Add support for calendars beside Gregorian

Add QCalendarBackend as a base class for calendar implementations and
QCalendar as a facade via which to access it.

QDate's implicit implementation of the Gregorian calendar becomes
QGregorianCalendar and QDate methods now support choice of calendar.

Convert QLocale's CLDR data for month names to a locale-data component
of each supported calendar and relevant QLocale methods now support
choice of calendar. Adapt Python scripts for locale data generation to
extract month name data from CLDR (keeping on version v35.1) into the
new calendar-locale files. The locale data for the Gregorian calendar
is held in a Roman calendar base, for sharing with other calendars.

Add tests for basic uses of the new API.

[ChangeLog][QtCore][QCalendar] Added QCalendar to support diverse
calendars, supported by implementing QCalendarBackend.

[ChangeLog][QtCore][QDate] Allow choice of calendar in various
operations, with Gregorian remaining the default.

Done-with: Lars Knoll <lars.knoll@qt.io>
Done-with: Edward Welbourne <edward.welbourne@qt.io>
Fixes: QTBUG-17110
Fixes: QTBUG-950
Change-Id: I9d6278f394269a183aee8156e990cec4d5198ab8
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 397 insertions, 181 deletions

diff --git a/src/corelib/text/qlocale.cpp b/src/corelib/text/qlocale.cpp
index 5685d87c85..91e393e343 100644
--- a/src/corelib/text/qlocale.cpp
+++ b/src/corelib/text/qlocale.cpp
@@ -72,6 +72,10 @@
 #   include <time.h>
 #endif
 
+#include "private/qcalendarbackend_p.h"
+#include "private/qgregoriancalendar_p.h"
+#include "qcalendar.h"
+
 QT_BEGIN_NAMESPACE
 
 #ifndef QT_NO_SYSTEMLOCALE
@@ -341,8 +345,10 @@ QByteArray QLocalePrivate::bcp47Name(char separator) const
     return localeId.withLikelySubtagsRemoved().name(separator);
 }
 
-static const QLocaleData *findLocaleDataById(const QLocaleId &localeId)
+static const QLocaleData *findLocaleDataById(const QLocaleId &lid)
 {
+    QLocaleId localeId = lid.withLikelySubtagsAdded();
+
     const uint idx = locale_index[localeId.language_id];
 
     const QLocaleData *data = locale_data + idx;
@@ -443,6 +449,12 @@ const QLocaleData *QLocaleData::findLocaleData(QLocale::Language language, QLoca
     return locale_data + idx;
 }
 
+uint QLocaleData::findLocaleOffset(QLocale::Language language, QLocale::Script script,
+                                   QLocale::Country country)
+{
+    return findLocaleData(language, script, country) - locale_data;
+}
+
 static bool parse_locale_tag(const QString &input, int &i, QString *result,
                              const QString &separators)
 {
@@ -550,6 +562,16 @@ static const QLocaleData *findLocaleData(const QString &name)
     return QLocaleData::findLocaleData(lang, script, cntry);
 }
 
+static uint findLocaleOffset(const QString &name)
+{
+    QLocale::Language lang;
+    QLocale::Script script;
+    QLocale::Country cntry;
+    QLocalePrivate::getLangAndCountry(name, lang, script, cntry);
+
+    return QLocaleData::findLocaleOffset(lang, script, cntry);
+}
+
 QString qt_readEscapedFormatString(QStringView format, int *idx)
 {
     int &i = *idx;
@@ -617,8 +639,8 @@ static QLocale::NumberOptions default_number_options = QLocale::DefaultNumberOpt
 static const QLocaleData *const c_data = locale_data;
 static QLocalePrivate *c_private()
 {
-    static QLocalePrivate c_locale =
-        { c_data, Q_BASIC_ATOMIC_INITIALIZER(1), QLocale::OmitGroupSeparator };
+    static QLocalePrivate c_locale{
+            c_data, Q_BASIC_ATOMIC_INITIALIZER(1), 0, QLocale::OmitGroupSeparator };
     return &c_locale;
 }
 
