From 2f60b8f02fe7cb83dd589d9664460082c13e85ef Mon Sep 17 00:00:00 2001
From: Krishna Chaitanya <141550576+XChaitanyaX@users.noreply.github.com>
Date: Sat, 1 Nov 2025 22:11:23 +0530
Subject: [PATCH] gh-140513: Fail to compile if `_Py_TAIL_CALL_INTERP` is set
 but `preserve_none` and `musttail` do not exist. (GH-140548)

Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
---
 .../Build/2025-10-25-08-07-06.gh-issue-140513.6OhLTs.rst  | 2 ++
 Python/ceval_macros.h                                     | 8 ++++++++
 2 files changed, 10 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Build/2025-10-25-08-07-06.gh-issue-140513.6OhLTs.rst

diff --git a/Misc/NEWS.d/next/Build/2025-10-25-08-07-06.gh-issue-140513.6OhLTs.rst b/Misc/NEWS.d/next/Build/2025-10-25-08-07-06.gh-issue-140513.6OhLTs.rst
new file mode 100644
index 000000000000..1035ebf8d781
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-10-25-08-07-06.gh-issue-140513.6OhLTs.rst
@@ -0,0 +1,2 @@
+Generate a clear compilation error when ``_Py_TAIL_CALL_INTERP`` is enabled but
+either ``preserve_none`` or ``musttail`` is not supported.
diff --git a/Python/ceval_macros.h b/Python/ceval_macros.h
index 8083913b1a1c..868ab6f75587 100644
--- a/Python/ceval_macros.h
+++ b/Python/ceval_macros.h
@@ -79,6 +79,14 @@
 #endif
 
 #if _Py_TAIL_CALL_INTERP
+#   if defined(__clang__) || defined(__GNUC__)
+#       if !_Py__has_attribute(preserve_none) || !_Py__has_attribute(musttail)
+#           error "This compiler does not have support for efficient tail calling."
+#       endif
+#   elif defined(_MSC_VER) && (_MSC_VER < 1950)
+#       error "You need at least VS 2026 / PlatformToolset v145 for tail calling."
+#   endif
+
     // Note: [[clang::musttail]] works for GCC 15, but not __attribute__((musttail)) at the moment.
 #   define Py_MUSTTAIL [[clang::musttail]]
 #   define Py_PRESERVE_NONE_CC __attribute__((preserve_none))
-- 
2.47.3