From 462abbb0cd2b61ce8da9f27a6f064507606220cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bal=C3=A1zs=20K=C3=A9ri?= <balazs.keri@ericsson.com>
Date: Thu, 22 Feb 2024 15:34:52 +0100
Subject: [PATCH] [clang][ASTImporter] Fix possible crash "given incorrect
 InsertPos for specialization".

---
 clang/lib/AST/ASTImporter.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 023aaa7f0572b..0036e506b6365 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -6504,6 +6504,11 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
       return D2;
   }
 
+  // Update InsertPos, because preceding import calls may have invalidated
+  // it by adding new specializations.
+  if (!VarTemplate->findSpecialization(TemplateArgs, InsertPos))
+    VarTemplate->AddSpecialization(D2, InsertPos);
+
   QualType T;
   if (Error Err = importInto(T, D->getType()))
     return std::move(Err);
@@ -6540,8 +6545,6 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
   if (FoundSpecialization)
     D2->setPreviousDecl(FoundSpecialization->getMostRecentDecl());
 
-  VarTemplate->AddSpecialization(D2, InsertPos);
-
   addDeclToContexts(D, D2);
 
   // Import the rest of the chain. I.e. import all subsequent declarations.