[clang] [Clang] Handle ?: operator in fold expression (PR #164019)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

@azmat-y I spent some time looking into this. because `?:` is never valid in a fold expression, we parse it as a conditional expression - so far so good. but we never check that the expressions involve don't contain packs.

So a proper fix would be something like:


```diff
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -9200,6 +9200,12 @@ ExprResult Sema::ActOnConditionalOp(SourceLocation QuestionLoc,
                                     SourceLocation ColonLoc,
                                     Expr *CondExpr, Expr *LHSExpr,
                                     Expr *RHSExpr) {
+
+  if(DiagnoseUnexpandedParameterPack(CondExpr) ||
+          (LHSExpr && DiagnoseUnexpandedParameterPack(LHSExpr))
+          || DiagnoseUnexpandedParameterPack(RHSExpr))
+          return ExprError();
+
```

Can you modify your patch? thanks!

https://github.com/llvm/llvm-project/pull/164019