From 386f87481632f1ba8de53fd94d314183034a4b06 Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Mon, 26 May 2025 14:11:51 -0400
Subject: [PATCH] Don't copy FL_PROMOTED to new object in Ractor move

We should not copy the FL_PROMOTED flag when we move an object in Ractor#send(move: true)
because the newly created object may not be old.
---
 bootstraptest/test_ractor.rb |  1 +
 ractor.c                     | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index e8940d98f9..cbe732e4ea 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -2427,6 +2427,7 @@ end
 assert_equal 'ok', %q{
   r = Ractor.new do
     o = Ractor.receive
+    GC.verify_internal_consistency
     GC.start
     o
   end
diff --git a/ractor.c b/ractor.c
index 94777cf512..b2446439a3 100644
--- a/ractor.c
+++ b/ractor.c
@@ -3656,8 +3656,15 @@ move_enter(VALUE obj, struct obj_traverse_replace_data *data)
 static enum obj_traverse_iterator_result
 move_leave(VALUE obj, struct obj_traverse_replace_data *data)
 {
-    size_t size = rb_gc_obj_slot_size(obj);
-    memcpy((void *)data->replacement, (void *)obj, size);
+    // Copy flags
+    VALUE ignored_flags = RUBY_FL_PROMOTED;
+    RBASIC(data->replacement)->flags = (RBASIC(obj)->flags & ~ignored_flags) | (RBASIC(data->replacement)->flags & ignored_flags);
+    // Copy contents without the flags
+    memcpy(
+        (char *)data->replacement + sizeof(VALUE),
+        (char *)obj + sizeof(VALUE),
+        rb_gc_obj_slot_size(obj) - sizeof(VALUE)
+    );
 
     void rb_replace_generic_ivar(VALUE clone, VALUE obj); // variable.c