QQmlEngine: Fine grained translation binding tracking

This commit changes translation bindings in such a way that they always
depend on the a newly introduced translationLanguage property of the QML
engine.
Moreover, captureTranslationBinding is changed in the same way, hence
any binding containing a call to a translation function like qsTr will
also be refreshed. After those changes, QQmlEngine::retranslate can be
implemented as a notify on translationLanguage. Finally,
QQmlTranslationPropertyBinding is also changed to depend on
translationLanguage instead of uiLanguage to ensure consistency between
the various binding types.

Note that we do not use the existing uiLanguage property of QJSEngine.
If we were to do this, changing uiLanguage would already trigger the
binding reevaluation, which is a behavior change. In case someone is
manually connecting uiLanguageChanged to QQmlEngine::retranslate, this
would cause a double evaluation of translation bindings. In a future
change, we can however introduce a new enableAutoTranslationUpdate
method, which would cause binding evaluation as soon as uiLanguage is
changed.

Special care is taken for ListModel/ListElement, which does not store a
proper translation binding, but instead operates on
QV4::CompiledData::Binding. For now, we simply refresh the complete
ListModel in case it contains a translation binding. It should be
possible to optimize this further in a future change.
Note that only "static" ListElement properties can contain translations:
The dynamic insertion API makes it impossible to insert a translation,
as it would already be resolved to a string when insert is called.

[ChangeLog][QQmlEngine] QQmlEngine::retranslate no longer refreshes all
bindings, but only translation bindings.

Pick-to: 6.2
Fixes: QTBUG-96192
Change-Id: I54d213fd46b6914e8f686843b49e155909117218
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

10 files changed, 74 insertions, 37 deletions

diff --git a/src/qml/qml/qqmlapplicationengine.cpp b/src/qml/qml/qqmlapplicationengine.cpp
index e0ab25892f..83323a7087 100644
--- a/src/qml/qml/qqmlapplicationengine.cpp
+++ b/src/qml/qml/qqmlapplicationengine.cpp
@@ -73,7 +73,9 @@ void QQmlApplicationEnginePrivate::init()
                &QCoreApplication::quit, Qt::QueuedConnection);
     q->connect(q, &QQmlApplicationEngine::exit, QCoreApplication::instance(),
                &QCoreApplication::exit, Qt::QueuedConnection);
-    q->connect(q, SIGNAL(uiLanguageChanged()), q_func(), SLOT(_q_loadTranslations()));
+    QObject::connect(q, &QJSEngine::uiLanguageChanged, q, [this](){
+        _q_loadTranslations();
+    });
 #if QT_CONFIG(translation)
     QTranslator* qtTranslator = new QTranslator(q);
     if (qtTranslator->load(QLocale(), QLatin1String("qt"), QLatin1String("_"), QLibraryInfo::path(QLibraryInfo::TranslationsPath), QLatin1String(".qm")))
@@ -89,11 +91,10 @@ void QQmlApplicationEnginePrivate::init()
 void QQmlApplicationEnginePrivate::_q_loadTranslations()
 {
 #if QT_CONFIG(translation)
+    Q_Q(QQmlApplicationEngine);
     if (translationsDirectory.isEmpty())
         return;
 
-    Q_Q(QQmlApplicationEngine);
-
     QScopedPointer<QTranslator> translator(new QTranslator);
     if (!uiLanguage.value().isEmpty()) {
         QLocale locale(uiLanguage);
diff --git a/src/qml/qml/qqmlbinding.cpp b/src/qml/qml/qqmlbinding.cpp
index a24e5ad373..f8d3daa28b 100644
--- a/src/qml/qml/qqmlbinding.cpp
+++ b/src/qml/qml/qqmlbinding.cpp
@@ -394,12 +394,14 @@ protected:
     }
 };
 
-class QQmlTranslationBinding : public GenericBinding<QMetaType::QString> {
+class QQmlTranslationBinding : public GenericBinding<QMetaType::QString>, public QPropertyObserver {
 public:
     QQmlTranslationBinding(const QQmlRefPointer<QV4::ExecutableCompilationUnit> &compilationUnit, const QV4::CompiledData::Binding *binding)
+        : QPropertyObserver(&QQmlTranslationBinding::onLanguageChange)
     {
         setCompilationUnit(compilationUnit);
         m_binding = binding;
+        setSource(QQmlEnginePrivate::get(compilationUnit->engine)->translationLanguage);
     }
 
