Enable lookups in QML

The main feature that needs to be implemented in order to enable lookups
in QML files is to respect that the QObject wrapper has its own storage
layer (meta-object properties). Lookups need to be able to index those
when the base is a QObject. This is done by caching the property data
and guarding the validity by comparing property cache pointers.

The same lookup logic is also implemented for value type wrappers.

OVerall there's more that can be done with lookups in meta-objects, for
constant properties for example.

For "global" lookups we have a safeguard in place that generates a
LoadName instruction for property access that should end up in the qml
context wrapper. So no changes are needed here at first, but the lookup
in the QML context can be optimized in the future.

The way of storing the property cache in the lookup itself trades
ugliness on destruction against the creation of less internal classes.
Another option would be to store the property cache in the internal
class and let QObjectWrapper always transition via the property cache.

Task-number: QTBUG-69898
Change-Id: I9c378c071acc6d7d4a34a2a76616f9594119d515
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

4 files changed, 170 insertions, 38 deletions

diff --git a/src/qml/jsruntime/qv4lookup_p.h b/src/qml/jsruntime/qv4lookup_p.h
index 83e561863b..b0d5706dea 100644
--- a/src/qml/jsruntime/qv4lookup_p.h
+++ b/src/qml/jsruntime/qv4lookup_p.h
@@ -116,6 +116,18 @@ struct Lookup {
             quintptr _unused2;
             uint index;
         } indexedLookup;
+        struct {
+            Heap::InternalClass *ic;
+            quintptr unused;
+            QQmlPropertyCache *propertyCache;
+            QQmlPropertyData *propertyData;
+        } qobjectLookup;
+        struct {
+            Heap::InternalClass *ic;
+            quintptr unused;
+            QQmlPropertyCache *propertyCache;
+            QQmlPropertyData *propertyData;
+        } qgadgetLookup;
     };
     uint nameIndex;
 
diff --git a/src/qml/jsruntime/qv4qobjectwrapper.cpp b/src/qml/jsruntime/qv4qobjectwrapper.cpp
index 40be6f41c8..711c910906 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper.cpp
+++ b/src/qml/jsruntime/qv4qobjectwrapper.cpp
@@ -56,6 +56,8 @@
 #include <private/qv4functionobject_p.h>
 #include <private/qv4runtime_p.h>
 #include <private/qv4variantobject_p.h>
+#include <private/qv4identifiertable_p.h>
+#include <private/qv4lookup_p.h>
 
 #if QT_CONFIG(qml_sequence_object)
 #include <private/qv4sequenceobject_p.h>
@@ -269,9 +271,53 @@ ReturnedValue QObjectWrapper::getProperty(ExecutionEngine *engine, QObject *obje
     }
 }
 
+static OptionalReturnedValue getDestroyOrToStringMethod(ExecutionEngine *v4, String *name, QObject *qobj, bool *hasProperty = nullptr)
+{
+    int index = 0;
+    if (name->equals(v4->id_destroy()))
+        index = QV4::QObjectMethod::DestroyMethod;
+    else if (name->equals(v4->id_toString()))
+        index = QV4::QObjectMethod::ToStringMethod;
+    else
+        return OptionalReturnedValue();
+
+    if (hasProperty)
+        *hasProperty = true;
+    ExecutionContext *global = v4->rootContext();
+    return OptionalReturnedValue(QV4::QObjectMethod::create(global, qobj, index));
+}
+
+static OptionalReturnedValue getPropertyFromImports(ExecutionEngine *v4, String *name, QQmlContextData *qmlContext, QObject *qobj,
+                                            bool *hasProperty = nullptr)
+{
+    if (!qmlContext || !qmlContext->imports)
+        return OptionalReturnedValue();
+
+    QQmlTypeNameCache::Result r = qmlContext->imports->query(name);
+
+    if (hasProperty)
+        *hasProperty = true;
+
+    if (!r.isValid())
+        return OptionalReturnedValue();
+
+    if (r.scriptIndex != -1) {
+        return OptionalReturnedValue(QV4::Encode::undefined());
+    } else if (r.type.isValid()) {
+        return OptionalReturnedValue(QQmlTypeWrapper::create(v4, qobj,r.type, Heap::QQmlTypeWrapper::ExcludeEnums));
+    } else if (r.importNamespace) {
+        return OptionalReturnedValue(QQmlTypeWrapper::create(v4, qobj, qmlContext->imports, r.importNamespace,
+                                     Heap::QQmlTypeWrapper::ExcludeEnums));
+    }
+    Q_UNREACHABLE();
+    return OptionalReturnedValue();
+}
+
 ReturnedValue QObjectWrapper::getQmlProperty(QQmlContextData *qmlContext, String *name, QObjectWrapper::RevisionMode revisionMode,
                                              bool *hasProperty, bool includeImports) const
 {
+    // Keep this code in sync with ::virtualResolveLookupGetter
+
     if (QQmlData::wasDeleted(d()->object())) {
         if (hasProperty)
             *hasProperty = false;
@@ -280,39 +326,17 @@ ReturnedValue QObjectWrapper::getQmlProperty(QQmlContextData *qmlContext, String
 
