[clang] [RFC] Initial implementation of P2719 (PR #113510)

[via cfe-commits]

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@@ -4778,6 +4784,16 @@ class Sema final : public SemaBase {
 
   CXXRecordDecl *getStdBadAlloc() const;
   EnumDecl *getStdAlignValT() const;
+  const ClassTemplateDecl *getStdTypeIdentity() const;
+  ClassTemplateDecl *getStdTypeIdentity();
+  std::optional<QualType> instantiateSpecializedTypeIdentity(QualType Subject);
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cor3ntin wrote:

QualType already has an invalid state, why do we need the optional?

https://github.com/llvm/llvm-project/pull/113510