qqmlpreviewbindingpatchcontext.cpp

Go to the documentation of this file.

// Copyright (C) 2026 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
 
#include "qqmlpreviewbindingpatchcontext_p.h"
 
#include <private/qqmlcomponent_p.h>
#include <private/qqmlnotifier_p.h>
#include <private/qqmlobjectcreator_p.h>
#include <private/qqmlproperty_p.h>
#include <private/qqmlproperty_p.h>
#include <private/qqmlpropertybinding_p.h>
#include <private/qqmlpropertytopropertybinding_p.h>
#include <private/qqmltypeloader_p.h>
#include <private/qqmlvaluetypeproxybinding_p.h>
#include <private/qqmlvme_p.h>
#include <private/qv4functionobject_p.h>
#include <private/qv4generatorobject_p.h>
#include <private/qv4qmlcontext_p.h>
#include <private/qv4resolvedtypereference_p.h>
 
#include <QtCore/qqueue.h>
#include <QtCore/qset.h>
 
QT_BEGIN_NAMESPACE
 
namespace QQmlPreview {
 
 
static bool functionBelongsToObject(const QV4::Function *f,
                                    const QQmlRefPointer<QV4::ExecutableCompilationUnit> &cu,
                                    int objectIndex)
{
    if (f->executableCompilationUnit() != cu)
        return false;
 
    const QV4::CompiledData::Object *obj = cu->objectAt(objectIndex);
    for (auto binding = obj->bindingsBegin(), end = obj->bindingsEnd(); binding != end; ++binding) {
        switch (binding->type()) {
        case QV4::CompiledData::Binding::Type_GroupedProperty:
        case QV4::CompiledData::Binding::Type_AttachedProperty:
        case QV4::CompiledData::Binding::Type_Object:
            if (functionBelongsToObject(f, cu, binding->value.objectIndex))
                return true;
            break;
        case QV4::CompiledData::Binding::Type_Script:
            if (cu->runtimeFunctions[binding->value.compiledScriptIndex] == f)
                return true;
        default:
            break;
        }
    }
    return false;
}
 
// A binding that lives in one of target's outer contexts is recreated when that context's root is
// rebuilt, so it is not actually external. Returns true if `cu` is reachable through the context
// chain before we leave the set of units being rebuilt.
static bool rebuildReachesUnitViaContext(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &cu,
                                         const std::vector<CompositeLevel> &internalUnits,
                                         QObject *target)
{
    const QQmlData *ddata = QQmlData::get(target);
    if (!ddata)
        return false;
 
    for (QQmlRefPointer<QQmlContextData> context = ddata->outerContext; context;
         context = context->parent()) {
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> ctxCu = context->typeCompilationUnit();
        if (!ctxCu)
            continue;
 
        if (ctxCu == cu)
            return true;
 
        if (std::any_of(internalUnits.begin(), internalUnits.end(),
                        [&](const CompositeLevel &level) {
                            return level.oldCu == ctxCu || level.newCu == ctxCu;
                        })) {
            break;
        }
    }
 
    return false;
}
 
// Classifies a single binding's JavaScript function: does it belong to one of the compilation
// units participating in the rebuild (internal, will be recreated), or to some other component
// (external, must be preserved)? A null function is treated as external.
static bool isExternalFunction(const QV4::Function *f,
                               const std::vector<CompositeLevel> &internalUnits, QObject *target)
{
    if (!f)
        return true;
 
    for (const auto &internalUnit : internalUnits) {
        if (functionBelongsToObject(f, internalUnit.oldCu, internalUnit.objectIndex)
            || functionBelongsToObject(f, internalUnit.newCu, internalUnit.objectIndex)) {
            return false;
        }
    }
 
    return !rebuildReachesUnitViaContext(f->executableCompilationUnit(), internalUnits, target);
}
 
// A translation binding has no JavaScript function, so it cannot be classified via
// isExternalFunction. Classify it by its compilation unit instead: it is internal if that unit is
// one of the units being rebuilt, directly or through the context chain.
static bool isExternalUnitBinding(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &cu,
                                  const std::vector<CompositeLevel> &internalUnits, QObject *target)
{
    if (!cu)
        return true;
 
    for (const auto &internalUnit : internalUnits) {
        if (internalUnit.oldCu == cu || internalUnit.newCu == cu)
            return false;
    }
 
    return !rebuildReachesUnitViaContext(cu, internalUnits, target);
}
 
// Determines whether a binding on a property is "external", i.e. not from any of the
// compilation units that participate in the rebuild of this object.
// External bindings come from other compilation units (e.g. a parent component setting a
// property binding on a child instance) and must be preserved across rebuilds.
static bool isExternalBinding(const QQmlAnyBinding &binding,
                              const std::vector<CompositeLevel> &internalUnits, QObject *target)
{
    if (!binding)
        return false;
 
