From b28214487d60cab1a9996a4b4e99d17d3ff86000 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Sat, 12 Apr 2025 08:37:15 -0700
Subject: [PATCH] Fix handling of %Z

---
 .github/workflows/windows.yml |  2 +-
 include/fmt/chrono.h          |  2 +-
 test/chrono-test.cc           | 18 ++----------------
 3 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index d2bb205c..2f3f676e 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -39,7 +39,7 @@ jobs:
     - uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938 # v4.2.0
 
     - name: Set timezone
-      run: tzutil /s "Ekaterinburg Standard Time"
+      run: tzutil /s "Pacific Standard Time"
 
     - name: Create Build Environment
       run: cmake -E make_directory ${{runner.workspace}}/build
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 252bfd3d..d44a1a24 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -1393,7 +1393,7 @@ class tm_writer {
   }
 
   void on_utc_offset(numeric_system ns) { format_utc_offset_impl(tm_, ns); }
-  void on_tz_name() { format_tz_name_impl(tm_); }
+  void on_tz_name() { out_ = std::copy_n("UTC", 3, out_); }
 
   void on_year(numeric_system ns, pad_type pad) {
     if (is_classic_ || ns == numeric_system::standard)
diff --git a/test/chrono-test.cc b/test/chrono-test.cc
index 1e73a146..5364bfde 100644
--- a/test/chrono-test.cc
+++ b/test/chrono-test.cc
@@ -263,8 +263,7 @@ auto strftime_full_utc(TimePoint tp) -> std::string {
   return system_strftime("%Y-%m-%d %H:%M:%S", &tm);
 }
 
-template <typename Time>
-void test_time(Time time) {
+template <typename Time> void test_time(Time time) {
   EXPECT_EQ(fmt::format("{}", time), "1979-03-12 12:00:00");
   EXPECT_EQ(fmt::format("{:}", time), "1979-03-12 12:00:00");
 
@@ -333,20 +332,7 @@ TEST(chrono_test, sys_time) {
   EXPECT_EQ(fmt::format("{:%z}", time), "+0000");
   EXPECT_EQ(fmt::format("{:%Ez}", time), "+00:00");
   EXPECT_EQ(fmt::format("{:%Oz}", time), "+00:00");
-
-  auto t1 = std::chrono::time_point_cast<std::chrono::seconds>(
-      std::chrono::system_clock::now());
-
-  // Separate tests for UTC, since std::time_put can use local time and ignoring
-  // the timezone in std::tm (if it presents on platform).
-  if (fmt::detail::has_member_data_tm_zone<std::tm>::value) {
-    auto t = std::chrono::system_clock::to_time_t(t1);
-    auto tm = *std::gmtime(&t);
-
-    std::vector<std::string> tz_names = {"GMT", "UTC"};
-    EXPECT_THAT(tz_names, Contains(fmt::format("{:%Z}", t1)));
-    EXPECT_THAT(tz_names, Contains(fmt::format("{:%Z}", tm)));
-  }
+  EXPECT_EQ(fmt::format("{:%Z}", time), "UTC");
 }
 
 TEST(chrono_test, local_time) {