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libstdc++: Make std::chrono::current_zone() default to UTC

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This is consistent with the behaviour of glibc, which assumes UTC when
/etc/localtime and TZ do not identify a valid time zone. The fallback
tzdb used when no valid tzdata exists always contains the UTC zone, so
this change means we have a valid tzdb and valid current zone even in
the degenerate case.

With this default we no longer need the AIX-specific kluge to try and
identify TZ values specifying a 0-offset zone. We can just use the UTC
default for those, as it has the same effect.

It's still possible for chrono::current_zone() to fail, because the user
could have provided a custom tzdata.zi file which doesn't contain the
UTC time zone, so the "UTC" default would fail to find a valid zone, and
throw an exception. That's just user error, they should not provide bad
data and expect reasonable behaviour.

libstdc++-v3/ChangeLog:

	* src/c++20/tzdb.cc (chrono::tzdb::current_zone()) Use "UTC" if
	current time zone cannot be determined.
	* testsuite/std/time/tzdb/1.cc: Remove conditions based on
	HAVE_TZDB macro and test all members unconditionally.
This commit is contained in:
Jonathan Wakely 2023-02-28 21:07:48 +00:00
parent 096f034a8f
commit 4abd5bc600
2 changed files with 17 additions and 20 deletions
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15
libstdc++-v3/src/c++20/tzdb.cc
View File

@ -1692,19 +1692,16 @@ namespace std::chrono
// https://www.ibm.com/support/pages/managing-time-zone-variable-posix
if (const char* env = std::getenv("TZ"))
{
string_view s(env);
if (s == "GMT0")
s = "Etc/GMT";
else if (s.size() == 4 && s[3] == '0')
s = "Etc/UTC";
// This will fail unless TZ contains an IANA time zone name,
// or one of the special cases above.
if (auto tz = do_locate_zone(this->zones, this->links, s))
// This will fail unless TZ contains an IANA time zone name.
if (auto tz = do_locate_zone(this->zones, this->links, env))
return tz;
}
#endif
// Default to UTC.
if (auto tz = do_locate_zone(this->zones, this->links, "UTC"))
return tz;
__throw_runtime_error("tzdb: cannot determine current zone");
}

22
libstdc++-v3/testsuite/std/time/tzdb/1.cc
View File

@ -1,7 +1,6 @@
// { dg-options "-std=gnu++20" }
// { dg-do run { target c++20 } }
// { dg-require-effective-target cxx11_abi }
// { dg-additional-options "-DHAVE_TZDB" { target tzdb } }
#include <chrono>
#include <testsuite_hooks.h>
@ -14,22 +13,25 @@ test_version()
const tzdb& db = get_tzdb();
VERIFY( &db == &get_tzdb_list().front() );
#ifdef HAVE_TZDB
VERIFY( db.version == remote_version() );
const tzdb& reloaded = reload_tzdb();
if (reloaded.version == db.version)
VERIFY( &reloaded == &db );
#endif
const char* func;
try {
func = "remote_version";
VERIFY( db.version == remote_version() );
func = "reload_tzdb";
const tzdb& reloaded = reload_tzdb();
if (reloaded.version == db.version)
VERIFY( &reloaded == &db );
} catch (const std::exception&) {
std::printf("std::chrono::%s() failed\n", func);
}
}
void
test_current()
{
#ifdef HAVE_TZDB
const tzdb& db = get_tzdb();
const time_zone* tz = db.current_zone();
VERIFY( tz == std::chrono::current_zone() );
#endif
}
void
@ -43,9 +45,7 @@ test_locate()
VERIFY( tz == db.locate_zone("Etc/GMT") );
VERIFY( tz == db.locate_zone("Etc/GMT+0") );
#ifdef HAVE_TZDB
VERIFY( db.locate_zone(db.current_zone()->name()) == db.current_zone() );
#endif
}
int main()