    if (const QQmlAbstractBinding *abstractBinding = binding.asAbstractBinding()) {
        switch (abstractBinding->kind()) {
        case QQmlAbstractBinding::QmlBinding: {
            const auto *qmlBinding = static_cast<const QQmlBinding *>(abstractBinding);
            if (const QV4::Function *f = qmlBinding->function())
                return isExternalFunction(f, internalUnits, target);
            // No function: this may be a translation binding. Classify it by its compilation unit.
            return isExternalUnitBinding(qmlBinding->compilationUnit(), internalUnits, target);
        }
        case QQmlAbstractBinding::ValueTypeProxy: {
            // A value-type group binding has no function of its own: it is a proxy holding one
            // QQmlBinding per bound sub-property. Classify it by its sub-bindings.
            const auto *proxy = static_cast<const QQmlValueTypeProxyBinding *>(abstractBinding);
            for (QQmlAbstractBinding *sub = proxy->subBindings(); sub; sub = sub->nextBinding()) {
                if (sub->kind() != QQmlAbstractBinding::QmlBinding)
                    continue;
                if (!isExternalFunction(static_cast<const QQmlBinding *>(sub)->function(),
                                        internalUnits, target)) {
                    return false;
                }
            }
            return true;
        }
        case QQmlAbstractBinding::PropertyToPropertyBinding:
            return true;
        }
        return true;
    }
 
    if (const QPropertyBindingPrivate *priv =
                QPropertyBindingPrivate::get(binding.asUntypedPropertyBinding())) {
        if (priv->isQmlBinding()) {
            // Check if it's a QQmlPropertyBinding with a JS expression we can trace back to a CU.
            const auto base = static_cast<const QQmlPropertyBindingBase *>(priv);
            if (base->bindingKind() == QQmlPropertyBindingBase::BindingKind::JavaScript) {
                if (const QQmlPropertyBindingJS *jsExpr =
                            static_cast<const QQmlPropertyBinding *>(base)->jsExpression()) {
                    return isExternalFunction(jsExpr->function(), internalUnits, target);
                }
            }
        } else if (const auto cu = QQmlTranslationPropertyBinding::compilationUnit(priv)) {
            // A translation binding on a bindable property is a plain QUntypedPropertyBinding
            // rather than a QQmlPropertyBinding. Recover its compilation unit to classify it like
            // the QQmlBinding case.
            return isExternalUnitBinding(cu, internalUnits, target);
        }
    }
 
    return true;
}
 
static QObject *propertyToPropertySource(const QQmlAnyBinding &binding)
{
    if (const QQmlAbstractBinding *abstractBinding = binding.asAbstractBinding()) {
        if (abstractBinding->kind() == QQmlAbstractBinding::PropertyToPropertyBinding) {
            return static_cast<const QQmlPropertyToUnbindablePropertyBinding *>(abstractBinding)
                    ->source();
        }
    } else if (const QPropertyBindingPrivate *priv =
                       QPropertyBindingPrivate::get(binding.asUntypedPropertyBinding());
               priv && priv->isQmlBinding()) {
        const auto base = static_cast<const QQmlPropertyBindingBase *>(priv);
        if (base->bindingKind() == QQmlPropertyBindingBase::BindingKind::PropertyToProperty)
            return static_cast<const QQmlPropertyToBindablePropertyBinding *>(priv)->source();
    }
    return nullptr;
}
 
static QVariant literalBindingValue(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit,
                             const QV4::CompiledData::Binding *binding)
{
    switch (binding->type()) {
    case QV4::CompiledData::Binding::Type_Number: {
        const double d = unit->bindingValueAsNumber(binding);
        return QV4::Value::isInt32(d) ? QVariant(int(d)) : QVariant(d);
    }
    case QV4::CompiledData::Binding::Type_Boolean:
        return QVariant(bool(binding->value.b));
    case QV4::CompiledData::Binding::Type_Translation:
    case QV4::CompiledData::Binding::Type_TranslationById:
    case QV4::CompiledData::Binding::Type_String:
        return unit->bindingValueAsString(binding);
    case QV4::CompiledData::Binding::Type_Null:
        return QVariant::fromValue(nullptr);
    default:
        // Script bindings, object bindings, etc. carry no constant value.
        return QVariant();
    }
}
 
static QVariant coerceToPropertyType(QV4::ExecutionEngine *v4, const QVariant &value,
                              QMetaType propertyType)
{
    if (propertyType == QMetaType::fromType<QVariant>() || value.metaType() == propertyType)
        return value;
 
    QV4::Scope scope(v4);
    QV4::ScopedValue v(scope, v4->metaTypeToJS(value.metaType(), value.constData()));
    QVariant result(propertyType);
    v4->metaTypeFromJS(v, propertyType, result.data());
    return result;
}
 
void BindingPatchContext::recordBindingValues(
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit, int cuIndex,
        QHash<QString, QVariant> *constantValues, QDuplicateTracker<QObject *> *seenChildren)
{
    Q_ASSERT(constantValues);
 
    if (!unit || cuIndex >= unit->objectCount())
        return;
 
    const QV4::CompiledData::Object *obj = unit->objectAt(cuIndex);
    const QQmlPropertyCache::ConstPtr cache = unit->propertyCachesPtr()->at(cuIndex);
 
    for (auto binding = obj->bindingsBegin(), end = obj->bindingsEnd(); binding != end; ++binding) {
 
