Fix assertion failure when parsing a doubly-invalid date-time text

When the date-time string falls in a spring-forward (so is invalid)
and one of the fields of the parsed string doesn't match the format
it's meant to (e.g. a single-digit seconds field when format ss was
specified), a check that the current fall-back date-time is between
the minimum and maximum for the parser object failed, triggering an
assertion.

In any case, an invalid default-value wasn't useful to the code that
parsed a single section of the date-time string, so brute-force the
current value to a valid date-time (when possible) using the usual
round-trip via milliseconds since the epoch.

Added the test-case which first revealed the problem, plus a couple
more informed by it, to exercise the same code-paths with fewer things
failing.

Fixes: QTBUG-102199
Change-Id: I658308614505ef25f4c97d0de6148acb54a65a0f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 9fee35a2eda68b5968d911d5e14d298b91418d2c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 22 insertions, 4 deletions

diff --git a/src/corelib/time/qdatetimeparser.cpp b/src/corelib/time/qdatetimeparser.cpp
index 0741ddcc57..d2375d258f 100644
--- a/src/corelib/time/qdatetimeparser.cpp
+++ b/src/corelib/time/qdatetimeparser.cpp
@@ -759,6 +759,11 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex, i
                          && m_text.at(offset) == QLatin1Char('-'));
     const int negativeYearOffset = negate ? 1 : 0;
 
+    // If the fields we've read thus far imply a time in a spring-forward,
+    // coerce to a nearby valid time:
+    const QDateTime defaultValue = currentValue.isValid() ? currentValue
+        : QDateTime::fromMSecsSinceEpoch(currentValue.toMSecsSinceEpoch());
+
     QStringView sectionTextRef =
             QStringView { m_text }.mid(offset + negativeYearOffset, sectionmaxsize);
 
@@ -794,7 +799,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex, i
             m_text.replace(offset, used, sectiontext.constData(), used);
         break; }
     case TimeZoneSection:
-        result = findTimeZone(sectionTextRef, currentValue,
+        result = findTimeZone(sectionTextRef, defaultValue,
                               absoluteMax(sectionIndex),
                               absoluteMin(sectionIndex));
         break;
@@ -806,7 +811,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex, i
             int num = 0, used = 0;
             if (sn.type == MonthSection) {
                 const QDate minDate = getMinimum().date();
-                const int year = currentValue.date().year(calendar);
+                const int year = defaultValue.date().year(calendar);
                 const int min = (year == minDate.year(calendar)) ? minDate.month(calendar) : 1;
                 num = findMonth(sectiontext.toLower(), min, sectionIndex, year, &sectiontext, &used);
             } else {
@@ -900,7 +905,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex, i
                     }
 
                 } else if (unfilled && (fi & (FixedWidth | Numeric)) == (FixedWidth | Numeric)) {
-                    if (skipToNextSection(sectionIndex, currentValue, digitsStr)) {
+                    if (skipToNextSection(sectionIndex, defaultValue, digitsStr)) {
                         const int missingZeroes = sectionmaxsize - digitsStr.size();
                         result = ParsedSection(Acceptable, last, sectionmaxsize, missingZeroes);
                         m_text.insert(offset, QString(missingZeroes, QLatin1Char('0')));
diff --git a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
index 17e8e0cfb3..8a81151ea6 100644
--- a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
@@ -1859,7 +1859,8 @@ void tst_QLocale::toDateTime_data()
     QTest::addColumn<QDateTime>("result");
     QTest::addColumn<QString>("format");
     QTest::addColumn<QString>("string");
-    QTest::addColumn<bool>("clean"); // No non-format letters in format string
+    // No non-format letters in format string, no time-zone (t format):
+    QTest::addColumn<bool>("clean");
 
     QTest::newRow("1C") << "C" << QDateTime(QDate(1974, 12, 1), QTime(5, 14, 0))
                         << "d/M/yyyy hh:h:mm" << "1/12/1974 05:5:14" << true;
@@ -1913,6 +1914,18 @@ void tst_QLocale::toDateTime_data()
     QTest::newRow("12no_NO") << "no_NO" << QDateTime(QDate(1974, 12, 1), QTime(15, 0, 0))
                              << "d'd'dd/M/yyh" << "1d01/12/7415" << false;
 
+    QTest::newRow("short-ss") // QTBUG-102199: trips over an assert in CET
+        << "C" << QDateTime() // Single-digit seconds does not match ss format.
+        << u"ddd, d MMM yyyy HH:mm:ss"_qs << u"Sun, 29 Mar 2020 02:26:3"_qs << true;
+
+    QTest::newRow("short-ss-Z") // Same, but with a valid date-time:
+        << "C" << QDateTime()
+        << u"ddd, d MMM yyyy HH:mm:ss t"_qs << u"Sun, 29 Mar 2020 02:26:3 Z"_qs << false;
+
+    QTest::newRow("s-Z") // Same, but with a format that accepts the single digit:
+        << "C" << QDateTime(QDate(2020, 3, 29), QTime(2, 26, 3), Qt::UTC)
+        << u"ddd, d MMM yyyy HH:mm:s t"_qs << u"Sun, 29 Mar 2020 02:26:3 Z"_qs << false;
+
     QTest::newRow("RFC-1123")
         << "C" << QDateTime(QDate(2007, 11, 1), QTime(18, 8, 30))
         << "ddd, dd MMM yyyy hh:mm:ss 'GMT'" << "Thu, 01 Nov 2007 18:08:30 GMT" << false;