From 12a828c7005e1225eaf32afb7f9236e03dcbcc44 Mon Sep 17 00:00:00 2001
From: Protobuf Team Bot <protobuf-github-bot@google.com>
Date: Wed, 1 May 2024 05:53:04 -0700
Subject: [PATCH] Add UPB_ASSUME(!IsExtension) on GetMutableMessage.

This function is UB to call on an extension field.

PiperOrigin-RevId: 629701038
---
 upb/message/accessors.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/upb/message/accessors.h b/upb/message/accessors.h
index 09ea66ae5b..f812e2da47 100644
--- a/upb/message/accessors.h
+++ b/upb/message/accessors.h
@@ -380,6 +380,7 @@ UPB_API_INLINE upb_Message* upb_Message_GetOrCreateMutableMessage(
     const upb_MiniTableField* field, upb_Arena* arena) {
   UPB_ASSERT(arena);
   UPB_ASSUME(upb_MiniTableField_CType(field) == kUpb_CType_Message);
+  UPB_ASSUME(!upb_MiniTableField_IsExtension(field));
   upb_Message* sub_message =
       *UPB_PTR_AT(msg, field->UPB_ONLYBITS(offset), upb_Message*);
   if (!sub_message) {