[clang] [Clang] [C++26] Implement P1306R5 Expansion Statements (PR #165195)

[Younan Zhang via cfe-commits]

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@@ -2393,9 +2413,13 @@ ExprResult
 TemplateInstantiator::TransformFunctionParmPackRefExpr(DeclRefExpr *E,
                                                        ValueDecl *PD) {
   typedef LocalInstantiationScope::DeclArgumentPack DeclArgumentPack;
-  llvm::PointerUnion<Decl *, DeclArgumentPack *> *Found
-    = getSema().CurrentInstantiationScope->findInstantiationOf(PD);
-  assert(Found && "no instantiation for parameter pack");
+  llvm::PointerUnion<Decl *, DeclArgumentPack *> *Found =
+      getSema().CurrentInstantiationScope->getInstantiationOfIfExists(PD);
+
+  // This can happen when instantiating an expansion statement that contains
+  // a pack (e.g. `template for (auto x : {{ts...}})`).
+  if (!Found)
+    return E;
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zyn0217 wrote:

Why? is it possible to ensure its existence?

https://github.com/llvm/llvm-project/pull/165195