        const QString name = targetPropertyName(unit, cuIndex, binding);
        if (name.isEmpty())
            continue;
 
        switch (binding->type()) {
        case QV4::CompiledData::Binding::Type_AttachedProperty:
            attachedContext(unit, binding, seenChildren);
            continue;
        case QV4::CompiledData::Binding::Type_GroupedProperty:
            childContext(unit, cuIndex, binding, seenChildren);
            continue;
        default:
            break;
        }
 
        if (unit->bindingIsSignalHandler(cuIndex, int(binding - obj->bindingsBegin())))
            continue;
 
        if (unit->bindingIsCustomParser(cuIndex, int(binding - obj->bindingsBegin())))
            continue;
 
        const qsizetype size = constantValues->size();
        QVariant &value = (*constantValues)[name];
        if (constantValues->size() == size)
            continue;
 
        // Extract constant value from the binding for comparison. Script and object bindings
        // yield an invalid QVariant: they shouldn't be touched since we've just installed the
        // new bindings (unless there is yet another, external binding).
        value = literalBindingValue(unit, binding);
    }
 
    for (int propertyIndex = 0, end = obj->propertyCount(); propertyIndex != end; ++propertyIndex) {
        const qsizetype size = constantValues->size();
        QVariant &value =
                (*constantValues)[unit->stringAt(obj->propertyTable()[propertyIndex].nameIndex())];
        if (constantValues->size() != size)
            value = QVariant(cache->property(cache->propertyOffset() + propertyIndex)->propType());
    }
}
 
void BindingPatchContext::stashExternalState(const std::vector<CompositeLevel> &internalUnits,
                                             QDuplicateTracker<QObject *> *seenChildren)
{
    // Determine which properties are assigned by the CU and their constant values
    QHash<QString, QVariant> constantValues;
    recordBindingValues(unit, objectIndex, &constantValues, seenChildren);
 
    if (prefix.isEmpty()) {
        const QQmlData *ddata = QQmlData::get(m_object);
        if (ddata->compilationUnit) {
            recordBindingValues(ddata->compilationUnit, ddata->cuObjectIndex, &constantValues,
                                seenChildren);
        }
 
        if (ddata->hasVMEMetaObject) {
            for (QQmlVMEMetaObject *vmeMeta = static_cast<QQmlVMEMetaObject *>(
                         QObjectPrivate::get(m_object)->metaObject);
                 vmeMeta; vmeMeta = vmeMeta->parentVMEMetaObject()) {
                if (auto cu = vmeMeta->compilationUnit())
                    recordBindingValues(cu, vmeMeta->qmlObjectId(), &constantValues, seenChildren);
            }
        }
    }
 
    // Iterate all properties. For those in the CU's binding table, check if the current state
    // differs from what the CU set (indicating an external override to preserve). For the rest,
    // check for external bindings installed by other components.
    // Additionally, for QObject* properties pointing to QML-created children, register them
    // as child contexts so their external signal handlers are stashed recursively at the end.
    const QMetaObject *mo = m_object->metaObject();
    for (int i = 0, count = mo->propertyCount(); i < count; ++i) {
        const QMetaProperty metaProp = mo->property(i);
        const QString propName = QString::fromUtf8(metaProp.name());
 
        const QQmlProperty qProp(m_object, propName);
        if (!qProp.isValid())
            continue;
 
        // Discover QML-created child objects accessible via QObject* properties.
        // Objects without a CU (like lazily-created grouped property objects) survive
        // rebuilds unchanged and don't need stashing.
        if (qProp.propertyMetaType().flags().testFlag(QMetaType::PointerToQObject)) {
            if (QObject *child = qProp.read().value<QObject *>()) {
                if (QQmlData *childDdata = QQmlData::get(child)) {
                    if (const auto &childCU = childDdata->compilationUnit; childCU
                        && std::find_if(internalUnits.begin(), internalUnits.end(),
                                        [&](const CompositeLevel &level) {
                                            return level.newCu == childCU || level.oldCu == childCU;
                                        })
                                != internalUnits.end()) {
                        childContext(propName, child, childCU, childDdata->cuObjectIndex,
                                     seenChildren);
                    }
                }
            }
        }
 
        const auto it = constantValues.constFind(propName);
        if (it == constantValues.cend()) {
            // Property not in CU's binding table — check for external bindings.
            const QQmlAnyBinding binding = QQmlAnyBinding::ofProperty(qProp);
            if (isExternalBinding(binding, internalUnits, m_object)) {
                QQmlAnyBinding taken = QQmlAnyBinding::takeFrom(qProp);
                m_storedBindings.push_back(
                        { propName, std::move(taken), propertyToPropertySource(binding) });
            }
            continue;
        }
 
        // Property is in the CU's binding table.
        const QQmlAnyBinding binding = QQmlAnyBinding::ofProperty(qProp);
        if (isExternalBinding(binding, internalUnits, m_object)) {
            QQmlAnyBinding taken = QQmlAnyBinding::takeFrom(qProp);
            m_storedBindings.push_back(
                    { propName, std::move(taken), propertyToPropertySource(binding) });
            continue;
        }
 
