From 7e5eacc9db2c53c4142f6c9a49ccd660f2aa5217 Mon Sep 17 00:00:00 2001
From: Liam <liamsandersliam@gmail.com>
Date: Wed, 19 Feb 2025 19:59:39 +1100
Subject: [PATCH 1/2] Default zoned time conversions to use earliest time

FMT_USE_EARLIEST_TIME is used to control if earliest or latest time is preferred
---
 include/fmt/chrono.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 50c777c841aa..37dc9051422d 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -281,6 +281,13 @@ struct local_t {};
 
 }  // namespace detail
 
+// When converting a local zoned time to system time, it could be ambigous
+// By default prefer the earliest time but this can be set to 0 to use latest
+// refer to std::chrono::time_zone::to_sys and std::chrono::choose for more info
+#ifndef FMT_USE_EARLIEST_TIME
+#  define FMT_USE_EARLIEST_TIME 1
+#endif
+
 template <typename Duration>
 using sys_time = std::chrono::time_point<std::chrono::system_clock, Duration>;
 
@@ -577,7 +584,12 @@ template <typename Duration,
 inline auto localtime(std::chrono::local_time<Duration> time) -> std::tm {
   using namespace std::chrono;
   using namespace fmt_detail;
-  return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time)));
+
+#if FMT_USE_EARLIEST_TIME
+  return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time, std::chrono::choose::earliest)));
+#else
+  return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time, std::chrono::choose::latest)));
+#endif
 }
 #endif
 

From cbed981acc9cb1ec2276ec332942fe9a500c7fef Mon Sep 17 00:00:00 2001
From: musshorn <musshorn@users.noreply.github.com>
Date: Wed, 19 Feb 2025 21:33:33 +1100
Subject: [PATCH 2/2] Run clang-format

---
 include/fmt/chrono.h | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 37dc9051422d..30ee8dc18da9 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -585,11 +585,13 @@ inline auto localtime(std::chrono::local_time<Duration> time) -> std::tm {
   using namespace std::chrono;
   using namespace fmt_detail;
 
-#if FMT_USE_EARLIEST_TIME
-  return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time, std::chrono::choose::earliest)));
-#else
-  return localtime(detail::to_time_t(current_zone()->to_sys<Duration>(time, std::chrono::choose::latest)));
-#endif
+#  if FMT_USE_EARLIEST_TIME
+  return localtime(detail::to_time_t(
+      current_zone()->to_sys<Duration>(time, std::chrono::choose::earliest)));
+#  else
+  return localtime(detail::to_time_t(
+      current_zone()->to_sys<Duration>(time, std::chrono::choose::latest)));
+#  endif
 }
 #endif