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. (For 5.15: converted u"..."_qs to QStringLiteral("...").)

Fixes: QTBUG-102199
Change-Id: I658308614505ef25f4c97d0de6148acb54a65a0f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 9fee35a2eda68b5968d911d5e14d298b91418d2c)
Reviewed-by: Ievgenii Meshcheriakov <ievgenii.meshcheriakov@qt.io>

2 files changed, 27 insertions, 6 deletions

diff --git a/src/corelib/time/qdatetimeparser.cpp b/src/corelib/time/qdatetimeparser.cpp
index 5df4b373c4..5f8267c2b9 100644
--- a/src/corelib/time/qdatetimeparser.cpp
+++ b/src/corelib/time/qdatetimeparser.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -761,6 +761,11 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex,
     const int sectionmaxsize = sectionMaxSize(sectionIndex);
     QStringRef sectionTextRef = text->midRef(offset, sectionmaxsize);
 
+    // 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());
+
     QDTPDEBUG << "sectionValue for" << sn.name()
               << "with text" << *text << "and (at" << offset
               << ") st:" << sectionTextRef;
@@ -793,7 +798,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex,
             text->replace(offset, used, sectiontext.constData(), used);
         break; }
     case TimeZoneSection:
-        result = findTimeZone(sectionTextRef, currentValue,
+        result = findTimeZone(sectionTextRef, defaultValue,
                               absoluteMax(sectionIndex),
                               absoluteMin(sectionIndex));
         break;
@@ -805,7 +810,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex,
             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 {
@@ -887,7 +892,7 @@ QDateTimeParser::parseSection(const QDateTime &currentValue, int sectionIndex,
                     else
                         QDTPDEBUG << "invalid because" << last << "is less than absoluteMin" << absMin;
                 } 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);
                         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 33fcb156b6..84901f8f75 100644
--- a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2020 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -1778,7 +1778,8 @@ 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;
@@ -1832,6 +1833,21 @@ 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.
+        << QStringLiteral("ddd, d MMM yyyy HH:mm:ss")
+        << QStringLiteral("Sun, 29 Mar 2020 02:26:3") << true;
+
+    QTest::newRow("short-ss-Z") // Same, but with a valid date-time:
+        << "C" << QDateTime()
+        << QStringLiteral("ddd, d MMM yyyy HH:mm:ss t")
+        << QStringLiteral("Sun, 29 Mar 2020 02:26:3 Z") << 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)
+        << QStringLiteral("ddd, d MMM yyyy HH:mm:s t")
+        << QStringLiteral("Sun, 29 Mar 2020 02:26:3 Z") << 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;