[Fix #9355] Fix Style/SingleLineMethods autocorrection to endless m…

…ethod when the original code had parens.

changelog/fix_fix_stylesinglelinemethods.md

@@ -0,0 +1 @@
+* [#9355](https://github.com/rubocop-hq/rubocop/issues/9355): Fix `Style/SingleLineMethods` autocorrection to endless method when the original code had parens. ([@dvandersluis][])

lib/rubocop/cop/style/single_line_methods.rb

@@ -89,7 +89,8 @@ def correct_to_multiline(corrector, node)
         end
 
         def correct_to_endless(corrector, node)
-          replacement = "def #{node.method_name}(#{node.arguments.source}) = #{node.body.source}"
+          arguments = node.arguments.any? ? node.arguments.source : '()'
+          replacement = "def #{node.method_name}#{arguments} = #{node.body.source}"
           corrector.replace(node, replacement)
         end
 

spec/rubocop/cop/style/single_line_methods_spec.rb

@@ -176,6 +176,18 @@ def some_method() = body # comment
         RUBY
       end
 
+      it 'handles arguments properly' do
+        expect_correction(<<~RUBY.strip, source: 'def some_method(a, b, c) body end')
+          def some_method(a, b, c) = body
+        RUBY
+      end
+
+      it 'does not add parens if they are already present' do
+        expect_correction(<<~RUBY.strip, source: 'def some_method() body end')
+          def some_method() = body
+        RUBY
+      end
+
       it 'does not correct to an endless method if the method body contains multiple statements' do
         expect_correction(<<~RUBY.strip, source: 'def some_method; foo; bar end')
           def some_method;#{trailing_whitespace}