qlocale_win: Fix non-standalone month names

We have previously been using the standalong (nominative) month names
both when asked for that and when asked for the plain (genitive) month
name, probably because there was no LCTYPE value for the
latter. However, MS's docs for the standalone values do contain a
comment telling us how to get the genitive names.

Rename the old monthName() to standaloneMonthName() and add a
monthName() that calls GetDateFormat() suitably, as described by the
MS doc.

Fixes: QTBUG-92018
Fixes: QTBUG-86279
Change-Id: I27f63198c3a15b792683f476d2019078b0860f99
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 38ec2c830b849ad44ca7e16bd9c4722e0bcdb61f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 40 insertions, 6 deletions

diff --git a/src/corelib/text/qlocale_win.cpp b/src/corelib/text/qlocale_win.cpp
index 24ddd37b65..52ad128b9c 100644
--- a/src/corelib/text/qlocale_win.cpp
+++ b/src/corelib/text/qlocale_win.cpp
@@ -94,6 +94,7 @@ struct QSystemLocalePrivate
     QVariant timeFormat(QLocale::FormatType);
     QVariant dateTimeFormat(QLocale::FormatType);
     QVariant dayName(int, QLocale::FormatType);
+    QVariant standaloneMonthName(int, QLocale::FormatType);
     QVariant monthName(int, QLocale::FormatType);
     QVariant toString(QDate, QLocale::FormatType);
     QVariant toString(QTime, QLocale::FormatType);
@@ -366,7 +367,7 @@ QVariant QSystemLocalePrivate::dayName(int day, QLocale::FormatType type)
     return getLocaleInfo(short_day_map[day]);
 }
 
-QVariant QSystemLocalePrivate::monthName(int month, QLocale::FormatType type)
+QVariant QSystemLocalePrivate::standaloneMonthName(int month, QLocale::FormatType type)
 {
     static const LCTYPE short_month_map[]
         = { LOCALE_SABBREVMONTHNAME1, LOCALE_SABBREVMONTHNAME2, LOCALE_SABBREVMONTHNAME3,
@@ -389,6 +390,30 @@ QVariant QSystemLocalePrivate::monthName(int month, QLocale::FormatType type)
     return getLocaleInfo(lctype);
 }
 
+QVariant QSystemLocalePrivate::monthName(int month, QLocale::FormatType type)
+{
+    SYSTEMTIME st = {};
+    st.wYear = 2001;
+    st.wMonth = month;
+    st.wDay = 10;
+
+    const DWORD flags{}; // Must be clear when passing a format string.
+    // MS's docs for the LOCALE_SMONTHNAME* say to include the day in a format.
+    // Educated guess: this works for the LOCALE_SABBREVMONTHNAME*, too, in so
+    // far as the abbreviated plain name might differ from abbreviated
+    // standalone one.
+    const wchar_t *const format = type == QLocale::LongFormat ? L"ddMMMM" : L"ddMMM";
+    wchar_t buf[255];
+    if (getDateFormat(flags, &st, format, buf, 255) > 2) {
+        // Elide the two digits of day number
+        QString text = QString::fromWCharArray(buf + 2);
+        if (substitution() == SAlways)
+            text = substituteDigits(std::move(text));
+        return text;
+    }
+    return {};
+}
+
 QVariant QSystemLocalePrivate::toString(QDate date, QLocale::FormatType type)
 {
     SYSTEMTIME st = {};
@@ -734,11 +759,13 @@ QVariant QSystemLocale::query(QueryType type, QVariant in) const
     case DayNameShort:
         return d->dayName(in.toInt(), QLocale::ShortFormat);
     case MonthNameLong:
-    case StandaloneMonthNameLong:
         return d->monthName(in.toInt(), QLocale::LongFormat);
+    case StandaloneMonthNameLong:
+        return d->standaloneMonthName(in.toInt(), QLocale::LongFormat);
     case MonthNameShort:
-    case StandaloneMonthNameShort:
         return d->monthName(in.toInt(), QLocale::ShortFormat);
+    case StandaloneMonthNameShort:
+        return d->standaloneMonthName(in.toInt(), QLocale::ShortFormat);
     case DateToStringShort:
         return d->toString(in.toDate(), QLocale::ShortFormat);
     case DateToStringLong:
diff --git a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
index 32b47dbe01..85f454810c 100644
--- a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
@@ -2570,6 +2570,10 @@ void tst_QLocale::dateFormat()
 
     const QLocale ir("ga_IE");
     QCOMPARE(ir.dateFormat(QLocale::ShortFormat), QLatin1String("dd/MM/yyyy"));
+
+    const auto sys = QLocale::system(); // QTBUG-92018, ru_RU on MS
+    const QDate date(2021, 3, 17);
+    QCOMPARE(sys.toString(date, sys.dateFormat(QLocale::LongFormat)), sys.toString(date));
 }
 
 void tst_QLocale::timeFormat()
@@ -2628,18 +2632,21 @@ void tst_QLocale::monthName()
     // 'de' locale doesn't have narrow month name
     QCOMPARE(de.monthName(12, QLocale::NarrowFormat), QLatin1String("D"));
 
-    QLocale ru("ru_RU");
+    const QLocale ru("ru_RU");
     QCOMPARE(ru.monthName(1, QLocale::LongFormat),
              QString::fromUtf8("\321\217\320\275\320\262\320\260\321\200\321\217"));
     QCOMPARE(ru.monthName(1, QLocale::ShortFormat),
              QString::fromUtf8("\321\217\320\275\320\262\56"));
     QCOMPARE(ru.monthName(1, QLocale::NarrowFormat), QString::fromUtf8("\320\257"));
+    const auto sys = QLocale::system();
+    if (sys.language() == QLocale::Russian) // QTBUG-92018
+        QVERIFY(sys.monthName(3) != sys.standaloneMonthName(3));
 
-    QLocale ir("ga_IE");
+    const QLocale ir("ga_IE");
     QCOMPARE(ir.monthName(1, QLocale::ShortFormat), QLatin1String("Ean"));
     QCOMPARE(ir.monthName(12, QLocale::ShortFormat), QLatin1String("Noll"));
 
-    QLocale cz("cs_CZ");
+    const QLocale cz("cs_CZ");
     QCOMPARE(cz.monthName(1, QLocale::ShortFormat), QLatin1String("led"));
     QCOMPARE(cz.monthName(12, QLocale::ShortFormat), QLatin1String("pro"));
 }