1 files changed, 16 insertions, 7 deletions
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 0b4bb9b09d..5768800947 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -801,7 +801,7 @@ QWindowCreationContext::QWindowCreationContext(const QWindow *w,
                                                const QRect &geometry,
                                                const QMargins &cm,
                                                DWORD style_, DWORD exStyle_) :
-    geometryHint(w, cm), style(style_), exStyle(exStyle_),
+    geometryHint(w, cm), window(w), style(style_), exStyle(exStyle_),
     requestedGeometry(geometry), obtainedGeometry(geometry),
     margins(QWindowsGeometryHint::frame(style, exStyle)), customMargins(cm),
     frameX(CW_USEDEFAULT), frameY(CW_USEDEFAULT),
@@ -1783,16 +1783,14 @@ void QWindowsWindow::propagateSizeHints()
     qCDebug(lcQpaWindows) << __FUNCTION__ << this << window();
 }
 
-bool QWindowsWindow::handleGeometryChanging(MSG *message) const
+bool QWindowsWindow::handleGeometryChangingMessage(MSG *message, const QWindow *qWindow, const QMargins &marginsDp)
 {
 #ifndef Q_OS_WINCE
-    QWindow *qWin = window();
-    if (!qWin->isTopLevel())
+    if (!qWindow->isTopLevel()) // Implement hasHeightForWidth().
         return false;
     WINDOWPOS *windowPos = reinterpret_cast<WINDOWPOS *>(message->lParam);
     if ((windowPos->flags & (SWP_NOCOPYBITS | SWP_NOSIZE)))
         return false;
-    const QMargins marginsDp = frameMarginsDp();
     const QRect suggestedFrameGeometryDp(windowPos->x, windowPos->y,
                                          windowPos->cx, windowPos->cy);
     const qreal factor = QWindowsScaling::factor();
@@ -1800,7 +1798,7 @@ bool QWindowsWindow::handleGeometryChanging(MSG *message) const
     const QRectF suggestedGeometry = QRectF(QPointF(suggestedGeometryDp.topLeft()) / factor,
                                             QSizeF(suggestedGeometryDp.size()) / factor);
     const QRectF correctedGeometryF =
-        qt_window_private(qWin)->closestAcceptableGeometry(suggestedGeometry);
+        qt_window_private(const_cast<QWindow *>(qWindow))->closestAcceptableGeometry(suggestedGeometry);
     if (!correctedGeometryF.isValid())
         return false;
     const QRect correctedFrameGeometryDp
@@ -1820,6 +1818,12 @@ bool QWindowsWindow::handleGeometryChanging(MSG *message) const
 #endif
 }
 
+bool QWindowsWindow::handleGeometryChanging(MSG *message) const
+{
+    const QMargins marginsDp = window()->isTopLevel() ? frameMarginsDp() : QMargins();
+    return QWindowsWindow::handleGeometryChangingMessage(message, window(), marginsDp);
+}
+
 QMargins QWindowsWindow::frameMarginsDp() const
 {
     // Frames are invalidated by style changes (window state, flags).
@@ -1827,7 +1831,12 @@ QMargins QWindowsWindow::frameMarginsDp() const
     // event sequences, introduce a dirty flag mechanism to be able
     // to cache results.
     if (testFlag(FrameDirty)) {
-        m_data.frame = QWindowsGeometryHint::frame(style(), exStyle());
+        // Always skip calculating style-dependent margins for windows claimed to be frameless.
+        // This allows users to remove the margins by handling WM_NCCALCSIZE with WS_THICKFRAME set
+        // to ensure Areo snap still works (QTBUG-40578).
+        m_data.frame = window()->flags() & Qt::FramelessWindowHint
+            ? QMargins(0, 0, 0, 0)
+            : QWindowsGeometryHint::frame(style(), exStyle());
         clearFlag(FrameDirty);
     }
     return m_data.frame + m_data.customMargins;