[clang] [Clang][Sema] Avoid pack expansion for expanded empty PackIndexingExprs (PR #92385)

[Aaron Ballman via cfe-commits]

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@@ -4381,11 +4381,13 @@ class PackIndexingExpr final
 
   PackIndexingExpr(QualType Type, SourceLocation EllipsisLoc,
                    SourceLocation RSquareLoc, Expr *PackIdExpr, Expr *IndexExpr,
-                   ArrayRef<Expr *> SubstitutedExprs = {})
+                   ArrayRef<Expr *> SubstitutedExprs = {},
+                   bool EmptyPack = false)
       : Expr(PackIndexingExprClass, Type, VK_LValue, OK_Ordinary),
         EllipsisLoc(EllipsisLoc), RSquareLoc(RSquareLoc),
         SubExprs{PackIdExpr, IndexExpr},
-        TransformedExpressions(SubstitutedExprs.size()) {
+        TransformedExpressions(EmptyPack ? size_t(-1)
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AaronBallman wrote:

FYI: the types of the bit-fields need to be the same, otherwise they won't pack together as expected with MSVC.

https://github.com/llvm/llvm-project/pull/92385