Enable menuless dialogs on Windows.

Handle the flags combination Qt::Dialog && !Qt::WindowSystemMenuHint
such that it results in exStyle = WS_EX_DLGMODALFRAME and style =
WS_POPUP | WS_BORDER | WS_SYSMENU and a window class without icon.

Do not set !Qt::WindowSystemMenuHint in QWidgetPrivate::adjustFlags()
for dialogs on Windows.

[ChangeLog][QtWidgets][QDialog][Windows] Dialogs can now be menuless.

Task-number: QTBUG-2027

Change-Id: Ieb86985e8a5291d826c103fe478ecde43971f08e
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index f67fb9bc19..c35af3623a 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -412,9 +412,17 @@ QString QWindowsContext::registerWindowClass(const QWindow *w, bool isGL)
         && (type == Qt::Popup || w->property("_q_windowsDropShadow").toBool())) {
         style |= CS_DROPSHADOW;
     }
-    if (type == Qt::Tool || type == Qt::ToolTip || type == Qt::Popup) {
+    switch (type) {
+    case Qt::Tool:
+    case Qt::ToolTip:
+    case Qt::Popup:
         style |= CS_SAVEBITS; // Save/restore background
         icon = false;
+        break;
+    case Qt::Dialog:
+        if (!(flags & Qt::WindowSystemMenuHint))
+            icon = false; // QTBUG-2027, dialogs without system menu.
+        break;
     }
     // Create a unique name for the flag combination
     QString cname = QStringLiteral("Qt5QWindow");