[Fix rubocop#11104] Fix an error for Style/CollectionCompact

Fixes rubocop#11104.

This PR fixes an error for `Style/CollectionCompact`
when using `reject` method and receiver is a variable.

changelog/fix_an_error_for_style_collection_compact.md

@@ -0,0 +1 @@
+* [#11104](https://github.com/rubocop/rubocop/issues/11104): Fix an error for `Style/CollectionCompact` when using `reject` method and receiver is a variable. ([@koic][])

lib/rubocop/cop/style/collection_compact.rb

@@ -96,7 +96,9 @@ def offense_range(node)
         end
 
         def to_enum_method?(node)
-          TO_ENUM_METHODS.include?(node.children.first.method_name)
+          return false unless node.receiver.send_type?
+
+          TO_ENUM_METHODS.include?(node.receiver.method_name)
         end
 
         def good_method_name(node)

spec/rubocop/cop/style/collection_compact_spec.rb

@@ -57,6 +57,21 @@
     RUBY
   end
 
+  it 'registers an offense and corrects when using `reject` and receiver is a variable' do
+    expect_offense(<<~RUBY)
+      def foo(params)
+        params.reject { |_k, v| v.nil? }
+               ^^^^^^^^^^^^^^^^^^^^^^^^^ Use `compact` instead of `reject { |_k, v| v.nil? }`.
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      def foo(params)
+        params.compact
+      end
+    RUBY
+  end
+
   it 'does not register an offense when using `reject` to not to rejecting nils' do
     expect_no_offenses(<<~RUBY)
       array.reject { |e| e.odd? }