     ExecutionEngine *v4 = engine();
 
-    if (name->equals(v4->id_destroy()) || name->equals(v4->id_toString())) {
-        int index = name->equals(v4->id_destroy()) ? QV4::QObjectMethod::DestroyMethod : QV4::QObjectMethod::ToStringMethod;
-        if (hasProperty)
-            *hasProperty = true;
-        ExecutionContext *global = v4->rootContext();
-        return QV4::QObjectMethod::create(global, d()->object(), index);
-    }
+    if (auto methodValue = getDestroyOrToStringMethod(v4, name, d()->object(), hasProperty))
+        return *methodValue;
 
     QQmlPropertyData local;
     QQmlPropertyData *result = findProperty(v4, qmlContext, name, revisionMode, &local);
 
     if (!result) {
+        // Check for attached properties
         if (includeImports && name->startsWithUpper()) {
-            // Check for attached properties
-            if (qmlContext && qmlContext->imports) {
-                QQmlTypeNameCache::Result r = qmlContext->imports->query(name);
-
-                if (hasProperty)
-                    *hasProperty = true;
-
-                if (r.isValid()) {
-                    if (r.scriptIndex != -1) {
-                        return QV4::Encode::undefined();
-                    } else if (r.type.isValid()) {
-                        return QQmlTypeWrapper::create(v4, d()->object(),
-                                                      r.type, Heap::QQmlTypeWrapper::ExcludeEnums);
-                    } else if (r.importNamespace) {
-                        return QQmlTypeWrapper::create(v4, d()->object(),
-                                                      qmlContext->imports, r.importNamespace, Heap::QQmlTypeWrapper::ExcludeEnums);
-                    }
-                    Q_ASSERT(!"Unreachable");
-                }
-            }
+            if (auto importProperty = getPropertyFromImports(v4, name, qmlContext, d()->object(), hasProperty))
+                return *importProperty;
         }
         return QV4::Object::virtualGet(this, name->propertyKey(), this, hasProperty);
     }
@@ -361,13 +385,8 @@ ReturnedValue QObjectWrapper::getQmlProperty(QV4::ExecutionEngine *engine, QQmlC
         return QV4::Encode::null();
     }
 
-    if (name->equals(engine->id_destroy()) || name->equals(engine->id_toString())) {
-        int index = name->equals(engine->id_destroy()) ? QV4::QObjectMethod::DestroyMethod : QV4::QObjectMethod::ToStringMethod;
-        if (hasProperty)
-            *hasProperty = true;
-        ExecutionContext *global = engine->rootContext();
-        return QV4::QObjectMethod::create(global, object, index);
-    }
+    if (auto methodValue = getDestroyOrToStringMethod(engine, name, object, hasProperty))
+        return *methodValue;
 
