Handle function expressions as signal handlers

There are two ways to use function expressions on the right-hand side
of bindings:

  property var somethingPressed
  somethingPressed: function() { /* ..press something else.. */ }

  signal buttonPressed
  onButtonPressed: function() { /* ..handle buttonPress.. */ }

In the former case, it declares a property that holds a function. So on
initialization, the right-hand side of the binding returns a closure
that gets assigned to the property 'somethingPressed'.

In the latter case, the signal handler is explicitly marked as a
function for clarity. So, the handler should not be returning the
closure, but the handler should *be* the closure.

In general, it is not possible to detect if the left-hand side is a
property or a signal handler when generating QML cache files ahead of
time. So for this case, we mark the function as only returning a
closure. Then when instantiating the object, we check if it is a signal
handler, and if the handler is marked as only returning a closure. If
so, we set that closure to be the signal handler.

This patch also handles function expressions in SignalTransition and
function expressions as signal handlers.

Task-number: QTBUG-57043
Task-number: QTBUG-50328
Task-number: QTBUG-50328
(cherry picked from commit 22b13921f8067f8a93164875a4ad59bed85b0400)
(cherry picked from commit dc4d6293f9473c0f03c570430d08867d2d01c6e2)
(cherry picked from commit 21301c1dbb00f4a2cd991e520423ed039b297ffb)
Change-Id: I3008ddd847e30b7d0adef07344a326f84d85f1ba
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/imports/statemachine/signaltransition.cpp b/src/imports/statemachine/signaltransition.cpp
index 0f88ec641b..7057fd0621 100644
--- a/src/imports/statemachine/signaltransition.cpp
+++ b/src/imports/statemachine/signaltransition.cpp
@@ -176,9 +176,10 @@ void SignalTransition::connectTriggered()
     QMetaMethod metaMethod = target->metaObject()->method(qobjectSignal->methodIndex());
     int signalIndex = QMetaObjectPrivate::signalIndex(metaMethod);
 
-    QQmlBoundSignalExpression *expression = ctxtdata ?
-                new QQmlBoundSignalExpression(target, signalIndex,
-                                              ctxtdata, this, m_compilationUnit->runtimeFunctions[binding->value.compiledScriptIndex]) : 0;
+    auto f = m_compilationUnit->runtimeFunctions[binding->value.compiledScriptIndex];
+    QQmlBoundSignalExpression *expression =
+            ctxtdata ? new QQmlBoundSignalExpression(target, signalIndex, ctxtdata, this, f)
+                     : nullptr;
     if (expression)
         expression->setNotifyOnValueChanged(false);
     m_signalExpression = expression;