Distinguish system locale from corresponding CLDR-derived one

Previously it was displayed as if it had been constructed from its
language, script and territory; but it is distinct from the locale
constructed in this way and may produce different results.

Report the system locale as QLocale::system() with its language,
script and country within /*...*/ following it, instead of as
QLocale(...) with these as its parameters. Add a test of the debug
output, verifying that it has the form intended.

[ChangeLog][Important Behavior Changes][QLocale] Message logging now
distinguishes the system locale from the corresponding locale -
generated from its language, script and territory - based on CLDR
data.

Pick-to: 6.9
Fixes: QTBUG-133922
Change-Id: Ic6fb137821fb7bf29d0f6446a46225cadd54b82a
Reviewed-by: Mate Barany <mate.barany@qt.io>

src/corelib/text/qlocale.cpp

@@ -5437,10 +5437,12 @@ QString QLocale::nativeCountryName() const
 QDebug operator<<(QDebug dbg, const QLocale &l)
 {
     QDebugStateSaver saver(dbg);
+    const bool isSys = l == QLocale::system();
     dbg.nospace().noquote()
-        << "QLocale(" << QLocale::languageToString(l.language())
+        << (isSys ? "QLocale::system()/* " : "QLocale(")
-        << ", " << QLocale::scriptToString(l.script())
+        << QLocale::languageToString(l.language()) << ", "
-        << ", " << QLocale::territoryToString(l.territory()) << ')';
+        << QLocale::scriptToString(l.script()) << ", "
+        << QLocale::territoryToString(l.territory()) << (isSys ? " */" : ")");
     return dbg;
 }
 #endif

tests/auto/corelib/text/qlocale/tst_qlocale.cpp

@@ -178,6 +178,7 @@ private slots:
     void unixLocaleName();
     void testNames_data();
     void testNames();
+    void debugOutput();
 private:
     QString m_decimal, m_thousand, m_sdate, m_ldate, m_time;
     QString m_sysapp;
@@ -3410,6 +3411,34 @@ void tst_QLocale::testNames()
     }
 }
 
+void tst_QLocale::debugOutput()
+{
+    // Test operator<<(QDebug, const QLocale &) works as intended:
+    QTest::failOnWarning();
+    {
+        const QLocale en(QLocale::English, QLocale::LatinScript, QLocale::UnitedStates);
+        QTest::ignoreMessage(QtMsgType::QtWarningMsg,
+                             "QLocale(English, Latin, United States)");
+        qWarning() << en;
+    }
+    {
+        const auto params = [](const QLocale &loc) {
+            return (QLocale::languageToString(loc.language())
+                    + u", " + QLocale::scriptToString(loc.script())
+                    + u", " + QLocale::territoryToString(loc.territory())).toLatin1();
+        };
+        const QLocale sys = QLocale::system();
+        QTest::ignoreMessage(QtMsgType::QtWarningMsg,
+                             ("QLocale::system()/* " + params(sys) + " */").constData());
+        // QTBUG-133922: system and its CLDR counterpart should differ.
+        qWarning() << sys;
+        const QLocale match(sys.language(), sys.script(), sys.territory());
+        QTest::ignoreMessage(QtMsgType::QtWarningMsg,
+                             ("QLocale(" + params(match) + ')').constData());
+        qWarning() << match;
+    }
+}
+
 void tst_QLocale::dayName_data()
 {
     QTest::addColumn<QString>("locale_name");