Do not allow trailing commas in calls without parenthesis

Author: haldun

src/prism.c

@@ -11921,6 +11921,13 @@ parse_arguments_list(pm_parser_t *parser, pm_arguments_t *arguments, bool accept
         // argument to this method call.
         parse_arguments(parser, arguments, true, PM_TOKEN_EOF);
 
+        // If we have done with the arguments and still not consumed the comma,
+        // then we have a trailing comma where we need to check whether it is
+        // allowed or not.
+        if (parser->previous.type == PM_TOKEN_COMMA && !match1(parser, PM_TOKEN_SEMICOLON)) {
+            pm_parser_err_previous(parser, PM_ERR_EXPECT_ARGUMENT);
+        }
+
         pm_accepts_block_stack_pop(parser);
     }
 

test/prism/errors_test.rb

@@ -1676,6 +1676,12 @@ def test_void_value_expression_in_binary_call
       ], compare_ripper: false # Ripper does not check 'void value expression'.
     end
 
+    def test_trailing_comma_in_calls
+      assert_errors expression("foo 1,"), "foo 1,", [
+        ["Expected an argument", 5..6]
+      ]
+    end
+
     private
 
     def assert_errors(expected, source, errors, compare_ripper: RUBY_ENGINE == "ruby")