qdeclarativeexpression.cpp

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#include "qdeclarativeexpression.h"
#include "private/qdeclarativeexpression_p.h"

#include "private/qdeclarativeengine_p.h"
#include "private/qdeclarativecontext_p.h"
#include "private/qdeclarativerewrite_p.h"
#include "private/qdeclarativescriptstring_p.h"
#include "private/qdeclarativecompiler_p.h"

#include <QtCore/qdebug.h>

QT_BEGIN_NAMESPACE

bool QDeclarativeDelayedError::addError(QDeclarativeEnginePrivate *e)
{
    if (!e) return false;

    if (e->inProgressCreations == 0) return false; // Not in construction

    if (prevError) return true; // Already in error chain

    prevError = &e->erroredBindings;
    nextError = e->erroredBindings;
    e->erroredBindings = this;
    if (nextError) nextError->prevError = &nextError;

    return true;
}

QDeclarativeJavaScriptExpression::QDeclarativeJavaScriptExpression()
: m_requiresThisObject(0), m_useSharedContext(0), m_notifyOnValueChanged(0), 
  m_scopeObject(0), m_notifyObject(0), m_notifyIndex(-1)
{
}

QDeclarativeJavaScriptExpression::~QDeclarativeJavaScriptExpression()
{
}

QDeclarativeExpressionPrivate::QDeclarativeExpressionPrivate()
: expressionFunctionValid(true), extractExpressionFromFunction(false), line(-1), dataRef(0)
{
}

QDeclarativeExpressionPrivate::~QDeclarativeExpressionPrivate()
{
    qPersistentDispose(v8qmlscope);
    qPersistentDispose(v8function);
    if (dataRef) dataRef->release();
    dataRef = 0;
}

void QDeclarativeExpressionPrivate::init(QDeclarativeContextData *ctxt, const QString &expr, 
                                         QObject *me)
{
    expression = expr;

    QDeclarativeAbstractExpression::setContext(ctxt);
    setScopeObject(me);
    expressionFunctionValid = false;
}

void QDeclarativeExpressionPrivate::init(QDeclarativeContextData *ctxt, v8::Handle<v8::Function> func,
                                         QObject *me)
{
    QDeclarativeAbstractExpression::setContext(ctxt);
    setScopeObject(me);

    v8function = qPersistentNew<v8::Function>(func);
    setUseSharedContext(false);
    expressionFunctionValid = true;
    extractExpressionFromFunction = true;
}

void QDeclarativeExpressionPrivate::init(QDeclarativeContextData *ctxt, const QString &expr, bool isRewritten,
                                         QObject *me, const QString &srcUrl, int lineNumber)
{
    url = srcUrl;
    line = lineNumber;

    expression = expr;

    if (!isRewritten) {
        expressionFunctionValid = false;
    } else {
        v8function = evalFunction(ctxt, me, expression, url, line, &v8qmlscope);
        expressionFunctionValid = true;
    }

    QDeclarativeAbstractExpression::setContext(ctxt);
    setScopeObject(me);
}

// Callee owns the persistent handle
v8::Persistent<v8::Function> 
QDeclarativeExpressionPrivate::evalFunction(QDeclarativeContextData *ctxt, QObject *scope, 
                                            const QString &code, const QString &filename, int line,
                                            v8::Persistent<v8::Object> *qmlscope)
{
    QDeclarativeEngine *engine = ctxt->engine;
    QDeclarativeEnginePrivate *ep = QDeclarativeEnginePrivate::get(engine);

    // XXX TODO: Implement script caching, like we used to do with QScriptProgram in the
    // QtScript days
    v8::HandleScope handle_scope;
    v8::Context::Scope ctxtscope(ep->v8engine()->context());
    
    v8::TryCatch tc;
    v8::Local<v8::Object> scopeobject = ep->v8engine()->qmlScope(ctxt, scope);
    v8::Local<v8::Script> script = ep->v8engine()->qmlModeCompile(code, filename, line);
    v8::Local<v8::Value> result = script->Run(scopeobject);
    if (tc.HasCaught()) return v8::Persistent<v8::Function>();
    if (qmlscope) *qmlscope = qPersistentNew<v8::Object>(scopeobject);
    return qPersistentNew<v8::Function>(v8::Local<v8::Function>::Cast(result));
}

/*!
    \class QDeclarativeExpression
    \since 4.7
    \brief The QDeclarativeExpression class evaluates JavaScript in a QML context.

