[Fix rubocop#6545] Fix Performance/RedundantMerge kwsplat regression

CHANGELOG.md

@@ -30,6 +30,7 @@
 * [#6511](https://github.com/rubocop-hq/rubocop/issues/6511): Fix an incorrect auto-correct for `Style/EmptyCaseCondition` when used as an argument of a method. ([@koic][])
 * [#6509](https://github.com/rubocop-hq/rubocop/issues/6509): Fix an incorrect auto-correct for `Style/RaiseArgs` when an exception object is assigned to a local variable. ([@koic][])
 * [#6534](https://github.com/rubocop-hq/rubocop/issues/6534): Fix a false positive for `Lint/UselessAccessModifier` when using `private_class_method`. ([@dduugg][])
+* [#6545](https://github.com/rubocop-hq/rubocop/issues/6545): Fix a regression where `Performance/RedundantMerge` raises an error on a sole double splat argument passed to `merge!`. ([@mmedal][])
 
 ### Changes
 
@@ -3670,3 +3671,4 @@
 [@takaram]: https://github.com/takaram
 [@gmcgibbon]: https://github.com/gmcgibbon
 [@dduugg]: https://github.com/dduugg
+[@mmedal]: https://github.com/mmedal

lib/rubocop/cop/performance/redundant_merge.rb

@@ -60,13 +60,18 @@ def each_redundant_merge(node)
 
         def non_redundant_merge?(node, receiver, pairs)
           non_redundant_pairs?(receiver, pairs) ||
+            kwsplat_used?(pairs) ||
             non_redundant_value_used?(receiver, node)
         end
 
         def non_redundant_pairs?(receiver, pairs)
           pairs.size > 1 && !receiver.pure? || pairs.size > max_key_value_pairs
         end
 
+        def kwsplat_used?(pairs)
+          pairs.any?(&:kwsplat_type?)
+        end
+
         def non_redundant_value_used?(receiver, node)
           node.value_used? &&
             !EachWithObjectInspector.new(node, receiver).value_used?

spec/rubocop/cop/performance/redundant_merge_spec.rb

@@ -46,7 +46,15 @@
   end
 
   context 'when any argument is a double splat' do
-    it 'does not register an offense' do
+    it 'does not register an offense when the only argument is a' \
+       'double splat' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        foo.merge!(**bar)
+      RUBY
+    end
+
+    it 'does not register an offense when there are multiple arguments ' \
+       'and at least one is a double splat' do
       expect_no_offenses(<<-RUBY.strip_indent)
         foo.merge!(baz: qux, **bar)
       RUBY