From 13cd23466e0c7777df67c4d89522ec1ad1e9ee58 Mon Sep 17 00:00:00 2001
From: Jean Boussier <byroot@ruby-lang.org>
Date: Fri, 14 Aug 2026 14:14:44 +0200
Subject: [PATCH] Don't use _Atomic in C99 mode

```
/github/workspace/src/ext/digest/blake3/blake3_dispatch.c:108:5: error: '_Atomic' is a C11 extension [-Werror,-Wc11-extensions]
      108 |     ATOMIC_INT g_cpu_features = UNDEFINED;
          |     ^
/github/workspace/src/ext/digest/blake3/blake3_dispatch.c:34:20: note: expanded from macro 'ATOMIC_INT'
       34 | #define ATOMIC_INT _Atomic int
          |                    ^
1 error generated.
```
---
 ext/digest/blake3/extconf.rb | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/ext/digest/blake3/extconf.rb b/ext/digest/blake3/extconf.rb
index df844d0..93e88fa 100644
--- a/ext/digest/blake3/extconf.rb
+++ b/ext/digest/blake3/extconf.rb
@@ -78,6 +78,15 @@ def blake3_have_isa?(name, flag, snippet)
 
 have_header("sys/cdefs.h")
 
+checking_for("C11 atomics") do
+  unless try_compile(<<~C)
+      static _Atomic int atomic_int = 0;
+      int main(void){ return 0 }
+    C
+    $defs << "-DBLAKE3_ATOMICS=0"
+  end
+end
+
 $preload = %w[digest]
 
 create_makefile("digest/blake3")