    For example, given a file \c main.qml like this:

    \qml
    import QtQuick 1.0

    Item {
        width: 200; height: 200
    }
    \endqml

    The following code evaluates a JavaScript expression in the context of the
    above QML:

    \code
    QDeclarativeEngine *engine = new QDeclarativeEngine;
    QDeclarativeComponent component(engine, QUrl::fromLocalFile("main.qml"));

    QObject *myObject = component.create();
    QDeclarativeExpression *expr = new QDeclarativeExpression(engine->rootContext(), myObject, "width * 2");
    int result = expr->evaluate().toInt();  // result = 400
    \endcode
*/

static int QDeclarativeExpression_notifyIdx = -1;

/*!
    Create an invalid QDeclarativeExpression.

    As the expression will not have an associated QDeclarativeContext, this will be a
    null expression object and its value will always be an invalid QVariant.
 */
QDeclarativeExpression::QDeclarativeExpression()
: QObject(*new QDeclarativeExpressionPrivate, 0)
{
    Q_D(QDeclarativeExpression);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!  \internal */
QDeclarativeExpression::QDeclarativeExpression(QDeclarativeContextData *ctxt, 
                                               QObject *object, const QString &expr, bool isRewritten,
                                               const QString &url, int lineNumber, 
                                               QDeclarativeExpressionPrivate &dd)
: QObject(dd, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expr, isRewritten, object, url, lineNumber);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!
    Create a QDeclarativeExpression object that is a child of \a parent.

    The \script provides the expression to be evaluated, the context to evaluate it in,
    and the scope object to evaluate it with.

    This constructor is functionally equivalent to the following, but in most cases
    is more efficient.
    \code
    QDeclarativeExpression expression(script.context(), script.scopeObject(), script.script(), parent);
    \endcode

    \sa QDeclarativeScriptString
*/
QDeclarativeExpression::QDeclarativeExpression(const QDeclarativeScriptString &script, QObject *parent)
: QObject(*new QDeclarativeExpressionPrivate, parent)
{
    Q_D(QDeclarativeExpression);
    bool defaultConstruction = false;

    int id = script.d.data()->bindingId;
    if (id < 0) {
        defaultConstruction = true;
    } else {
        QDeclarativeContextData *ctxtdata = QDeclarativeContextData::get(script.context());

        QDeclarativeEnginePrivate *engine = QDeclarativeEnginePrivate::get(qmlEngine(script.scopeObject()));
        QDeclarativeCompiledData *cdata = 0;
        QDeclarativeTypeData *typeData = 0;
        if (engine && ctxtdata && !ctxtdata->url.isEmpty()) {
            typeData = engine->typeLoader.get(ctxtdata->url);
            cdata = typeData->compiledData();
        }

        if (cdata)
            d->init(ctxtdata, cdata->primitives.at(id), cdata, script.scopeObject(),
                    cdata->name, script.d.data()->lineNumber);
        else
           defaultConstruction = true;

        if (typeData)
            typeData->release();
    }

    if (defaultConstruction)
        d->init(QDeclarativeContextData::get(script.context()), script.script(), script.scopeObject());

    if (QDeclarativeExpression_notifyIdx == -1)
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!
    Create a QDeclarativeExpression object that is a child of \a parent.

    The \a expression JavaScript will be executed in the \a ctxt QDeclarativeContext.
    If specified, the \a scope object's properties will also be in scope during
    the expression's execution.
*/
QDeclarativeExpression::QDeclarativeExpression(QDeclarativeContext *ctxt,
                                               QObject *scope,
                                               const QString &expression,
                                               QObject *parent)
: QObject(*new QDeclarativeExpressionPrivate, parent)
{
    Q_D(QDeclarativeExpression);
    d->init(QDeclarativeContextData::get(ctxt), expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*! 
    \internal
*/
QDeclarativeExpression::QDeclarativeExpression(QDeclarativeContextData *ctxt, QObject *scope,
                                               const QString &expression)
: QObject(*new QDeclarativeExpressionPrivate, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!  \internal */
QDeclarativeExpression::QDeclarativeExpression(QDeclarativeContextData *ctxt, QObject *scope,
                                               const QString &expression, QDeclarativeExpressionPrivate &dd)
: QObject(dd, 0)
{
    Q_D(QDeclarativeExpression);
    d->init(ctxt, expression, scope);

    if (QDeclarativeExpression_notifyIdx == -1) 
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");
    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!  
    \internal 

