Speed up PropertyChange state application

Every time we decode a potential binding of a PropertyChanges{} object,
we call qmlContext(this) and we go through a full QQmlProperty
construction (which involves property name decoding by dots and property
lookups), just to determine if we're doing a binding on a property or a
signal. QQmlProperty::isSignalProperty() will only return true if the
property is valid and if it's a "function" type. The QQmlProperty
constructor on the other hand only constructs a valid regular property
if it's _not_ a function type and a signal property _has_ to start with
"on" followed by an upper case character. We can copy this shortcut out
into decodeBinding() to avoid the QQmlProperty construction in the
common case of plain property bindings.

This is also legit in the scope of group properties, as signal bindings
on group properties are not supported (we always use the state's target
object for signal lookup, never the group object).

In addition, avoid creating a public QQmlContext for the PropertyChange
object by allowing for the construction of the QQmlProperty object via
the QQmlContextData, as that's the only data structure we really need.

These two changes used to be separate, but they need to go together to
keep the tests passing, as the property validation and warning issuing
is now moved from decodeBinding() into ::actions() itself.

Shaves off 1.5% off delegates_item_states.qml

Task-number: QTBUG-65708
Change-Id: I32a17d815bd3495a907a51068a971eb7cb69c6ef
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 24 insertions, 18 deletions

diff --git a/src/quick/util/qquickpropertychanges.cpp b/src/quick/util/qquickpropertychanges.cpp
index 61380b3ea0..aecb7115ea 100644
--- a/src/quick/util/qquickpropertychanges.cpp
+++ b/src/quick/util/qquickpropertychanges.cpp
@@ -281,15 +281,19 @@ void QQuickPropertyChangesPrivate::decodeBinding(const QString &propertyPrefix,
         return;
     }
 
-    QQmlProperty prop = property(propertyName);      //### better way to check for signal property?
-
-    if (prop.type() & QQmlProperty::SignalProperty) {
-        QQuickReplaceSignalHandler *handler = new QQuickReplaceSignalHandler;
-        handler->property = prop;
-        handler->expression.take(new QQmlBoundSignalExpression(object, QQmlPropertyPrivate::get(prop)->signalIndex(),
-                                                               QQmlContextData::get(qmlContext(q)), object, compilationUnit->runtimeFunctions.at(binding->value.compiledScriptIndex)));
-        signalReplacements << handler;
-        return;
+    if (propertyName.count() >= 3 &&
+        propertyName.at(0) == QLatin1Char('o') &&
+        propertyName.at(1) == QLatin1Char('n') &&
+        propertyName.at(2).isUpper()) {
+        QQmlProperty prop = property(propertyName);
+        if (prop.isSignalProperty()) {
+            QQuickReplaceSignalHandler *handler = new QQuickReplaceSignalHandler;
+            handler->property = prop;
+            handler->expression.take(new QQmlBoundSignalExpression(object, QQmlPropertyPrivate::get(prop)->signalIndex(),
+                                                                   QQmlContextData::get(qmlContext(q)), object, compilationUnit->runtimeFunctions.at(binding->value.compiledScriptIndex)));
+            signalReplacements << handler;
+            return;
+        }
     }
 
     if (binding->type == QV4::CompiledData::Binding::Type_Script) {
@@ -395,7 +399,10 @@ QQmlProperty
 QQuickPropertyChangesPrivate::property(const QString &property)
 {
     Q_Q(QQuickPropertyChanges);
-    QQmlProperty prop(object, property, qmlContext(q));
+    QQmlContextData *context = nullptr;
+    if (QQmlData *ddata = QQmlData::get(q))
+        context = ddata->outerContext;
+    QQmlProperty prop = QQmlPropertyPrivate::create(object, property, context);
     if (!prop.isValid()) {
         qmlWarning(q) << QQuickPropertyChanges::tr("Cannot assign to non-existent property \"%1\"").arg(property);
         return QQmlProperty();
@@ -415,9 +422,10 @@ QQuickPropertyChanges::ActionList QQuickPropertyChanges::actions()
     ActionList list;
 
     for (int ii = 0; ii < d->properties.count(); ++ii) {
+        QQmlProperty prop = d->property(d->properties.at(ii).first);
 
-        QQuickStateAction a(d->object, d->properties.at(ii).first,
-                 qmlContext(this), d->properties.at(ii).second);
+        QQuickStateAction a(d->object, prop, d->properties.at(ii).first,
+                            d->properties.at(ii).second);
 
         if (a.property.isValid()) {
             a.restore = restoreEntryValues();
@@ -426,7 +434,6 @@ QQuickPropertyChanges::ActionList QQuickPropertyChanges::actions()
     }
 
     for (int ii = 0; ii < d->signalReplacements.count(); ++ii) {
-
         QQuickReplaceSignalHandler *handler = d->signalReplacements.at(ii);
 
         if (handler->property.isValid()) {
diff --git a/src/quick/util/qquickstate.cpp b/src/quick/util/qquickstate.cpp
index 0a49d41491..ca8b7bbc2b 100644
--- a/src/quick/util/qquickstate.cpp
+++ b/src/quick/util/qquickstate.cpp
@@ -68,10 +68,9 @@ QQuickStateAction::QQuickStateAction(QObject *target, const QString &propertyNam
         fromValue = property.read();
 }
 
-QQuickStateAction::QQuickStateAction(QObject *target, const QString &propertyName,
-               QQmlContext *context, const QVariant &value)
+QQuickStateAction::QQuickStateAction(QObject *target, const QQmlProperty &property, const QString &propertyName, const QVariant &value)
 : restore(true), actionDone(false), reverseEvent(false), deletableToBinding(false),
-  property(target, propertyName, context), toValue(value),
+  property(property), toValue(value),
   fromBinding(0), event(0),
   specifiedObject(target), specifiedProperty(propertyName)
 {
diff --git a/src/quick/util/qquickstate_p.h b/src/quick/util/qquickstate_p.h
index 7d22ca9f8c..3826daf283 100644
--- a/src/quick/util/qquickstate_p.h
+++ b/src/quick/util/qquickstate_p.h
@@ -69,8 +69,8 @@ class Q_QUICK_PRIVATE_EXPORT QQuickStateAction
 public:
     QQuickStateAction();
     QQuickStateAction(QObject *, const QString &, const QVariant &);
-    QQuickStateAction(QObject *, const QString &,
-                       QQmlContext *, const QVariant &);
+    QQuickStateAction(QObject *, const QQmlProperty &property, const QString &,
+                      const QVariant &);
 
     bool restore:1;
     bool actionDone:1;