Fix edge case in signal emission semantics

Signal emission triggered by property changes during an onDestruction
handler was previously not well tested.  This commit adds several
unit tests to ensure correct behaviour in that situation.

Those unit tests showed a problem in signal emission related to when
children objects are cleaned up.  This commit also ensures that if
such children own their own context, their onDestruction handlers
are called prior to marking the child as deleted.

Change-Id: Ibf84ae56ba1134e5d6402b742aee1bdc0e5e4e15
Reviewed-by: Matthew Vogt <matthew.vogt@nokia.com>

7 files changed, 201 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlecmascript/data/SignalEmittedComponent.qml b/tests/auto/qml/qqmlecmascript/data/SignalEmittedComponent.qml
new file mode 100644
index 0000000000..a7866a33fb
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/SignalEmittedComponent.qml
@@ -0,0 +1,14 @@
+import QtQuick 2.0
+import Qt.test 1.0 as ModApi
+
+Item {
+    id: sec
+    property int a: 10
+    Component.onDestruction: {
+        ModApi.setSpecificProperty(sec, "a", 20);
+    }
+
+    function setSuccessPropertyOf(obj, val) {
+        obj.success = val;
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/data/signalEmitted.2.qml b/tests/auto/qml/qqmlecmascript/data/signalEmitted.2.qml
new file mode 100644
index 0000000000..8b2daa2a52
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/signalEmitted.2.qml
@@ -0,0 +1,29 @@
+import QtQuick 2.0
+import Qt.test 1.0 as ModApi
+
+Item {
+    id: root
+
+    property bool success: false
+    property bool c1HasBeenDestroyed: false
+
+    SignalEmittedComponent {
+        id: c1
+    }
+
+    SignalEmittedComponent {
+        id: c2
+        property int c1a: if (c1) c1.a; else 0; // will change during onDestruction handler of c1.
+        onC1aChanged: {
+            // this should still be called, after c1 has been destroyed.
+            if (root.c1HasBeenDestroyed && c1a == 20) c1.setSuccessPropertyOf(root, true);
+        }
+    }
+
+    Component.onCompleted: {
+        // destroy c1 directly
+        c1HasBeenDestroyed = true;
+        c1.destroy();
+        // return to event loop.
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/data/signalEmitted.3.qml b/tests/auto/qml/qqmlecmascript/data/signalEmitted.3.qml
new file mode 100644
index 0000000000..0cae5c02d8
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/signalEmitted.3.qml
@@ -0,0 +1,34 @@
+import QtQuick 2.0
+import Qt.test 1.0 as ModApi
+
+Item {
+    id: root
+
+    property bool success: false
+    property bool c1HasBeenDestroyed: false
+
+    property Item c1 // not a js reference, so won't keep it alive
+
+    SignalEmittedComponent {
+        id: c2
+        property int c1a: if (root.c1) root.c1.a; else 0; // will change during onDestruction handler of c1.
+        function c1aChangedHandler() {
+            // this should still be called, after c1 has been destroyed by gc,
+            // because the onDestruction handler of c1 will be triggered prior
+            // to when c1 will be invalidated.
+            if (root.c1HasBeenDestroyed && c1a == 20) root.c1.setSuccessPropertyOf(root, true);
+        }
+    }
+
+    Component.onCompleted: {
+        // dynamically construct sibling.  When it goes out of scope, it should be gc'd.
+        // note that the gc() will call weakqobjectcallback which will set queued for
+        // deletion flag -- thus QQmlData::wasDeleted() will return true for that object..
+        var c = Qt.createComponent("SignalEmittedComponent.qml", root);
+        var o = c.createObject(null); // JS ownership
+        o.onAChanged.connect(c2.c1aChangedHandler);
+        c1 = o;
+        c1HasBeenDestroyed = true;
+        // return to event loop.
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/data/signalEmitted.4.qml b/tests/auto/qml/qqmlecmascript/data/signalEmitted.4.qml
new file mode 100644
index 0000000000..e7dc0243fd
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/signalEmitted.4.qml
@@ -0,0 +1,39 @@
+import QtQuick 2.0
+import Qt.test 1.0 as ModApi
+
+Item {
+    id: root
+
+    property bool success: false
+    property bool c1HasBeenDestroyed: false
+
+    property Item c1 // not a js reference, so won't keep it alive
+
+    SignalEmittedComponent {
+        id: c2
+        property int c1a: if (root.c1) root.c1.a; else 0; // will change during onDestruction handler of c1.
+        function c1aChangedHandler() {
+            // this should still be called, after c1 has been destroyed by gc,
+            // because the onDestruction handler of c1 will be triggered prior
+            // to when c1 will be invalidated.
+            if (root.c1HasBeenDestroyed && c1a == 20) root.c1.setSuccessPropertyOf(root, true);
+        }
+    }
+
+    Component.onCompleted: {
+        // dynamically construct sibling.  When it goes out of scope, it should be gc'd.
+        // note that the gc() will call weakqobjectcallback which will set queued for
+        // deletion flag -- thus QQmlData::wasDeleted() will return true for that object..
+        var c = Qt.createComponent("SignalEmittedComponent.qml", root);
+        var o = c.createObject(null); // JS ownership
+        o.onAChanged.connect(c2.c1aChangedHandler);
+        c1 = o;
+        c1HasBeenDestroyed = true;
+        // return to event loop.
+    }
+
+    function destroyC2() {
+        // we must gc() c1 first, then destroy c2, then handle events.
+        c2.destroy();
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/data/signalEmitted.qml b/tests/auto/qml/qqmlecmascript/data/signalEmitted.qml
new file mode 100644
index 0000000000..6de606e62b
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/signalEmitted.qml
@@ -0,0 +1,36 @@
+import QtQuick 2.0
+import Qt.test 1.0 as ModApi
+
+Item {
+    id: root
+
+    property bool success: false
+    property bool c1HasBeenDestroyed: false
+
+    Item {
+        id: container
+
+        SignalEmittedComponent {
+            id: c1
+        }
+
+        SignalEmittedComponent {
+            id: c2
+            property int c1a: if (c1) c1.a; else 0; // will change during onDestruction handler of c1.
+            onC1aChanged: {
+                // this should still be called, after c1 has been destroyed.
+                if (root.c1HasBeenDestroyed && c1a == 20) c1.setSuccessPropertyOf(root, true);
+            }
+        }
+    }
+
+    Component.onCompleted: {
+        // firstly, reparent c2 so that it doesn't get destroyed.
+        ModApi.changeQObjectParent(c2);
+
+        // then, destroy container (and thus also c1)
+        c1HasBeenDestroyed = true;
+        container.destroy();
+        // return to event loop.
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/testtypes.h b/tests/auto/qml/qqmlecmascript/testtypes.h
index a289d97fd2..90eda77fee 100644
--- a/tests/auto/qml/qqmlecmascript/testtypes.h
+++ b/tests/auto/qml/qqmlecmascript/testtypes.h
@@ -1022,6 +1022,7 @@ public:
     Q_INVOKABLE QVariant trackedObjectProperty(const QString &propName) const { return m_trackedObject->property(qPrintable(propName)); }
 
