Fixes crash in QWidget::effectiveWinId.

Widgets are left in a transitional (and incosistent) state while being
re-parented, which caused QWidget::effectiveWinId() to crash in certain
circumstances. See patch for more details.

Auto test included.

Reviewed-by: ogoffart
(cherry picked from commit 6db0153cd7e35e4a919a76ae2aadbf2d2510bfb7)

1 files changed, 25 insertions, 0 deletions

diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index e266efb794..f282b5d7d3 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -345,6 +345,7 @@ private slots:
     void immediateRepaintAfterInvalidateBuffer();
 #endif
     void effectiveWinId();
+    void effectiveWinId2();
     void customDpi();
     void customDpiProperty();
 
@@ -8495,6 +8496,30 @@ void tst_QWidget::effectiveWinId()
     QVERIFY(child.effectiveWinId());
 }
 
+void tst_QWidget::effectiveWinId2()
+{
+    QWidget parent;
+
+    class MyWidget : public QWidget {
+        bool event(QEvent *e)
+        {
+            if (e->type() == QEvent::WinIdChange) {
+                // Shouldn't crash.
+                effectiveWinId();
+            }
+
+            return QWidget::event(e);
+        }
+    };
+
+    MyWidget child;
+    child.setParent(&parent);
+    parent.show();
+
+    child.setParent(0);
+    child.setParent(&parent);
+}
+
 class CustomWidget : public QWidget
 {
 public: