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.

Task-number: QTBUG-57043
Task-number: QTBUG-50328
Change-Id: I3008ddd847e30b7d0adef07344a326f84d85f1ba
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 11 insertions, 3 deletions

diff --git a/src/qml/types/qqmlconnections.cpp b/src/qml/types/qqmlconnections.cpp
index a43562a7b8..d1a7aa9b6f 100644
--- a/src/qml/types/qqmlconnections.cpp
+++ b/src/qml/types/qqmlconnections.cpp
@@ -288,9 +288,17 @@ void QQmlConnections::connectSignals()
                 new QQmlBoundSignal(target, signalIndex, this, qmlEngine(this));
             signal->setEnabled(d->enabled);
 
-            QQmlBoundSignalExpression *expression = ctxtdata ?
-                new QQmlBoundSignalExpression(target, signalIndex,
-                                              ctxtdata, this, d->compilationUnit->runtimeFunctions[binding->value.compiledScriptIndex]) : nullptr;
+            auto f = d->compilationUnit->runtimeFunctions[binding->value.compiledScriptIndex];
+
+            // If the function is marked as having a nested function, then the user wrote:
+            //   onSomeSignal: function() { /*....*/ }
+            // So take that nested function:
+            if (auto closure = f->nestedFunction())
+                f = closure;
+
+            QQmlBoundSignalExpression *expression =
+                    ctxtdata ? new QQmlBoundSignalExpression(target, signalIndex, ctxtdata, this, f)
+                             : nullptr;
             signal->takeExpression(expression);
             d->boundsignals += signal;
         } else {