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

[Azmat Yusuf via cfe-commits]

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@@ -1510,7 +1510,7 @@ static void CheckFoldOperand(Sema &S, Expr *E) {
   E = E->IgnoreImpCasts();
   auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
   if ((OCE && OCE->isInfixBinaryOp()) || isa<BinaryOperator>(E) ||
-      isa<AbstractConditionalOperator>(E)) {
+      isa<AbstractConditionalOperator>(E) || isa<RecoveryExpr>(E)) {
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azmat-y wrote:

Yeah it no longer looks like a good idea to me either. 

Instead of making any changes here instead maybe we can change `Sema::ActOnConditionalOp`. After checking for absence of `LHSExpr` we can check if our `CondExpr` contains Unexpanded parameter pack. If it does we don't lower otherwise we do.

Thoughts? 

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