        // Internal binding is still valid. Apparently it doesn't get overridden by an external
        // constant or binding. Nothing to store.
        if (binding)
            continue;
 
        if (!it->isValid()) {
            // This is potentially an internal binding overridden by an external constant. But
            // it can also be an enum assignment optimized away to omit the binding itself. We
            // can't discern those. So we don't store them for now.
            // TODO: We can probably do better here.
            continue;
        }
 
        // Two constant values. Figure out if they're the same. If not, store.
 
        const QVariant expected = coerceToPropertyType(unit->engine, *it, qProp.propertyMetaType());
        if (const QVariant current = qProp.read(); current != expected)
            m_storedValues.push_back({ propName, current });
    }
 
    const auto stashBoundSignal = [&](QQmlBoundSignal *boundSignal) {
        const QByteArray signature =
                QMetaObjectPrivate::signal(m_object->metaObject(), boundSignal->signalIndex())
                        .methodSignature();
        QQmlNotifierEndpoint *next = boundSignal->nextEndpoint();
        boundSignal->disconnect();
        m_storedSignalHandlers.push_back(
                { QString::fromUtf8(signature), std::unique_ptr<QQmlBoundSignal>(boundSignal) });
        return next;
    };
 
    // Stash external signal handlers connected to this object's signals.
    // A handler is "internal" only if its function will be recreated during repopulation
    // (i.e., it's a signal handler binding at one of the specific object indices being rebuilt).
    // Only QQmlBoundSignal endpoints are stashed — other notifier endpoints (e.g. alias
    // tracking) are embedded in VME data arrays and cannot be safely owned or relocated.
    if (QQmlNotifyList *list = QQmlData::get(m_object)->notifyList.loadRelaxed()) {
        // Ensure all endpoints are moved from the pending 'todo' list into the
        // laid-out 'notifies' array. Endpoints remain in 'todo' until a signal
        // with a high enough index is actually delivered, so without this call
        // we'd miss handlers for signals that were never fired (e.g. clicked()).
        if (list->todo)
            list->layout();
        for (quint16 i = 0, end = list->notifiesSize; i < end; ++i) {
            for (QQmlNotifierEndpoint *ep = list->notifies[i]; ep;) {
                if (ep->callbackType() != QQmlNotifierEndpoint::QQmlBoundSignal) {
                    ep = ep->nextEndpoint();
                    continue;
                }
 
                QQmlBoundSignal *boundSignal = static_cast<QQmlBoundSignal *>(ep);
                QQmlBoundSignalExpression *expr = boundSignal->expression();
                if (!expr) {
                    ep = stashBoundSignal(boundSignal);
                    continue;
                }
 
                const QV4::Function *f = expr->function();
                if (!f) {
                    ep = stashBoundSignal(boundSignal);
                    continue;
                }
 
                bool isInternal = false;
                for (const CompositeLevel &internalUnit : internalUnits) {
                    if (functionBelongsToObject(f, internalUnit.oldCu, internalUnit.objectIndex)
                        || functionBelongsToObject(f, internalUnit.newCu,
                                                   internalUnit.objectIndex)) {
                        isInternal = true;
                        break;
                    }
                }
 
                ep = isInternal ? ep->nextEndpoint() : stashBoundSignal(boundSignal);
            }
        }
    }
 
    // Recurse into child contexts (grouped properties)
    for (auto &[name, child] : m_children) {
        if (child)
            child->stashExternalState(internalUnits, seenChildren);
    }
}
 
void BindingPatchContext::refreshObjects()
{
    if (!m_object)
        return;
 
    // After a rebuild, child objects (accessed via grouped properties) may have
    // been replaced. Re-fetch QObject pointers from the parent's properties so
    // that restoreExternalState() reconnects to the new objects.
    for (auto &[name, child] : m_children) {
        if (!child)
            continue;
 
        // Children with a non-empty prefix share m_object with their parent
        // (value-type grouped properties like "font."). Update them to match.
        if (!child->prefix.isEmpty()) {
            child->m_object = m_object;
            child->refreshObjects();
            continue;
        }
 
        if (QObject *newObj = m_object->property(name.toUtf8()).value<QObject *>())
            child->m_object = newObj;
 
        child->refreshObjects();
    }
}
 
void BindingPatchContext::restoreExternalState()
{
    if (!m_object)
        return;
 
    // Restore external bindings (look up by name since indices may have shifted)
    for (auto &stored : m_storedBindings) {
        if (!stored.binding)
            continue;
 
        // If this was a property-to-property binding, verify the source object survived the
        // rebuild. Delegate model items (the source for required-property bindings) are
        // destroyed when the delegate is re-instantiated and new bindings are created
        // automatically. Restoring a stale binding would dereference freed memory.
        if (stored.sourceGuard.isNull()) {
            bool isPTP = false;
            if (auto *abstractBinding = stored.binding.asAbstractBinding()) {
                isPTP = abstractBinding->kind()
                        == QQmlAbstractBinding::PropertyToPropertyBinding;
            } else if (const QPropertyBindingPrivate *priv = QPropertyBindingPrivate::get(
                               stored.binding.asUntypedPropertyBinding())) {
                const auto base = static_cast<const QQmlPropertyBindingBase *>(priv);
                isPTP = base->bindingKind()
                        == QQmlPropertyBindingBase::BindingKind::PropertyToProperty;
            }
            if (isPTP)
                continue;
        }
 
