Fix Rails/FindBy when calling Range#first or #take

- Minimal working example
- Fix failing spec
- Extract #where_method?
- Add spec for Range#first

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Bug fixes
 
 * [#509](https://github.com/rubocop/rubocop-rails/pull/509): Fix an error for `Rails/ReflectionClassName` when using `class_name: to_s`. ([@skryukov][])
+* [#510](https://github.com/rubocop/rubocop-rails/pull/510): Fix an error for `Rails/FindBy` when calling `#first` or `#take` on a `Range` object. ([@johnsyweb][])
 * [#507](https://github.com/rubocop/rubocop-rails/pull/507): Fix an error for `Rails/FindBy` when calling `take` after block. ([@koic][])
 * [#504](https://github.com/rubocop/rubocop-rails/issues/504): Fix a false positive for `Rails/FindBy` when receiver is not an Active Record. ([@nvasilevski][])
 
@@ -413,3 +414,4 @@
 [@aesthetikx]: https://github.com/aesthetikx
 [@nvasilevski]: https://github.com/nvasilevski
 [@skryukov]: https://github.com/skryukov
+[@johnsyweb]: https://github.com/johnsyweb

lib/rubocop/cop/rails/find_by.rb

@@ -32,8 +32,7 @@ class FindBy < Base
         RESTRICT_ON_SEND = %i[first take].freeze
 
         def on_send(node)
-          receiver = node.receiver
-          return unless receiver&.method?(:where)
+          return unless where_method?(node.receiver)
           return if ignore_where_first? && node.method?(:first)
 
           range = range_between(node.receiver.loc.selector.begin_pos, node.loc.selector.end_pos)
@@ -46,6 +45,12 @@ def on_send(node)
 
         private
 
+        def where_method?(receiver)
+          return false unless receiver
+
+          receiver.respond_to?(:method?) && receiver.method?(:where)
+        end
+
         def autocorrect(corrector, node)
           return if node.method?(:first)
 

spec/rubocop/cop/rails/find_by_spec.rb

@@ -92,5 +92,17 @@
         RUBY
       end
     end
+
+    context 'when method is Range#first' do
+      it 'does not register an offense' do
+        expect_no_offenses('(1..2).first')
+      end
+    end
+
+    context 'when method is Range#take' do
+      it 'does not register an offense' do
+        expect_no_offenses('(1..2).take(1)')
+      end
+    end
   end
 end