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, 174 insertions, 0 deletions

diff --git a/src/corelib/time/qcalendar.h b/src/corelib/time/qcalendar.h
new file mode 100644
index 0000000000..1f85647cab
--- /dev/null
+++ b/src/corelib/time/qcalendar.h
@@ -0,0 +1,174 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
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+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
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+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QCALENDAR_H
+#define QCALENDAR_H
+
+#include <limits>
+
+#include <QtCore/qglobal.h>
+#include <QtCore/qlocale.h>
+#include <QtCore/qstring.h>
+#include <QtCore/qstringview.h>
+
+/* Suggested enum names for other calendars known to CLDR (v33.1)
+
+   Not yet implemented - see QCalendar::System - contributions welcome:
+
+   * Buddhist -- Thai Buddhist, to be specific
+   * Chinese
+   * Coptic
+   * Dangi -- Korean
+   * Ethiopic (Amete Mihret - epoch approx. 8 C.E.)
+   * EthiopicAmeteAlem (Amete Alem - epoch approx. 5493 B.C.E; data from
+     type="ethiopic-amete-alem", an alias for type="ethioaa")
+   * Hebrew
+   * Indian -- National
+   * Islamic -- Based on astronomical observations, not predictions, so hard to
+     implement. CLDR's data for type="islamic" apply, unless overridden, to the
+     other Islamic calendar variants.
+   * IslamicTabular -- tabular, astronomical epoch, CLDR type="islamic-tbla"
+   * Saudi -- Saudi Arabia, sighting; CLDR type="islamic-rgsa"
+   * UmmAlQura -- Umm al-Qura, Saudi Arabia, calculated; CLDR type="islamic-umalqura"
+   * Iso8601 -- as Gregorian, but treating ISO 8601 weeks as "months"
+   * Japanese -- Imperial calendar
+   * Minguo -- Republic of China, Taiwan; CLDR type="roc"
+
+   See:
+   http://www.unicode.org/repos/cldr/tags/latest/common/bcp47/calendar.xml
+
+   These can potentially be supported, as features, using CLDR's data; any
+   others shall need hand-crafted localization data; it would probably be best
+   to do that by contributing data for them to CLDR.
+*/
+
+QT_BEGIN_NAMESPACE
+
+class QCalendarBackend;
+class QDate;
+
+class Q_CORE_EXPORT QCalendar
+{
+    Q_GADGET
+public:
+    // (Extra parentheses to suppress bogus reading of min() as a macro.)
+    enum : int { Unspecified = (std::numeric_limits<int>::min)() };
+    struct YearMonthDay
+    {
+        YearMonthDay() = default;
+        YearMonthDay(int y, int m = 1, int d = 1) : year(y), month(m), day(d) {}
+
+        bool isValid() const
+        { return month != Unspecified && day != Unspecified; }
+        // (The first year supported by QDate has year == Unspecified.)
+
+        int year = Unspecified;
+        int month = Unspecified;
+        int day = Unspecified;
+    };
+    // Feature (\w+)calendar uses CLDR type="\1" data, except as noted in type="..." comments below
+    enum class System {
+        Gregorian, // CLDR: type = "gregory", alias = "gregorian"
+        Last = Gregorian,
+        User = -1
+    };
+    // New entries must be added to the \enum doc in qcalendar.cpp and
+    // handled in QCalendar::fromEnum()
+    Q_ENUM(System)
+
+    explicit QCalendar(); // Gregorian, optimised
+    explicit QCalendar(System system);
+    explicit QCalendar(QLatin1String name);
+    explicit QCalendar(QStringView name);
+
+    // QCalendar is a trivially copyable value type.
+    bool isValid() { return d != nullptr; }
+
+    // Date queries:
+    int daysInMonth(int month, int year = Unspecified) const;
+    int daysInYear(int year) const;
+    int monthsInYear(int year) const;
+    bool isDateValid(int year, int month, int day) const;
+
+    // Leap years:
+    bool isLeapYear(int year) const;
+
+    // Properties of the calendar:
+    bool isGregorian() const;
+    bool isLunar() const;
+    bool isLuniSolar() const;
+    bool isSolar() const;
+    bool isProleptic() const;
+    bool hasYearZero() const;
+    int maxDaysInMonth() const;
+    int minDaysInMonth() const;
+    int maxMonthsInYear() const;
+    QString name() const;
+
+    // QDate conversions:
+    QDate dateFromParts(int year, int month, int day) const;
+    QDate dateFromParts(const YearMonthDay &parts) const;
+    YearMonthDay partsFromDate(QDate date) const;
+    int dayOfWeek(QDate date) const;
+
+    // Month and week-day names (as in QLocale):
+    QString monthName(const QLocale &locale, int month, int year = Unspecified,
+                      QLocale::FormatType format=QLocale::LongFormat) const;
+    QString standaloneMonthName(const QLocale &locale, int month, int year = Unspecified,
+                                QLocale::FormatType format = QLocale::LongFormat) const;
+    QString weekDayName(const QLocale &locale, int day,
+                        QLocale::FormatType format = QLocale::LongFormat) const;
+    QString standaloneWeekDayName(const QLocale &locale, int day,
+                                  QLocale::FormatType format=QLocale::LongFormat) const;
+
+    // Formatting of date-times:
+    QString dateTimeToString(QStringView format, const QDateTime &datetime,
+                             const QDate &dateOnly, const QTime &timeOnly,
+                             const QLocale &locale) const;
+
+    // What's available ?
+    static QStringList availableCalendars();
+private:
+    // Always supplied by QCalendarBackend and expected to be a singleton
+    const QCalendarBackend *d;
+};
+
+QT_END_NAMESPACE
+
+#endif // QCALENDAR_H