     QQmlData *ddata = QQmlData::get(object, false);
     QQmlPropertyData local;
@@ -829,6 +848,86 @@ OwnPropertyKeyIterator *QObjectWrapper::virtualOwnPropertyKeys(const Object *m,
     return new QObjectWrapperOwnPropertyKeyIterator;
 }
 
+ReturnedValue QObjectWrapper::virtualResolveLookupGetter(const Object *object, ExecutionEngine *engine, Lookup *lookup)
+{
+    // Keep this code in sync with ::getQmlProperty
+    PropertyKey id = engine->identifierTable->asPropertyKey(engine->currentStackFrame->v4Function->compilationUnit->
+                                                            runtimeStrings[lookup->nameIndex]);
+    if (!id.isString())
+        return Object::virtualResolveLookupGetter(object, engine, lookup);
+    Scope scope(engine);
+
+    const QObjectWrapper *This = static_cast<const QObjectWrapper *>(object);
+    ScopedString name(scope, id.asStringOrSymbol());
+    QQmlContextData *qmlContext = engine->callingQmlContext();
+
+    QObject * const qobj = This->d()->object();
+
+    if (QQmlData::wasDeleted(qobj))
+        return QV4::Encode::undefined();
+
+    if (auto methodValue = getDestroyOrToStringMethod(engine, name, qobj))
+        return *methodValue;
+
+    QQmlData *ddata = QQmlData::get(qobj, false);
+    if (!ddata || !ddata->propertyCache) {
+        QQmlPropertyData local;
+        QQmlPropertyData *property = QQmlPropertyCache::property(engine->jsEngine(), qobj, name, qmlContext, local);
+        return getProperty(engine, qobj, property, /*captureRequired*/true);
+    }
+    QQmlPropertyData *property = ddata->propertyCache->property(name.getPointer(), qobj, qmlContext);
+
+    if (!property) {
+        // Check for attached properties
+        if (name->startsWithUpper()) {
+            if (auto importProperty = getPropertyFromImports(engine, name, qmlContext, qobj))
+                return *importProperty;
+        }
+        return QV4::Object::virtualResolveLookupGetter(object, engine, lookup);
+    }
+
+    lookup->qobjectLookup.ic = This->internalClass();
+    lookup->qobjectLookup.propertyCache = ddata->propertyCache;
+    lookup->qobjectLookup.propertyCache->addref();
+    lookup->qobjectLookup.propertyData = property;
+    lookup->getter = QV4::QObjectWrapper::lookupGetter;
+    return lookup->getter(lookup, engine, *object);
+}
+
+ReturnedValue QObjectWrapper::lookupGetter(Lookup *lookup, ExecutionEngine *engine, const Value &object)
+{
+    const auto revertLookup = [lookup, engine, &object]() {
+        lookup->qobjectLookup.propertyCache->release();
+        lookup->qobjectLookup.propertyCache = nullptr;
+        lookup->getter = Lookup::getterGeneric;
+        return Lookup::getterGeneric(lookup, engine, object);
+    };
+
+    // we can safely cast to a QV4::Object here. If object is something else,
+    // the internal class won't match
+    Heap::Object *o = static_cast<Heap::Object *>(object.heapObject());
+    if (!o || o->internalClass != lookup->qobjectLookup.ic)
+        return revertLookup();
+
+    const Heap::QObjectWrapper *This = static_cast<const Heap::QObjectWrapper *>(o);
+    QObject *qobj = This->object();
+    if (QQmlData::wasDeleted(qobj))
+        return QV4::Encode::undefined();
+
+    QQmlData *ddata = QQmlData::get(qobj, /*create*/false);
+    if (!ddata || ddata->propertyCache != lookup->qobjectLookup.propertyCache)
+        return revertLookup();
+
+    QQmlPropertyData *property = lookup->qobjectLookup.propertyData;
+    return getProperty(engine, qobj, property, /*captureRequired = */true);
+}
+
+bool QObjectWrapper::virtualResolveLookupSetter(Object *object, ExecutionEngine *engine, Lookup *lookup,
+                                                const Value &value)
+{
+    return Object::virtualResolveLookupSetter(object, engine, lookup, value);
+}
+
 namespace QV4 {
 
 struct QObjectSlotDispatcher : public QtPrivate::QSlotObjectBase
@@ -1920,13 +2019,13 @@ ReturnedValue QObjectMethod::create(ExecutionContext *scope, QObject *object, in
     return method.asReturnedValue();
 }
 
