[Fix rubocop#4967] Fix Rails/DynamicFindBy false-positives on non A…

…ctiveRecord

Fixes rubocop#4967.
This change applies `Rails/DynamicFindBy` cop only to receiver classes
that inherit `ActiveRecord::Base` class.

CHANGELOG.md

@@ -17,6 +17,7 @@
 * [#4987](https://github.com/bbatsov/rubocop/pull/4987): Skip permission check when using stdin option. ([@mtsmfm][])
 * [#4909](https://github.com/bbatsov/rubocop/issues/4909): Make `Rails/HasManyOrHasOneDependent` aware of multiple associations in `with_options`. ([@koic][])
 * [#4794](https://github.com/bbatsov/rubocop/issues/4794): Fix an error in `Layout/MultilineOperationIndentation` when an operation spans multiple lines and contains a ternary expression. ([@rrosenblum][])
+* [#4967](https://github.com/bbatsov/rubocop/issues/4967): Fix `Rails/DynamicFindBy` false-positives on non ActiveRecord model. ([@koic][])
 
 ### Changes
 

lib/rubocop/cop/rails/dynamic_find_by.rb

@@ -30,6 +30,9 @@ class DynamicFindBy < Cop
         METHOD_PATTERN = /^find_by_(.+?)(!)?$/
 
         def on_send(node)
+          return if node.receiver.nil? ||
+                    !inherited_active_record?(node.receiver.const_name)
+
           method_name = node.method_name.to_s
 
           return if whitelist.include?(method_name)
@@ -75,6 +78,13 @@ def static_method_name(method_name)
           return nil unless match
           match[2] ? 'find_by!' : 'find_by'
         end
+
+        def inherited_active_record?(class_name)
+          klass = Object.const_get(class_name)
+
+          klass.respond_to?(:ancestors) &&
+            klass.ancestors.include?(ActiveRecord::Base)
+        end
       end
     end
   end

spec/rubocop/cop/rails/dynamic_find_by_spec.rb

@@ -7,6 +7,21 @@
     { 'Whitelist' => %w[find_by_sql] }
   end
 
+  before do
+    module ActiveRecord
+      class Base
+      end
+    end
+
+    class User < ActiveRecord::Base; end
+  end
+
+  after do
+    Object.send(:remove_const, 'User')
+    ActiveRecord.send(:remove_const, 'Base')
+    Object.send(:remove_const, 'ActiveRecord')
+  end
+
   shared_examples 'register an offense and auto correct' do |message, corrected|
     it 'registers an offense' do
       inspect_source(source)
@@ -138,4 +153,12 @@
       User.find_by_sql(["select * from users where name = ?", name])
     RUBY
   end
+
+  context 'When receiver class does not inherit `ActiveRecord::Base`' do
+    it 'accepts find_by_* method' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        Gem::Specification.find_by_name('loremipsum')
+      RUBY
+    end
+  end
 end