4 files changed, 84 insertions, 53 deletions
diff --git a/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp b/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp
index e2e46a7b215..55e36b4587a 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp
+++ b/src/plugins/platforms/windows/qwindowswindowclassdescription.cpp
@@ -11,6 +11,55 @@ QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
 
+QString QWindowsWindowClassDescription::classNameSuffix(Qt::WindowFlags type, unsigned int style, bool hasIcon)
+{
+    QString suffix;
+
+    switch (type) {
+        case Qt::Popup:
+            suffix += "Popup"_L1;
+            break;
+        case Qt::Tool:
+            suffix += "Tool"_L1;
+            break;
+        case Qt::ToolTip:
+            suffix += "ToolTip"_L1;
+            break;
+        default:
+            break;
+    }
+
+    if (style & CS_DROPSHADOW)
+        suffix += "DropShadow"_L1;
+    if (style & CS_SAVEBITS)
+        suffix += "SaveBits"_L1;
+    if (style & CS_OWNDC)
+        suffix += "OwnDC"_L1;
+    if (hasIcon)
+        suffix += "Icon"_L1;
+
+    return suffix;
+}
+
+bool QWindowsWindowClassDescription::computeHasIcon(Qt::WindowFlags flags, Qt::WindowFlags type)
+{
+    bool hasIcon = true;
+
+    switch (type) {
+        case Qt::Tool:
+        case Qt::ToolTip:
+        case Qt::Popup:
+            hasIcon = false;
+            break;
+        case Qt::Dialog:
+            if (!(flags & Qt::WindowSystemMenuHint))
+                hasIcon = false; // QTBUG-2027, dialogs without system menu.
+            break;
+    }
+
+    return hasIcon;
+}
+
 QWindowsWindowClassDescription QWindowsWindowClassDescription::fromName(QString name, WNDPROC procedure)
 {
     return { std::move(name), procedure };
@@ -27,7 +76,7 @@ QWindowsWindowClassDescription QWindowsWindowClassDescription::fromWindow(const
     const Qt::WindowFlags type = flags & Qt::WindowType_Mask;
     // Determine style and icon.
     description.style = CS_DBLCLKS;
-    description.hasIcon = true;
+    description.hasIcon = computeHasIcon(flags, type);
     // The following will not set CS_OWNDC for any widget window, even if it contains a
     // QOpenGLWidget or QQuickWidget later on. That cannot be detected at this stage.
     if (window->surfaceType() == QSurface::OpenGLSurface || (flags & Qt::MSWindowsOwnDC))
@@ -41,36 +90,9 @@ QWindowsWindowClassDescription QWindowsWindowClassDescription::fromWindow(const
         case Qt::ToolTip:
         case Qt::Popup:
             description.style |= CS_SAVEBITS; // Save/restore background
-            description.hasIcon = false;
-            break;
-        case Qt::Dialog:
-            if (!(flags & Qt::WindowSystemMenuHint))
-                description.hasIcon = false; // QTBUG-2027, dialogs without system menu.
-            break;
-    }
-    // Create a unique name for the flag combination
-    description.name = "QWindow"_L1;
-    switch (type) {
-        case Qt::Tool:
-            description.name += "Tool"_L1;
-            break;
-        case Qt::ToolTip:
-            description.name += "ToolTip"_L1;
-            break;
-        case Qt::Popup:
-            description.name += "Popup"_L1;
-            break;
-        default:
             break;
     }
-    if (description.style & CS_DROPSHADOW)
-        description.name += "DropShadow"_L1;
-    if (description.style & CS_SAVEBITS)
-        description.name += "SaveBits"_L1;
-    if (description.style & CS_OWNDC)
-        description.name += "OwnDC"_L1;
-    if (description.hasIcon)
-        description.name += "Icon"_L1;
+    description.name = "QWindow"_L1 + classNameSuffix(type, description.style, description.hasIcon);
 
     return description;
 }
diff --git a/src/plugins/platforms/windows/qwindowswindowclassdescription.h b/src/plugins/platforms/windows/qwindowswindowclassdescription.h
index 3acca65b8a2..78d99b4c525 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassdescription.h
+++ b/src/plugins/platforms/windows/qwindowswindowclassdescription.h
@@ -25,6 +25,9 @@ struct QWindowsWindowClassDescription
     bool shouldAddPrefix{ true };
 
 private:
+    static QString classNameSuffix(Qt::WindowFlags type, unsigned int style, bool hasIcon);
+    static bool computeHasIcon(Qt::WindowFlags flags, Qt::WindowFlags type);
+
     friend QDebug operator<<(QDebug dbg, const QWindowsWindowClassDescription &description);
 };
 
diff --git a/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp b/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
index 9c9ffcfeefa..8bf2fb887f1 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
+++ b/src/plugins/platforms/windows/qwindowswindowclassregistry.cpp
@@ -18,8 +18,8 @@ Q_LOGGING_CATEGORY(lcQpaWindowClass, "qt.qpa.windowclass")
 
 QWindowsWindowClassRegistry *QWindowsWindowClassRegistry::m_instance = nullptr;
 
