QQuickShaderEffect: fix crash when hiding parent

It's possible for itemChange to be called during destruction when
deleting the QQuickShaderEffectImpl. We nullify m_impl before deleting
it via another pointer to it, so we must check that it's not null
before trying to use it.

Fixes: QTBUG-86402
Change-Id: If4955445f7cc0d1f376bc9b86b95e1cca4d88ede
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit 266cd7638d887b31d56964a0f13fe208821703b1)
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 152 insertions, 1 deletions

diff --git a/src/quick/items/qquickshadereffect.cpp b/src/quick/items/qquickshadereffect.cpp
index b3c8386fd9..8db4e7dc9e 100644
--- a/src/quick/items/qquickshadereffect.cpp
+++ b/src/quick/items/qquickshadereffect.cpp
@@ -868,7 +868,11 @@ void QQuickShaderEffect::itemChange(ItemChange change, const ItemChangeData &val
         return;
     }
 #endif
-    m_impl->handleItemChange(change, value);
+    // It's possible for itemChange to be called during destruction when deleting
+    // the QQuickShaderEffectImpl. We nullify m_impl before deleting it via another pointer
+    // to it, so we must check that it's not null before trying to use it here.
+    if (m_impl)
+        m_impl->handleItemChange(change, value);
     QQuickItem::itemChange(change, value);
 }
 
diff --git a/tests/auto/quick/qquickshadereffect/data/hideParent.qml b/tests/auto/quick/qquickshadereffect/data/hideParent.qml
new file mode 100644
index 0000000000..aeeb5b5f78
--- /dev/null
+++ b/tests/auto/quick/qquickshadereffect/data/hideParent.qml
@@ -0,0 +1,133 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.12
+
+Item {
+    id: root
+    width: 640
+    height: 480
+    objectName: "qtbug86402Container"
+
+    property bool finished
+
+    Item {
+        id: popup
+        objectName: "popup"
+        width: 200
+        height: 200
+
+        Rectangle {
+            id: rect
+            objectName: "rect"
+            implicitWidth: 100
+            implicitHeight: 100
+            color: "blue"
+
+            Item {
+                id: ripple
+                objectName: "ripple"
+                anchors.fill: parent
+                visible: false
+
+                Rectangle {
+                    id: rippleBox
+                    objectName: "rippleBox"
+                    property real cx
+                    property real cy
+                    x: cx - width / 2
+                    y: cy - height / 2
+                    width: 0
+                    height: width
+                    radius: width / 2
+                    color: Qt.darker("red", 1.8)
+                }
+                layer.effect: ShaderEffect {
+                    id: mask
+                    objectName: "shaderEffect"
+                    property variant source
+                    property variant mask: rect
+
+                    fragmentShader: "
+                        uniform lowp sampler2D source;
+                        uniform lowp sampler2D mask;
+                        varying highp vec2 qt_TexCoord0;
+                        void main() {
+                            gl_FragColor = texture2D(source, qt_TexCoord0) * texture2D(mask, qt_TexCoord0).a;
+                        }"
+                }
+            }
+
+            SequentialAnimation {
+                id: rippleStartAnimation
+                running: popup.visible
+                onFinished: {
+                    popup.parent = null
+                    rippleEndAnimation.start()
+                }
+
+                ScriptAction {
+                    script: {
+                        rippleBox.width = 0
+                        rippleBox.opacity = 0.3
+                        ripple.visible = true
+                        ripple.layer.enabled = true
+                    }
+                }
+                NumberAnimation {
+                    target: rippleBox
+                    property: "width"
+                    from: 0
+                    to: Math.max(rect.width,
+                                 rect.height) * 2.2
+                    duration: 100
+                }
+            }
+            SequentialAnimation {
+                id: rippleEndAnimation
+
+                onFinished: root.finished = true
+
+                //Causes Crash on QT Versions > 5.12.5
+                NumberAnimation {
+                    target: rippleBox
+                    property: "opacity"
+                    to: 0
+                    duration: 100
+                }
+                ScriptAction {
+                    script: {
+                        rippleBox.opacity = 0
+                        ripple.layer.enabled = false
+                        ripple.visible = false
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickshadereffect/tst_qquickshadereffect.cpp b/tests/auto/quick/qquickshadereffect/tst_qquickshadereffect.cpp
index a57b7d4c1f..6537a64889 100644
--- a/tests/auto/quick/qquickshadereffect/tst_qquickshadereffect.cpp
+++ b/tests/auto/quick/qquickshadereffect/tst_qquickshadereffect.cpp
@@ -85,6 +85,8 @@ private slots:
 
     void withoutQmlEngine();
 
+    void hideParent();
+
 private:
     enum PresenceFlags {
         VertexPresent = 0x01,
@@ -336,6 +338,18 @@ void tst_qquickshadereffect::withoutQmlEngine()
     delete window;
 }
 
+// QTBUG-86402: hiding the parent of an item that uses an effect should not cause a crash.
+void tst_qquickshadereffect::hideParent()
+{
+    QScopedPointer<QQuickView> view(new QQuickView);
+    view->setSource(testFileUrl("hideParent.qml"));
+    QCOMPARE(view->status(), QQuickView::Ready);
+    view->show();
+    QVERIFY(QTest::qWaitForWindowExposed(view.data()));
+    // Should finish without crashing.
+    QTRY_VERIFY(view->rootObject()->property("finished").toBool());
+}
+
 QTEST_MAIN(tst_qquickshadereffect)
 
 #include "tst_qquickshadereffect.moc"