MonthGrid: fix dates being incorrect for certain timezonesHEADdev

When a QDate is passed to QML, it becomes to a JavaScript Date.
As Dates are stored in local time, the QDates we were passing to
QML had the potential to be one day off in certain timezones.
For example: 00:00 UTC converted to UTC-8 is 20:00 the day before.

Fix this by storing and providing dates as QDateTime so that we can
give it a time of day that can't possibly result in a different day
when converted to local time. It's fine to change the C++ API since
it's private, and nothing will change for the type that users see,
since they always get a Date.

Add a SystemEnvironment singleton to QQuickControlsTestUtils
(Qt.test.controls) to allow reading and writing environment
variables from QML.

Fixes: QTBUG-72208
Pick-to: 6.8 6.9 6.10
Change-Id: Idb4ab26568d8f1eddd5ab4cebe691e38173d02a9
Reviewed-by: Ulf Hermann <[email protected]>

6 files changed, 70 insertions, 18 deletions

diff --git a/src/quickcontrolstestutils/controlstestutils.cpp b/src/quickcontrolstestutils/controlstestutils.cpp
index fb88d00d29..f6b02abbe3 100644
--- a/src/quickcontrolstestutils/controlstestutils.cpp
+++ b/src/quickcontrolstestutils/controlstestutils.cpp
@@ -186,6 +186,21 @@ QString QQuickControlsTestUtils::StyleInfo::styleName() const
     return QQuickStyle::name();
 }
 
+/*!
+    It's recommended to use try-finally (see tst_monthgrid.qml for an example)
+    or init/initTestCase and cleanup/cleanupTestCase if setting environment
+    variables, in order to restore previous values.
+*/
+QString QQuickControlsTestUtils::SystemEnvironment::value(const QString &name)
+{
+    return QString::fromLocal8Bit(qgetenv(name.toLocal8Bit()));
+}
+
+bool QQuickControlsTestUtils::SystemEnvironment::setValue(const QString &name, const QString &value)
+{
+    return qputenv(name.toLocal8Bit(), value.toLocal8Bit());
+}
+
 QString QQuickControlsTestUtils::visualFocusFailureMessage(QQuickControl *control)
 {
     QString message;
diff --git a/src/quickcontrolstestutils/controlstestutils_p.h b/src/quickcontrolstestutils/controlstestutils_p.h
index 839c376e9e..b4ecc58b73 100644
--- a/src/quickcontrolstestutils/controlstestutils_p.h
+++ b/src/quickcontrolstestutils/controlstestutils_p.h
@@ -96,6 +96,17 @@ namespace QQuickControlsTestUtils
         Qt::ColorScheme m_colorScheme = QGuiApplication::styleHints()->colorScheme();
     };
 
+    class SystemEnvironment : public QObject
+    {
+        Q_OBJECT
+        QML_ELEMENT
+        QML_SINGLETON
+
+    public:
+        Q_INVOKABLE QString value(const QString &name);
+        Q_INVOKABLE bool setValue(const QString &name, const QString &value);
+    };
+
     [[nodiscard]] bool arePopupWindowsSupported();
 }
 
diff --git a/src/quicktemplates/qquickmonthgrid.cpp b/src/quicktemplates/qquickmonthgrid.cpp
index 07717512d0..1fc81b514f 100644
--- a/src/quicktemplates/qquickmonthgrid.cpp
+++ b/src/quicktemplates/qquickmonthgrid.cpp
@@ -83,7 +83,7 @@ public:
     void resizeItems();
 
     QQuickItem *cellAt(const QPointF &pos) const;
-    QDate dateOf(QQuickItem *cell) const;
+    QDateTime dateOf(QQuickItem *cell) const;
 
     void updatePress(const QPointF &pos);
     void clearPress(bool clicked);
@@ -95,7 +95,7 @@ public:
 
