QCalendar: Delete registered calendar backends on program exit

Add code to check if the calendar registry is destroyed to all
QCalendar methods that dereference QCalendarBackend pointer.

Pick-to: 6.2
Change-Id: I9b562355e2e0579396b52968f6065c6927cc9ca8
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/corelib/time/qcalendar.h b/src/corelib/time/qcalendar.h
index aedbae94fb..3238fff7d8 100644
--- a/src/corelib/time/qcalendar.h
+++ b/src/corelib/time/qcalendar.h
@@ -153,7 +153,7 @@ public:
     explicit QCalendar(SystemId id);
 
     // QCalendar is a trivially copyable value type.
-    bool isValid() const { return d != nullptr; }
+    bool isValid() const { return d_ptr != nullptr; }
 
     // Date queries:
     int daysInMonth(int month, int year = Unspecified) const;
@@ -201,7 +201,10 @@ public:
     static QStringList availableCalendars();
 private:
     // Always supplied by QCalendarBackend and expected to be a singleton
-    const QCalendarBackend *d;
+    // Note that the calendar registry destroys all backends when it is itself
+    // destroyed. The code should check if the registry is destroyed before
+    // dereferencing this pointer.
+    const QCalendarBackend *d_ptr;
 };
 
 QT_END_NAMESPACE