[Fix #717] Fix an error for Rails/DeprecatedActiveModelErrorsMethods

Fixes #717.

This PR fixes an error for `Rails/DeprecatedActiveModelErrorsMethods`
when root receiver is a variable.

Author: koic

changelog/fix_an_error_for_rails_deprecated_active_model_errors_methods.md

@@ -0,0 +1 @@
+* [#717](https://github.com/rubocop/rubocop-rails/issues/717): Fix an error for `Rails/DeprecatedActiveModelErrorsMethods` when root receiver is a variable. ([@koic][])

lib/rubocop/cop/rails/deprecated_active_model_errors_methods.rb

@@ -119,7 +119,7 @@ def on_send(node)
         def autocorrect(corrector, node)
           receiver = node.receiver
 
-          if receiver.receiver.method?(:messages)
+          if receiver.receiver.send_type? && receiver.receiver.method?(:messages)
             corrector.remove(receiver.receiver.loc.dot)
             corrector.remove(receiver.receiver.loc.selector)
           end

spec/rubocop/cop/rails/deprecated_active_model_errors_methods_spec.rb

@@ -37,7 +37,20 @@
       end
 
       context 'when using `keys` method' do
-        it 'registers and corrects an offense' do
+        it 'registers and corrects an offense when root receiver is a variable' do
+          expect_offense(<<~RUBY, file_path)
+            user = create_user
+            user.errors.keys
+            ^^^^^^^^^^^^^^^^ Avoid manipulating ActiveModel errors as hash directly.
+          RUBY
+
+          expect_correction(<<~RUBY)
+            user = create_user
+            user.errors.attribute_names
+          RUBY
+        end
+
+        it 'registers and corrects an offense when root receiver is a method' do
           expect_offense(<<~RUBY, file_path)
             user.errors.keys.include?(:name)
             ^^^^^^^^^^^^^^^^ Avoid manipulating ActiveModel errors as hash directly.