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

This implements support for the `= delete("message")` syntax that was
only just added to C++26
([P2573R2](https://isocpp.org/files/papers/P2573R2.html#proposal-scope)).

1 files changed, 11 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 17032d1..8b3b9d0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16083,7 +16083,17 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
     // This is meant to pop the context added in ActOnStartOfFunctionDef().
     ExitFunctionBodyRAII ExitRAII(*this, isLambdaCallOperator(FD));
     if (FD) {
-      FD->setBody(Body);
+      // If this is called by Parser::ParseFunctionDefinition() after marking
+      // the declaration as deleted, and if the deleted-function-body contains
+      // a message (C++26), then a DefaultedOrDeletedInfo will have already been
+      // added to store that message; do not overwrite it in that case.
+      //
+      // Since this would always set the body to 'nullptr' in that case anyway,
+      // which is already done when the function decl is initially created,
+      // always skipping this irrespective of whether there is a delete message
+      // should not be a problem.
+      if (!FD->isDeletedAsWritten())
+        FD->setBody(Body);
       FD->setWillHaveBody(false);
       CheckImmediateEscalatingFunctionDefinition(FD, FSI);