QString::localeAwareCompare: adapt to QLocale::setDefault() being called

Because we're using a thread-specific global static, we need to recreate
the QCollator type every time setDefault() is called. Since one is
stored per-thread, we simply increment a generational counter and check
that the next time that QString::localeAwareCompare is called in each
thread.

The issue was introduced on f6425da424
(5.12) even though we were supposed to be using QCollator since commit
5279134935 (5.3).

Fixes: QTBUG-95050
Pick-to: 6.2
Change-Id: I7e0b82c2d2fe464082d8fffd1696a8c9f74e5b30
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/text/qlocale.cpp

@@ -780,9 +780,9 @@ QDataStream &operator>>(QDataStream &ds, QLocale &l)
 }
 #endif // QT_NO_DATASTREAM
 
-
 static const int locale_data_size = sizeof(locale_data)/sizeof(QLocaleData) - 1;
 
+QBasicAtomicInt QLocalePrivate::s_generation = Q_BASIC_ATOMIC_INITIALIZER(0);
 Q_GLOBAL_STATIC_WITH_ARGS(QSharedDataPointer<QLocalePrivate>, defaultLocalePrivate,
                           (new QLocalePrivate(defaultData(), defaultIndex())))
 
@@ -1206,6 +1206,7 @@ void QLocale::setDefault(const QLocale &locale)
 
     // update the cached private
     *defaultLocalePrivate = locale.d;
+    QLocalePrivate::s_generation.fetchAndAddRelaxed(1);
 }
 
 /*!

src/corelib/text/qlocale_p.h

@@ -424,6 +424,8 @@ public:
     QBasicAtomicInt ref;
     const uint m_index;
     QLocale::NumberOptions m_numberOptions;
+
+    static QBasicAtomicInt s_generation;
 };
 
 #ifndef QT_NO_SYSTEMLOCALE

src/corelib/text/qstring.cpp

@@ -6141,7 +6141,25 @@ int QString::localeAwareCompare(const QString &other) const
 }
 
 #if QT_CONFIG(icu)
-Q_GLOBAL_STATIC(QThreadStorage<QCollator>, defaultCollator)
+namespace {
+class GenerationalCollator
+{
+    QCollator theCollator;
+    int generation = QLocalePrivate::s_generation.loadRelaxed();
+public:
+    QCollator &collator()
+    {
+        int currentGeneration = QLocalePrivate::s_generation.loadRelaxed();
+        if (Q_UNLIKELY(generation != currentGeneration)) {
+            // reinitialize the collator
+            generation = currentGeneration;
+            theCollator = QCollator();
+        }
+        return theCollator;
+    }
+};
+}
+Q_GLOBAL_STATIC(QThreadStorage<GenerationalCollator>, defaultCollator)
 #endif
 
 /*!
@@ -6163,8 +6181,8 @@ int QString::localeAwareCompare_helper(const QChar *data1, qsizetype length1,
 
 #if QT_CONFIG(icu)
     if (!defaultCollator()->hasLocalData())
-        defaultCollator()->setLocalData(QCollator());
-    return defaultCollator()->localData().compare(data1, length1, data2, length2);
+        defaultCollator()->setLocalData(GenerationalCollator());
+    return defaultCollator()->localData().collator().compare(data1, length1, data2, length2);
 #else
     const QString lhs = QString::fromRawData(data1, length1).normalized(QString::NormalizationForm_C);
     const QString rhs = QString::fromRawData(data2, length2).normalized(QString::NormalizationForm_C);