     QString title;
     QVariant source;
-    QDate pressedDate;
+    QDateTime pressedDate;
     int pressTimer;
     QQuickItem *pressedItem;
     QQuickMonthModel *model;
@@ -128,11 +128,11 @@ QQuickItem *QQuickMonthGridPrivate::cellAt(const QPointF &pos) const
     return nullptr;
 }
 
-QDate QQuickMonthGridPrivate::dateOf(QQuickItem *cell) const
+QDateTime QQuickMonthGridPrivate::dateOf(QQuickItem *cell) const
 {
     if (contentItem)
         return model->dateAt(contentItem->childItems().indexOf(cell));
-    return QDate();
+    return {};
 }
 
 void QQuickMonthGridPrivate::updatePress(const QPointF &pos)
@@ -153,7 +153,7 @@ void QQuickMonthGridPrivate::clearPress(bool clicked)
         if (clicked)
             emit q->clicked(pressedDate);
     }
-    pressedDate = QDate();
+    pressedDate = {};
     pressedItem = nullptr;
 }
 
diff --git a/src/quicktemplates/qquickmonthgrid_p.h b/src/quicktemplates/qquickmonthgrid_p.h
index e7e4421e50..87f10813c6 100644
--- a/src/quicktemplates/qquickmonthgrid_p.h
+++ b/src/quicktemplates/qquickmonthgrid_p.h
@@ -58,10 +58,10 @@ Q_SIGNALS:
     void titleChanged();
     void delegateChanged();
 
-    void pressed(QDate date);
-    void released(QDate date);
-    void clicked(QDate date);
-    void pressAndHold(QDate date);
+    void pressed(QDateTime date);
+    void released(QDateTime date);
+    void clicked(QDateTime date);
+    void pressAndHold(QDateTime date);
 
 protected:
     void componentComplete() override;
diff --git a/src/quicktemplates/qquickmonthmodel.cpp b/src/quicktemplates/qquickmonthmodel.cpp
index 60d5e6fce2..0cbdb448e1 100644
--- a/src/quicktemplates/qquickmonthmodel.cpp
+++ b/src/quicktemplates/qquickmonthmodel.cpp
@@ -4,6 +4,8 @@
 #include "qquickmonthmodel_p.h"
 
 #include <QtCore/private/qabstractitemmodel_p.h>
+#include <QtCore/qloggingcategory.h>
+#include <QtCore/qtimezone.h>
 
 namespace {
     static const int daysInAWeek = 7;
@@ -13,6 +15,8 @@ namespace {
 
 QT_BEGIN_NAMESPACE
 
+Q_STATIC_LOGGING_CATEGORY(lcMonthModel, "qt.quick.controls.monthmodel")
+
 class QQuickMonthModelPrivate : public QAbstractItemModelPrivate
 {
     Q_DECLARE_PUBLIC(QQuickMonthModel)
@@ -31,7 +35,7 @@ public:
     int year;
     QString title;
     QLocale locale;
-    QVector<QDate> dates;
+    QVector<QDateTime> dates;
     QDate today;
 };
 
@@ -42,13 +46,23 @@ bool QQuickMonthModelPrivate::populate(int m, int y, const QLocale &l, bool forc
         return false;
 
     // The actual first (1st) day of the month.
-    QDate firstDayOfMonthDate(y, m, 1);
+    const QDate firstDayOfMonthDate = QDate(y, m, 1);
+    // QDate is converted to local time when converted to a JavaScript Date,
+    // so if we stored our dates as QDates, it's possible that the date provided
+    // to delegates will be wrong in certain timezones:
+    // e.g. 00:00 UTC converted to UTC-8 is 20:00 the day before.
+    // To account for this, we pick a time of day that can't possibly result
+    // in a different day when converted to local time.
+    QDateTime firstDayOfMonthDateTime(firstDayOfMonthDate, QTime(0, 0), QTimeZone(QTimeZone::UTC));
+    const int localTimeOffsetFromUtc = QDateTime(firstDayOfMonthDate, QTime(0, 0), QTimeZone(QTimeZone::LocalTime)).offsetFromUtc();
+    const int timeOffsetAdjustment = localTimeOffsetFromUtc * -1;
+    firstDayOfMonthDateTime.setSecsSinceEpoch(firstDayOfMonthDateTime.toSecsSinceEpoch() + timeOffsetAdjustment);
     int difference = ((firstDayOfMonthDate.dayOfWeek() - l.firstDayOfWeek()) + 7) % 7;
     // The first day to display should never be the 1st of the month, as we want some days from
     // the previous month to be visible.
     if (difference == 0)
         difference += 7;
-    QDate firstDateToDisplay = firstDayOfMonthDate.addDays(-difference);
+    QDateTime firstDateToDisplay = firstDayOfMonthDateTime.addDays(-difference);
 
