[Fix #10031] Fix a false positive for Style/HashExcept

changelog/fix_false_positive_for_style_hash_except.md

@@ -0,0 +1 @@
+* [#10031](https://github.com/rubocop/rubocop/issues/10031): Fix a false positive for `Style/HashExcept` when comparing with hash value. ([@koic][])

lib/rubocop/cop/style/hash_except.rb

@@ -49,7 +49,7 @@ def on_send(node)
           return unless bad_method?(block) && semantically_except_method?(node, block)
 
           except_key = except_key(block)
-          return unless safe_to_register_offense?(block, except_key)
+          return if except_key.nil? || !safe_to_register_offense?(block, except_key)
 
           range = offense_range(node)
           preferred_method = "except(#{except_key.source})"
@@ -81,10 +81,11 @@ def safe_to_register_offense?(block, except_key)
         end
 
         def except_key(node)
-          key_argument = node.argument_list.first
+          key_argument = node.argument_list.first.source
           lhs, _method_name, rhs = *node.body
+          return if [lhs, rhs].map(&:source).none?(key_argument)
 
-          [lhs, rhs].find { |operand| operand.source != key_argument.source }
+          [lhs, rhs].find { |operand| operand.source != key_argument }
         end
 
         def offense_range(node)

spec/rubocop/cop/style/hash_except_spec.rb

@@ -96,6 +96,12 @@
         {foo: 1, bar: 2, baz: 3}.keep_if { |k, v| k != :bar }
       RUBY
     end
+
+    it 'does not register an offense when comparing with hash value' do
+      expect_no_offenses(<<~RUBY)
+        {foo: 1, bar: 2, baz: 3}.reject { |k, v| v.eql? :bar }
+      RUBY
+    end
   end
 
   context 'Ruby 2.7 or lower', :ruby27 do