Teach QWinRegistryKey to observe changes to the key

In some cases there are no explicit notification APIs for
changes to system settings, and the developer is expected
to observe changes to the registry keys directly.

For example this applies to color profile associations, as
documented in:

 https://learn.microsoft.com/en-us/windows/win32/wcs/wcs-registry-keys

Change-Id: I3507058d90b1d32b8b5256f40861126277242cd6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qwinregistry.cpp

@@ -8,6 +8,8 @@
 #include <QtCore/qdebug.h>
 #include <QtCore/qendian.h>
 #include <QtCore/qlist.h>
+#include <QtCore/qwineventnotifier.h>
+#include <QtCore/private/qsystemerror_p.h>
 
 #include <ntstatus.h>
 
@@ -20,14 +22,17 @@ QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
 
-QWinRegistryKey::QWinRegistryKey()
+QWinRegistryKey::QWinRegistryKey(QObject *parent)
+    : QObject(parent)
 {
 }
 
 // Open a key with the specified permissions (KEY_READ/KEY_WRITE).
 // "access" is to explicitly use the 32- or 64-bit branch.
 QWinRegistryKey::QWinRegistryKey(HKEY parentHandle, QStringView subKey,
-                                 REGSAM permissions, REGSAM access)
+                                 REGSAM permissions, REGSAM access,
+                                 QObject *parent)
+    : QObject(parent)
 {
     if (RegOpenKeyExW(parentHandle, reinterpret_cast<const wchar_t *>(subKey.utf16()),
                       0, permissions | access, &m_key) != ERROR_SUCCESS) {
@@ -174,6 +179,45 @@ QString QWinRegistryKey::stringValue(QStringView subKey) const
     return value<QString>(subKey).value_or(QString());
 }
 
+void QWinRegistryKey::connectNotify(const QMetaMethod &signal)
+{
+    if (signal != QMetaMethod::fromSignal(&QWinRegistryKey::valueChanged))
+        return;
+
+    if (!isValid())
+        return;
+
+    if (m_keyChangedEvent)
+        return;
+
+    m_keyChangedEvent.reset(CreateEvent(nullptr, false, false, nullptr));
+    auto *notifier = new QWinEventNotifier(m_keyChangedEvent.get(), this);
+
+    auto registerForNotification = [this] {
+        constexpr auto changeFilter =
+              REG_NOTIFY_CHANGE_NAME
+            | REG_NOTIFY_CHANGE_ATTRIBUTES
+            | REG_NOTIFY_CHANGE_LAST_SET
+            | REG_NOTIFY_CHANGE_SECURITY;
+
+        if (auto status = RegNotifyChangeKeyValue(m_key, true, changeFilter,
+            m_keyChangedEvent.get(), true); status != ERROR_SUCCESS) {
+            qWarning() << "Failed to register notification for registry key"
+                       << this << "due to" << QSystemError::windowsString(status);
+        }
+    };
+
+    QObject::connect(notifier, &QWinEventNotifier::activated, this,
+        [this, registerForNotification] {
+            emit valueChanged();
+            registerForNotification();
+        });
+
+    registerForNotification();
+
+    return QObject::connectNotify(signal);
+}
+
 #ifndef QT_NO_DEBUG_STREAM
 QDebug operator<<(QDebug debug, const QWinRegistryKey &key)
 {

src/corelib/kernel/qwinregistry_p.h

@@ -20,17 +20,21 @@
 #include <QtCore/qstringview.h>
 #include <QtCore/qt_windows.h>
 #include <QtCore/qvariant.h>
+#include <QtCore/qmetaobject.h>
+#include <QtCore/private/quniquehandle_types_p.h>
 
 QT_BEGIN_NAMESPACE
 
-class Q_CORE_EXPORT QWinRegistryKey
+class Q_CORE_EXPORT QWinRegistryKey : public QObject
 {
     Q_DISABLE_COPY(QWinRegistryKey)
+    Q_OBJECT
 
 public:
-    QWinRegistryKey();
+    QWinRegistryKey(QObject *parent = nullptr);
     explicit QWinRegistryKey(HKEY parentHandle, QStringView subKey,
-                             REGSAM permissions = KEY_READ, REGSAM access = 0);
+                             REGSAM permissions = KEY_READ, REGSAM access = 0,
+                             QObject *parent = nullptr);
     ~QWinRegistryKey();
 
     QWinRegistryKey(QWinRegistryKey &&other) noexcept
@@ -64,8 +68,15 @@ public:
     friend Q_CORE_EXPORT QDebug operator<<(QDebug dbg, const QWinRegistryKey &);
 #endif
 
+Q_SIGNALS:
+    void valueChanged();
+
+protected:
+    void connectNotify(const QMetaMethod &signal) override;
+
 private:
     HKEY m_key = nullptr;
+    QUniqueWin32NullHandle m_keyChangedEvent;
 };
 
 QT_END_NAMESPACE

tests/auto/corelib/kernel/qwinregistrykey/tst_qwinregistrykey.cpp

@@ -99,6 +99,7 @@ private Q_SLOTS:
     void cleanupTestCase();
     void qwinregistrykey();
     void name();
+    void valueChanged();
 
 private:
     bool m_available = false;
@@ -266,6 +267,28 @@ void tst_qwinregistrykey::name()
     }
 }
 
+void tst_qwinregistrykey::valueChanged()
+{
+    if (!m_available)
+        QSKIP("The test data is not ready.");
+
+    QWinRegistryKey testKey(HKEY_CURRENT_USER, TEST_KEY, KEY_READ | KEY_WRITE);
+    QVERIFY(testKey.isValid());
+
+    QVERIFY(write(testKey, u"valueThatCanChange", -1));
+
+    bool valueChanged = false;
+    QObject::connect(&testKey, &QWinRegistryKey::valueChanged, [&] {
+        valueChanged = true;
+    });
+
+    for (int i = 0; i < 10; ++i) {
+        valueChanged = false;
+        QVERIFY(write(testKey, u"valueThatCanChange", i));
+        QTRY_VERIFY(valueChanged);
+    }
+}
+
 QTEST_MAIN(tst_qwinregistrykey)
 
 #include "tst_qwinregistrykey.moc"