Deprecate usage of qt_ntfs_permission_lookup

With the introduction of a new atomic variable the users should use the
class QNtfsPermissionCheckGuard or the helper functions
- qEnableNtfsPermissionChecks()
- qDisableNtfsPermissionChecks()
- qAreNtfsPermissionChecksEnabled()
to enable/disable permission checks instead of manually managing the
variable qt_ntfs_permission_lookup (which is a non-atomic variable and
as such prone to data races).

Also moved the variable qt_ntfs_permission_lookup to qfile.h to make it
clash with the user-side declarations the documentation suggested to
use (and it is probably also a better fit thematically anyway).

[ChangeLog][QtCore][Deprecation Notice] Deprecated the variable
qt_ntfs_permission_lookup to avoid race conditions while enabling or
disabling permission checks. It can be replaced by the RAII class
QNtfsPermissionCheckGuard or with the functions
qEnableNtfsPermissionChecks(), qDisableNtfsPermissionChecks() and
qAreNtfsPermissionChecksEnabled().

Fixes: QTBUG-105804
Change-Id: I93a563864ffb3f9945551c34004d8ca393603b25
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/io/qfile.h

@@ -27,6 +27,12 @@ namespace std {
 QT_BEGIN_NAMESPACE
 
 #ifdef Q_OS_WIN
+
+#if QT_DEPRECATED_SINCE(6,6)
+QT_DEPRECATED_VERSION_X_6_6("Use QNtfsPermissionCheckGuard RAII class instead.")
+Q_CORE_EXPORT extern int qt_ntfs_permission_lookup;      // defined in qfilesystemengine_win.cpp
+#endif
+
 Q_CORE_EXPORT bool qEnableNtfsPermissionChecks() noexcept;
 Q_CORE_EXPORT bool qDisableNtfsPermissionChecks() noexcept;
 Q_CORE_EXPORT bool qAreNtfsPermissionChecksEnabled() noexcept;

src/corelib/io/qfilesystemengine_win.cpp

@@ -381,11 +381,15 @@ constexpr QFileDevice::Permissions toSpecificPermissions(PermissionTag tag,
 } // anonymous namespace
 #endif // QT_CONFIG(fslibs)
 
-
-Q_CORE_EXPORT int qt_ntfs_permission_lookup = 0;
+#if QT_DEPRECATED_SINCE(6,6)
+int qt_ntfs_permission_lookup = 0;
+#endif
 
 static QBasicAtomicInt qt_ntfs_permission_lookup_v2 = Q_BASIC_ATOMIC_INITIALIZER(0);
 
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_DEPRECATED
+
 /*!
     \internal
 
@@ -395,7 +399,7 @@ static QBasicAtomicInt qt_ntfs_permission_lookup_v2 = Q_BASIC_ATOMIC_INITIALIZER
 bool qEnableNtfsPermissionChecks() noexcept
 {
     return qt_ntfs_permission_lookup_v2.fetchAndAddRelaxed(1)
-        + qt_ntfs_permission_lookup
+QT_IF_DEPRECATED_SINCE(6, 6, /*nothing*/, + qt_ntfs_permission_lookup)
         != 0;
 }
 
@@ -408,7 +412,7 @@ bool qEnableNtfsPermissionChecks() noexcept
 bool qDisableNtfsPermissionChecks() noexcept
 {
     return qt_ntfs_permission_lookup_v2.fetchAndSubRelaxed(1)
-        + qt_ntfs_permission_lookup
+QT_IF_DEPRECATED_SINCE(6, 6, /*nothing*/, + qt_ntfs_permission_lookup)
         == 1;
 }
 
@@ -421,8 +425,10 @@ bool qDisableNtfsPermissionChecks() noexcept
 bool qAreNtfsPermissionChecksEnabled() noexcept
 {
     return qt_ntfs_permission_lookup_v2.loadRelaxed()
-        + qt_ntfs_permission_lookup;
+QT_IF_DEPRECATED_SINCE(6, 6, /*nothing*/, + qt_ntfs_permission_lookup)
+        ;
 }
+QT_WARNING_POP
 
 /*!
     \class QNativeFilePermissions

tests/auto/corelib/io/qfile/tst_qfile.cpp

@@ -171,7 +171,9 @@ private slots:
 #ifdef Q_OS_WIN
     void permissionsNtfs_data();
     void permissionsNtfs();
+#if QT_DEPRECATED_SINCE(6,6)
     void deprecatedNtfsPermissionCheck();
+#endif
 #endif
     void setPermissions_data();
     void setPermissions();
@@ -1418,6 +1420,9 @@ void tst_QFile::permissionsNtfs()
     permissions();
 }
 
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_DEPRECATED
+#if QT_DEPRECATED_SINCE(6,6)
 void tst_QFile::deprecatedNtfsPermissionCheck()
 {
     QScopedValueRollback<int> guard(qt_ntfs_permission_lookup);
@@ -1428,6 +1433,8 @@ void tst_QFile::deprecatedNtfsPermissionCheck()
     qt_ntfs_permission_lookup--;
     QCOMPARE(qAreNtfsPermissionChecksEnabled(), false);
 }
+#endif
+QT_WARNING_POP
 
 #endif