[Fix rubocop#51] Add ability to whitelist receiver class names

In `Rails/DynamicFindBy`.

Also use `AllowedReceivers` & `AllowedMethods` instead of `Whitelist`
which will be deprecated soon.

Fixes rubocop#51.

CHANGELOG.md

@@ -36,6 +36,7 @@
 * [#197](https://github.com/rubocop-hq/rubocop-rails/pull/197): Add `Rails/UniqueValidationWithoutIndex` cop. ([@pocke][])
 * [#208](https://github.com/rubocop-hq/rubocop-rails/pull/208): Add new `Rails/IndexBy` and `Rails/IndexWith` cops. ([@djudd][], [@eugeneius][])
 * [#150](https://github.com/rubocop-hq/rubocop-rails/issues/150): Add `EnforcedStyle: refute` for `Rails/RefuteMethods` cop. ([@koic][])
+* [#51](https://github.com/rubocop-hq/rubocop-rails/issues/51): Add ability to whitelist receiver class names in `Rails/DynamicFindBy`. ([@tejasbubane][])
 
 ### Bug fixes
 
@@ -178,3 +179,4 @@
 [@djudd]: https://github.com/djudd
 [@sunny]: https://github.com/sunny
 [@hoshinotsuyoshi]: https://github.com/hoshinotsuyoshi
+[@tejasbubane]: https://github.com/tejasbubane

config/default.yml

@@ -165,8 +165,13 @@ Rails/DynamicFindBy:
   StyleGuide: 'https://rails.rubystyle.guide#find_by'
   Enabled: true
   VersionAdded: '0.44'
+  # The `Whitelist` has been deprecated, Please use `AllowedMethods` instead.
   Whitelist:
     - find_by_sql
+  AllowedMethods:
+    - find_by_sql
+  AllowedReceivers:
+    - Gem::Specification
 
 Rails/EnumHash:
   Description: 'Prefer hash syntax over array syntax when defining enums.'

lib/rubocop/cop/mixin/allowed.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    # Common functionality for checking whitelisted methods & class names.
+    module Allowed
+      def allowed?(node)
+        allowed_method?(node) || allowed_receiver?(node) ||
+          whitelisted?(node)
+      end
+
+      private
+
+      def allowed_method?(node)
+        return unless cop_config['AllowedMethods']
+
+        cop_config['AllowedMethods'].include?(node.method_name.to_s)
+      end
+
+      def allowed_receiver?(node)
+        return unless cop_config['AllowedReceivers'] && node.receiver
+
+        cop_config['AllowedReceivers'].include?(node.receiver.source.to_s)
+      end
+
+      # config option `WhiteList` will be deprecated soon
+      def whitelisted?(node)
+        whitelist_config = cop_config['Whitelist']
+        return unless whitelist_config
+
+        whitelist_config.include?(node.method_name.to_s) ||
+          node.receiver && whitelist_config.include?(node.receiver.source.to_s)
+      end
+    end
+  end
+end

lib/rubocop/cop/rails/dynamic_find_by.rb

@@ -10,37 +10,29 @@ module Rails
       # @example
       #   # bad
       #   User.find_by_name(name)
-      #
-      #   # bad
       #   User.find_by_name_and_email(name)
-      #
-      #   # bad
       #   User.find_by_email!(name)
       #
       #   # good
       #   User.find_by(name: name)
-      #
-      #   # good
       #   User.find_by(name: name, email: email)
-      #
-      #   # good
       #   User.find_by!(email: email)
       class DynamicFindBy < Cop
+        include Allowed
+
         MSG = 'Use `%<static_name>s` instead of dynamic `%<method>s`.'
         METHOD_PATTERN = /^find_by_(.+?)(!)?$/.freeze
 
         def on_send(node)
-          method_name = node.method_name.to_s
-
-          return if whitelist.include?(method_name)
+          return if allowed?(node)
 
+          method_name = node.method_name
           static_name = static_method_name(method_name)
-
           return unless static_name
 
           add_offense(node,
                       message: format(MSG, static_name: static_name,
-                                           method: node.method_name))
+                                           method: method_name))
         end
         alias on_csend on_send
 
@@ -68,10 +60,6 @@ def autocorrect_argument_keywords(corrector, node, keywords)
           end
         end
 
-        def whitelist
-          cop_config['Whitelist']
-        end
-
         def column_keywords(method)
           keyword_string = method.to_s[METHOD_PATTERN, 1]
           keyword_string.split('_and_').map { |keyword| "#{keyword}: " }

lib/rubocop/cop/rails_cops.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require_relative 'mixin/active_record_helper'
+require_relative 'mixin/allowed'
 require_relative 'mixin/index_method'
 require_relative 'mixin/target_rails_version'
 

manual/cops_rails.md

@@ -659,20 +659,12 @@ See. https://rails.rubystyle.guide#find_by
 ```ruby
 # bad
 User.find_by_name(name)
-
-# bad
 User.find_by_name_and_email(name)
-
-# bad
 User.find_by_email!(name)
 
 # good
 User.find_by(name: name)
-
-# good
 User.find_by(name: name, email: email)
-
-# good
 User.find_by!(email: email)
 ```
 
@@ -681,6 +673,8 @@ User.find_by!(email: email)
 Name | Default value | Configurable values
 --- | --- | ---
 Whitelist | `find_by_sql` | Array
+AllowedMethods | `find_by_sql` | Array
+AllowedReceivers | `Gem::Specification` | Array
 
 ### References
 

spec/rubocop/cop/rails/dynamic_find_by_spec.rb

@@ -4,7 +4,7 @@
   subject(:cop) { described_class.new(config) }
 
   let(:cop_config) do
-    { 'Whitelist' => %w[find_by_sql] }
+    { 'AllowedMethods' => %w[find_by_sql] }
   end
 
   shared_examples 'register an offense and auto correct' do |message, corrected|
@@ -139,6 +139,18 @@
     RUBY
   end
 
+  context 'with allowed receiver name' do
+    let(:cop_config) do
+      { 'AllowedReceivers' => %w[Gem::Specification] }
+    end
+
+    it 'accepts dynamic find_by for receiver names in whitelist' do
+      expect_no_offenses(<<~RUBY)
+        Gem::Specification.find_by_name("backend").gem_dir
+      RUBY
+    end
+  end
+
   context 'when using safe navigation operator' do
     context 'with dynamic find_by_*' do
       let(:source) { 'user&.find_by_name(name)' }
@@ -150,4 +162,31 @@
       )
     end
   end
+
+  # Whitelisted config will be deprecated.
+  context 'with WhiteListed config' do
+    context 'allowed class-names' do
+      let(:cop_config) do
+        { 'Whitelist' => %w[Gem::Specification] }
+      end
+
+      it 'accepts class methods in whitelist' do
+        expect_no_offenses(<<~RUBY)
+          Gem::Specification.find_by_name("backend").gem_dir
+        RUBY
+      end
+    end
+
+    context 'allowed method-names' do
+      let(:cop_config) do
+        { 'Whitelist' => %w[find_by_name] }
+      end
+
+      it 'accepts class methods in whitelist' do
+        expect_no_offenses(<<~RUBY)
+          User.find_by_name("backend").gem_dir
+        RUBY
+      end
+    end
+  end
 end