[clang] [Clang][C++26] Implement Pack Indexing (P2662R3). (PR #72644)

[Erich Keane via cfe-commits]

================
@@ -1061,6 +1070,59 @@ ExprResult Sema::ActOnSizeofParameterPackExpr(Scope *S,
                                 RParenLoc);
 }
 
+static bool isParameterPack(Expr *PackExpression) {
+  if (auto D = dyn_cast<DeclRefExpr>(PackExpression); D) {
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erichkeane wrote:

```suggestion
  if (auto *D = dyn_cast<DeclRefExpr>(PackExpression); D) {
```

https://github.com/llvm/llvm-project/pull/72644