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Formatting of system clocks ought to be to UTC, not to local time.
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This improves standards conformance of fmt.
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@ned14 @vitaut
ned14 authored and vitaut committed Dec 21, 2022
1 parent b908954 commit 115001a
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Showing 3 changed files with 133 additions and 17 deletions.
48 changes: 46 additions & 2 deletions include/fmt/chrono.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,15 @@

FMT_BEGIN_NAMESPACE

// Check if std::chrono::local_t is available.
#ifndef FMT_USE_LOCAL_TIME
# ifdef __cpp_lib_chrono
# define FMT_USE_LOCAL_TIME (__cpp_lib_chrono >= 201907L)
# else
# define FMT_USE_LOCAL_TIME 0
# endif
#endif

// Check if std::chrono::utc_timestamp is available.
#ifndef FMT_USE_UTC_TIME
# ifdef __cpp_lib_chrono
Expand Down Expand Up @@ -453,6 +462,7 @@ auto write(OutputIt out, const std::tm& time, const std::locale& loc,

FMT_MODULE_EXPORT_BEGIN

#if FMT_USE_LOCAL_TIME
/**
Converts given time since epoch as ``std::time_t`` value into calendar time,
expressed in local time. Unlike ``std::localtime``, this function is
Expand Down Expand Up @@ -494,10 +504,12 @@ inline std::tm localtime(std::time_t time) {
return lt.tm_;
}

template<class Duration>
inline std::tm localtime(
std::chrono::time_point<std::chrono::system_clock> time_point) {
return localtime(std::chrono::system_clock::to_time_t(time_point));
std::chrono::local_time<Duration> time_point) {
return localtime(std::chrono::system_clock::to_time_t(std::chrono::current_zone()->to_sys(time_point)));
}
#endif

/**
Converts given time since epoch as ``std::time_t`` value into calendar time,
Expand Down Expand Up @@ -2103,6 +2115,37 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
auto format(std::chrono::time_point<std::chrono::system_clock, Duration> val,
FormatContext& ctx) const -> decltype(ctx.out()) {
using period = typename Duration::period;
if (period::num != 1 || period::den != 1 ||
std::is_floating_point<typename Duration::rep>::value) {
const auto epoch = val.time_since_epoch();
const auto subsecs = std::chrono::duration_cast<Duration>(
epoch - std::chrono::duration_cast<std::chrono::seconds>(epoch));

return formatter<std::tm, Char>::do_format(
gmtime(std::chrono::time_point_cast<std::chrono::seconds>(val)),
ctx, &subsecs);
}

return formatter<std::tm, Char>::format(
gmtime(std::chrono::time_point_cast<std::chrono::seconds>(val)),
ctx);
}
};

#if FMT_USE_LOCAL_TIME
template <typename Char, typename Duration>
struct formatter<std::chrono::local_time<Duration>,
Char> : formatter<std::tm, Char> {
FMT_CONSTEXPR formatter() {
basic_string_view<Char> default_specs =
detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>{};
this->do_parse(default_specs.begin(), default_specs.end());
}

template <typename FormatContext>
auto format(std::chrono::local_time<Duration> val,
FormatContext& ctx) const -> decltype(ctx.out()) {
using period = typename Duration::period;
if (period::num != 1 || period::den != 1 ||
std::is_floating_point<typename Duration::rep>::value) {
const auto epoch = val.time_since_epoch();
Expand All @@ -2119,6 +2162,7 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
ctx);
}
};
#endif

#if FMT_USE_UTC_TIME
template <typename Char, typename Duration>
Expand Down
100 changes: 86 additions & 14 deletions test/chrono-test.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -235,33 +235,28 @@ auto equal(const std::tm& lhs, const std::tm& rhs) -> bool {
lhs.tm_isdst == rhs.tm_isdst;
}

TEST(chrono_test, localtime) {
auto t = std::time(nullptr);
auto tm = *std::localtime(&t);
EXPECT_TRUE(equal(tm, fmt::localtime(t)));
}

