Fix a false positive for Style/TrailingBodyOnMethodDefinition

changelog/fix_false_positive_for_style_trailing_body_on_method_definition.md

@@ -0,0 +1 @@
+* [#9548](https://github.com/rubocop/rubocop/pull/9548): Fix a false positive for `Style/TrailingBodyOnMethodDefinition` when endless method definition body is after newline in opening parenthesis. ([@koic][])

lib/rubocop/cop/style/trailing_body_on_method_definition.rb

@@ -34,6 +34,7 @@ class TrailingBodyOnMethodDefinition < Base
 
         def on_def(node)
           return unless trailing_body?(node)
+          return if node.endless? && node.body.parenthesized_call?
 
           add_offense(first_part_of(node.body)) do |corrector|
             LineBreakCorrector.correct_trailing_body(

spec/rubocop/cop/style/trailing_body_on_method_definition_spec.rb

@@ -91,6 +91,16 @@ def some_method
     RUBY
   end
 
+  context 'Ruby 3.0 or higher', :ruby30 do
+    it 'does not register offense when endless method definition body is after newline in opening parenthesis' do
+      expect_no_offenses(<<~RUBY)
+        def some_method = (
+          body
+        )
+      RUBY
+    end
+  end
+
   it 'auto-corrects with comment after body' do
     expect_offense(<<-RUBY.strip_margin('|'))
       |  def some_method; body # stuff