@@ -803,9 +825,11 @@ static QLocalePrivate *localePrivateByName(const QString &name)
 {
     if (name == QLatin1String("C"))
         return c_private();
+    // TODO: Remove this version, and use offset everywhere
     const QLocaleData *data = findLocaleData(name);
-    return QLocalePrivate::create(data, data->m_language_id == QLocale::C ?
-                                      QLocale::OmitGroupSeparator : QLocale::DefaultNumberOptions);
+    return QLocalePrivate::create(data, findLocaleOffset(name),
+                                  data->m_language_id == QLocale::C
+                                  ? QLocale::OmitGroupSeparator : QLocale::DefaultNumberOptions);
 }
 
 static QLocalePrivate *findLocalePrivate(QLocale::Language language, QLocale::Script script,
@@ -814,7 +838,9 @@ static QLocalePrivate *findLocalePrivate(QLocale::Language language, QLocale::Sc
     if (language == QLocale::C)
         return c_private();
 
+    // TODO: Remove pointer, use index instead
     const QLocaleData *data = QLocaleData::findLocaleData(language, script, country);
+    const uint offset = QLocaleData::findLocaleOffset(language, script, country);
 
     QLocale::NumberOptions numberOptions = QLocale::DefaultNumberOptions;
 
@@ -823,7 +849,7 @@ static QLocalePrivate *findLocalePrivate(QLocale::Language language, QLocale::Sc
         numberOptions = default_number_options;
         data = defaultData();
     }
-    return QLocalePrivate::create(data, numberOptions);
+    return QLocalePrivate::create(data, offset, numberOptions);
 }
 
 
@@ -1957,7 +1983,7 @@ QString QLocale::toString(qulonglong i) const
 
 QString QLocale::toString(const QDate &date, const QString &format) const
 {
-    return d->dateTimeToString(format, QDateTime(), date, QTime(), this);
+    return QCalendar().dateTimeToString(format, QDateTime(), date, QTime(), *this);
 }
 #endif
 
@@ -1972,7 +1998,7 @@ QString QLocale::toString(const QDate &date, const QString &format) const
 */
 QString QLocale::toString(const QDate &date, QStringView format) const
 {
-    return d->dateTimeToString(format, QDateTime(), date, QTime(), this);
+    return QCalendar().dateTimeToString(format, QDateTime(), date, QTime(), *this);
 }
 
 /*!
@@ -2027,7 +2053,7 @@ static bool timeFormatContainsAP(QStringView format)
 */
 QString QLocale::toString(const QTime &time, const QString &format) const
 {
-    return d->dateTimeToString(format, QDateTime(), QDate(), time, this);
+    return QCalendar().dateTimeToString(format, QDateTime(), QDate(), time, *this);
 }
 #endif
 
@@ -2042,7 +2068,7 @@ QString QLocale::toString(const QTime &time, const QString &format) const
 */
 QString QLocale::toString(const QTime &time, QStringView format) const
 {
-    return d->dateTimeToString(format, QDateTime(), QDate(), time, this);
+    return QCalendar().dateTimeToString(format, QDateTime(), QDate(), time, *this);
 }
 
 #if QT_STRINGVIEW_LEVEL < 2
@@ -2058,7 +2084,7 @@ QString QLocale::toString(const QTime &time, QStringView format) const
 
 QString QLocale::toString(const QDateTime &dateTime, const QString &format) const
 {
-    return d->dateTimeToString(format, dateTime, QDate(), QTime(), this);
+    return QCalendar().dateTimeToString(format, dateTime, QDate(), QTime(), *this);
 }
 #endif
 
@@ -2073,7 +2099,58 @@ QString QLocale::toString(const QDateTime &dateTime, const QString &format) cons
 */
 QString QLocale::toString(const QDateTime &dateTime, QStringView format) const
 {
-    return d->dateTimeToString(format, dateTime, QDate(), QTime(), this);
+    return QCalendar().dateTimeToString(format, dateTime, QDate(), QTime(), *this);
+}
+
+QString QLocale::toString(const QDate &date, QStringView format, QCalendar cal) const
+{
+    return cal.dateTimeToString(format, QDateTime(), date, QTime(), *this);
+}
+
+QString QLocale::toString(const QDate &date, QLocale::FormatType format, QCalendar cal) const
+{
+    if (!date.isValid())
+        return QString();
+
+#ifndef QT_NO_SYSTEMLOCALE
+    if (cal.isGregorian() && d->m_data == systemData()) {
+        QVariant res = systemLocale()->query(format == LongFormat
+                                             ? QSystemLocale::DateToStringLong
+                                             : QSystemLocale::DateToStringShort,
+                                             date);
+        if (!res.isNull())
+            return res.toString();
+    }
+#endif
+
+    QString format_str = dateFormat(format);
+    return toString(date, format_str, cal);
+}
+
+QString QLocale::toString(const QDateTime &dateTime, QLocale::FormatType format,
+                          QCalendar cal) const
+{
+    if (!dateTime.isValid())
+        return QString();
+
+#ifndef QT_NO_SYSTEMLOCALE
+    if (cal.isGregorian() && d->m_data == systemData()) {
+        QVariant res = systemLocale()->query(format == LongFormat
+                                             ? QSystemLocale::DateTimeToStringLong
+                                             : QSystemLocale::DateTimeToStringShort,
+                                             dateTime);
+        if (!res.isNull())
+            return res.toString();
+    }
+#endif
+
+    const QString format_str = dateTimeFormat(format);
+    return toString(dateTime, format_str, cal);
+}
+
+QString QLocale::toString(const QDateTime &dateTime, QStringView format, QCalendar cal) const
+{
+    return cal.dateTimeToString(format, dateTime, QDate(), QTime(), *this);
 }
 
