From 7b10660974dcdd7882a48a62cfc2a32c4a17aa85 Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Tue, 20 May 2025 17:28:30 -0700
Subject: [PATCH] Use rb_inspect for Ractor error

Previously the object was used directly, which calls `to_s` if defined.
We should use rb_inspect to get a value suitable for display to the
programmer.
---
 ractor.c                 | 2 +-
 test/ruby/test_ractor.rb | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/ractor.c b/ractor.c
index 75371cfa6f..2388729f83 100644
--- a/ractor.c
+++ b/ractor.c
@@ -3163,7 +3163,7 @@ make_shareable_check_shareable(VALUE obj)
             return traverse_cont;
         }
         else {
-            rb_raise(rb_eRactorError, "can not make shareable object for %"PRIsVALUE, obj);
+            rb_raise(rb_eRactorError, "can not make shareable object for %+"PRIsVALUE, obj);
         }
     }
 
diff --git a/test/ruby/test_ractor.rb b/test/ruby/test_ractor.rb
index ec94df361f..e61c6beffc 100644
--- a/test/ruby/test_ractor.rb
+++ b/test/ruby/test_ractor.rb
@@ -60,6 +60,14 @@ class TestRactor < Test::Unit::TestCase
     assert_unshareable(x, "can not make shareable object for #<Method: String(Kernel)#itself()>", exception: Ractor::Error)
   end
 
+  def test_shareability_error_uses_inspect
+    x = (+"").instance_exec { method(:to_s) }
+    def x.to_s
+      raise "this should not be called"
+    end
+    assert_unshareable(x, "can not make shareable object for #<Method: String#to_s()>", exception: Ractor::Error)
+  end
+
   def test_default_thread_group
     assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
     begin;