From 2eda43e9be177109a1557a59eee3fe7825a9b479 Mon Sep 17 00:00:00 2001
From: Mike Vastola <mike@vasto.la>
Date: Tue, 3 Feb 2026 15:45:07 -0500
Subject: [PATCH] Add FMT_USE_FLOCKFILE macro to force has_flockfile trait to
 false (#4666)

Fixes fmtlib/fmt#4646
---
 include/fmt/format-inl.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 838ac7df..76eed5f1 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -1489,12 +1489,16 @@ template <typename F> auto getc_unlocked(F* f) -> decltype(_fgetc_nolock(f)) {
 }
 #endif
 
+#ifndef FMT_USE_FLOCKFILE
+#  define FMT_USE_FLOCKFILE 1
+#endif
+
 template <typename F = FILE, typename Enable = void>
 struct has_flockfile : std::false_type {};
 
 template <typename F>
 struct has_flockfile<F, void_t<decltype(flockfile(&std::declval<F&>()))>>
-    : std::true_type {};
+    : bool_constant<FMT_USE_FLOCKFILE != 0> {};
 
 // A FILE wrapper. F is FILE defined as a template parameter to make system API
 // detection work.