        QQmlProperty qProp(m_object, stored.propertyName);
        if (!qProp.isValid())
            continue;
 
        // After a rebuild, child objects may have been replaced (refreshObjects).
        // The stashed binding's targetObject still references the old object.
        // Update it to the new object before installing, otherwise installOn()
        // asserts that targetObject() == target.object().
        if (auto *abstractBinding = stored.binding.asAbstractBinding()) {
            if (abstractBinding->targetObject() != qProp.object())
                abstractBinding->setTarget(qProp);
        }
 
        stored.binding.installOn(qProp);
    }
    m_storedBindings.clear();
 
    // Restore externally set values (only if no new binding was installed)
    for (auto &stored : m_storedValues) {
        const QMetaObject *mo = m_object->metaObject();
        const int idx = mo->indexOfProperty(stored.propertyName.toUtf8().constData());
        if (idx < 0)
            continue;
 
        // Don't overwrite if a binding was just installed by repopulateBindings
        QQmlProperty qProp(m_object, stored.propertyName);
        if (!qProp.isValid())
            continue;
        QQmlAnyBinding currentBinding = QQmlAnyBinding::ofProperty(qProp);
        if (currentBinding)
            continue;
 
        mo->property(idx).write(m_object, stored.value);
    }
    m_storedValues.clear();
 
    // Restore external signal handlers that were detached during stash.
    // Reconnect them to this object's signals.
    if (!m_storedSignalHandlers.empty()) {
        QQmlEngine *engine = unit->engine->qmlEngine();
        for (auto &stored : m_storedSignalHandlers) {
            const QMetaObject *metaObject = m_object->metaObject();
            const int signalIndex = QMetaObjectPrivate::signalIndex(
                    metaObject->method(metaObject->indexOfSignal(stored.signature.toUtf8())));
            if (signalIndex >= 0)
                QQmlData::connectEndpoint(stored.handler.release(), m_object, signalIndex, engine);
        }
    }
    m_storedSignalHandlers.clear();
 
    // Recurse into child contexts (grouped properties)
    for (auto &[name, child] : m_children) {
        if (child)
            child->restoreExternalState();
    }
}
 
// The object referenced by the id "name" in the context the object belongs to, or nullptr if
// there is no such id. Used to resolve the first chain part of a generalized grouped property
// ("someId.x": here name == "someId").
static QObject *idTarget(QObject *object, const QString &name)
{
    const QQmlData *ddata = QQmlData::get(object);
    Q_ASSERT(ddata);
    QQmlContextData *context = ddata->ownContext ? ddata->ownContext.data() : ddata->context;
    Q_ASSERT(context);
    return context->asQQmlContext()->objectForName(name);
}
 
BindingPatchContext *
BindingPatchContext::childContext(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit,
                                  int objectIndex, const QV4::CompiledData::Binding *binding,
                                  QDuplicateTracker<QObject *> *seenChildren)
{
    const QString name = unit->stringAt(binding->propertyNameIndex);
 
    const size_t size = m_children.size();
    std::unique_ptr<BindingPatchContext> &child = m_children[name];
    if (size == m_children.size())
        return child.get();
 
    if (!seenChildren)
        return nullptr;
 
    const QByteArray nameUtf8 = name.toUtf8();
    QObject *groupObject = nullptr;
    if (m_object->metaObject()->indexOfProperty(nameUtf8.constData()) >= 0) {
        // "name" is a property of m_object, so it always wins over an id of the same name. A
        // QObject-valued property recurses into that object; a value-type property
        // ("font.pixelSize") uses a prefix on m_object (target stays null).
        groupObject = m_object->property(nameUtf8).value<QObject *>();
    } else if (unit->bindingIsDeferred(
                       objectIndex, int(binding - unit->objectAt(objectIndex)->bindingTable()))) {
        // Not a property of m_object: a deferred group binding is a generalized grouped
        // property whose first chain part is an id ("someId.x"), targeting an external object.
        //
        // This is a deferred property, so it's not actually guaranteed to do what we think
        // it does. However, if we actually find the expected object and if we can patch its
        // property, that is it's current value is the one we'd expect from the old binding, we
        // assume we're guessing right.
        groupObject = idTarget(m_object, name);
    }
 
    if (groupObject) {
        if (seenChildren->hasSeen(groupObject))
            return nullptr;
        child = std::make_unique<BindingPatchContext>(groupObject, unit,
                                                      binding->value.objectIndex);
    } else {
        child = std::make_unique<BindingPatchContext>(m_object, unit, binding->value.objectIndex,
                                                      name);
    }
    return child.get();
}
 
