[clang] [Clang] Fix crash when visting a fold expression in a default argument (PR #67514)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/67514.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaDeclCXX.cpp (+2-1) 
- (modified) clang/test/SemaTemplate/cxx1z-fold-expressions.cpp (+8) 


``````````diff
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 0091e0ecf6f3986..302e944d5d74f1c 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -86,7 +86,8 @@ class CheckDefaultArgumentVisitor
 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 518eaf0e05239e0..47a252eb335f6e5 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>() || ...));
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/67514