    To avoid exposing v8 in the public API, functionPtr must be a pointer to a v8::Handle<v8::Function>.  
    For example:
        v8::Handle<v8::Function> function;
        new QDeclarativeExpression(ctxt, scope, &function, ...);
 */
QDeclarativeExpression::QDeclarativeExpression(QDeclarativeContextData *ctxt, QObject *scope, void *functionPtr,
                                               QDeclarativeExpressionPrivate &dd)
: QObject(dd, 0)
{
    v8::Handle<v8::Function> function = *(v8::Handle<v8::Function> *)functionPtr;

    Q_D(QDeclarativeExpression);
    d->init(ctxt, function, scope);

    if (QDeclarativeExpression_notifyIdx == -1)
        QDeclarativeExpression_notifyIdx = QDeclarativeExpression::staticMetaObject.indexOfMethod("_q_notify()");

    d->setNotifyObject(this, QDeclarativeExpression_notifyIdx);
}

/*!
    Destroy the QDeclarativeExpression instance.
*/
QDeclarativeExpression::~QDeclarativeExpression()
{
}

/*!
    Returns the QDeclarativeEngine this expression is associated with, or 0 if there
    is no association or the QDeclarativeEngine has been destroyed.
*/
QDeclarativeEngine *QDeclarativeExpression::engine() const
{
    Q_D(const QDeclarativeExpression);
    return d->context()?d->context()->engine:0;
}

/*!
    Returns the QDeclarativeContext this expression is associated with, or 0 if there
    is no association or the QDeclarativeContext has been destroyed.
*/
QDeclarativeContext *QDeclarativeExpression::context() const
{
    Q_D(const QDeclarativeExpression);
    QDeclarativeContextData *data = d->context();
    return data?data->asQDeclarativeContext():0;
}

/*!
    Returns the expression string.
*/
QString QDeclarativeExpression::expression() const
{
    Q_D(const QDeclarativeExpression);
    if (d->extractExpressionFromFunction && context()->engine()) {
        QV8Engine *v8engine = QDeclarativeEnginePrivate::getV8Engine(context()->engine());
        v8::HandleScope handle_scope;
        v8::Context::Scope scope(v8engine->context());

        return v8engine->toString(v8::Handle<v8::Value>(d->v8function));
    }
    return d->expression;
}

/*!
    Set the expression to \a expression.
*/
void QDeclarativeExpression::setExpression(const QString &expression)
{
    Q_D(QDeclarativeExpression);

    d->resetNotifyOnValueChanged();
    d->expression = expression;
    d->expressionFunctionValid = false;
    qPersistentDispose(d->v8function);
    qPersistentDispose(d->v8qmlscope);
}

void QDeclarativeExpressionPrivate::exceptionToError(v8::Handle<v8::Message> message, 
                                                     QDeclarativeError &error)
{
    Q_ASSERT(!message.IsEmpty());

    v8::Handle<v8::Value> name = message->GetScriptResourceName();
    v8::Handle<v8::String> description = message->Get();
    int lineNumber = message->GetLineNumber();

    v8::Local<v8::String> file = name->IsString()?name->ToString():v8::Local<v8::String>();
    if (file.IsEmpty() || file->Length() == 0) 
        error.setUrl(QUrl(QLatin1String("<Unknown File>")));
    else 
        error.setUrl(QUrl(QV8Engine::toStringStatic(file)));

    error.setLine(lineNumber);
    error.setColumn(-1);

    QString qDescription = QV8Engine::toStringStatic(description);
    if (qDescription.startsWith(QLatin1String("Uncaught ")))
        qDescription = qDescription.mid(9 /* strlen("Uncaught ") */);

    error.setDescription(qDescription);
}

void QDeclarativeJavaScriptExpression::setNotifyOnValueChanged(bool v)
{
    m_notifyOnValueChanged = v;
    if (!v) guardList.clear();
}

void QDeclarativeJavaScriptExpression::resetNotifyOnValueChanged()
{
    guardList.clear();
}

void QDeclarativeJavaScriptExpression::setNotifyObject(QObject *object, int index)
{
    guardList.clear();

    m_notifyObject = object;
    m_notifyIndex = index;

    if (!object || index == -1) {
        m_notifyObject = 0;
        m_notifyIndex = -1;
    }
}

v8::Local<v8::Value> QDeclarativeJavaScriptExpression::evaluate(v8::Handle<v8::Function> function, bool *isUndefined)
{
    Q_ASSERT(context() && context()->engine);
    Q_ASSERT(!notifyOnValueChanged() || (m_notifyObject && m_notifyIndex != -1));

    if (function.IsEmpty() || function->IsUndefined()) {
        if (isUndefined) *isUndefined = true;
        return v8::Local<v8::Value>();
    }

