Clean-up in QDateTime's parsing of ISODate{,WithMs}

Actually check that there's a T where ISO 8601 wants it (instead of
just skipping over whatever's there), with something after it; move
some declarations later; add some comments; and use the QStringRef API
more cleanly (so that it's easier to see what's going on).  Simplify a
loop condition to avoid the need for a post-loop fix-up.

This incidentally prevents an assertion failure (which brought the
mess to my attention) parsing a short string as an ISO date-time; if
there's a T with nothing after it, we won't try to read at index -1 in
the following text.  (The actual fail seen had a Z where the T should
have been, with nothing after it.)

Add tests for invalid ISOdate cases that triggered the assertion.

Task-number: QTBUG-66076
Change-Id: Ided9adf62a56d98f144bdf91b40f918e22bd82cd
Reviewed-by: Israel Lins Albuquerque <israelins85@yahoo.com.br>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit a9c111ed8c30a5a8fec3f02244f0d5a4bd08e931)

2 files changed, 20 insertions, 7 deletions

diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index 9d26207a0f..045ad10755 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -4720,25 +4720,35 @@ QDateTime QDateTime::fromString(const QString& string, Qt::DateFormat format)
         if (size < 10)
             return QDateTime();
 
-        QStringRef isoString(&string);
-        Qt::TimeSpec spec = Qt::LocalTime;
-
         QDate date = QDate::fromString(string.left(10), Qt::ISODate);
         if (!date.isValid())
             return QDateTime();
         if (size == 10)
             return QDateTime(date);
 
-        isoString = isoString.right(isoString.length() - 11);
+        Qt::TimeSpec spec = Qt::LocalTime;
+        QStringRef isoString(&string);
+        isoString = isoString.mid(10); // trim "yyyy-MM-dd"
+
+        // Must be left with T and at least one digit for the hour:
+        if (isoString.size() < 2
+            || !(isoString.startsWith(QLatin1Char('T'))
+                 // FIXME: QSql relies on QVariant::toDateTime() accepting a space here:
+                 || isoString.startsWith(QLatin1Char(' ')))) {
+            return QDateTime();
+        }
+        isoString = isoString.mid(1); // trim 'T' (or space)
+
         int offset = 0;
         // Check end of string for Time Zone definition, either Z for UTC or [+-]HH:mm for Offset
         if (isoString.endsWith(QLatin1Char('Z'))) {
             spec = Qt::UTC;
-            isoString = isoString.left(isoString.size() - 1);
+            isoString.chop(1); // trim 'Z'
         } else {
             // the loop below is faster but functionally equal to:
             // const int signIndex = isoString.indexOf(QRegExp(QStringLiteral("[+-]")));
             int signIndex = isoString.size() - 1;
+            Q_ASSERT(signIndex >= 0);
             bool found = false;
             {
                 const QChar plus = QLatin1Char('+');
@@ -4746,8 +4756,7 @@ QDateTime QDateTime::fromString(const QString& string, Qt::DateFormat format)
                 do {
                     QChar character(isoString.at(signIndex));
                     found = character == plus || character == minus;
-                } while (--signIndex >= 0 && !found);
-                ++signIndex;
+                } while (!found && --signIndex >= 0);
             }
 
             if (found) {
diff --git a/tests/auto/corelib/tools/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/tools/qdatetime/tst_qdatetime.cpp
index 28ad2d193c..91b5966fa8 100644
--- a/tests/auto/corelib/tools/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/tools/qdatetime/tst_qdatetime.cpp
@@ -2277,6 +2277,10 @@ void tst_QDateTime::fromStringDateFormat_data()
     QTest::newRow("ISO .99999 of a minute (comma)") << QString::fromLatin1("2012-01-01T08:00,99999")
         << Qt::ISODate << QDateTime(QDate(2012, 1, 1), QTime(8, 0, 59, 999), Qt::LocalTime);
     QTest::newRow("ISO empty") << QString::fromLatin1("") << Qt::ISODate << invalidDateTime();
+    QTest::newRow("ISO short") << QString::fromLatin1("2017-07-01T") << Qt::ISODate << invalidDateTime();
+    QTest::newRow("ISO zoned date") << QString::fromLatin1("2017-07-01Z") << Qt::ISODate << invalidDateTime();
+    QTest::newRow("ISO zoned empty time") << QString::fromLatin1("2017-07-01TZ") << Qt::ISODate << invalidDateTime();
+    QTest::newRow("ISO mis-punctuated") << QString::fromLatin1("2018/01/30 ") << Qt::ISODate << invalidDateTime();
 
     // Test Qt::RFC2822Date format (RFC 2822).
     QTest::newRow("RFC 2822 +0100") << QString::fromLatin1("13 Feb 1987 13:24:51 +0100")