-QWindowsWindowClassRegistry::QWindowsWindowClassRegistry(WNDPROC proc)
-    : m_proc(proc)
+QWindowsWindowClassRegistry::QWindowsWindowClassRegistry(WNDPROC defaultProcedure)
+    : m_defaultProcedure(defaultProcedure)
 {
     m_instance = this;
 }
@@ -69,25 +69,19 @@ QString QWindowsWindowClassRegistry::registerWindowClass(const QWindowsWindowCla
     // add a UUID. The check needs to be performed for each name
     // in case new message windows are added (QTBUG-81347).
     // Note: GetClassInfo() returns != 0 when a class exists.
-    const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
-    WNDCLASS wcinfo;
-    const bool classExists = GetClassInfo(appInstance, reinterpret_cast<LPCWSTR>(className.utf16()), &wcinfo) != FALSE
-        && wcinfo.lpfnWndProc != description.procedure;
-
-    if (classExists)
+    if (shouldDecorateWindowClassName(description))
         className += QUuid::createUuid().toString();
 
     if (m_registeredWindowClassNames.contains(className))        // already registered in our list
         return className;
 
-    WNDCLASSEX wc;
+    const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
+
+    WNDCLASSEX wc{};
     wc.cbSize = sizeof(WNDCLASSEX);
     wc.style = description.style;
     wc.lpfnWndProc = description.procedure;
-    wc.cbClsExtra = 0;
-    wc.cbWndExtra = 0;
     wc.hInstance = appInstance;
-    wc.hCursor = nullptr;
     wc.hbrBackground = description.brush;
     if (description.hasIcon) {
         wc.hIcon = static_cast<HICON>(LoadImage(appInstance, L"IDI_ICON1", IMAGE_ICON, 0, 0, LR_DEFAULTSIZE));
@@ -98,20 +92,14 @@ QString QWindowsWindowClassRegistry::registerWindowClass(const QWindowsWindowCla
         }
         else {
             wc.hIcon = static_cast<HICON>(LoadImage(nullptr, IDI_APPLICATION, IMAGE_ICON, 0, 0, LR_DEFAULTSIZE | LR_SHARED));
-            wc.hIconSm = nullptr;
         }
     }
-    else {
-        wc.hIcon = nullptr;
-        wc.hIconSm = nullptr;
-    }
 
-    wc.lpszMenuName = nullptr;
     wc.lpszClassName = reinterpret_cast<LPCWSTR>(className.utf16());
     ATOM atom = RegisterClassEx(&wc);
     if (!atom)
-        qErrnoWarning("QApplication::regClass: Registering window class '%s' failed.",
-            qPrintable(className));
+        qCWarning(lcQpaWindowClass) << "Failed to register window class" << className
+            << "(" << qt_error_string(-1) << ")";
 
     m_registeredWindowClassNames.insert(className);
 
@@ -122,7 +110,7 @@ QString QWindowsWindowClassRegistry::registerWindowClass(const QWindowsWindowCla
 
 QString QWindowsWindowClassRegistry::registerWindowClass(const QWindow *window)
 {
-    return registerWindowClass(QWindowsWindowClassDescription::fromWindow(window, m_proc));
+    return registerWindowClass(QWindowsWindowClassDescription::fromWindow(window, m_defaultProcedure));
 }
 
 QString QWindowsWindowClassRegistry::registerWindowClass(QString name, WNDPROC procedure)
@@ -130,13 +118,29 @@ QString QWindowsWindowClassRegistry::registerWindowClass(QString name, WNDPROC p
     return registerWindowClass(QWindowsWindowClassDescription::fromName(name, procedure));
 }
 
+bool QWindowsWindowClassRegistry::shouldDecorateWindowClassName(const QWindowsWindowClassDescription &description) const
+{
+    return shouldDecorateWindowClassName(description.name, description.procedure);
+}
+
+bool QWindowsWindowClassRegistry::shouldDecorateWindowClassName(const QString &name, WNDPROC procedure) const
+{
+    const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
+
+    WNDCLASS wc{};
+
+    return GetClassInfo(appInstance, reinterpret_cast<LPCWSTR>(name.utf16()), &wc) != FALSE
+        && wc.lpfnWndProc != procedure;
+}
+
 void QWindowsWindowClassRegistry::unregisterWindowClasses()
 {
     const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
 
     for (const QString &name : std::as_const(m_registeredWindowClassNames)) {
         if (!UnregisterClass(reinterpret_cast<LPCWSTR>(name.utf16()), appInstance) && QWindowsContext::verbose)
-            qErrnoWarning("UnregisterClass failed for '%s'", qPrintable(name));
+            qCWarning(lcQpaWindowClass) << "Failed to unregister window class" << name
+                << "(" << qt_error_string(-1) << ")";
     }
     m_registeredWindowClassNames.clear();
 }
diff --git a/src/plugins/platforms/windows/qwindowswindowclassregistry.h b/src/plugins/platforms/windows/qwindowswindowclassregistry.h
index c19b4f616fb..c4a36b7f3c4 100644
--- a/src/plugins/platforms/windows/qwindowswindowclassregistry.h
+++ b/src/plugins/platforms/windows/qwindowswindowclassregistry.h
@@ -22,7 +22,7 @@ class QWindowsWindowClassRegistry
 {
     Q_DISABLE_COPY_MOVE(QWindowsWindowClassRegistry)
 public:
-    QWindowsWindowClassRegistry(WNDPROC proc);
+    QWindowsWindowClassRegistry(WNDPROC defaultProcedure);
     ~QWindowsWindowClassRegistry();
 
     static QWindowsWindowClassRegistry *instance();
@@ -34,11 +34,13 @@ public:
 private:
     static QString classNamePrefix();
 
+    bool shouldDecorateWindowClassName(const QWindowsWindowClassDescription &description) const;
+    bool shouldDecorateWindowClassName(const QString &name, WNDPROC procedure) const;
     void unregisterWindowClasses();
 
     static QWindowsWindowClassRegistry *m_instance;
 
-    WNDPROC m_proc;
+    WNDPROC m_defaultProcedure;
     QSet<QString> m_registeredWindowClassNames;
 };