BindingPatchContext *
BindingPatchContext::childContext(const QString &name, QObject *object,
                                  const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit,
                                  int objectIndex, QDuplicateTracker<QObject *> *seenChildren)
{
    const size_t size = m_children.size();
    std::unique_ptr<BindingPatchContext> &child = m_children[name];
    if (size == m_children.size()) {
        Q_ASSERT(!child || child->m_object == object);
        return child.get();
    }
 
    if (!seenChildren || seenChildren->hasSeen(object))
        return nullptr;
 
    child = std::make_unique<BindingPatchContext>(object, unit, objectIndex);
    return child.get();
}
 
BindingPatchContext *
BindingPatchContext::attachedContext(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit,
                                     const QV4::CompiledData::Binding *binding,
                                     QDuplicateTracker<QObject *> *seenChildren)
{
    const QString name = unit->stringAt(binding->propertyNameIndex);
 
    const size_t size = m_children.size();
    std::unique_ptr<BindingPatchContext> &child = m_children[name];
    if (size == m_children.size())
        return child.get();
 
    if (!seenChildren)
        return nullptr;
 
    QV4::ResolvedTypeReference *typeRef = unit->resolvedType(binding->propertyNameIndex);
    Q_ASSERT(typeRef);
    QQmlAttachedPropertiesFunc func =
            typeRef->type().attachedPropertiesFunction(unit->engine->typeLoader());
    Q_ASSERT(func);
 
    if (QObject *attached = QQmlData::get(m_object)->attachedProperties()->value(func)) {
        if (seenChildren->hasSeen(attached))
            return nullptr;
        child = std::make_unique<BindingPatchContext>(attached, unit, binding->value.objectIndex);
    }
    return child.get();
}
 
bool BindingPatchContext::applyBindingChange(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &newUnit,
                                      const QV4::CompiledData::Change &change)
{
    Q_ASSERT(change.type == QV4::CompiledData::ChangeType::BindingChanged);
 
    if (!m_object || objectIndex < 0 || objectIndex >= unit->objectCount())
        return false;
 
    if (objectIndex == change.objectIndex) {
        patchBinding(newUnit, change);
        return true;
    }
 
    QDuplicateTracker<QObject *> seenChildren;
    const QV4::CompiledData::Object *obj = unit->objectAt(objectIndex);
    for (auto binding = obj->bindingsBegin(), end = obj->bindingsEnd(); binding != end; ++binding) {
        BindingPatchContext *child = nullptr;
        switch (binding->type()) {
        case QV4::CompiledData::Binding::Type_GroupedProperty:
            child = childContext(unit, objectIndex, binding, &seenChildren);
            break;
        case QV4::CompiledData::Binding::Type_AttachedProperty:
            child = attachedContext(unit, binding, &seenChildren);
            break;
        default:
            continue;
        }
        if (child && child->applyBindingChange(newUnit, change))
            return true;
    }
 
    return false;
}
 
void BindingPatchContext::reset(
        const std::vector<QQmlRefPointer<QV4::ExecutableCompilationUnit>> &unitsToUnparent,
        const std::vector<CompositeLevel> &internalUnits)
{
    QQmlData *ddata = QQmlData::get(m_object);
 
    const auto levelFor = [&internalUnits](
            const QQmlRefPointer<QV4::ExecutableCompilationUnit> &oldCu, int oldIndex) {
        for (const CompositeLevel &level : internalUnits) {
            if (level.oldCu == oldCu && level.objectIndex == oldIndex)
                return level;
        }
        return CompositeLevel();
    };
 
    const QHash<QQmlAttachedPropertiesFunc, QObject *> *attachedProperties =
            ddata->hasExtendedData() ? ddata->attachedProperties() : nullptr;
    QObjectList children = m_object->children();
 
    // Remove the children we shouldn't retire from the list. That is the ones that haven't been
    // created by the relevant compilation units.
    const auto newEnd = std::remove_if(children.begin(), children.end(), [&](QObject *child) {
        const QQmlData *childDdata = QQmlData::get(child);
        if (!childDdata)
            return true;
 
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &cu = childDdata->compilationUnit;
        if (!cu)
            return true;
 
        if (std::find(unitsToUnparent.begin(), unitsToUnparent.end(), cu) == unitsToUnparent.end())
            return true;
 
        if (!attachedProperties)
            return false;
 
        for (QObject *attached : *attachedProperties) {
            if (attached == child)
                return true;
        }
 
        return false;
    });
    children.erase(newEnd, children.end());
 
    // Remove childrens' bindings before resetBindings() runs.
    // resetBindings() clears list/default properties via list.clear(), which calls
    // setParentItem(nullptr) and emits parentChanged. Any QProperty binding on a
    // child that reads 'parent' would then fire with parent == null. Clearing those
    // bindings first prevents a flood of related warnings.
    for (QObject *child : children)
        clearBindingsRecursive(child);
 
    const CompositeLevel level = levelFor(unit, objectIndex);
    resetBindings(unit, objectIndex, level.newCu, level.objectIndex);
 
    for (QQmlVMEMetaObject *vmeMeta = ddata->hasVMEMetaObject
                 ? static_cast<QQmlVMEMetaObject *>(QObjectPrivate::get(m_object)->metaObject)
                 : nullptr;
         vmeMeta; vmeMeta = vmeMeta->parentVMEMetaObject()) {
        const CompositeLevel level = levelFor(vmeMeta->compilationUnit(), vmeMeta->qmlObjectId());
        resetBindings(vmeMeta->compilationUnit(), vmeMeta->qmlObjectId(), level.newCu,
                      level.objectIndex);
    }
 
