[clang] Fix #99858 (PR #99859)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ahmet Faruk Aktaş (ahfakt)

<details>
<summary>Changes</summary>

Fix crash caused by template parameter pack expansion when no instantiation exist.

---
Full diff: https://github.com/llvm/llvm-project/pull/99859.diff


1 Files Affected:

- (modified) clang/lib/Sema/SemaTemplateVariadic.cpp (+2-2) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index 3d4ccaf68c700..70ceea1dda65b 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -732,7 +732,7 @@ bool Sema::CheckParameterPacksForExpansion(
       llvm::PointerUnion<Decl *, DeclArgumentPack *> *Instantiation =
           CurrentInstantiationScope->findInstantiationOf(
               ParmPack.first.get<NamedDecl *>());
-      if (Instantiation->is<DeclArgumentPack *>()) {
+      if (Instantiation && Instantiation->is<DeclArgumentPack *>()) {
         // We could expand this function parameter pack.
         NewPackSize = Instantiation->get<DeclArgumentPack *>()->size();
       } else {
@@ -850,7 +850,7 @@ std::optional<unsigned> Sema::getNumArgumentsInExpansion(
         llvm::PointerUnion<Decl *, DeclArgumentPack *> *Instantiation =
             CurrentInstantiationScope->findInstantiationOf(
                 Unexpanded[I].first.get<NamedDecl *>());
-        if (Instantiation->is<Decl *>())
+        if (Instantiation && Instantiation->is<Decl *>())
           // The pattern refers to an unexpanded pack. We're not ready to expand
           // this pack yet.
           return std::nullopt;

``````````

</details>


https://github.com/llvm/llvm-project/pull/99859