 /*!
@@ -2232,6 +2309,7 @@ QString QLocale::dateTimeFormat(FormatType format) const
     return dateFormat(format) + QLatin1Char(' ') + timeFormat(format);
 }
 
+#if QT_CONFIG(datestring)
 /*!
     \since 4.4
 
@@ -2243,12 +2321,19 @@ QString QLocale::dateTimeFormat(FormatType format) const
 
     \sa timeFormat(), toDate(), toDateTime(), QTime::fromString()
 */
-#if QT_CONFIG(datestring)
 QTime QLocale::toTime(const QString &string, FormatType format) const
 {
     return toTime(string, timeFormat(format));
 }
-#endif
+
+/*!
+    \since 5.14
+    \overload
+*/
+QTime QLocale::toTime(const QString &string, FormatType format, QCalendar cal) const
+{
+    return toTime(string, timeFormat(format), cal);
+}
 
 /*!
     \since 4.4
@@ -2261,12 +2346,19 @@ QTime QLocale::toTime(const QString &string, FormatType format) const
 
     \sa dateFormat(), toTime(), toDateTime(), QDate::fromString()
 */
-#if QT_CONFIG(datestring)
 QDate QLocale::toDate(const QString &string, FormatType format) const
 {
     return toDate(string, dateFormat(format));
 }
-#endif
+
+/*!
+    \since 5.14
+    \overload
+*/
+QDate QLocale::toDate(const QString &string, FormatType format, QCalendar cal) const
+{
+    return toDate(string, dateFormat(format), cal);
+}
 
 /*!
     \since 4.4
@@ -2279,13 +2371,19 @@ QDate QLocale::toDate(const QString &string, FormatType format) const
 
     \sa dateTimeFormat(), toTime(), toDate(), QDateTime::fromString()
 */
-
-#if QT_CONFIG(datestring)
 QDateTime QLocale::toDateTime(const QString &string, FormatType format) const
 {
     return toDateTime(string, dateTimeFormat(format));
 }
-#endif
+
+/*!
+    \since 5.14
+    \overload
+*/
+QDateTime QLocale::toDateTime(const QString &string, FormatType format, QCalendar cal) const
+{
+    return toDateTime(string, dateTimeFormat(format), cal);
+}
 
 /*!
     \since 4.4
@@ -2298,22 +2396,30 @@ QDateTime QLocale::toDateTime(const QString &string, FormatType format) const
 
     \sa timeFormat(), toDate(), toDateTime(), QTime::fromString()
 */
-#if QT_CONFIG(datestring)
 QTime QLocale::toTime(const QString &string, const QString &format) const
 {
+    return toTime(string, format, QCalendar());
+}
+
+/*!
+    \since 5.14
+    \overload
+*/
+QTime QLocale::toTime(const QString &string, const QString &format, QCalendar cal) const
+{
     QTime time;
 #if QT_CONFIG(datetimeparser)
-    QDateTimeParser dt(QVariant::Time, QDateTimeParser::FromString);
+    QDateTimeParser dt(QVariant::Time, QDateTimeParser::FromString, cal);
     dt.setDefaultLocale(*this);
     if (dt.parseFormat(format))
         dt.fromString(string, 0, &time);
 #else
+    Q_UNUSED(cal);
     Q_UNUSED(string);
     Q_UNUSED(format);
 #endif
     return time;
 }
-#endif
 
