[clang] [clang-tools-extra] [Clang] Add __type_list_dedup builtin to deduplicate types in template arguments (PR #106730)

[Utkarsh Saxena via cfe-commits]

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@@ -309,7 +309,10 @@ enum BuiltinTemplateKind : int {
   BTK__make_integer_seq,
 
   /// This names the __type_pack_element BuiltinTemplateDecl.
-  BTK__type_pack_element
+  BTK__type_pack_element,
+
+  /// This names the __type_list_dedup BuiltinTemplateDecl.
+  BTK__type_list_dedup,
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usx95 wrote:

What do you think about implementing this as a TypeTrait? This could be part of clang/Basic/TransformTypeTraits.def. Looking at the other transform type traits, their implementation looks much less complex and needs to touch much fewer files if we want to add more traits.

(That currently uses `"Unary"TransformType`. If this does not fit our purpose, we could introduce a variadic version of `VariadicTransformType`. This would be particularly helpful for future when we want to add more of such useful type_traits, we would be sharing a lot of code and would introducing such traits much less complex.)

https://github.com/llvm/llvm-project/pull/106730