[clang] [Clang][C++23] Implement P2448R2: Relaxing some constexpr restrictions (PR #77753)

[via cfe-commits]

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@@ -1767,10 +1780,16 @@ static bool CheckConstexprParameterTypes(Sema &SemaRef,
 /// true. If not, produce a suitable diagnostic and return false.
 static bool CheckConstexprReturnType(Sema &SemaRef, const FunctionDecl *FD,
                                      Sema::CheckConstexprKind Kind) {
-  if (CheckLiteralType(SemaRef, Kind, FD->getLocation(), FD->getReturnType(),
-                       diag::err_constexpr_non_literal_return,
-                       FD->isConsteval()))
+  if (CheckLiteralType(
+          SemaRef, Kind, FD->getLocation(), FD->getReturnType(),
+          SemaRef.getLangOpts().CPlusPlus23
+              ? diag::warn_cxx23_compat_constexpr_non_literal_return
+              : diag::ext_constexpr_non_literal_return,
+          FD->isConsteval())) {
+    if (SemaRef.getLangOpts().CPlusPlus23)
+      return true;
     return false;
+  }
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cor3ntin wrote:

ditto

https://github.com/llvm/llvm-project/pull/77753