #   end
+      #
+      class SchemaComment < Base
+        include ActiveRecordMigrationsHelper
+
+        COLUMN_MSG = 'New database column without `comment`.'
+        TABLE_MSG = 'New database table without `comment`.'
+        RESTRICT_ON_SEND = %i[add_column create_table].freeze
+        CREATE_TABLE_COLUMN_METHODS = Set[
+          *(
+            RAILS_ABSTRACT_SCHEMA_DEFINITIONS |
+            RAILS_ABSTRACT_SCHEMA_DEFINITIONS_HELPERS |
+            POSTGRES_SCHEMA_DEFINITIONS |
+            MYSQL_SCHEMA_DEFINITIONS
+          )
+        ].freeze
+
+        # @!method comment_present?(node)
+        def_node_matcher :comment_present?, <<~PATTERN
+          (hash <(pair {(sym :comment) (str "comment")} (_ [present?])) ...>)
+        PATTERN
+
+        # @!method add_column?(node)
+        def_node_matcher :add_column?, <<~PATTERN
+          (send nil? :add_column _table _column _type _?)
+        PATTERN
+
+        # @!method add_column_with_comment?(node)
+        def_node_matcher :add_column_with_comment?, <<~PATTERN
+          (send nil? :add_column _table _column _type #comment_present?)
+        PATTERN
+
+        # @!method create_table?(node)
+        def_node_matcher :create_table?, <<~PATTERN
+          (send nil? :create_table _table _?)
+        PATTERN
+
+        # @!method create_table?(node)
+        def_node_matcher :create_table_with_comment?, <<~PATTERN
+          (send nil? :create_table _table #comment_present? ...)
+        PATTERN
+
+        # @!method t_column?(node)
+        def_node_matcher :t_column?, <<~PATTERN
+          (send _var CREATE_TABLE_COLUMN_METHODS ...)
+        PATTERN
+
+        # @!method t_column_with_comment?(node)
+        def_node_matcher :t_column_with_comment?, <<~PATTERN
+          (send _var CREATE_TABLE_COLUMN_METHODS _column _type? #comment_present?)
+        PATTERN
+
+        def on_send(node)
+          if add_column_without_comment?(node)
+            add_offense(node, message: COLUMN_MSG)
+          elsif create_table?(node)
+            if create_table_without_comment?(node)
+              add_offense(node, message: TABLE_MSG)
+            elsif create_table_column_call_without_comment?(node)
+              add_offense(node.parent.body, message: COLUMN_MSG)
+            end
+          end
+        end
+
+        private
+
+        def add_column_without_comment?(node)
+          add_column?(node) && !add_column_with_comment?(node)
+        end
+
+        def create_table_without_comment?(node)
+          create_table?(node) && !create_table_with_comment?(node)
+        end
+
+        def create_table_column_call_without_comment?(node)
+          create_table_with_block?(node.parent) &&
+            t_column?(node.parent.body) &&
+            !t_column_with_comment?(node.parent.body)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative 'mixin/active_record_helper'
+require_relative 'mixin/active_record_migrations_helper'
 require_relative 'mixin/enforce_superclass'
 require_relative 'mixin/index_method'
 require_relative 'mixin/target_rails_version'
@@ -10,6 +11,7 @@
 require_relative 'rails/active_record_callbacks_order'
 require_relative 'rails/active_record_override'
 require_relative 'rails/active_support_aliases'
+require_relative 'rails/schema_comment'
 require_relative 'rails/add_column_index'
 require_relative 'rails/after_commit_override'
 require_relative 'rails/application_controller'

spec/rubocop/cop/rails/schema_comment_spec.rb

@@ -0,0 +1,117 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::SchemaComment, :config do
+  context 'when send add_column' do
+    it 'registers an offense when `add_column` has no `comment` option' do
+      expect_offense(<<~RUBY)
+        add_column :table, :column, :integer
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database column without `comment`.
+      RUBY
+    end
+
+    it 'registers an offense when `add_column` has no `comment` option, but other options' do
+      expect_offense(<<~RUBY)
+        add_column :table, :column, :integer, default: 0
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database column without `comment`.
+      RUBY
+    end
+
+    it 'registers an offense when `add_column` has a nil `comment` option' do
+      expect_offense(<<~RUBY)
+        add_column :table, :column, :integer, comment: nil
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database column without `comment`.
+      RUBY
+    end
+
+    it 'registers an offense when `add_column` has an empty `comment` option' do
+      expect_offense(<<~RUBY)
+        add_column :table, :column, :integer, comment: ''
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database column without `comment`.
+      RUBY
+    end
+
+    it 'does not register an offense when `add_column` has `comment` option' do
+      expect_no_offenses(<<~RUBY)
+        add_column :table, :column, :integer, comment: 'An integer field'
+      RUBY
+    end
+
+    it 'does not register an offense when `add_column` has `comment` option'\
+       'among other options' do
+      expect_no_offenses(<<~RUBY)
+        add_column :table, :column, :integer, null: false, comment: 'An integer field', default: 0
+      RUBY
+    end
+  end
+
+  context 'when send create_table' do
+    it 'registers an offense when `create_table` has no `comment` option' do
+      expect_offense(<<~RUBY)
+        create_table :users do |t|
+        ^^^^^^^^^^^^^^^^^^^ New database table without `comment`.
+        end
+      RUBY
+    end
+
+    it 'registers an offense when `create_table` has a nil `comment` option' do
+      expect_offense(<<~RUBY)
+        create_table :users, comment: nil do |t|
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database table without `comment`.
+        end
+      RUBY
+    end
+
+    it 'registers an offense when `create_table` has a empty `comment` option' do
+      expect_offense(<<~RUBY)
+        create_table :users, comment: '' do |t|
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ New database table without `comment`.
+
+        end
+      RUBY
+    end
+
+    it 'registers an offense when `t.column` has no `comment` option' do
+      expect_offense(<<~RUBY)
+        create_table :users, comment: 'Table' do |t|
+          t.column :column, :integer
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^ New database column without `comment`.
+        end
+      RUBY
+    end
+
+    it 'registers an offense when `t.integer` has no `comment` option' do
+      expect_offense(<<~RUBY)
+        create_table :users, comment: 'Table' do |t|
+          t.integer :column
+          ^^^^^^^^^^^^^^^^^ New database column without `comment`.
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when `t.column` has `comment` option' do
+      expect_no_offenses(<<~RUBY)
+        create_table :users, comment: 'Table' do |t|
+          t.column :column, :integer, comment: 'I am a column'
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when `t.column` has `comment` option' \
+       'among other options' do
+      expect_no_offenses(<<~RUBY)
+        create_table :users, comment: 'Table' do |t|
+          t.column :column, :integer, default: nil, comment: 'I am a column', null: true
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when `t.integer` has `comment` option'\
+       'among other options' do
+      expect_no_offenses(<<~RUBY)
+        create_table :users, comment: 'Table' do |t|
+          t.integer :column, default: nil, comment: 'I am a column', null: true
+        end
+      RUBY
+    end
+  end
+end