 /*!
     \since 4.4
@@ -2329,22 +2435,30 @@ QTime QLocale::toTime(const QString &string, const QString &format) const
 
     \sa dateFormat(), toTime(), toDateTime(), QDate::fromString()
 */
-#if QT_CONFIG(datestring)
 QDate QLocale::toDate(const QString &string, const QString &format) const
 {
+    return toDate(string, format, QCalendar());
+}
+
+/*!
+    \since 5.14
+    \overload
+*/
+QDate QLocale::toDate(const QString &string, const QString &format, QCalendar cal) const
+{
     QDate date;
 #if QT_CONFIG(datetimeparser)
-    QDateTimeParser dt(QVariant::Date, QDateTimeParser::FromString);
+    QDateTimeParser dt(QVariant::Date, QDateTimeParser::FromString, cal);
     dt.setDefaultLocale(*this);
     if (dt.parseFormat(format))
         dt.fromString(string, &date, 0);
 #else
     Q_UNUSED(string);
     Q_UNUSED(format);
+    Q_UNUSED(cal);
 #endif
     return date;
 }
-#endif
 
 /*!
     \since 4.4
@@ -2360,25 +2474,33 @@ QDate QLocale::toDate(const QString &string, const QString &format) const
 
     \sa dateTimeFormat(), toTime(), toDate(), QDateTime::fromString()
 */
-#if QT_CONFIG(datestring)
 QDateTime QLocale::toDateTime(const QString &string, const QString &format) const
 {
+    return toDateTime(string, format, QCalendar());
+}
+
+/*!
+    \since 5.14
+    \overload
+*/
+QDateTime QLocale::toDateTime(const QString &string, const QString &format, QCalendar cal) const
+{
 #if QT_CONFIG(datetimeparser)
     QTime time;
     QDate date;
 
-    QDateTimeParser dt(QVariant::DateTime, QDateTimeParser::FromString);
+    QDateTimeParser dt(QVariant::DateTime, QDateTimeParser::FromString, cal);
     dt.setDefaultLocale(*this);
     if (dt.parseFormat(format) && dt.fromString(string, &date, &time))
         return QDateTime(date, time);
 #else
     Q_UNUSED(string);
     Q_UNUSED(format);
+    Q_UNUSED(cal);
 #endif
     return QDateTime(QDate(), QTime(-1, -1, -1));
 }
-#endif
-
+#endif // datestring
 
 /*!
     \since 4.1
@@ -2623,38 +2745,7 @@ QList<QLocale::Country> QLocale::countriesForLanguage(Language language)
 */
 QString QLocale::monthName(int month, FormatType type) const
 {
-    if (month < 1 || month > 12)
-        return QString();
-
-#ifndef QT_NO_SYSTEMLOCALE
-    if (d->m_data == systemData()) {
-        QVariant res = systemLocale()->query(type == LongFormat
-                                             ? QSystemLocale::MonthNameLong
-                                             : QSystemLocale::MonthNameShort,
-                                             month);
-        if (!res.isNull())
-            return res.toString();
-    }
-#endif
-
-    quint32 idx, size;
-    switch (type) {
-    case QLocale::LongFormat:
-        idx = d->m_data->m_long_month_names_idx;
-        size = d->m_data->m_long_month_names_size;
-        break;
-    case QLocale::ShortFormat:
-        idx = d->m_data->m_short_month_names_idx;
-        size = d->m_data->m_short_month_names_size;
-        break;
-    case QLocale::NarrowFormat:
-        idx = d->m_data->m_narrow_month_names_idx;
-        size = d->m_data->m_narrow_month_names_size;
-        break;
-    default:
-        return QString();
-    }
-    return getLocaleListData(months_data + idx, size, month - 1);
+    return QCalendar().monthName(*this, month, QCalendar::Unspecified, type);
 }
 
 /*!
@@ -2670,110 +2761,221 @@ QString QLocale::monthName(int month, FormatType type) const
 */
 QString QLocale::standaloneMonthName(int month, FormatType type) const
 {
-    if (month < 1 || month > 12)
-        return QString();
+    return QCalendar().standaloneMonthName(*this, month, QCalendar::Unspecified, type);
+}
 
