From 82bbdbd15b9ac4c66a947bf82d3ffb00fa403d64 Mon Sep 17 00:00:00 2001
From: Joshua Root <jmr@macports.org>
Date: Thu, 16 Jan 2025 14:12:25 +1100
Subject: [PATCH 1/2] Fix check for fallthrough attribute support

Clang versions prior to 10 (which corresponds to Apple Clang 12) do not
support the GCC extension syntax __attribute__((fallthrough)), but do
evaluate __has_attribute(fallthrough) to 1 because they support the
C++11 style syntax [[fallthrough]]. The only way to tell if the GCC
style syntax is supported is thus to check the clang version.

Ref: https://github.com/llvm/llvm-project/commit/1e0affb6e564b7361b0aadb38805f26deff4ecfc
---
 Include/pyport.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Include/pyport.h b/Include/pyport.h
index 2b6bd4c21110e5..aabd094df54a74 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -625,8 +625,13 @@ extern "C" {
 //     case 2: code; break;
 //     }
 //
-// __attribute__((fallthrough)) was introduced in GCC 7.
-#if _Py__has_attribute(fallthrough)
+// __attribute__((fallthrough)) was introduced in GCC 7 and Clang 10 /
+// Apple Clang 12.0. Earlier Clang versions support only the C++11
+// style fallthrough attribute, not the GCC extension syntax used here,
+// and __has_attribute(fallthrough) evaluates to 1.
+#if _Py__has_attribute(fallthrough) && (!defined(__clang__) || \
+    (!defined(__apple_build_version__) && __clang_major__ >= 10) || \
+    (defined(__apple_build_version__) && __clang_major__ >= 12))
 #  define _Py_FALLTHROUGH __attribute__((fallthrough))
 #else
 #  define _Py_FALLTHROUGH do { } while (0)

From e24773d88da48414618bf5c92b2dac477f6e9c75 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Thu, 16 Jan 2025 03:35:40 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../next/Build/2025-01-16-03-35-37.gh-issue-128902.Dt7xtV.rst    | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Build/2025-01-16-03-35-37.gh-issue-128902.Dt7xtV.rst

diff --git a/Misc/NEWS.d/next/Build/2025-01-16-03-35-37.gh-issue-128902.Dt7xtV.rst b/Misc/NEWS.d/next/Build/2025-01-16-03-35-37.gh-issue-128902.Dt7xtV.rst
new file mode 100644
index 00000000000000..42ac492498e029
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-01-16-03-35-37.gh-issue-128902.Dt7xtV.rst
@@ -0,0 +1 @@
+Fix compile errors with Clang 9 and older due to lack of ``__attribute__((fallthrough))`` support.