Add new Rails/DuplicateIgnoredColumns cop

changelog/new_add_new_rails_avoid_duplicate_ignored_colums_cop.md

@@ -0,0 +1 @@
+* [#761](https://github.com/rubocop/rubocop-rails/pull/761): Add new `Rails/AvoidDuplicateIgnoredColumns` cop. ([@sikachu][])

config/default.yml

@@ -195,6 +195,11 @@ Rails/AttributeDefaultBlockValue:
   Include:
     - 'app/models/**/*'
 
+Rails/AvoidDuplicateIgnoredColumns:
+  Description: 'Checks for duplicate calls to `ActiveRecord::Base.ignore_columns=` in a single file.'
+  Enabled: 'pending'
+  VersionAdded: '<<next>>'
+
 Rails/BelongsTo:
   Description: >-
                   Use `optional: true` instead of `required: false` for

docs/modules/ROOT/pages/cops_rails.adoc

@@ -647,6 +647,40 @@ end
 | Array
 |===
 
+== Rails/AvoidDuplicateIgnoredColumns
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Pending
+| Yes
+| No
+| -
+| -
+|===
+
+Checks for duplicate calls to ActiveRecord::Base.ignore_columns= as the
+subsequent calls will override the first call.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+class User < ApplicationRecord
+  self.ignored_columns = %w(profile)
+
+  # ...
+
+  self.ignored_columns = %w(birthday)
+end
+
+# good
+class User < ApplicationRecord
+  self.ignored_columns = %w(profile birthday)
+end
+----
+
 == Rails/BelongsTo
 
 |===

lib/rubocop/cop/rails/avoid_duplicate_ignored_columns.rb

@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Checks for duplicate calls to ActiveRecord::Base.ignore_columns= as the
+      # subsequent calls will override the first call.
+      #
+      # @example
+      #   # bad
+      #   class User < ApplicationRecord
+      #     self.ignored_columns = %w(profile)
+      #     self.ignored_columns = %w(birthday)
+      #   end
+      #
+      #   # good
+      #   class User < ApplicationRecord
+      #     self.ignored_columns = %w(profile birthday)
+      #   end
+      #
+      class AvoidDuplicateIgnoredColumns < Base
+        MESSAGE = 'self.ignored_columns= has already been called on line %<other_line_number>s.'
+        ACTIVE_RECORD_CLASSES = %w[ApplicationRecord ActiveRecord::Base].freeze
+
+        def initialize(config = nil, options = nil)
+          super
+
+          @found_nodes = {}
+          @reported_lines = []
+        end
+
+        def on_send(current_node)
+          return unless current_node.method?(:ignored_columns=)
+          return unless current_node.self_receiver?
+
+          parent_class_name = find_parent_class_name(current_node)
+          return unless active_model?(parent_class_name)
+
+          @found_nodes[current_node.first_line] = current_node
+          return if @found_nodes.size == 1
+
+          add_offenses
+        end
+
+        private
+
+        def active_model?(parent_class_name)
+          ACTIVE_RECORD_CLASSES.include?(parent_class_name)
+        end
+
+        def find_parent_class_name(node)
+          return nil unless node
+
+          if node.class_type?
+            parent_class_name = node.node_parts[1]
+
+            return nil if parent_class_name.nil?
+
+            return parent_class_name.source
+          end
+
+          find_parent_class_name(node.parent)
+        end
+
+        def add_offenses
+          # Remove the earliest found node as we don't want to report offense on it.
+          first_occurance_line_number = @found_nodes.keys.min
+          @found_nodes.delete(first_occurance_line_number)
+
+          @found_nodes.each do |line_number, node|
+            next if @reported_lines.include?(line_number)
+
+            add_offense(node, message: format(MESSAGE, other_line_number: first_occurance_line_number))
+
+            @reported_lines << line_number
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -24,6 +24,7 @@
 require_relative 'rails/arel_star'
 require_relative 'rails/assert_not'
 require_relative 'rails/attribute_default_block_value'
+require_relative 'rails/avoid_duplicate_ignored_columns'
 require_relative 'rails/belongs_to'
 require_relative 'rails/blank'
 require_relative 'rails/bulk_change_table'

spec/rubocop/cop/rails/avoid_duplicate_ignored_columns_spec.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::AvoidDuplicateIgnoredColumns, :config do
+  context 'with no duplicate self.ignored_columns= call' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        class User < ApplicationRecord
+          self.ignored_columns = %w(profile birthday)
+        end
+      RUBY
+    end
+  end
+
+  context 'with duplicate self.ignored_columns= call' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        class User < ApplicationRecord
+          self.ignored_columns = %w(profile)
+          self.ignored_columns = %w(birthday)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ self.ignored_columns= has already been called on line 2.
+        end
+      RUBY
+    end
+  end
+end