QLocale: fix handling of milliseconds in string format and document

[ChangeLog][QtCore][QLocale] Fixed the conversion of QTime to string
form and parsing from string form to always treat the value as the
decimal fraction of the seconds component. That is, the string format
".z" produces/parses ".2" for 200 milliseconds and ".002" for 2
milliseconds. Use of "z" or "zzz" is discouraged outside decimal
fractions to avoid surprises.

Task-number: QTBUG-53565
Change-Id: Ia19de85ad35e4eb7bb95fffd14792caf9b4a5156
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

2 files changed, 20 insertions, 14 deletions

diff --git a/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp b/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
index 9ca8766592..f278a7470b 100644
--- a/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/tools/qlocale/tst_qlocale.cpp
@@ -1302,10 +1302,11 @@ void tst_QLocale::formatTime_data()
     QTest::newRow("28") << QTime(1, 2, 3, 456) << "H:m:s.z" << "1:2:3.456";
     QTest::newRow("29") << QTime(1, 2, 3, 456) << "H:m:s.zz" << "1:2:3.456456";
     QTest::newRow("30") << QTime(1, 2, 3, 456) << "H:m:s.zzz" << "1:2:3.456";
-    QTest::newRow("31") << QTime(1, 2, 3, 4) << "H:m:s.z" << "1:2:3.4";
-    QTest::newRow("32") << QTime(1, 2, 3, 4) << "H:m:s.zzz" << "1:2:3.004";
-    QTest::newRow("33") << QTime() << "H:m:s.zzz" << "";
-    QTest::newRow("34") << QTime(1, 2, 3, 4) << "dd MM yyyy H:m:s.zzz" << "dd MM yyyy 1:2:3.004";
+    QTest::newRow("31") << QTime(1, 2, 3, 400) << "H:m:s.z" << "1:2:3.4";
+    QTest::newRow("32") << QTime(1, 2, 3, 4) << "H:m:s.z" << "1:2:3.004";
+    QTest::newRow("33") << QTime(1, 2, 3, 4) << "H:m:s.zzz" << "1:2:3.004";
+    QTest::newRow("34") << QTime() << "H:m:s.zzz" << "";
+    QTest::newRow("35") << QTime(1, 2, 3, 4) << "dd MM yyyy H:m:s.zzz" << "dd MM yyyy 1:2:3.004";
 }
 
 void tst_QLocale::formatTime()
@@ -1542,10 +1543,12 @@ void tst_QLocale::toDateTime_data()
                         << "d/M/yyyy hh:h:mm" << "1/12/1974 05:5:14";
     QTest::newRow("2C") << "C" << QDateTime(QDate(1974, 12, 1), QTime(15, 0, 0))
                         << "d/M/yyyyy h" << "1/12/1974y 15";
-    QTest::newRow("4C") << "C" << QDateTime(QDate(1974, 1, 1), QTime(0, 0, 0))
-                        << "d/M/yyyy zzz" << "1/1/1974 000";
-    QTest::newRow("5C") << "C" << QDateTime(QDate(1974, 1, 1), QTime(0, 0, 0))
-                        << "dd/MM/yyy z" << "01/01/74y 0";
+    QTest::newRow("4C") << "C" << QDateTime(QDate(1974, 1, 1), QTime(0, 0, 0, 1))
+                        << "d/M/yyyy zzz" << "1/1/1974 001";
+    QTest::newRow("5C") << "C" << QDateTime(QDate(1974, 1, 1), QTime(0, 0, 0, 1))
+                        << "dd/MM/yyy z" << "01/01/74y 001";
+    QTest::newRow("5Cbis") << "C" << QDateTime(QDate(1974, 1, 1), QTime(0, 0, 0, 100))
+                        << "dd/MM/yyy z" << "01/01/74y 1";
     QTest::newRow("8C") << "C" << QDateTime(QDate(1974, 12, 2), QTime(0, 0, 13))
                         << "ddddd/MMMMM/yy ss" << "Monday2/December12/74 13";
     QTest::newRow("9C") << "C" << QDateTime(QDate(1974, 12, 1), QTime(0, 0, 13))
diff --git a/tests/auto/corelib/tools/qtime/tst_qtime.cpp b/tests/auto/corelib/tools/qtime/tst_qtime.cpp
index 71bf39fc4e..162047b537 100644
--- a/tests/auto/corelib/tools/qtime/tst_qtime.cpp
+++ b/tests/auto/corelib/tools/qtime/tst_qtime.cpp
@@ -560,6 +560,8 @@ void tst_QTime::fromStringFormat_data()
     QTest::newRow("data9") << QString("2221") << QString("hhhh") << invalidTime();
     QTest::newRow("data10") << QString("02:23PM") << QString("hh:mmAP") << QTime(14,23,0,0);
     QTest::newRow("data11") << QString("02:23pm") << QString("hh:mmap") << QTime(14,23,0,0);
+    QTest::newRow("short-msecs-lt100") << QString("10:12:34:045") << QString("hh:m:ss:z") << QTime(10,12,34,45);
+    QTest::newRow("short-msecs-gt100") << QString("10:12:34:45") << QString("hh:m:ss:z") << QTime(10,12,34,450);
 }
 
 void tst_QTime::fromStringFormat()
@@ -711,12 +713,13 @@ void tst_QTime::toStringFormat_data()
     QTest::addColumn<QString>("format");
     QTest::addColumn<QString>("str");
 
-    QTest::newRow( "data0" ) << QTime(0,0,0,0) << QString("h:m:s:z") << QString("0:0:0:0");
-    QTest::newRow( "data1" ) << QTime(10,12,34,53) << QString("hh:mm:ss:zzz") << QString("10:12:34:053");
-    QTest::newRow( "data2" ) << QTime(10,12,34,45) << QString("hh:m:ss:z") << QString("10:12:34:45");
-    QTest::newRow( "data3" ) << QTime(10,12,34,45) << QString("hh:ss ap") << QString("10:34 am");
-    QTest::newRow( "data4" ) << QTime(22,12,34,45) << QString("hh:zzz AP") << QString("10:045 PM");
-    QTest::newRow( "data5" ) << QTime(230,230,230,230) << QString("hh:mm:ss") << QString();
+    QTest::newRow( "midnight" ) << QTime(0,0,0,0) << QString("h:m:s:z") << QString("0:0:0:0");
+    QTest::newRow( "full" ) << QTime(10,12,34,53) << QString("hh:mm:ss:zzz") << QString("10:12:34:053");
+    QTest::newRow( "short-msecs-lt100" ) << QTime(10,12,34,45) << QString("hh:m:ss:z") << QString("10:12:34:045");
+    QTest::newRow( "short-msecs-gt100" ) << QTime(10,12,34,450) << QString("hh:m:ss:z") << QString("10:12:34:45");
+    QTest::newRow( "am-pm" ) << QTime(10,12,34,45) << QString("hh:ss ap") << QString("10:34 am");
+    QTest::newRow( "AM-PM" ) << QTime(22,12,34,45) << QString("hh:zzz AP") << QString("10:045 PM");
+    QTest::newRow( "invalid" ) << QTime(230,230,230,230) << QString("hh:mm:ss") << QString();
 }
 
 void tst_QTime::toStringFormat()