    QDeclarativeEnginePrivate *ep = QDeclarativeEnginePrivate::get(context()->engine);

    bool lastCaptureProperties = ep->captureProperties;
    QPODVector<QDeclarativeEnginePrivate::CapturedProperty> lastCapturedProperties;
    ep->captureProperties = notifyOnValueChanged();

    if (ep->capturedProperties.count())
        ep->capturedProperties.copyAndClear(lastCapturedProperties);

    QDeclarativeContextData *lastSharedContext = 0;
    QObject *lastSharedScope = 0;

    bool sharedContext = useSharedContext();

    // All code that follows must check with watcher before it accesses data members 
    // incase we have been deleted.
    QDeclarativeDeleteWatcher watcher(this);

    if (sharedContext) {
        lastSharedContext = ep->sharedContext;
        lastSharedScope = ep->sharedScope;
        ep->sharedContext = context();
        ep->sharedScope = scopeObject();
    }

    v8::Local<v8::Value> result;
    {
        v8::TryCatch try_catch;
        v8::Handle<v8::Object> This = ep->v8engine()->global();
        if (scopeObject() && requiresThisObject()) {
            v8::Handle<v8::Value> value = ep->v8engine()->newQObject(scopeObject());
            if (value->IsObject()) This = v8::Handle<v8::Object>::Cast(value);
        }

        result = function->Call(This, 0, 0);

        if (isUndefined)
            *isUndefined = try_catch.HasCaught() || result->IsUndefined();

        if (watcher.wasDeleted()) {
        } else if (try_catch.HasCaught()) {
            v8::Context::Scope scope(ep->v8engine()->context());
            v8::Local<v8::Message> message = try_catch.Message();
            if (!message.IsEmpty()) {
                QDeclarativeExpressionPrivate::exceptionToError(message, error);
            } else {
                error = QDeclarativeError();
            }
        } else {
            error = QDeclarativeError();
        }
    }

    if (sharedContext) {
        ep->sharedContext = lastSharedContext;
        ep->sharedScope = lastSharedScope;
    }

    if (!watcher.wasDeleted() && notifyOnValueChanged()) {
        guardList.updateGuards(m_notifyObject, m_notifyIndex, this, ep->capturedProperties);
    }

    if (lastCapturedProperties.count())
        lastCapturedProperties.copyAndClear(ep->capturedProperties);
    else
        ep->capturedProperties.clear();

    ep->captureProperties = lastCaptureProperties;

    return result;
}

void QDeclarativeJavaScriptExpression::GuardList::updateGuards(QObject *notifyObject, int notifyIndex,
                                                               QDeclarativeJavaScriptExpression *expression,
                                                               const CapturedProperties &properties)
{
    Q_ASSERT(notifyObject);
    Q_ASSERT(notifyIndex != -1);

    if (properties.count() == 0) {
        clear();
        return;
    }

    if (properties.count() != length) {
        QDeclarativeNotifierEndpoint *newGuardList = new QDeclarativeNotifierEndpoint[properties.count()];

        for (int ii = 0; ii < qMin(length, properties.count()); ++ii) 
           endpoints[ii].copyAndClear(newGuardList[ii]);

        delete [] endpoints;
        endpoints = newGuardList;
        length = properties.count();
    }

    bool outputWarningHeader = false;
    bool noChanges = true;
    for (int ii = 0; ii < properties.count(); ++ii) {
        QDeclarativeNotifierEndpoint &guard = endpoints[ii];
        const QDeclarativeEnginePrivate::CapturedProperty &property = properties.at(ii);

        guard.target = notifyObject;
        guard.targetMethod = notifyIndex;

        if (property.notifier != 0) {

            if (!noChanges && guard.isConnected(property.notifier)) {
                // Nothing to do