-#ifndef QT_NO_SYSTEMLOCALE
-    if (d->m_data == systemData()) {
-        QVariant res = systemLocale()->query(type == LongFormat
-                                             ? QSystemLocale::StandaloneMonthNameLong
-                                             : QSystemLocale::StandaloneMonthNameShort,
-                                             month);
-        if (!res.isNull())
-            return res.toString();
+/*!
+    \since 4.2
+
+    Returns the localized name of the \a day (where 1 represents
+    Monday, 2 represents Tuesday and so on), in the format specified
+    by \a type.
+
+    \sa monthName(), standaloneDayName()
+*/
+QString QLocale::dayName(int day, FormatType type) const
+{
+    return QCalendar().weekDayName(*this, day, type);
+}
+
+/*!
+    \since 4.5
+
+    Returns the localized name of the \a day (where 1 represents
+    Monday, 2 represents Tuesday and so on) that is used as a
+    standalone text, in the format specified by \a type.
+
+    If the locale information does not specify the standalone day
+    name then return value is the same as in dayName().
+
+    \sa dayName(), standaloneMonthName()
+*/
+QString QLocale::standaloneDayName(int day, FormatType type) const
+{
+    return QCalendar().standaloneWeekDayName(*this, day, type);
+}
+
+// Calendar look-up of month and day names:
+
+/*!
+  \internal
+ */
+
+static QString rawMonthName(const QCalendarLocale &localeData,
+                            const ushort *monthsData, int month,
+                            QLocale::FormatType type)
+{
+    quint32 idx, size;
+    switch (type) {
+    case QLocale::LongFormat:
+       idx = localeData.m_long.index;
+       size = localeData.m_long.size;
+       break;
+    case QLocale::ShortFormat:
+       idx = localeData.m_short.index;
+       size = localeData.m_short.size;
+       break;
+    case QLocale::NarrowFormat:
+       idx = localeData.m_narrow.index;
+       size = localeData.m_narrow.size;
+       break;
+    default:
+       return QString();
     }
-#endif
+    return getLocaleListData(monthsData + idx, size, month - 1);
+}
+
+/*!
+  \internal
+ */
 
+static QString rawStandaloneMonthName(const QCalendarLocale &localeData,
+                                      const ushort *monthsData, int month,
+                                      QLocale::FormatType type)
+{
     quint32 idx, size;
     switch (type) {
     case QLocale::LongFormat:
-        idx = d->m_data->m_standalone_long_month_names_idx;
-        size = d->m_data->m_standalone_long_month_names_size;
+        idx = localeData.m_standalone_long.index;
+        size = localeData.m_standalone_long.size;
         break;
     case QLocale::ShortFormat:
-        idx = d->m_data->m_standalone_short_month_names_idx;
-        size = d->m_data->m_standalone_short_month_names_size;
+        idx = localeData.m_standalone_short.index;
+        size = localeData.m_standalone_short.size;
         break;
     case QLocale::NarrowFormat:
-        idx = d->m_data->m_standalone_narrow_month_names_idx;
-        size = d->m_data->m_standalone_narrow_month_names_size;
+        idx = localeData.m_standalone_narrow.index;
+        size = localeData.m_standalone_narrow.size;
         break;
     default:
         return QString();
     }
-    QString name = getLocaleListData(months_data + idx, size, month - 1);
-    if (name.isEmpty())
-        return monthName(month, type);
-    return name;
+    QString name = getLocaleListData(monthsData + idx, size, month - 1);
+    return name.isEmpty() ? rawMonthName(localeData, monthsData, month, type) : name;
 }
 
 /*!
-    \since 4.2
-
-    Returns the localized name of the \a day (where 1 represents
-    Monday, 2 represents Tuesday and so on), in the format specified
-    by \a type.
+  \internal
+ */
 
-    \sa monthName(), standaloneDayName()
-*/
-QString QLocale::dayName(int day, FormatType type) const
+static QString rawWeekDayName(const QLocaleData *data, const int day,
+                              QLocale::FormatType type)
 {
-    if (day < 1 || day > 7)
+    quint32 idx, size;
+    switch (type) {
+    case QLocale::LongFormat:
+        idx = data->m_long_day_names_idx;
+        size = data->m_long_day_names_size;
+        break;
+    case QLocale::ShortFormat:
+        idx = data->m_short_day_names_idx;
+        size = data->m_short_day_names_size;
+        break;
+    case QLocale::NarrowFormat:
+        idx = data->m_narrow_day_names_idx;
+        size = data->m_narrow_day_names_size;
+        break;
+    default:
         return QString();
-
-#ifndef QT_NO_SYSTEMLOCALE
-    if (d->m_data == systemData()) {
-        QVariant res = systemLocale()->query(type == LongFormat
-                                             ? QSystemLocale::DayNameLong
-                                             : QSystemLocale::DayNameShort,
-                                             day);
-        if (!res.isNull())
-            return res.toString();
     }
-#endif
-    if (day == 7)
-        day = 0;
+    return getLocaleListData(days_data + idx, size, day == 7 ? 0 : day);
+}
 
