Make time parsing accept zz as equivalent to z

Expand a test to cover millsecond format variants more thoroughly,
including a test for the new usage of zz. This applies to parsing the
complement to commit 0a36a7c1db173089c25ea09029505a589a1c59e5's change
to serialization. Fixed minor glitch in the serialization's doc, too.

[ChangeLog][QtCore][QDateTime] When parsing a datetime, the 'zz'
format specifier is now equivalent to 'z', as for serialization.

Change-Id: I1c5700064738d9c92d5e8ce10bff8050131e190f
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/time/qdatetime.cpp

@@ -1929,12 +1929,15 @@ QString QTime::toString(Qt::DateFormat format) const
     \row \li ss \li The whole second, with a leading zero where applicable (00 to 59)
     \row \li z or zz
          \li The fractional part of the second, to go after a decimal point,
-             without trailing zeroes.  Thus "\c{s.z}" reports the seconds to
+             without trailing zeroes. Thus \c{"s.z"} reports the seconds to full
-             full available (millisecond) precision without trailing zeroes (0
+             available (millisecond) precision without trailing zeroes (0 to
-             to 999).
+             999). For example, \c{"s.z"} would produce \c{"0.25"} for a time a
+             quarter second into a minute.
     \row \li zzz
          \li The fractional part of the second, to millisecond precision,
-             including trailing zeroes where applicable (000 to 999).
+             including trailing zeroes where applicable (000 to 999). For
+             example, \c{"ss.zzz"} would produce \c{"00.250"} for a time a
+             quarter second into a minute.
     \row \li AP or A
          \li Use AM/PM display. \c A/AP will be replaced by 'AM' or 'PM'. In
              localized forms (only relevant to \l{QLocale::toString()}), the
@@ -2332,12 +2335,20 @@ QTime QTime::fromString(QStringView string, Qt::DateFormat format)
     \row \li mm \li The minute with a leading zero (00 to 59)
     \row \li s \li The whole second, without any leading zero (0 to 59)
     \row \li ss \li The whole second, with a leading zero where applicable (00 to 59)
-    \row \li z \li The fractional part of the second, to go after a decimal
+    \row \li z or zz
-                point, without trailing zeroes (0 to 999).  Thus "\c{s.z}"
+         \li The fractional part of the second, as would usually follow a
-                reports the seconds to full available (millisecond) precision
+             decimal point, without requiring trailing zeroes (0 to 999). Thus
-                without trailing zeroes.
+             \c{"s.z"} matches the seconds with up to three digits of fractional
-    \row \li zzz \li The fractional part of the second, to millisecond
+             part supplying millisecond precision, without needing trailing
-                precision, including trailing zeroes where applicable (000 to 999).
+             zeroes. For example, \c{"s.z"} would recognize either \c{"00.250"}
+             or \c{"0.25"} as representing a time a quarter second into its
+             minute.
+    \row \li zzz
+         \li Three digit fractional part of the second, to millisecond
+             precision, including trailing zeroes where applicable (000 to 999).
+             For example, \c{"ss.zzz"} would reject \c{"0.25"} but recognize
+             \c{"00.250"} as representing a time a quarter second into its
+             minute.
     \row \li AP, A, ap, a, aP or Ap
          \li Either 'AM' indicating a time before 12:00 or 'PM' for later times,
              matched case-insensitively.

src/corelib/time/qdatetimeparser.cpp

@@ -501,10 +501,11 @@ bool QDateTimeParser::parseFormat(QStringView newFormat)
 
             case 'z':
                 if (parserType != QMetaType::QDate) {
-                    const SectionNode sn = { MSecSection, i - add, countRepeat(newFormat, i, 3) < 3 ? 1 : 3, 0 };
+                    const int repeat = countRepeat(newFormat, i, 3);
+                    const SectionNode sn = { MSecSection, i - add, repeat < 3 ? 1 : 3, 0 };
                     newSectionNodes.append(sn);
                     appendSeparator(&newSeparators, newFormat, index, i - index, lastQuote);
-                    i += sn.count - 1;
+                    i += repeat - 1;
                     index = i + 1;
                     newDisplay |= MSecSection;
                 }

tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp

@@ -2752,9 +2752,15 @@ void tst_QDateTime::fromStringStringFormat_data()
     QTest::newRow("data15")
         << QString("Thu January 2004") << QString("ddd MMMM yyyy")
         << QDate(2004, 1, 1).startOfDay();
-    QTest::newRow("data16") << QString("2005-06-28T07:57:30.001Z")
+    QTest::newRow("zulu-time-with-z-centisec")
-                            << QString("yyyy-MM-ddThh:mm:ss.zt")
+        << QString("2005-06-28T07:57:30.01Z") << QString("yyyy-MM-ddThh:mm:ss.zt")
-                            << QDateTime(QDate(2005, 06, 28), QTime(07, 57, 30, 1), Qt::UTC);
+        << QDateTime(QDate(2005, 06, 28), QTime(07, 57, 30, 10), Qt::UTC);
+    QTest::newRow("zulu-time-with-zz-decisec")
+        << QString("2005-06-28T07:57:30.1Z") << QString("yyyy-MM-ddThh:mm:ss.zzt")
+        << QDateTime(QDate(2005, 06, 28), QTime(07, 57, 30, 100), Qt::UTC);
+    QTest::newRow("zulu-time-with-zzz-centisec")
+        << QString("2005-06-28T07:57:30.01Z") << QString("yyyy-MM-ddThh:mm:ss.zzzt")
+        << QDateTime(); // Invalid because too few digits for zzz
     QTest::newRow("utc-time-spec-as:UTC+0")
         << QString("2005-06-28T07:57:30.001UTC+0") << QString("yyyy-MM-ddThh:mm:ss.zt")
         << QDateTime(QDate(2005, 6, 28), QTime(7, 57, 30, 1), Qt::UTC);