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>

2 files changed, 18 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlproperty.cpp b/src/qml/qml/qqmlproperty.cpp
index 9a138dcf80..b79418761b 100644
--- a/src/qml/qml/qqmlproperty.cpp
+++ b/src/qml/qml/qqmlproperty.cpp
@@ -223,6 +223,22 @@ QQmlProperty::QQmlProperty(QObject *obj, const QString &name, QQmlEngine *engine
     if (!isValid()) { d->object = 0; d->context = 0; d->engine = 0; }
 }
 
+QQmlProperty QQmlPropertyPrivate::create(QObject *target, const QString &propertyName, QQmlContextData *context)
+{
+    QQmlProperty result;
+    auto d = new QQmlPropertyPrivate;
+    result.d = d;
+    d->context = context;
+    d->engine = context->engine;
+    d->initProperty(target, propertyName);
+    if (!result.isValid()) {
+        d->object = nullptr;
+        d->context = nullptr;
+        d->engine = nullptr;
+    }
+    return result;
+}
+
 QQmlPropertyPrivate::QQmlPropertyPrivate()
 : context(0), engine(0), object(0), isNameCached(false)
 {
diff --git a/src/qml/qml/qqmlproperty_p.h b/src/qml/qml/qqmlproperty_p.h
index 53062a2f13..7a66d8113c 100644
--- a/src/qml/qml/qqmlproperty_p.h
+++ b/src/qml/qml/qqmlproperty_p.h
@@ -144,6 +144,8 @@ public:
     static void flushSignal(const QObject *sender, int signal_index);
 
     static QVariant resolvedUrlSequence(const QVariant &value, QQmlContextData *context);
+    static QQmlProperty create(QObject *target, const QString &propertyName, QQmlContextData *context);
+
 };
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QQmlPropertyPrivate::BindingFlags)