+/*!
+  \internal
+ */
+
+static QString rawStandaloneWeekDayName(const QLocaleData *data, const int day,
+                                        QLocale::FormatType type)
+{
     quint32 idx, size;
     switch (type) {
     case QLocale::LongFormat:
-        idx = d->m_data->m_long_day_names_idx;
-        size = d->m_data->m_long_day_names_size;
+        idx = data->m_standalone_long_day_names_idx;
+        size = data->m_standalone_long_day_names_size;
         break;
     case QLocale::ShortFormat:
-        idx = d->m_data->m_short_day_names_idx;
-        size = d->m_data->m_short_day_names_size;
+        idx = data->m_standalone_short_day_names_idx;
+        size = data->m_standalone_short_day_names_size;
         break;
     case QLocale::NarrowFormat:
-        idx = d->m_data->m_narrow_day_names_idx;
-        size = d->m_data->m_narrow_day_names_size;
+        idx = data->m_standalone_narrow_day_names_idx;
+        size = data->m_standalone_narrow_day_names_size;
         break;
     default:
         return QString();
     }
-    return getLocaleListData(days_data + idx, size, day);
+    QString name = getLocaleListData(days_data + idx, size, day == 7 ? 0 : day);
+    if (name.isEmpty())
+        return rawWeekDayName(data, day, type);
+    return name;
 }
 
-/*!
-    \since 4.5
+// Refugees from qcalendar.cpp that need functions above:
 
-    Returns the localized name of the \a day (where 1 represents
-    Monday, 2 represents Tuesday and so on) that is used as a
-    standalone text, in the format specified by \a type.
+QString QCalendarBackend::monthName(const QLocale &locale, int month, int,
+                                    QLocale::FormatType format) const
+{
+    Q_ASSERT(month >= 1 && month <= maxMonthsInYear());
+    return rawMonthName(localeMonthIndexData()[locale.d->m_data_offset],
+                        localeMonthData(), month, format);
+}
 
-    If the locale information does not specify the standalone day
-    name then return value is the same as in dayName().
+QString QGregorianCalendar::monthName(const QLocale &locale, int month, int year,
+                                      QLocale::FormatType format) const
+{
+#ifndef QT_NO_SYSTEMLOCALE
+    if (locale.d->m_data == systemData()) {
+        Q_ASSERT(month >= 1 && month <= 12);
+        QVariant res = systemLocale()->query(format == QLocale::LongFormat
+                                             ? QSystemLocale::MonthNameLong
+                                             : QSystemLocale::MonthNameShort,
+                                             month);
+        if (!res.isNull())
+            return res.toString();
+    }
+#endif
 
-    \sa dayName(), standaloneMonthName()
-*/
-QString QLocale::standaloneDayName(int day, FormatType type) const
+    return QCalendarBackend::monthName(locale, month, year, format);
+}
+
+QString QCalendarBackend::standaloneMonthName(const QLocale &locale, int month, int,
+                                              QLocale::FormatType format) const
+{
+    Q_ASSERT(month >= 1 && month <= maxMonthsInYear());
+    return rawStandaloneMonthName(localeMonthIndexData()[locale.d->m_data_offset],
+                                  localeMonthData(), month, format);
+}
+
+QString QGregorianCalendar::standaloneMonthName(const QLocale &locale, int month, int year,
+                                                QLocale::FormatType format) const
+{
+#ifndef QT_NO_SYSTEMLOCALE
+    if (locale.d->m_data == systemData()) {
+        Q_ASSERT(month >= 1 && month <= 12);
+        QVariant res = systemLocale()->query(format == QLocale::LongFormat
+                                             ? QSystemLocale::StandaloneMonthNameLong
+                                             : QSystemLocale::StandaloneMonthNameShort,
+                                             month);
+        if (!res.isNull())
+            return res.toString();
+    }
+#endif
+
+    return QCalendarBackend::standaloneMonthName(locale, month, year, format);
+}
+
+// Most calendars share the common week-day naming, modulo locale.
+// Calendars that don't must override these methods.
+QString QCalendarBackend::weekDayName(const QLocale &locale, int day,
+                                      QLocale::FormatType format) const
 {
     if (day < 1 || day > 7)
         return QString();
 