            } else {
                noChanges = false;

                bool existing = false;
                for (int jj = 0; !existing && jj < ii; ++jj) 
                    if (endpoints[jj].isConnected(property.notifier)) 
                        existing = true;

                if (existing) {
                    // duplicate
                    guard.disconnect();
                } else {
                    guard.connect(property.notifier);
                }
            }


        } else if (property.notifyIndex != -1) {

            if (!noChanges && guard.isConnected(property.object, property.notifyIndex)) {
                // Nothing to do

            } else {
                noChanges = false;

                bool existing = false;
                for (int jj = 0; !existing && jj < ii; ++jj) 
                    if (endpoints[jj].isConnected(property.object, property.notifyIndex)) 
                        existing = true;

                if (existing) {
                    // duplicate
                    guard.disconnect();
                } else {
                    guard.connect(property.object, property.notifyIndex);
                }
            }

        } else {
            if (!outputWarningHeader) {
                QString e = expression->expressionIdentifier();
                outputWarningHeader = true;
                qWarning() << "QDeclarativeExpression: Expression" << qPrintable(e)
                           << "depends on non-NOTIFYable properties:";
            }

            const QMetaObject *metaObj = property.object->metaObject();
            QMetaProperty metaProp = metaObj->property(property.coreIndex);

            qWarning().nospace() << "    " << metaObj->className() << "::" << metaProp.name();
        }
    }
}

// Must be called with a valid handle scope
v8::Local<v8::Value> QDeclarativeExpressionPrivate::v8value(QObject *secondaryScope, bool *isUndefined)
{
    if (!expressionFunctionValid) {
        QDeclarativeRewrite::RewriteBinding rewriteBinding;
        rewriteBinding.setName(name);
        bool ok = true;
        const QString code = rewriteBinding(expression, &ok);
        if (ok) v8function = evalFunction(context(), scopeObject(), code, url, line, &v8qmlscope);
        setUseSharedContext(false);
        expressionFunctionValid = true;
    }


    if (secondaryScope) {
        v8::Local<v8::Value> result;
        QDeclarativeEnginePrivate *ep = QDeclarativeEnginePrivate::get(context()->engine);
        QObject *restoreSecondaryScope = 0;
        restoreSecondaryScope = ep->v8engine()->contextWrapper()->setSecondaryScope(v8qmlscope, secondaryScope);
        result = evaluate(v8function, isUndefined);
        ep->v8engine()->contextWrapper()->setSecondaryScope(v8qmlscope, restoreSecondaryScope);
        return result;
    } else {
        return evaluate(v8function, isUndefined);
    }
}

QVariant QDeclarativeExpressionPrivate::value(QObject *secondaryScope, bool *isUndefined)
{
    Q_Q(QDeclarativeExpression);

    if (!context() || !context()->isValid()) {
        qWarning("QDeclarativeExpression: Attempted to evaluate an expression in an invalid context");
        return QVariant();
    }

    QDeclarativeEnginePrivate *ep = QDeclarativeEnginePrivate::get(q->engine());
    QVariant rv;

    ep->referenceScarceResources(); // "hold" scarce resources in memory during evaluation.

    {
        v8::HandleScope handle_scope;
        v8::Context::Scope context_scope(ep->v8engine()->context());
        v8::Local<v8::Value> result = v8value(secondaryScope, isUndefined);
        rv = ep->v8engine()->toVariant(result, qMetaTypeId<QList<QObject*> >());
    }

    ep->dereferenceScarceResources(); // "release" scarce resources if top-level expression evaluation is complete.

    return rv;
}

/*!
    Evaulates the expression, returning the result of the evaluation,
    or an invalid QVariant if the expression is invalid or has an error.

    \a valueIsUndefined is set to true if the expression resulted in an
    undefined value.

    \sa hasError(), error()
*/
QVariant QDeclarativeExpression::evaluate(bool *valueIsUndefined)
{
    Q_D(QDeclarativeExpression);
    return d->value(0, valueIsUndefined);
}

/*!
Returns true if the valueChanged() signal is emitted when the expression's evaluated
value changes.
*/
bool QDeclarativeExpression::notifyOnValueChanged() const
{
    Q_D(const QDeclarativeExpression);
    return d->notifyOnValueChanged();
}

/*!
  Sets whether the valueChanged() signal is emitted when the
  expression's evaluated value changes.

  If \a notifyOnChange is true, the QDeclarativeExpression will
  monitor properties involved in the expression's evaluation, and emit
  QDeclarativeExpression::valueChanged() if they have changed.  This
  allows an application to ensure that any value associated with the
  result of the expression remains up to date.

