Support POSIX rules as $TZ values

The TZ environment variable can validly contain a POSIX rule, rather
than an IANA ID, as described here:
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03

However, if TZ were set to such a value, leading to it being used as
systemTimeZoneId(), it would be passed to QTzTimeZonePrivate::init(),
which is a no-op unless it manages to open a zoneinfo/ file with the
given ianaId as name.  When the environment variable doesn't name a
zoneinfo/ file, we would thus get an invalid time-zone.  We can,
instead, check whether the ianaId looks like a valid POSIX rule and,
if it does, use it as m_posixRule, enabling us to correctly handle
this case.

Tweak parsing of POSIX rules so that a zone using name "UTC" or "GMT"
with an offset other than 0 will be rejected as invalid.  This avoids
parsing a zone name such as "GMT+17" or "UTC+00:01" as a POSIX rule,
where it should be understood as an offset from UTC (and only certain
well-established offsets are supported).

Added two test-cases to tst_QTimeZone::tzTest() for validity of a
POSIX zone value - a simple one constructed during discussion of the
bug, the other taken from an example in:
http://leaf.sourceforge.net/doc/buci-tz3.html

Task-number: QTBUG-75565
Change-Id: Ia5cb1cc56b13b0f6b56258e48be98d04d909e32a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 22 insertions, 1 deletions

diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index fab0b2cbf1..d9e87212d3 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -516,6 +516,10 @@ PosixZone PosixZone::parse(const char *&pos, const char *end)
     QString name = QString::fromUtf8(nameBegin, nameEnd - nameBegin);
     const int offset = zoneEnd > zoneBegin ? parsePosixOffset(zoneBegin, zoneEnd) : InvalidOffset;
     pos = zoneEnd;
+    // UTC+hh:mm:ss or GMT+hh:mm:ss should be read as offsets from UTC, not as a
+    // POSIX rule naming a zone as UTC or GMT and specifying a non-zero offset.
+    if (offset != 0 && (name == QLatin1String("UTC") || name == QLatin1String("GMT")))
+        return invalid();
     return {std::move(name), offset};
 }
 
@@ -654,8 +658,17 @@ void QTzTimeZonePrivate::init(const QByteArray &ianaId)
         tzif.setFileName(QLatin1String("/usr/share/zoneinfo/") + QString::fromLocal8Bit(ianaId));
         if (!tzif.open(QIODevice::ReadOnly)) {
             tzif.setFileName(QLatin1String("/usr/lib/zoneinfo/") + QString::fromLocal8Bit(ianaId));
-            if (!tzif.open(QIODevice::ReadOnly))
+            if (!tzif.open(QIODevice::ReadOnly)) {
+                // ianaId may be a POSIX rule, taken from $TZ
+                const QByteArray zoneInfo = ianaId.split(',').at(0);
+                const char *begin = zoneInfo.constBegin();
+                if (PosixZone::parse(begin, zoneInfo.constEnd()).hasValidOffset()
+                    && (begin == zoneInfo.constEnd()
+                        || PosixZone::parse(begin, zoneInfo.constEnd()).hasValidOffset())) {
+                    m_id = m_posixRule = ianaId;
+                }
                 return;
+            }
         }
     }
 
diff --git a/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
index 4160a00f71..9904719f7c 100644
--- a/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/tools/qtimezone/tst_qtimezone.cpp
@@ -915,6 +915,14 @@ void tst_QTimeZone::tzTest()
     QTzTimeZonePrivate tzp("Europe/Berlin");
     QVERIFY(tzp.isValid());
 
+    // Test POSIX-format value for $TZ:
+    QTzTimeZonePrivate tzposix("MET-1METDST-2,M3.5.0/02:00:00,M10.5.0/03:00:00");
+    QVERIFY(tzposix.isValid());
+
+    QTimeZone tzBrazil("BRT+3"); // parts of Northern Brazil, as a POSIX rule
+    QVERIFY(tzBrazil.isValid());
+    QCOMPARE(tzBrazil.offsetFromUtc(QDateTime(QDate(1111, 11, 11).startOfDay())), -10800);
+
     // Test display names by type, either ICU or abbreviation only
     QLocale enUS("en_US");
     // Only test names in debug mode, names used can vary by ICU version installed