[libcxx-commits] [libcxx] [libc++][chrono] implements UTC clock. (PR #90393)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,106 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: no-filesystem, no-localization, no-tzdb
+
+// XFAIL: libcpp-has-no-incomplete-tzdb
+// XFAIL: availability-tzdb-missing
+
+// <chrono>
+//
+// class utc_clock;
+
+// template<class Duration>
+// static utc_time<common_type_t<Duration, seconds>>
+// from_sys(const sys_time<Duration>& time);
+
+#include <chrono>
+#include <cassert>
+#include <fstream>
+#include <string>
+#include <string_view>
+
+#include "test_macros.h"
+#include "assert_macros.h"
+#include "concat_macros.h"
+#include "filesystem_test_helper.h"
+#include "test_tzdb.h"
+
+scoped_test_env env;
+[[maybe_unused]] const std::filesystem::path dir = env.create_dir("zoneinfo");
+const std::filesystem::path tzdata               = env.create_file("zoneinfo/tzdata.zi");
+const std::filesystem::path leap_seconds         = env.create_file("zoneinfo/leap-seconds.list");
+
+std::string_view std::chrono::__libcpp_tzdb_directory() {
+  static std::string result = dir.string();
+  return result;
+}
+
+static void write(std::string_view input) {
+  static int version = 0;
+
+  std::ofstream f{tzdata};
+  f << "# version " << version++ << '\n';
+  std::ofstream{leap_seconds}.write(input.data(), input.size());
+}
+
+template <class Duration>
+static void
+test_leap_seconds(std::chrono::time_point<std::chrono::system_clock, Duration> time, std::chrono::seconds expected) {
+  auto utc  = std::chrono::utc_clock::from_sys(time);
+  auto diff = utc.time_since_epoch() - time.time_since_epoch();
+  TEST_REQUIRE(
+      diff == expected,
+      TEST_WRITE_CONCATENATED("\tTime: ", time, "\nExpected output ", expected, "\nActual output   ", diff, '\n'));
+}
+
+// Note at the time of writing all leap seconds are positive. This test uses
+// fake data to test the behaviour of negative leap seconds.
+int main(int, const char**) {
+  using namespace std::literals::chrono_literals;
+
+  // Use small values for simplicity. The dates are seconds since 1.1.1970.
+  write(
+      R"(
+1 10
+60 11
----------------
ldionne wrote:

Same comment applies here w.r.t. positive and negative >= 2 leap seconds

https://github.com/llvm/llvm-project/pull/90393