[PlasmaComponents Menu] Don't crash on null action

You can assign a QAction as "action", this way you can just pass it e.g. plasmoid.action("configure").
However, when assigning a null action as can happen with kiosk restrictions, it would crash
as it assigns m_action the nullptr but never checks for that.

This patch ensures we always have a QAction, creating a new empty one, if neccessary.
Also deletes our own action if an external one is assigned

Differential Revision: https://phabricator.kde.org/D6608

src/declarativeimports/plasmacomponents/qmenuitem.cpp

@@ -38,8 +38,24 @@ void QMenuItem::setAction(QAction *a)
     if (m_action != a) {
         if (m_action) {
             disconnect(m_action, 0, this, 0);
+
+            if (m_action->parent() == this) {
+                delete m_action;
+                m_action = nullptr;
+            }
         }
-        m_action = a;
+
+        if (a) {
+            m_action = a;
+        } else {
+            // don't end up with no action, create an invisible one instead
+            m_action = new QAction(this);
+            m_action->setVisible(false);
+        }
+
+        setVisible(m_action->isVisible());
+        setEnabled(m_action->isEnabled());
+
         connect(m_action, &QAction::changed, this, &QMenuItem::textChanged);
         connect(m_action, &QAction::changed, this, &QMenuItem::checkableChanged);
         connect(m_action, SIGNAL(toggled(bool)), this, SIGNAL(toggled(bool)));

tests/components/menu.qml

@@ -3,7 +3,7 @@ import org.kde.plasma.components 2.0 as PlasmaComponents
 
 Rectangle {
     width: 600
-    height: 200
+    height: 250
     color: "white"
 
     Flow {
@@ -99,5 +99,19 @@ Rectangle {
                 checked: true
             }
         }
+
+        PlasmaComponents.Button {
+            text: "Don't crash on null MenuItem action"
+            onClicked: noActionCrashMenu.open(0, height)
+
+            PlasmaComponents.Menu {
+                id: noActionCrashMenu
+
+                PlasmaComponents.MenuItem { text: "This is an item" }
+                PlasmaComponents.MenuItem { text: "Below me should NOT be an empty item"}
+                PlasmaComponents.MenuItem { action: null }
+                PlasmaComponents.MenuItem { text: "I am not empty" }
+            }
+        }
     }
 }