-ReturnedValue QObjectMethod::create(ExecutionContext *scope, const QQmlValueTypeWrapper *valueType, int index)
+ReturnedValue QObjectMethod::create(ExecutionContext *scope, Heap::QQmlValueTypeWrapper *valueType, int index)
 {
     Scope valueScope(scope);
     Scoped<QObjectMethod> method(valueScope, valueScope.engine->memoryManager->allocate<QObjectMethod>(scope));
-    method->d()->setPropertyCache(valueType->d()->propertyCache());
+    method->d()->setPropertyCache(valueType->propertyCache());
     method->d()->index = index;
-    method->d()->valueTypeWrapper.set(valueScope.engine, valueType->d());
+    method->d()->valueTypeWrapper.set(valueScope.engine, valueType);
     return method.asReturnedValue();
 }
 
diff --git a/src/qml/jsruntime/qv4qobjectwrapper_p.h b/src/qml/jsruntime/qv4qobjectwrapper_p.h
index 6465ee0fa6..a09e7b6e95 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper_p.h
+++ b/src/qml/jsruntime/qv4qobjectwrapper_p.h
@@ -183,6 +183,11 @@ struct Q_QML_EXPORT QObjectWrapper : public Object
     void destroyObject(bool lastCall);
 
     static ReturnedValue getProperty(ExecutionEngine *engine, QObject *object, QQmlPropertyData *property, bool captureRequired = true);
+
+    static ReturnedValue virtualResolveLookupGetter(const Object *object, ExecutionEngine *engine, Lookup *lookup);
+    static ReturnedValue lookupGetter(Lookup *l, ExecutionEngine *engine, const Value &object);
+    static bool virtualResolveLookupSetter(Object *object, ExecutionEngine *engine, Lookup *lookup, const Value &value);
+
 protected:
     static void setProperty(ExecutionEngine *engine, QObject *object, QQmlPropertyData *property, const Value &value);
 
@@ -228,7 +233,7 @@ struct Q_QML_EXPORT QObjectMethod : public QV4::FunctionObject
     enum { DestroyMethod = -1, ToStringMethod = -2 };
 
     static ReturnedValue create(QV4::ExecutionContext *scope, QObject *object, int index);
-    static ReturnedValue create(QV4::ExecutionContext *scope, const QQmlValueTypeWrapper *valueType, int index);
+    static ReturnedValue create(QV4::ExecutionContext *scope, Heap::QQmlValueTypeWrapper *valueType, int index);
 
     int methodIndex() const { return d()->index; }
     QObject *object() const { return d()->object(); }
diff --git a/src/qml/jsruntime/qv4value_p.h b/src/qml/jsruntime/qv4value_p.h
index 20a84beccd..b4a045edfb 100644
--- a/src/qml/jsruntime/qv4value_p.h
+++ b/src/qml/jsruntime/qv4value_p.h
@@ -863,6 +863,22 @@ struct ValueArray {
 // have wrong offsets between host and target.
 Q_STATIC_ASSERT(offsetof(ValueArray<0>, values) == 8);
 
+class OptionalReturnedValue {
+    ReturnedValue value;
+public:
+
+    OptionalReturnedValue() : value(Value::emptyValue().asReturnedValue()) {}
+    explicit OptionalReturnedValue(ReturnedValue v)
+        : value(v)
+    {
+        Q_ASSERT(!Value::fromReturnedValue(v).isEmpty());
+    }
+
+    ReturnedValue operator->() const { return value; }
+    ReturnedValue operator*() const { return value; }
+    explicit operator bool() const { return !Value::fromReturnedValue(value).isEmpty(); }
+};
+
 }
 
 QT_END_NAMESPACE