Fix crash when grabbing a QQuickWidget before it is shown.

Do not access null share contexts.

Task-number: QTBUG-49929
Change-Id: I1c88563df71dd6c5d186b6f2ae147614fcc6ded9
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

2 files changed, 16 insertions, 6 deletions

diff --git a/src/quickwidgets/qquickwidget.cpp b/src/quickwidgets/qquickwidget.cpp
index 748b450643..2120be768c 100644
--- a/src/quickwidgets/qquickwidget.cpp
+++ b/src/quickwidgets/qquickwidget.cpp
@@ -724,12 +724,13 @@ void QQuickWidgetPrivate::createContext()
         context = new QOpenGLContext;
         context->setFormat(offscreenWindow->requestedFormat());
 
-        if (qt_gl_global_share_context())
-            context->setShareContext(qt_gl_global_share_context());
-        else
-            context->setShareContext(QWidgetPrivate::get(q->window())->shareContext());
-        context->setScreen(context->shareContext()->screen());
-
+        QOpenGLContext *shareContext = qt_gl_global_share_context();
+        if (!shareContext)
+            shareContext = QWidgetPrivate::get(q->window())->shareContext();
+        if (shareContext) {
+            context->setShareContext(shareContext);
+            context->setScreen(shareContext->screen());
+        }
         if (!context->create()) {
             const bool isEs = context->isOpenGLES();
             delete context;
diff --git a/tests/auto/quickwidgets/qquickwidget/tst_qquickwidget.cpp b/tests/auto/quickwidgets/qquickwidget/tst_qquickwidget.cpp
index 79ff18011d..bec3de524c 100644
--- a/tests/auto/quickwidgets/qquickwidget/tst_qquickwidget.cpp
+++ b/tests/auto/quickwidgets/qquickwidget/tst_qquickwidget.cpp
@@ -59,6 +59,7 @@ private slots:
     void engine();
     void readback();
     void renderingSignals();
+    void grabBeforeShow();
 };
 
 
@@ -297,6 +298,14 @@ void tst_qquickwidget::renderingSignals()
     QTRY_VERIFY(afterRenderingSpy.size() > 0);
 }
 
+// QTBUG-49929, verify that Qt Designer grabbing the contents before drag
+// does not crash due to missing GL contexts or similar.
+void tst_qquickwidget::grabBeforeShow()
+{
+    QQuickWidget widget;
+    QVERIFY(!widget.grab().isNull());
+}
+
 QTEST_MAIN(tst_qquickwidget)
 
 #include "tst_qquickwidget.moc"