 #ifndef QT_NO_SYSTEMLOCALE
-    if (d->m_data == systemData()) {
-        QVariant res = systemLocale()->query(type == LongFormat
+    if (locale.d->m_data == systemData()) {
+        QVariant res = systemLocale()->query(format == QLocale::LongFormat
                                              ? QSystemLocale::DayNameLong
                                              : QSystemLocale::DayNameShort,
                                              day);
@@ -2781,32 +2983,32 @@ QString QLocale::standaloneDayName(int day, FormatType type) const
             return res.toString();
     }
 #endif
-    if (day == 7)
-        day = 0;
 
-    quint32 idx, size;
-    switch (type) {
-    case QLocale::LongFormat:
-        idx = d->m_data->m_standalone_long_day_names_idx;
-        size = d->m_data->m_standalone_long_day_names_size;
-        break;
-    case QLocale::ShortFormat:
-        idx = d->m_data->m_standalone_short_day_names_idx;
-        size = d->m_data->m_standalone_short_day_names_size;
-        break;
-    case QLocale::NarrowFormat:
-        idx = d->m_data->m_standalone_narrow_day_names_idx;
-        size = d->m_data->m_standalone_narrow_day_names_size;
-        break;
-    default:
+    return rawWeekDayName(locale.d->m_data, day, format);
+}
+
+QString QCalendarBackend::standaloneWeekDayName(const QLocale &locale, int day,
+                                                QLocale::FormatType format) const
+{
+    if (day < 1 || day > 7)
         return QString();
+
+#ifndef QT_NO_SYSTEMLOCALE
+    if (locale.d->m_data == systemData()) {
+        QVariant res = systemLocale()->query(format == QLocale::LongFormat
+                                             ? QSystemLocale::DayNameLong
+                                             : QSystemLocale::DayNameShort,
+                                             day);
+        if (!res.isNull())
+            return res.toString();
     }
-    QString name = getLocaleListData(days_data + idx, size, day);
-    if (name.isEmpty())
-        return dayName(day == 0 ? 7 : day, type);
-    return name;
+#endif
+
+    return rawStandaloneWeekDayName(locale.d->m_data, day, format);
 }
 
+// End of this block of qcalendar.cpp refugees.  (One more follows.)
+
 /*!
     \since 4.8
 
@@ -3010,10 +3212,11 @@ QString QLocale::pmText() const
     return getLocaleData(pm_data + d->m_data->m_pm_idx, d->m_data->m_pm_size);
 }
 
+// Another intrusion from QCalendar, using some of the tools above:
 
-QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &datetime,
-                                         const QDate &dateOnly, const QTime &timeOnly,
-                                         const QLocale *q) const
+QString QCalendarBackend::dateTimeToString(QStringView format, const QDateTime &datetime,
+                                           const QDate &dateOnly, const QTime &timeOnly,
+                                           const QLocale &locale) const
 {
     QDate date;
     QTime time;
@@ -3035,6 +3238,15 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
     }
 
     QString result;
+    int year = 0, month = 0, day = 0;
+    if (formatDate) {
+        const auto parts = julianDayToDate(date.toJulianDay());
+        if (!parts.isValid())
+            return QString();
+        year = parts.year;
+        month = parts.month;
+        day = parts.day;
+    }
 
     int i = 0;
     while (i < format.size()) {
@@ -3057,15 +3269,14 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
 
                 switch (repeat) {
                 case 4: {
-                    const int yr = date.year();
-                    const int len = (yr < 0) ? 5 : 4;
-                    result.append(m_data->longLongToString(yr, -1, 10, len,
-                                                           QLocaleData::ZeroPadded));
+                    const int len = (year < 0) ? 5 : 4;
+                    result.append(locale.d->m_data->longLongToString(year, -1, 10, len,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 }
                 case 2:
-                    result.append(m_data->longLongToString(date.year() % 100, -1, 10, 2,
-                                                   QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(year % 100, -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 default:
                     repeat = 1;
@@ -3079,17 +3290,17 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
                 repeat = qMin(repeat, 4);
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(date.month()));
+                    result.append(locale.d->m_data->longLongToString(month));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(date.month(), -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(month, -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 case 3:
-                    result.append(q->monthName(date.month(), QLocale::ShortFormat));
+                    result.append(monthName(locale, month, year, QLocale::ShortFormat));
                     break;
                 case 4:
-                    result.append(q->monthName(date.month(), QLocale::LongFormat));
+                    result.append(monthName(locale, month, year, QLocale::LongFormat));
                     break;
                 }
                 break;
@@ -3099,17 +3310,19 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
                 repeat = qMin(repeat, 4);
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(date.day()));
+                    result.append(locale.d->m_data->longLongToString(day));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(date.day(), -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(day, -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 case 3:
-                    result.append(q->dayName(date.dayOfWeek(), QLocale::ShortFormat));
+                    result.append(locale.dayName(
+                                      dayOfWeek(date.toJulianDay()), QLocale::ShortFormat));
                     break;
                 case 4:
-                    result.append(q->dayName(date.dayOfWeek(), QLocale::LongFormat));
+                    result.append(locale.dayName(
+                                      dayOfWeek(date.toJulianDay()), QLocale::LongFormat));
                     break;
                 }
                 break;
@@ -3133,11 +3346,11 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
 
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(hour));
+                    result.append(locale.d->m_data->longLongToString(hour));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(hour, -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(hour, -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 }
                 break;
@@ -3147,11 +3360,11 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
                 repeat = qMin(repeat, 2);
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(time.hour()));
+                    result.append(locale.d->m_data->longLongToString(time.hour()));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(time.hour(), -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(time.hour(), -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 }
                 break;
@@ -3161,11 +3374,11 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
                 repeat = qMin(repeat, 2);
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(time.minute()));
+                    result.append(locale.d->m_data->longLongToString(time.minute()));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(time.minute(), -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(time.minute(), -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 }
                 break;
@@ -3175,11 +3388,11 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
                 repeat = qMin(repeat, 2);
                 switch (repeat) {
                 case 1:
-                    result.append(m_data->longLongToString(time.second()));
+                    result.append(locale.d->m_data->longLongToString(time.second()));
                     break;
                 case 2:
-                    result.append(m_data->longLongToString(time.second(), -1, 10, 2,
-                                                           QLocaleData::ZeroPadded));
+                    result.append(locale.d->m_data->longLongToString(time.second(), -1, 10, 2,
+                                                                     QLocaleData::ZeroPadded));
                     break;
                 }
                 break;
@@ -3187,13 +3400,15 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
             case 'a':
                 used = true;
                 repeat = format.mid(i + 1).startsWith(QLatin1Char('p')) ? 2 : 1;
-                result.append(time.hour() < 12 ? q->amText().toLower() : q->pmText().toLower());
+                result.append(time.hour() < 12 ? locale.amText().toLower()
+                                               : locale.pmText().toLower());
                 break;
 
             case 'A':
                 used = true;
                 repeat = format.mid(i + 1).startsWith(QLatin1Char('P')) ? 2 : 1;
-                result.append(time.hour() < 12 ? q->amText().toUpper() : q->pmText().toUpper());
+                result.append(time.hour() < 12 ? locale.amText().toUpper()
+                                                : locale.pmText().toUpper());
                 break;
 
             case 'z':
@@ -3202,15 +3417,14 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
 
                 // note: the millisecond component is treated like the decimal part of the seconds
                 // so ms == 2 is always printed as "002", but ms == 200 can be either "2" or "200"
-                result.append(m_data->longLongToString(time.msec(), -1, 10, 3,
-                                                       QLocaleData::ZeroPadded));
+                result.append(locale.d->m_data->longLongToString(time.msec(), -1, 10, 3,
+                                                                 QLocaleData::ZeroPadded));
                 if (repeat == 1) {
-                    if (result.endsWith(zero()))
+                    if (result.endsWith(locale.d->zero()))
                         result.chop(1);
-                    if (result.endsWith(zero()))
+                    if (result.endsWith(locale.d->zero()))
                         result.chop(1);
                 }
-
                 break;
 
             case 't':
@@ -3233,6 +3447,8 @@ QString QLocalePrivate::dateTimeToString(QStringView format, const QDateTime &da
     return result;
 }
 
+// End of QCalendar intrustions
+
 QString QLocaleData::doubleToString(double d, int precision, DoubleForm form,
                                     int width, unsigned flags) const
 {