From 1db5ad0c4c04d3f0f11804d88a587fc0431daf9d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alexis=20Laferri=C3=A8re?= <alaf@apple.com>
Date: Wed, 8 Oct 2025 15:01:33 -0700
Subject: [PATCH] Serialization: Fix null dereference in witness
 deserialization

Fix null dereference in deserialization logic for conformances. If
deserializing the witness itself failed, don't try to
get its actor isolation.

rdar://162158608
---
 lib/Serialization/Deserialization.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index 4eb8d9e12905c..82464cea3fb7b 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -9158,7 +9158,7 @@ void ModuleFile::finishNormalConformance(NormalProtocolConformance *conformance,
 
     // Determine whether we need to enter the actor isolation of the witness.
     std::optional<ActorIsolation> enterIsolation;
-    if (*rawIDIter++) {
+    if (*rawIDIter++ && witness) {
       enterIsolation = getActorIsolation(witness);
     }