TEST(chrono_test, gmtime) {
auto t = std::time(nullptr);
auto tm = *std::gmtime(&t);
EXPECT_TRUE(equal(tm, fmt::gmtime(t)));
}

template <typename TimePoint> auto strftime_full(TimePoint tp) -> std::string {
template <typename TimePoint>
auto strftime_full_utc(TimePoint tp) -> std::string {
auto t = std::chrono::system_clock::to_time_t(tp);
auto tm = *std::localtime(&t);
auto tm = *std::gmtime(&t);
return system_strftime("%Y-%m-%d %H:%M:%S", &tm);
}

TEST(chrono_test, time_point) {
TEST(chrono_test, system_clock_time_point) {
auto t1 = std::chrono::time_point_cast<std::chrono::seconds>(
std::chrono::system_clock::now());
EXPECT_EQ(strftime_full(t1), fmt::format("{:%Y-%m-%d %H:%M:%S}", t1));
EXPECT_EQ(strftime_full(t1), fmt::format("{}", t1));
EXPECT_EQ(strftime_full_utc(t1), fmt::format("{:%Y-%m-%d %H:%M:%S}", t1));
EXPECT_EQ(strftime_full_utc(t1), fmt::format("{}", t1));
using time_point =
std::chrono::time_point<std::chrono::system_clock, std::chrono::seconds>;
auto t2 = time_point(std::chrono::seconds(42));
EXPECT_EQ(strftime_full(t2), fmt::format("{:%Y-%m-%d %H:%M:%S}", t2));
EXPECT_EQ(strftime_full_utc(t2), fmt::format("{:%Y-%m-%d %H:%M:%S}", t2));

std::vector<std::string> spec_list = {
"%%", "%n", "%t", "%Y", "%EY", "%y", "%Oy", "%Ey", "%C",
Expand All @@ -283,7 +278,7 @@ TEST(chrono_test, time_point) {

for (const auto& spec : spec_list) {
auto t = std::chrono::system_clock::to_time_t(t1);
auto tm = *std::localtime(&t);
auto tm = *std::gmtime(&t);

auto sys_output = system_strftime(spec, &tm);

Expand All @@ -295,6 +290,81 @@ TEST(chrono_test, time_point) {
if (std::find(spec_list.cbegin(), spec_list.cend(), "%z") !=
spec_list.cend()) {
auto t = std::chrono::system_clock::to_time_t(t1);
auto tm = *std::gmtime(&t);

auto sys_output = system_strftime("%z", &tm);
sys_output.insert(sys_output.end() - 2, 1, ':');

EXPECT_EQ(sys_output, fmt::format("{:%Ez}", t1));
EXPECT_EQ(sys_output, fmt::format("{:%Ez}", tm));

EXPECT_EQ(sys_output, fmt::format("{:%Oz}", t1));
EXPECT_EQ(sys_output, fmt::format("{:%Oz}", tm));
}
}

#if FMT_USE_LOCAL_TIME

TEST(chrono_test, localtime) {
auto t = std::time(nullptr);
auto tm = *std::localtime(&t);
EXPECT_TRUE(equal(tm, fmt::localtime(t)));
}

template <typename Duration>
auto strftime_full_local(std::chrono::local_time<Duration> tp) -> std::string {
auto t = std::chrono::system_clock::to_time_t(
std::chrono::current_zone()->to_sys(tp));
auto tm = *std::localtime(&t);
return system_strftime("%Y-%m-%d %H:%M:%S", &tm);
}