     QQmlSourceLocation sourceLocation() const override final
@@ -407,6 +409,9 @@ public:
         return QQmlSourceLocation(m_compilationUnit->fileName(), m_binding->valueLocation.line, m_binding->valueLocation.column);
     }
 
+    static void onLanguageChange(QPropertyObserver *observer, QUntypedPropertyData *)
+    { static_cast<QQmlTranslationBinding *>(observer)->update(); }
+
     void doUpdate(const DeleteWatcher &watcher,
                   QQmlPropertyData::WriteFlags flags, QV4::Scope &scope) override final
     {
@@ -792,7 +797,7 @@ QVector<QQmlProperty> QQmlBinding::dependencies() const
 
 bool QQmlBinding::hasDependencies() const
 {
-    return !activeGuards.isEmpty() || translationsCaptured() || qpropertyChangeTriggers;
+    return !activeGuards.isEmpty() || qpropertyChangeTriggers;
 }
 
 class QObjectPointerBinding: public QQmlNonbindingBinding
diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index cd2457c486..ed7687cc40 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -1264,21 +1264,12 @@ QJSValue QQmlEngine::singletonInstance<QJSValue>(int qmlTypeId)
   QCoreApplication::installTranslator, to ensure that your user-interface
   shows up-to-date translations.
 
-  \note Due to a limitation in the implementation, this function
-  refreshes all the engine's bindings, not only those that use strings
-  marked for translation.
-  This may be optimized in a future release.
-
   \since 5.10
 */
 void QQmlEngine::retranslate()
 {
     Q_D(QQmlEngine);
-    for (QQmlRefPointer<QQmlContextData> context
-                = QQmlContextData::get(d->rootContext)->childContexts();
-         context; context = context->nextChild()) {
-        context->refreshExpressions();
-    }
+    d->translationLanguage.notify();
 }
 
 /*!
diff --git a/src/qml/qml/qqmlengine_p.h b/src/qml/qml/qqmlengine_p.h
index b3c77dfa83..b1b3b588f8 100644
--- a/src/qml/qml/qqmlengine_p.h
+++ b/src/qml/qml/qqmlengine_p.h
@@ -162,6 +162,7 @@ public:
     QRecyclePool<TriggerList> qPropertyTriggerPool;
 
     QQmlContext *rootContext;
+    Q_OBJECT_BINDABLE_PROPERTY(QQmlEnginePrivate, QString, translationLanguage);
 
 #if !QT_CONFIG(qml_debug)
     static const quintptr profiler = 0;
diff --git a/src/qml/qml/qqmljavascriptexpression.cpp b/src/qml/qml/qqmljavascriptexpression.cpp
index b8b34d2071..854a22d8ba 100644
--- a/src/qml/qml/qqmljavascriptexpression.cpp
+++ b/src/qml/qml/qqmljavascriptexpression.cpp
@@ -221,9 +221,6 @@ public:
         while (QQmlJavaScriptExpressionGuard *g = capture.guards.takeFirst())
             g->Delete();
 
-        if (!watcher.wasDeleted())
-            capture.expression->setTranslationsCaptured(capture.translationCaptured);
-
         ep->propertyCapture = lastPropertyCapture;
     }
 
@@ -389,6 +386,21 @@ void QQmlPropertyCapture::captureProperty(
     captureNonBindableProperty(o, propertyData->notifyIndex(), propertyData->coreIndex(), doNotify);
 }
 
+void QQmlPropertyCapture::captureTranslation()
+{
+    // use a unique invalid index to avoid needlessly querying the metaobject for
+    // the correct index of of the  translationLanguage property
+    int const invalidIndex = -2;
+    for (auto trigger = expression->qpropertyChangeTriggers; trigger;
+         trigger = trigger->next) {
+        if (trigger->target == engine && trigger->propertyIndex == invalidIndex)
+            return; // already installed
+    }
+    auto trigger = expression->allocatePropertyChangeTrigger(engine, invalidIndex);
+
+    trigger->setSource(QQmlEnginePrivate::get(engine)->translationLanguage);
+}
+
 void QQmlPropertyCapture::captureBindableProperty(
         QObject *o, const QMetaObject *metaObjectForBindable, int c)
 {
diff --git a/src/qml/qml/qqmljavascriptexpression_p.h b/src/qml/qml/qqmljavascriptexpression_p.h
index dc2289a357..bfdc922729 100644
--- a/src/qml/qml/qqmljavascriptexpression_p.h
+++ b/src/qml/qml/qqmljavascriptexpression_p.h
@@ -187,22 +187,12 @@ protected:
 
     QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next, GuardTag> activeGuards;
 
-    void setTranslationsCaptured(bool captured) {
-        Tag newTag = captured ? TranslationsCaptured : NoTag;
-        if (m_error.tag() & InEvaluationLoop)
-            newTag = Tag(newTag | InEvaluationLoop);
-        m_error.setTag(newTag);
-    }
-    bool translationsCaptured() const { return m_error.tag() & TranslationsCaptured; }
-
     enum Tag {
         NoTag,
-        TranslationsCaptured,
         InEvaluationLoop
     };
 
-    // m_error:flag1 translationsCapturedDuringEvaluation
-    QTaggedPointer<QQmlDelayedError> m_error;
+    QTaggedPointer<QQmlDelayedError, Tag> m_error;
 
 private:
     friend class QQmlContextData;
@@ -239,14 +229,13 @@ public:
     void captureProperty(QQmlNotifier *);
     void captureProperty(QObject *, int, int, bool doNotify = true);
     void captureProperty(QObject *, const QQmlPropertyCache *, const QQmlPropertyData *, bool doNotify = true);
-    void captureTranslation() { translationCaptured = true; }
+    void captureTranslation();
 
     QQmlEngine *engine;
     QQmlJavaScriptExpression *expression;
     QQmlJavaScriptExpression::DeleteWatcher *watcher;
     QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> guards;
     QStringList *errorString;
-    bool translationCaptured = false;
 
 private:
     void captureBindableProperty(QObject *o, const QMetaObject *metaObjectForBindable, int c);
diff --git a/src/qml/qml/qqmlpropertybinding.cpp b/src/qml/qml/qqmlpropertybinding.cpp
index 50fd1a14b0..952f1ce26b 100644
--- a/src/qml/qml/qqmlpropertybinding.cpp
+++ b/src/qml/qml/qqmlpropertybinding.cpp
@@ -125,7 +125,7 @@ void QQmlPropertyBindingJS::expressionChanged()
     if (!asBinding()->propertyDataPtr)
         return;
     const auto currentTag = m_error.tag();
-    if (currentTag & InEvaluationLoop) {
+    if (currentTag == InEvaluationLoop) {
         QQmlError err;
         auto location = QQmlJavaScriptExpression::sourceLocation();
         err.setUrl(QUrl{location.sourceFile});
@@ -141,10 +141,10 @@ void QQmlPropertyBindingJS::expressionChanged()
         qmlWarning(this->scopeObject(), err);
         return;
     }
-    m_error.setTag(currentTag | InEvaluationLoop);
+    m_error.setTag(InEvaluationLoop);
     asBinding()->evaluateRecursive();
     asBinding()->notifyRecursive();
-    m_error.setTag(currentTag);
+    m_error.setTag(NoTag);
 }
 
 QQmlPropertyBinding::QQmlPropertyBinding(QMetaType mt, QObject *target, QQmlPropertyIndex targetIndex, TargetData::BoundFunction hasBoundFunction)
@@ -293,8 +293,8 @@ void QQmlPropertyBinding::bindingErrorCallback(QPropertyBindingPrivate *that)
 QUntypedPropertyBinding QQmlTranslationPropertyBinding::create(const QQmlPropertyData *pd, const QQmlRefPointer<QV4::ExecutableCompilationUnit> &compilationUnit, const QV4::CompiledData::Binding *binding)
 {
     auto translationBinding = [compilationUnit, binding](QMetaType metaType, void *dataPtr) -> bool {
-        // Create a dependency to the uiLanguage
-        QJSEnginePrivate::get(compilationUnit->engine)->uiLanguage.value();
+        // Create a dependency to the translationLanguage
+        QQmlEnginePrivate::get(compilationUnit->engine)->translationLanguage.value();
 