     Q_INVOKABLE void setSpecificProperty(QObject *obj, const QString & propName, const QVariant & v) const { obj->setProperty(qPrintable(propName), v); }
+    Q_INVOKABLE void changeQObjectParent(QObject *obj) { obj->setParent(this); }
 
     int qobjectTestProperty() const { return m_testProperty; }
     void setQObjectTestProperty(int tp) { m_testProperty = tp; emit qobjectTestPropertyChanged(tp); }
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 3740d73415..a523bea003 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -262,6 +262,8 @@ private slots:
     void onDestruction();
     void bindingSuppression();
 
+    void signalEmitted();
+
 private:
     static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
     QQmlEngine engine;
@@ -6712,6 +6714,52 @@ void tst_qqmlecmascript::bindingSuppression()
     QCOMPARE(transientErrorsMsgCount, 0);
 }
 
+void tst_qqmlecmascript::signalEmitted()
+{
+    {
+        // calling destroy on the parent.
+        QQmlEngine engine;
+        QQmlComponent c(&engine, testFileUrl("signalEmitted.qml"));
+        QObject *obj = c.create();
+        QVERIFY(obj != 0);
+        QTRY_VERIFY(obj->property("success").toBool());
+        delete obj;
+    }
+
+    {
+        // calling destroy on the sibling.
+        QQmlEngine engine;
+        QQmlComponent c(&engine, testFileUrl("signalEmitted.2.qml"));
+        QObject *obj = c.create();
+        QVERIFY(obj != 0);
+        QTRY_VERIFY(obj->property("success").toBool());
+        delete obj;
+    }
+
+    {
+        // allowing gc to clean up the sibling.
+        QQmlEngine engine;
+        QQmlComponent c(&engine, testFileUrl("signalEmitted.3.qml"));
+        QObject *obj = c.create();
+        QVERIFY(obj != 0);
+        gc(engine); // should collect c1.
+        QTRY_VERIFY(obj->property("success").toBool());
+        delete obj;
+    }
+
+    {
+        // allowing gc to clean up the sibling after manually destroying target.
+        QQmlEngine engine;
+        QQmlComponent c(&engine, testFileUrl("signalEmitted.4.qml"));
+        QObject *obj = c.create();
+        QVERIFY(obj != 0);
+        gc(engine); // should collect c1.
+        QMetaObject::invokeMethod(obj, "destroyC2");
+        QTRY_VERIFY(obj->property("success").toBool());
+        delete obj;
+    }
+}
+
 QTEST_MAIN(tst_qqmlecmascript)
 
 #include "tst_qqmlecmascript.moc"