    // Remove remaining composite signal handlers (all internal ones).
    // External handlers were already detached by stashExternalState() and are invisible here.
    // The object creator will recreate the internal handlers when it rebuilds the object.
    while (QQmlBoundSignal *signalHandler = ddata->signalHandlers)
        delete signalHandler;
 
    // Objects from the old CU or composite-level CUs will be recreated by
    // repopulateBindings. Unparent them so they don't interfere with the new objects.
    // Attached property objects are reused across rebuilds.
    for (QObject *child : children)
        retireObject(child);
}
 
// Fully retire an old object that is being replaced by repopulateBindings.
// Recursively removes bindings from all descendants (unlinking expressions
// from context lists), then removes the subtree from the tree and schedules it
// for deletion. compilationUnit is intentionally left intact. The GC needs it.
void BindingPatchContext::retireObject(QObject *object)
{
    // Remove from parent (in QtQuick "visual parent" or parentItem) via the meta property system.
    // We must not assume any particular property to be the "parent" property here. That's what
    // we have the ParentProperty classInfo for.
    const QMetaObject *mo = object->metaObject();
    if (const int classInfoIndex = mo->indexOfClassInfo("ParentProperty"); classInfoIndex >= 0) {
        const QMetaClassInfo classInfo = mo->classInfo(classInfoIndex);
        if (const int propertyIndex = mo->indexOfProperty(classInfo.value()); propertyIndex >= 0) {
            const QMetaProperty property = mo->property(propertyIndex);
            if ((!property.isResettable() || !property.reset(object)) && property.isWritable())
                property.write(object, QVariant(property.metaType()));
        }
    }
 
    // Unparent from QObject hierarchy so it no longer appears in
    // parent->children(), then schedule deletion. The destructor will
    // cascade-delete all QObject children (the recursive descendants).
    // Mark the whole subtree as queued for deletion right away. Descendants may themselves be
    // pending rebuild targets (e.g. inline component instances); they must not be rebuilt anymore.
    QQml_setParent_noEvent(object, nullptr);
    QQmlData::markAsDeleted(object);
    object->deleteLater();
}
 
void BindingPatchContext::clearBindingsRecursive(QObject *object)
{
    QQueue<QObject *> queue;
    queue.enqueue(object);
 
    while (!queue.isEmpty()) {
        QObject *next = queue.dequeue();
        queue.append(next->children());
 
        QQmlData *ddata = QQmlData::get(next);
        if (!ddata)
            continue;
 
        while (ddata->bindings)
            QQmlPropertyPrivate::removeBinding(ddata->bindings);
 
        // QProperty (BINDABLE) bindings live in the property's QPropertyBindingStorage,
        // not in ddata->bindings. Remove them so they don't re-evaluate when
        // setParentItem(nullptr) emits parentChanged during retireObject().
        const QMetaObject *mo = next->metaObject();
        for (int i = 0, n = mo->propertyCount(); i < n; ++i) {
            if (!ddata->hasBindingBit(i))
                continue;
            const QMetaProperty prop = mo->property(i);
            if (!prop.isBindable())
                continue;
            QUntypedBindable bindable = prop.bindable(next);
            if (bindable.hasBinding())
                bindable.takeBinding();
        }
 
        // Don't delete signal handlers right away since we might still have
        // them in other objects "external" state. Disable them so that they
        // don't fire anymore until this object is actually deleted.
        for (QQmlBoundSignal *sig = ddata->signalHandlers; sig; sig = sig->m_nextSignal)
            sig->setEnabled(false);
    }
}
 
// Map the names of the properties that the new compilation unit binds on the given object
// to their bindings. repopulateBindings() will re-assign these, so resetting them before
// is redundant.
static ReboundBindings reboundBindings(
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit, int cuIndex)
{
    ReboundBindings bindings;
    if (!unit || cuIndex < 0 || cuIndex >= unit->objectCount())
        return bindings;
 
    const QV4::CompiledData::Object *obj = unit->objectAt(cuIndex);
 
    for (auto binding = obj->bindingsBegin(), end = obj->bindingsEnd(); binding != end; ++binding)
        bindings.insert(BindingPatchContext::targetPropertyName(unit, cuIndex, binding), binding);
    return bindings;
}
 
