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

[Erich Keane via cfe-commits]

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@@ -1713,6 +1716,11 @@ class ASTContext : public RefCountedBase<ASTContext> {
   /// C++11 decltype.
   QualType getDecltypeType(Expr *e, QualType UnderlyingType) const;
 
+  QualType getPackIndexingType(QualType Pattern, Expr *IndexExpr,
+                               bool FullyExpanded = false,
+                               ArrayRef<QualType> Expansions = {},
+                               int Index = -1) const;
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erichkeane wrote:

The 'index' being here seems a little suspicious... I would expect us to be just getting this from the expression.  We MIGHT be able to cache it along the way, but it'll be fragile to consistently update along the way.

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