  If \a notifyOnChange is false (default), the QDeclarativeExpression
  will not montitor properties involved in the expression's
  evaluation, and QDeclarativeExpression::valueChanged() will never be
  emitted.  This is more efficient if an application wants a "one off"
  evaluation of the expression.
*/
void QDeclarativeExpression::setNotifyOnValueChanged(bool notifyOnChange)
{
    Q_D(QDeclarativeExpression);
    d->setNotifyOnValueChanged(notifyOnChange);
}

/*!
    Returns the source file URL for this expression.  The source location must
    have been previously set by calling setSourceLocation().
*/
QString QDeclarativeExpression::sourceFile() const
{
    Q_D(const QDeclarativeExpression);
    return d->url;
}

/*!
    Returns the source file line number for this expression.  The source location 
    must have been previously set by calling setSourceLocation().
*/
int QDeclarativeExpression::lineNumber() const
{
    Q_D(const QDeclarativeExpression);
    return d->line;
}

/*!
    Set the location of this expression to \a line of \a url. This information
    is used by the script engine.
*/
void QDeclarativeExpression::setSourceLocation(const QString &url, int line)
{
    Q_D(QDeclarativeExpression);
    d->url = url;
    d->line = line;
}

/*!
    Returns the expression's scope object, if provided, otherwise 0.

    In addition to data provided by the expression's QDeclarativeContext, the scope
    object's properties are also in scope during the expression's evaluation.
*/
QObject *QDeclarativeExpression::scopeObject() const
{
    Q_D(const QDeclarativeExpression);
    return d->scopeObject();
}

/*!
    Returns true if the last call to evaluate() resulted in an error,
    otherwise false.
    
    \sa error(), clearError()
*/
bool QDeclarativeExpression::hasError() const
{
    Q_D(const QDeclarativeExpression);
    return d->error.isValid();
}

/*!
    Clear any expression errors.  Calls to hasError() following this will
    return false.

    \sa hasError(), error()
*/
void QDeclarativeExpression::clearError()
{
    Q_D(QDeclarativeExpression);
    d->error = QDeclarativeError();
}

/*!
    Return any error from the last call to evaluate().  If there was no error,
    this returns an invalid QDeclarativeError instance.

    \sa hasError(), clearError()
*/

QDeclarativeError QDeclarativeExpression::error() const
{
    Q_D(const QDeclarativeExpression);
    return d->error;
}

/*! \internal */
void QDeclarativeExpressionPrivate::_q_notify()
{
    emitValueChanged();
}

/*!
    \fn void QDeclarativeExpression::valueChanged()

    Emitted each time the expression value changes from the last time it was
    evaluated.  The expression must have been evaluated at least once (by
    calling QDeclarativeExpression::evaluate()) before this signal will be emitted.
*/

void QDeclarativeExpressionPrivate::emitValueChanged()
{
    Q_Q(QDeclarativeExpression);
    emit q->valueChanged();
}

QDeclarativeAbstractExpression::QDeclarativeAbstractExpression()
: m_context(0), m_prevExpression(0), m_nextExpression(0)
{
}

QDeclarativeAbstractExpression::~QDeclarativeAbstractExpression()
{
    if (m_prevExpression) {
        *m_prevExpression = m_nextExpression;
        if (m_nextExpression) 
            m_nextExpression->m_prevExpression = m_prevExpression;
    }
}

QDeclarativeContextData *QDeclarativeAbstractExpression::context() const
{
    return m_context;
}

void QDeclarativeAbstractExpression::setContext(QDeclarativeContextData *context)
{
    if (m_prevExpression) {
        *m_prevExpression = m_nextExpression;
        if (m_nextExpression) 
            m_nextExpression->m_prevExpression = m_prevExpression;
        m_prevExpression = 0;
        m_nextExpression = 0;
    }

    m_context = context;

    if (m_context) {
        m_nextExpression = m_context->expressions;
        if (m_nextExpression) 
            m_nextExpression->m_prevExpression = &m_nextExpression;
        m_prevExpression = &context->expressions;
        m_context->expressions = this;
    }
}

void QDeclarativeAbstractExpression::refresh()
{
}

bool QDeclarativeAbstractExpression::isValid() const
{
    return m_context != 0;
}

QT_END_NAMESPACE

#include <moc_qdeclarativeexpression.cpp>