Add new 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][])
+* [TODO](https://github.com/rubocop-hq/rubocop-rails/pull/TODO): Add new `Rails/CalendarTypeSuffix` cop. ([@jmks][])
 
 ### Bug fixes
 
@@ -298,3 +299,4 @@
 [@bubaflub]: https://github.com/bubaflub
 [@dvandersluis]: https://github.com/dvandersluis
 [@Tietew]: https://github.com/Tietew
+[@jmks]: https://github.com/jmks

config/default.yml

@@ -135,6 +135,14 @@ Rails/BulkChangeTable:
   Include:
     - db/migrate/*.rb
 
+Rails/CalendarTypeSuffix:
+  Description: 'Check whether database columns for calendar types follow a naming convention.'
+  Enabled: false
+  DateSuffix: "on"
+  DateTimeSuffix: "at"
+  TimeSuffix: "time"
+  VersionAdded: '2.9'
+
 Rails/ContentTag:
   Description: 'Use `tag` instead of `content_tag`.'
   Reference:

docs/modules/ROOT/pages/cops.adoc

@@ -30,6 +30,7 @@ based on the https://rails.rubystyle.guide/[Rails Style Guide].
 * xref:cops_rails.adoc#railsbelongsto[Rails/BelongsTo]
 * xref:cops_rails.adoc#railsblank[Rails/Blank]
 * xref:cops_rails.adoc#railsbulkchangetable[Rails/BulkChangeTable]
+* xref:cops_rails.adoc#railscalendartypesuffix[Rails/CalendarTypeSuffix]
 * xref:cops_rails.adoc#railscontenttag[Rails/ContentTag]
 * xref:cops_rails.adoc#railscreatetablewithtimestamps[Rails/CreateTableWithTimestamps]
 * xref:cops_rails.adoc#railsdate[Rails/Date]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -657,6 +657,60 @@ end
 | Array
 |===
 
+== Rails/CalendarTypeSuffix
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Disabled
+| Yes
+| No
+| 2.9
+| -
+|===
+
+It is convenient to follow a convention when naming database columns.
+For calendar-type columns, a reasonable convention is:
+
+date     => * _on
+datetime => *_at (e.g. timestamps)
+time     => *_time
+
+"Inspired" by https://github.com/thoughtbot/guides/tree/master/rails
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+t.date "started_at"
+t.datetime "created_datetime"
+t.time "end_at"
+
+# good
+t.date "started_on"
+t.datetime "created_at"
+t.time "end_time"
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| DateSuffix
+| `on`
+| String
+
+| DateTimeSuffix
+| `at`
+| String
+
+| TimeSuffix
+| `time`
+| String
+|===
+
 == Rails/ContentTag
 
 |===

lib/rubocop/cop/rails/calendar_type_suffix.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # It is convenient to follow a convention when naming database columns.
+      # For calendar-type columns, a reasonable convention is:
+      #
+      # date     => * _on
+      # datetime => *_at (e.g. timestamps)
+      # time     => *_time
+      #
+      # @example
+      #   # bad
+      #   t.date "started_at"
+      #   t.datetime "created_datetime"
+      #   t.time "end_at"
+      #
+      #   # good
+      #   t.date "started_on"
+      #   t.datetime "created_at"
+      #   t.time "end_time"
+      #
+      # "Inspired" by https://github.com/thoughtbot/guides/tree/master/rails
+      class CalendarTypeSuffix < Cop
+        MSG = 'Columns of type `%<type>s` should be named with a `%<suffix>s` suffix.'
+
+        def_node_matcher :calendar_type?, '(send _ ${:date :datetime :time} (str $_) ...)'
+
+        def on_send(node)
+          calendar_type?(node) do |type, name|
+            unless follows_convention?(type, name)
+              add_offense(
+                node,
+                location: highlight_range(node),
+                message: format(MSG, type: type, suffix: suffix_for(type))
+              )
+            end
+          end
+        end
+
+        def relevant_file?(file)
+          schema_file?(file) && super
+        end
+
+        private
+
+        def schema_file?(file)
+          File.basename(file) == 'schema.rb'
+        end
+
+        def follows_convention?(type, name)
+          name.end_with?("_#{suffix_for(type)}")
+        end
+
+        def suffix_for(type)
+          case type
+          when :date then cop_config['DateSuffix']
+          when :datetime then cop_config['DateTimeSuffix']
+          when :time then cop_config['TimeSuffix']
+          end
+        end
+
+        def highlight_range(node)
+          node.loc.expression.with(
+            end_pos: node.children[2].loc.expression.end_pos
+          )
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -18,6 +18,7 @@
 require_relative 'rails/belongs_to'
 require_relative 'rails/blank'
 require_relative 'rails/bulk_change_table'
+require_relative 'rails/calendar_type_suffix'
 require_relative 'rails/content_tag'
 require_relative 'rails/create_table_with_timestamps'
 require_relative 'rails/date'

spec/rubocop/cop/rails/calendar_type_suffix_spec.rb

@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::CalendarTypeSuffix, :config do
+  subject(:cop) do
+    cop = described_class.new(config)
+    allow(cop).to receive(:relevant_file?).and_return(true)
+    cop
+  end
+
+  let(:schema_path) do
+    f = Tempfile.create('rubocop-rails-CalendarTypeSuffix-test-')
+    f.close
+    Pathname(f.path)
+  end
+
+  let(:cop_config) do
+    {
+      'DateSuffix' => 'on',
+      'DateTimeSuffix' => 'at',
+      'TimeSuffix' => 'time'
+    }
+  end
+
+  before do
+    RuboCop::Rails::SchemaLoader.reset!
+    schema_path.write(schema)
+    allow(RuboCop::Rails::SchemaLoader).to receive(:db_schema_path)
+      .and_return(schema_path)
+  end
+
+  after do
+    RuboCop::Rails::SchemaLoader.reset!
+    schema_path.unlink
+  end
+
+  context 'when calendar type columns do no follow the conventional suffixes' do
+    let(:schema) { <<~RUBY }
+      ActiveRecord::Schema.define(version: 2020_02_02_075409) do
+        create_table "users", force: :cascade do |t|
+          t.date "sign_up", null: false
+          t.datetime "last_login"
+          t.time "lock_until"
+        end
+      end
+    RUBY
+
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        ActiveRecord::Schema.define(version: 2020_02_02_075409) do
+          create_table "users", force: :cascade do |t|
+            t.date "sign_up", null: false
+            ^^^^^^^^^^^^^^^^ Columns of type `date` should be named with a `on` suffix.
+            t.datetime "last_login"
+            ^^^^^^^^^^^^^^^^^^^^^^^ Columns of type `datetime` should be named with a `at` suffix.
+            t.time "lock_until"
+            ^^^^^^^^^^^^^^^^^^^ Columns of type `time` should be named with a `time` suffix.
+          end
+        end
+      RUBY
+    end
+  end
+
+  context 'when calendar type columns follow the conventional suffixes' do
+    let(:schema) { <<~RUBY }
+      ActiveRecord::Schema.define(version: 2020_02_02_075409) do
+        create_table "users", force: :cascade do |t|
+          t.date "signed_up_on", null: false
+          t.datetime "last_login_at"
+          t.time "locked_until_time"
+        end
+      end
+    RUBY
+
+    it 'does not register an offense' do
+      expect_no_offenses(schema)
+    end
+  end
+end