From 8f768ec00592009cda496c8f7bfeef013887b5f3 Mon Sep 17 00:00:00 2001
From: Shafik Yaghmour <shafik@users.noreply.github.com>
Date: Thu, 28 Sep 2023 12:20:22 -0700
Subject: [PATCH] [Clang] Fix crash when visting a fold expression in a default
 argument (#67514)

CheckDefaultArgumentVisitor::Visit(...) assumes that the children of
Expr will not be NULL. This is not a valid assumption and when we have a
CXXFoldExpr the children can be NULL and this causes a crash.

Fixes: https://github.com/llvm/llvm-project/issues/67395
---
 clang/docs/ReleaseNotes.rst                        | 4 ++++
 clang/lib/Sema/SemaDeclCXX.cpp                     | 3 ++-
 clang/test/SemaTemplate/cxx1z-fold-expressions.cpp | 8 ++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f314c9c72fa2..1d74c492845a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -363,6 +363,10 @@ Bug Fixes to C++ Support
   in the enclosing expression of a lambda expression with a noexcept specifier.
   (`#67492 <https://github.com/llvm/llvm-project/issues/67492>`_)
 
+- Fix crash when fold expression was used in the initialization of default
+  argument. Fixes:
+  (`#67395 <https://github.com/llvm/llvm-project/issues/67395>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 0091e0ecf6f3..302e944d5d74 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -86,7 +86,8 @@ public:
 bool CheckDefaultArgumentVisitor::VisitExpr(const Expr *Node) {
   bool IsInvalid = false;
   for (const Stmt *SubStmt : Node->children())
-    IsInvalid |= Visit(SubStmt);
+    if (SubStmt)
+      IsInvalid |= Visit(SubStmt);
   return IsInvalid;
 }
 
diff --git a/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp b/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
index 518eaf0e0523..47a252eb335f 100644
--- a/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
+++ b/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
@@ -124,3 +124,11 @@ namespace PR30738 {
   int test_h3 = h<struct X>(1, 2, 3);
   N::S test_h4 = h<struct X>(N::S(), N::S(), N::S()); // expected-note {{instantiation of}}
 }
+
+namespace GH67395 {
+template <typename>
+bool f();
+
+template <typename... T>
+void g(bool = (f<T>() || ...));
+}