Fix a false positive for Rails/TopLevelHashWithIndifferentAccess

This PR fixes a false positive for `Rails/TopLevelHashWithIndifferentAccess`
when using `HashWithIndifferentAccess` under namespace module.

Author: koic

changelog/fix_a_false_positive_for_rails_top_level_hash_with_indifferent_access.md

@@ -0,0 +1 @@
+* [#772](https://github.com/rubocop/rubocop-rails/pull/772): Fix a false positive for `Rails/TopLevelHashWithIndifferentAccess` when using `HashWithIndifferentAccess` under namespace module. ([@koic][])

lib/rubocop/cop/rails/top_level_hash_with_indifferent_access.rb

@@ -31,6 +31,7 @@ class TopLevelHashWithIndifferentAccess < Base
         # @param [RuboCop::AST::ConstNode] node
         def on_const(node)
           return unless top_level_hash_with_indifferent_access?(node)
+          return if node.parent&.class_type? && node.parent.ancestors.any?(&:module_type?)
 
           add_offense(node) do |corrector|
             autocorrect(corrector, node)

spec/rubocop/cop/rails/top_level_hash_with_indifferent_access_spec.rb

@@ -27,6 +27,19 @@
     end
   end
 
+  context 'with top-level `HashWithIndifferentAccess` without method call' do
+    it 'registers and corrects an offense' do
+      expect_offense(<<~RUBY)
+        HashWithIndifferentAccess
+        ^^^^^^^^^^^^^^^^^^^^^^^^^ Avoid top-level `HashWithIndifferentAccess`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        ActiveSupport::HashWithIndifferentAccess
+      RUBY
+    end
+  end
+
   context 'with ActiveSupport::HashWithIndifferentAccess' do
     it 'does not register an offense' do
       expect_no_offenses(<<~RUBY)
@@ -35,6 +48,17 @@
     end
   end
 
+  context 'with `HashWithIndifferentAccess` under the namespace' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        module CoreExt
+          class HashWithIndifferentAccess
+          end
+        end
+      RUBY
+    end
+  end
+
   context 'with ActiveSupport::HashWithIndifferentAccess on Rails 5.0', :rails50 do
     it 'does not register an offense' do
       expect_no_offenses(<<~RUBY)