[clang] [clang-tools-extra] [Clang][C++29] Template pack indexing (PR #218738)

[Corentin Jabot via cfe-commits]

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@@ -482,6 +507,56 @@ class DeducedTemplateStorage : public UncommonTemplateNameStorage,
                       TemplateName Underlying, const DefaultArguments &DefArgs);
 };
 
+/// A structure for storing a pack-index-template-name ([temp.names]).
+///
+/// C++29 [temp.names]p1:
+///   pack-index-template-name:
+///     simple-template-name ... [ constant-expression ]
+class PackIndexingTemplateStorage final
+    : public UncommonTemplateNameStorage,
+      public llvm::FoldingSetNode,
+      private llvm::TrailingObjects<PackIndexingTemplateStorage, TemplateName> {
+  friend class ASTContext;
+  friend TrailingObjects;
+
+  TemplateName Pattern;
+  Expr *IndexExpr;
+  bool FullySubstituted;
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cor3ntin wrote:

I'm not sure this is an improvements, but... why not

https://github.com/llvm/llvm-project/pull/218738