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[libc++][TZDB] Improves system time zone detection. #127339

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Merged
merged 2 commits into from
Feb 18, 2025
Merged

[libc++][TZDB] Improves system time zone detection. #127339

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d00a18e
[libc++][TZDB] Improves system time zone detection.
mordante Feb 15, 2025
46efd3d
Update libcxx/src/experimental/tzdb.cpp
mordante Feb 18, 2025
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67 changes: 49 additions & 18 deletions libcxx/src/experimental/tzdb.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -708,6 +708,39 @@ void __init_tzdb(tzdb& __tzdb, __tz::__rules_storage_type& __rules) {
std::__throw_runtime_error("unknown time zone");
}
#else // ifdef _WIN32

[[nodiscard]] static string __current_zone_environment() {
if (const char* __tz = std::getenv("TZ"))
return __tz;

return {};
}

[[nodiscard]] static string __current_zone_etc_localtime() {
filesystem::path __path = "/etc/localtime";
if (!filesystem::exists(__path) || !filesystem::is_symlink(__path))
return {};

filesystem::path __tz = filesystem::read_symlink(__path);
// The path may be a relative path, in that case convert it to an absolute
// path based on the proper initial directory.
if (__tz.is_relative())
__tz = filesystem::canonical("/etc" / __tz);

return filesystem::relative(__tz, "/usr/share/zoneinfo/");
}

[[nodiscard]] static string __current_zone_etc_timezone() {
filesystem::path __path = "/etc/timezone";
if (!filesystem::exists(__path))
return {};

ifstream __f(__path);
string __name;
std::getline(__f, __name);
return __name;
}

[[nodiscard]] static const time_zone* __current_zone_posix(const tzdb& tzdb) {
// On POSIX systems there are several ways to configure the time zone.
// In order of priority they are:
Expand All @@ -726,30 +759,28 @@ void __init_tzdb(tzdb& __tzdb, __tz::__rules_storage_type& __rules) {
//
// - The time zone name is the target of the symlink /etc/localtime
// relative to /usr/share/zoneinfo/
//
// - The file /etc/timezone. This text file contains the name of the time
// zone.
//
// On Linux systems it seems /etc/timezone is deprecated and being phased
// out. This file is used when /etc/localtime does not exist, or when it exists but is not a symlink. For more information and links see
// https://github.com/llvm/llvm-project/issues/105634

// The algorithm is like this:
// - If the environment variable TZ is set and points to a valid
// record use this value.
// - Else use the name based on the `/etc/localtime` symlink.
string __name = chrono::__current_zone_environment();

if (const char* __tz = getenv("TZ"))
if (const time_zone* __result = tzdb.__locate_zone(__tz))
// Ignore invalid names in the environment.
if (!__name.empty())
if (const time_zone* __result = tzdb.__locate_zone(__name))
return __result;

filesystem::path __path = "/etc/localtime";
if (!filesystem::exists(__path))
std::__throw_runtime_error("tzdb: the symlink '/etc/localtime' does not exist");

if (!filesystem::is_symlink(__path))
std::__throw_runtime_error("tzdb: the path '/etc/localtime' is not a symlink");
__name = chrono::__current_zone_etc_localtime();
if (__name.empty())
__name = chrono::__current_zone_etc_timezone();

filesystem::path __tz = filesystem::read_symlink(__path);
// The path may be a relative path, in that case convert it to an absolute
// path based on the proper initial directory.
if (__tz.is_relative())
__tz = filesystem::canonical("/etc" / __tz);
if (__name.empty())
std::__throw_runtime_error("tzdb: unable to determine the name of the current time zone");

string __name = filesystem::relative(__tz, "/usr/share/zoneinfo/");
if (const time_zone* __result = tzdb.__locate_zone(__name))
return __result;

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