TEST(chrono_test, local_system_clock_time_point) {
# ifdef _WIN32
return; // Not supported on Windows.
# endif
auto t1 = std::chrono::time_point_cast<std::chrono::seconds>(
std::chrono::current_zone()->to_local(std::chrono::system_clock::now()));
EXPECT_EQ(strftime_full_local(t1), fmt::format("{:%Y-%m-%d %H:%M:%S}", t1));
EXPECT_EQ(strftime_full_local(t1), fmt::format("{}", t1));
using time_point = std::chrono::local_time<std::chrono::seconds>;
auto t2 = time_point(std::chrono::seconds(86400 + 42));
EXPECT_EQ(strftime_full_local(t2), fmt::format("{:%Y-%m-%d %H:%M:%S}", t2));

std::vector<std::string> spec_list = {
"%%", "%n", "%t", "%Y", "%EY", "%y", "%Oy", "%Ey", "%C",
"%EC", "%G", "%g", "%b", "%h", "%B", "%m", "%Om", "%U",
"%OU", "%W", "%OW", "%V", "%OV", "%j", "%d", "%Od", "%e",
"%Oe", "%a", "%A", "%w", "%Ow", "%u", "%Ou", "%H", "%OH",
"%I", "%OI", "%M", "%OM", "%S", "%OS", "%x", "%Ex", "%X",
"%EX", "%D", "%F", "%R", "%T", "%p", "%z", "%Z"};
# ifndef _WIN32
// Disabled on Windows because these formats are not consistent among
// platforms.
spec_list.insert(spec_list.end(), {"%c", "%Ec", "%r"});
# elif defined(__MINGW32__) && !defined(_UCRT)
// Only C89 conversion specifiers when using MSVCRT instead of UCRT
spec_list = {"%%", "%Y", "%y", "%b", "%B", "%m", "%U", "%W", "%j", "%d", "%a",
"%A", "%w", "%H", "%I", "%M", "%S", "%x", "%X", "%p", "%Z"};
# endif
spec_list.push_back("%Y-%m-%d %H:%M:%S");

for (const auto& spec : spec_list) {
auto t = std::chrono::system_clock::to_time_t(
std::chrono::current_zone()->to_sys(t1));
auto tm = *std::localtime(&t);

auto sys_output = system_strftime(spec, &tm);

auto fmt_spec = fmt::format("{{:{}}}", spec);
EXPECT_EQ(sys_output, fmt::format(fmt::runtime(fmt_spec), t1));
EXPECT_EQ(sys_output, fmt::format(fmt::runtime(fmt_spec), tm));
}

if (std::find(spec_list.cbegin(), spec_list.cend(), "%z") !=
spec_list.cend()) {
auto t = std::chrono::system_clock::to_time_t(
std::chrono::current_zone()->to_sys(t1));
auto tm = *std::localtime(&t);

auto sys_output = system_strftime("%z", &tm);
Expand All @@ -308,6 +378,8 @@ TEST(chrono_test, time_point) {
}
}

#endif // FMT_USE_LOCAL_TIME

#ifndef FMT_STATIC_THOUSANDS_SEPARATOR

TEST(chrono_test, format_default) {
Expand Down Expand Up @@ -757,7 +829,7 @@ TEST(chrono_test, timestamps_sub_seconds) {
const auto t9_sec = std::chrono::time_point_cast<std::chrono::seconds>(t9);
auto t9_sub_sec_part = fmt::format("{0:09}", (t9 - t9_sec).count());

EXPECT_EQ(fmt::format("{}.{}", strftime_full(t9_sec), t9_sub_sec_part),
EXPECT_EQ(fmt::format("{}.{}", strftime_full_utc(t9_sec), t9_sub_sec_part),
fmt::format("{:%Y-%m-%d %H:%M:%S}", t9));

const std::chrono::time_point<std::chrono::system_clock,
Expand Down
2 changes: 1 addition & 1 deletion test/xchar-test.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -309,7 +309,7 @@ TEST(chrono_test_wchar, time_point) {

for (const auto& spec : spec_list) {
auto t = std::chrono::system_clock::to_time_t(t1);
auto tm = *std::localtime(&t);
auto tm = *std::gmtime(&t);

auto sys_output = system_wcsftime(spec, &tm);

Expand Down

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