[clang] [Clang] [C++26] Implement P2573R2: `= delete("should have a reason");` (PR #86526)

[via cfe-commits]

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@@ -2484,6 +2498,9 @@ class FunctionDecl : public DeclaratorDecl,
 
   void setDeletedAsWritten(bool D = true) { FunctionDeclBits.IsDeleted = D; }
 
+  /// Only valid if isDeletedAsWritten() returns true.
+  void setDeletedMessage(StringLiteral *Message);
+
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Sirraide wrote:

> there is no scenario in which we would call setDeletedMessage without first calling setDeletedAsWritten

That’s true; I was thinking we might want to set the message elsewhere at some point, but I think that I was remembering the situation before I included it it in the `DefaultedOrDeletedInfo`. I’ll move it to `setDeletedAsWritten()` and just give it a default argument.

https://github.com/llvm/llvm-project/pull/86526