Change QTimeZone's offset range into constants, not an enum

Use static constexpr int values instead of abusing enum.

[ChangeLog][QtCore][QTimeZone] The MinUtcOffsetSecs and
MaxUtcOffsetSecs constants are now static constexpr members of
QTimeZone, rather than members of an anonymous enum. Their values are
now 16 hours either side of zero, to allow for some historical zones.

Change-Id: I1c3a0f85a2b83b5010f021ca0f5ca5baefbf32e4
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/time/qtimezone.cpp

@@ -254,31 +254,34 @@ Q_GLOBAL_STATIC(QTimeZoneSingleton, global_tz);
 */
 
 /*!
-  \enum QTimeZone::anonymous
+    \variable QTimeZone::MinUtcOffsetSecs
+    \brief Timezone offsets from UTC are expected to be no lower than this.
 
-  This enumeration provides constants bounding the range of plausible timezone
-  offsets from UTC, measured in seconds.
+    The lowest UTC offset of any early 21st century timezone is -12 hours (Baker
+    Island, USA), or 12 hours west of Greenwich.
 
-  Sane modern zones' UTC offsets range from -14 to +12 hours.
-  No known modern zone has offset > 12 hrs West of Greenwich (Baker Island, USA).
-  No known modern zone has offset > 14 hrs East of Greenwich
-  (Kiritimati, Christmas Island, Kiribati).
-  Note that there are zones whose offsets differ by more than a day.
+    Historically, until 1844, The Philippines (then controlled by Spain) used
+    the same date as Spain's American holdings, so had offsets close to 16 hours
+    west of Greenwich. As The Philippines was using local solar mean time, it is
+    possible some outlying territory of it may have been operating at more than
+    16 hours west of Greenwich, but no early 21st century timezone traces its
+    history back to such an extreme.
 
-  Historically, before 1867, when Russia sold Alaska to America, Alaska used the
-  same date as Russia, so had offsets over 15 hours East of Greenwich.
-  Earlier still, until 1844, The Philippines (then controlled by Spain) used the
-  same date as Spain's American holdings, so had offsets close to 16 hours West
-  of Greenwich.
-  Each made its one-day transition to cross the international date line while
-  using local solar mean time, before adopting a unified time-zone, so the
-  offsets within their territories were variable.
-  As a result, The Philippines might have exceeded 16 hours as offset at the
-  extremities of its territory, but no modern zone's representative location was
-  at such an extremity.
+    \sa MaxUtcOffsetSecs
+*/
+/*!
+    \variable QTimeZone::MaxUtcOffsetSecs
+    \brief Timezone offsets from UTC are expected to be no higher than this.
 
-  \value MinUtcOffsetSecs -16 * 3600,
-  \value MaxUtcOffsetSecs +16 * 3600
+    The highest UTC offset of any early 21st century timezone is +14 hours
+    (Christmas Island, Kiribati, Kiritimati), or 14 hours east of Greenwich.
+
+    Historically, before 1867, when Russia sold Alaska to America, Alaska used
+    the same date as Russia, so had offsets over 15 hours east of Greenwich. As
+    Alaska was using local solar mean time, its offsets varied, but all were
+    less than 16 hours east of Greenwich.
+
+    \sa MinUtcOffsetSecs
 */
 
 #if QT_CONFIG(timezone)
@@ -489,6 +492,8 @@ QTimeZone::QTimeZone(const QByteArray &ianaId)
     returned instance is equivalent to the lightweight time representation
     \c{QTimeZone::fromSecondsAfterUtc(offsetSeconds)}, albeit implemented as a
     time zone.
+
+    \sa MinUtcOffsetSecs, MaxUtcOffsetSecs
 */
 
 QTimeZone::QTimeZone(int offsetSeconds)
@@ -516,7 +521,8 @@ QTimeZone::QTimeZone(int offsetSeconds)
 
     This constructor is only available when feature \c timezone is enabled.
 
-    \sa id(), offsetFromUtc(), displayName(), abbreviation(), territory(), comment()
+    \sa id(), offsetFromUtc(), displayName(), abbreviation(), territory(), comment(),
+        MinUtcOffsetSecs, MaxUtcOffsetSecs
 */
 
 QTimeZone::QTimeZone(const QByteArray &ianaId, int offsetSeconds, const QString &name,
@@ -629,7 +635,8 @@ QTimeZone QTimeZone::asBackendZone() const
     Qt::OffsetFromUTC. An invalid time zone, when returned, has Qt::TimeZone as
     its timeSpec().
 
-    \sa QTimeZone(int), asBackendZone(), fixedSecondsAheadOfUtc()
+    \sa QTimeZone(int), asBackendZone(), fixedSecondsAheadOfUtc(),
+        MinUtcOffsetSecs, MaxUtcOffsetSecs
 */
 
 /*!

src/corelib/time/qtimezone.h

@@ -83,14 +83,12 @@ class Q_CORE_EXPORT QTimeZone
 
 public:
     // Sane UTC offsets range from -16 to +16 hours:
-    enum {
+    static constexpr int MinUtcOffsetSecs = -16 * 3600;
     // No known modern zone > 12 hrs West of Greenwich.
     // Until 1844, Asia/Manila (in The Philippines) was at 15:56 West.
-        MinUtcOffsetSecs = -16 * 3600,
+    static constexpr int MaxUtcOffsetSecs = +16 * 3600;
     // No known modern zone > 14 hrs East of Greenwich.
     // Until 1867, America/Metlakatla (in Alaska) was at 15:13:42 East.
-        MaxUtcOffsetSecs = +16 * 3600
-    };
 
     enum Initialization { LocalTime, UTC };
 

tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp

@@ -1163,8 +1163,8 @@ void tst_QTimeZone::utcTest()
     QCOMPARE(tz.daylightTimeOffset(now), 0);
 
     // Test validity range of UTC offsets:
-    int min = int(QTimeZone::MinUtcOffsetSecs);
-    int max = int(QTimeZone::MaxUtcOffsetSecs);
+    int min = QTimeZone::MinUtcOffsetSecs;
+    int max = QTimeZone::MaxUtcOffsetSecs;
     QCOMPARE(QTimeZone(min - 1).isValid(), false);
     QCOMPARE(QTimeZone(min).isValid(), true);
     QCOMPARE(QTimeZone(min + 1).isValid(), true);