From a8c70ed2b42013158c1d5ebe11b8ed5aeed8eb45 Mon Sep 17 00:00:00 2001
From: HParker <HParker@github.com>
Date: Thu, 10 Aug 2023 10:17:43 -0700
Subject: [PATCH] [ruby/yarp] add a diagnostic for *rest in order after
 optional state

https://github.com/ruby/yarp/commit/908244ba12
---
 test/yarp/errors_test.rb | 16 ++++++++++++++++
 yarp/yarp.c              |  4 ++++
 2 files changed, 20 insertions(+)

diff --git a/test/yarp/errors_test.rb b/test/yarp/errors_test.rb
index e705a6423c..0777efe47a 100644
--- a/test/yarp/errors_test.rb
+++ b/test/yarp/errors_test.rb
@@ -1076,6 +1076,22 @@ class ErrorsTest < Test::Unit::TestCase
     assert_errors expected, "def foo(a,b,&a);end", [
       ["Duplicated parameter name.", 13..14]
     ]
+
+    expected = DefNode(
+      Location(),
+      nil,
+      ParametersNode([], [OptionalParameterNode(:a, Location(), Location(), IntegerNode())], [RequiredParameterNode(:b)], RestParameterNode(Location(), Location()), [], nil, nil),
+      nil,
+      [:a, :b, :c],
+      Location(),
+      nil,
+      Location(),
+      Location(),
+      nil,
+      Location()
+    )
+
+    assert_errors expected, "def foo(a = 1,b,*c);end", [["Unexpected parameter *", 16..17]]
   end
 
   private
diff --git a/yarp/yarp.c b/yarp/yarp.c
index dcfde47d01..59ec35a03d 100644
--- a/yarp/yarp.c
+++ b/yarp/yarp.c
@@ -8312,6 +8312,10 @@ update_parameter_state(yp_parser_t *parser, yp_token_t *token, yp_parameters_ord
         return;
     }
 
+    if (token->type == YP_TOKEN_USTAR && *current == YP_PARAMETERS_ORDER_AFTER_OPTIONAL) {
+        yp_diagnostic_list_append(&parser->error_list, token->start, token->end, "Unexpected parameter *");
+    }
+
     if (*current == YP_PARAMETERS_ORDER_NOTHING_AFTER || state > *current) {
         // We know what transition we failed on, so we can provide a better error here.
         yp_diagnostic_list_append(&parser->error_list, token->start, token->end, "Unexpected parameter order");