     today = QDate::currentDate();
     for (int i = 0; i < daysOnACalendarMonth; ++i)
@@ -56,6 +70,13 @@ bool QQuickMonthModelPrivate::populate(int m, int y, const QLocale &l, bool forc
 
     q->setTitle(l.standaloneMonthName(m) + QStringLiteral(" ") + QString::number(y));
 
+    qCDebug(lcMonthModel) << "populated model for month" << m << "year" << y << "locale" << locale
+        << "initial firstDayOfMonthDateTime" << QDateTime(firstDayOfMonthDate, QTime(0, 0), QTimeZone(QTimeZone::UTC))
+        << "localTimeOffsetFromUtc" << localTimeOffsetFromUtc / 60 / 60
+        << "timeOffsetAdjustment" << timeOffsetAdjustment / 60 / 60
+        << "firstDayOfMonthDateTime" << firstDayOfMonthDateTime
+        << "firstDayOfMonthDateTime.toLocalTime()" << firstDayOfMonthDateTime.toLocalTime();
+
     return true;
 }
 
@@ -132,13 +153,13 @@ void QQuickMonthModel::setTitle(const QString &title)
     }
 }
 
-QDate QQuickMonthModel::dateAt(int index) const
+QDateTime QQuickMonthModel::dateAt(int index) const
 {
     Q_D(const QQuickMonthModel);
     return d->dates.value(index);
 }
 
-int QQuickMonthModel::indexOf(QDate date) const
+int QQuickMonthModel::indexOf(QDateTime date) const
 {
     Q_D(const QQuickMonthModel);
     if (date < d->dates.first() || date > d->dates.last())
@@ -150,10 +171,15 @@ QVariant QQuickMonthModel::data(const QModelIndex &index, int role) const
 {
     Q_D(const QQuickMonthModel);
     if (index.isValid() && index.row() < daysOnACalendarMonth) {
-        const QDate date = d->dates.at(index.row());
+        const QDateTime dateTime = d->dates.at(index.row());
+        // As mentioned in populate, we store dates whose time is adjusted
+        // by the timezone offset, so we need to convert back to local time
+        // to get the correct date if the conversion to JavaScript's Date
+        // isn't being done for us.
+        const QDate date = d->dates.at(index.row()).toLocalTime().date();
         switch (role) {
         case DateRole:
-            return date;
+            return dateTime;
         case DayRole:
             return date.day();
         case TodayRole:
diff --git a/src/quicktemplates/qquickmonthmodel_p.h b/src/quicktemplates/qquickmonthmodel_p.h
index e629a7f8d1..b988489162 100644
--- a/src/quicktemplates/qquickmonthmodel_p.h
+++ b/src/quicktemplates/qquickmonthmodel_p.h
@@ -49,8 +49,8 @@ public:
     QString title() const;
     void setTitle(const QString &title);
 
-    Q_INVOKABLE QDate dateAt(int index) const;
-    Q_INVOKABLE int indexOf(QDate date) const;
+    Q_INVOKABLE QDateTime dateAt(int index) const;
+    Q_INVOKABLE int indexOf(QDateTime date) const;
 
     enum {
         DateRole = Qt::UserRole + 1,