// The new sub-object index for a group/attached property that the new CU rebinds with the
// same kind of binding, or -1 if the new CU doesn't rebind it.
static int reboundSubObjectIndex(const ReboundBindings &rebound,
                                 const QString &name, QV4::CompiledData::Binding::Type type)
{
    const QV4::CompiledData::Binding *newBinding = rebound.value(name);
    return (newBinding && newBinding->type() == type) ? newBinding->value.objectIndex : -1;
}
 
void BindingPatchContext::resetBinding(
        int objectIndex, const QV4::CompiledData::Binding *binding, const QString &name,
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &oldUnit,
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &newUnit,
        const ReboundBindings &rebound)
{
    QQmlProperty prop(m_object, prefix + name);
    QQmlPropertyIndex propIdx = QQmlPropertyPrivate::propertyIndex(prop);
    if (propIdx.coreIndex() < 0) {
        // A generalized grouped property whose first chain part is an id (e.g. "someId.x")
        // does not name a property of m_object; it targets an external object resolved by id.
        // Reset the sub-bindings on that target.
        Q_ASSERT(binding->isGroupedProperty());
        if (BindingPatchContext *child = childContext(oldUnit, objectIndex, binding, nullptr)) {
            child->resetBindings(
                    oldUnit, binding->value.objectIndex, newUnit,
                    reboundSubObjectIndex(rebound, name,
                                          QV4::CompiledData::Binding::Type_GroupedProperty));
        }
        return;
    }
 
    const QMetaType type = prop.propertyMetaType();
 
    const QMetaType::TypeFlags flags = type.flags();
    if (flags.testFlag(QMetaType::IsQmlList)) {
        // Lists need to always be cleared because they're generally additive.
        // TODO: Handle ListPropertyAssignBehavior
        QQmlListReference list = prop.read().value<QQmlListReference>();
        if (list.clear())
            return;
    } else if (flags.testFlag(QMetaType::PointerToQObject) && binding->isGroupedProperty()) {
        if (BindingPatchContext *child = childContext(oldUnit, objectIndex, binding, nullptr)) {
            child->resetBindings(
                    oldUnit, binding->value.objectIndex, newUnit,
                    reboundSubObjectIndex(rebound, name,
                                          QV4::CompiledData::Binding::Type_GroupedProperty));
        }
        return;
    }
 
    // Don't reset individual bindings that are re-bound anyway.
    if (rebound.contains(name))
        return;
 
    if ((!prop.isResettable() || !prop.reset()) && prop.isWritable())
        prop.write(QVariant(type));
}
 
void BindingPatchContext::resetBindings(
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &oldUnit, int cuIndex,
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &newUnit, int newCuIndex)
{
    const QV4::CompiledData::Object *obj = oldUnit->objectAt(cuIndex);
 
    const ReboundBindings rebound = reboundBindings(newUnit, newCuIndex);
 
    for (auto binding = obj->bindingsBegin(), end = obj->bindingsEnd(); binding != end; ++binding) {
        const QString name = targetPropertyName(oldUnit, cuIndex, binding);
        if (name.isEmpty())
            continue;
 
        if (binding->isAttachedProperty()) {
            // Recurse into existing attached objects to reset their bindings.
            // The object creator will reuse them via qmlAttachedPropertiesObject().
            if (!QQmlData::get(m_object)->hasExtendedData())
                continue;
 
            if (BindingPatchContext *attached = attachedContext(oldUnit, binding, nullptr)) {
                attached->resetBindings(
                        oldUnit, binding->value.objectIndex, newUnit,
                        reboundSubObjectIndex(rebound, name,
                                              QV4::CompiledData::Binding::Type_AttachedProperty));
            }
 
            continue;
        }
 
        if (oldUnit->bindingIsCustomParser(cuIndex, int(binding - obj->bindingsBegin())))
            continue;
 
        // Signal handlers are disconnected centrally.
        if (!oldUnit->bindingIsSignalHandler(cuIndex, int(binding - obj->bindingsBegin())))
            resetBinding(cuIndex, binding, name, oldUnit, newUnit, rebound);
    }
}
 
// The name of the property a binding assigns, resolving the default property for unnamed bindings.
QString
BindingPatchContext::targetPropertyName(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &unit,
                                        int objectIndex, const QV4::CompiledData::Binding *binding)
{
    if (binding->propertyNameIndex != 0)
        return unit->stringAt(binding->propertyNameIndex);
    const QQmlPropertyCache::ConstPtr cache = unit->propertyCachesPtr()->at(objectIndex);
    return cache ? cache->defaultPropertyName() : QString();
}
 
void BindingPatchContext::patchBinding(
        const QQmlRefPointer<QV4::ExecutableCompilationUnit> &newUnit,
        const QV4::CompiledData::Change &change)
{
    const QV4::CompiledData::Binding *newBinding =
            newUnit->objectAt(change.objectIndex)->bindingTable() + change.index;
    const QVariant newValue = literalBindingValue(newUnit, newBinding);
    if (!newValue.isValid())
        return; // Script binding: handled by function translation.
 
    const QQmlProperty qProp(m_object,
                             prefix + targetPropertyName(newUnit, change.objectIndex, newBinding));
    if (!qProp.isValid())
        return;
 
    QV4::ExecutionEngine *v4 = unit->engine;
    const QMetaType metaType = qProp.propertyMetaType();
 
    const QV4::CompiledData::Binding *oldBinding =
            unit->objectAt(change.objectIndex)->bindingTable() + change.index;
    const QVariant expectedOld =
            coerceToPropertyType(v4, literalBindingValue(unit, oldBinding), metaType);
    if (qProp.read() == expectedOld)
        qProp.write(coerceToPropertyType(v4, newValue, metaType));
}
 
} // namespace QQmlPreview
 
QT_END_NAMESPACE