         QVariant resultVariant(compilationUnit->bindingValueAsString(binding));
         if (metaType != QMetaType::fromType<QString>())
diff --git a/src/qmlmodels/qqmllistmodel.cpp b/src/qmlmodels/qqmllistmodel.cpp
index bcda4e6598..6e7afed183 100644
--- a/src/qmlmodels/qqmllistmodel.cpp
+++ b/src/qmlmodels/qqmllistmodel.cpp
@@ -587,6 +587,17 @@ ListModel *ListModel::getListProperty(int elementIndex, const ListLayout::Role &
     return e->getListProperty(role);
 }
 
+void ListModel::updateTranslations()
+{
+    for (int index = 0; index != elements.count(); ++index) {
+        ListElement *e = elements[index];
+        if (ModelNodeMetaObject *cache = e->objectCache()) {
+            // TODO: more fine grained tracking?
+            cache->updateValues();
+        }
+    }
+}
+
 void ListModel::set(int elementIndex, QV4::Object *object, QVector<int> *roles)
 {
     ListElement *e = elements[elementIndex];
@@ -2519,6 +2530,17 @@ void QQmlListModel::removeElements(int index, int removeCount)
         destroyer();
 }
 
+void QQmlListModel::updateTranslations()
+{
+    // assumption: it is impossible to have retranslatable strings in a
+    // dynamic list model, as they would already have "decayed" to strings
+    // when they were inserted
+    if (m_dynamicRoles)
+        return;
+    Q_ASSERT(m_listModel);
+    m_listModel->updateTranslations();
+}
+
 /*!
     \qmlmethod ListModel::insert(int index, jsobject dict)
 
@@ -2944,7 +2966,8 @@ bool QQmlListModelParser::applyProperty(
     } else {
         QVariant value;
 
-        if (binding->isTranslationBinding()) {
+        const bool isTranslationBinding = binding->isTranslationBinding();
+        if (isTranslationBinding) {
             value = QVariant::fromValue<const QV4::CompiledData::Binding*>(binding);
         } else if (binding->evaluatesToString()) {
             value = compilationUnit->bindingValueAsString(binding);
@@ -2986,7 +3009,17 @@ bool QQmlListModelParser::applyProperty(
             Q_UNREACHABLE();
         }
 
+        if (!model)
+            return roleSet;
         model->setOrCreateProperty(outterElementIndex, elementName, value);
+        auto listModel = model->m_modelCache;
+        if (isTranslationBinding && listModel) {
+            if (!listModel->translationChangeHandler) {
+                auto ep = QQmlEnginePrivate::get(compilationUnit->engine);
+                model->m_modelCache->translationChangeHandler = std::make_unique<QPropertyNotifier>(
+                            ep->translationLanguage.addNotifier([listModel](){ listModel->updateTranslations(); }));
+            }
+        }
         roleSet = true;
     }
     return roleSet;
diff --git a/src/qmlmodels/qqmllistmodel_p.h b/src/qmlmodels/qqmllistmodel_p.h
index 2e8181e10c..7cd2b4662b 100644
--- a/src/qmlmodels/qqmllistmodel_p.h
+++ b/src/qmlmodels/qqmllistmodel_p.h
@@ -148,6 +148,7 @@ private:
 
     ListLayout *m_layout;
     ListModel *m_listModel;
+    std::unique_ptr<QPropertyNotifier> translationChangeHandler;
 
     QVector<class DynamicRoleModelNode *> m_modelObjects;
     QVector<QString> m_roles;
@@ -169,6 +170,8 @@ private:
     void emitItemsInserted();
 
     void removeElements(int index, int removeCount);
+
+    void updateTranslations();
 };
 
 // ### FIXME
diff --git a/src/qmlmodels/qqmllistmodel_p_p.h b/src/qmlmodels/qqmllistmodel_p_p.h
index e751918cd4..1257bcfb35 100644
--- a/src/qmlmodels/qqmllistmodel_p_p.h
+++ b/src/qmlmodels/qqmllistmodel_p_p.h
@@ -399,6 +399,8 @@ public:
     QVariant getProperty(int elementIndex, int roleIndex, const QQmlListModel *owner, QV4::ExecutionEngine *eng);
     ListModel *getListProperty(int elementIndex, const ListLayout::Role &role);
 
+    void updateTranslations();
+
     int roleCount() const
     {
         return m_layout->roleCount();