add std::function overload to qmlRegisterSingletonType

This changes enables passing stateful lambdas to
qmlRegisterSingletonType, which helps when porting away from
setContextProperty.

Unfortunately, we cannot directly add an overload for std::function, as
this causes ambiguity in the overload set when a lambda of the form
auto f = [](QQmlEngine*, QJSEngine*) -> QObject*
is passed to the function (which is what the examples do)

We therefore use a template to support abribtrary callables f, then SFINAE
them out if f is not convertible to the desired std::function, or when
f is convertible to a plain C function pointer, thus removing the
ambiguity

Change-Id: I6ca95ad692d8bb785e420b85bf3d8c1d0007ce17
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
 
 
 
 

6 files changed, 62 insertions, 7 deletions

diff --git a/src/qml/doc/src/qmlfunctions.qdoc b/src/qml/doc/src/qmlfunctions.qdoc
index 3c80f16c8f..ab54b5fd1d 100644
--- a/src/qml/doc/src/qmlfunctions.qdoc
+++ b/src/qml/doc/src/qmlfunctions.qdoc
@@ -564,6 +564,14 @@
    \sa {Choosing the Correct Integration Method Between C++ and QML}
 */
 
+
+/*!
+   \fn int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName, std::function<QObject*(QQmlEngine *, QJSEngine *)> callback)
+   \relates QQmlEngine
+
+   \overload qmlRegisterSingletonType
+*/
+
 /*!
    \fn int qmlRegisterSingletonType(const QUrl &url, const char *uri, int versionMajor, int versionMinor, const char *qmlName)
    \relates QQmlEngine
diff --git a/src/qml/qml/qqml.h b/src/qml/qml/qqml.h
index f84a1b2109..4f3bfb76b0 100644
--- a/src/qml/qml/qqml.h
+++ b/src/qml/qml/qqml.h
@@ -624,13 +624,13 @@ inline int qmlRegisterSingletonType(const char *uri, int versionMajor, int versi
 
         uri, versionMajor, versionMinor, typeName,
 
-        callback, nullptr, nullptr, 0, 0
+        callback, nullptr, nullptr, 0, 0, {}
     };
 
     return QQmlPrivate::qmlregister(QQmlPrivate::SingletonRegistration, &api);
 }
 
-enum { QmlCurrentSingletonTypeRegistrationVersion = 2 };
+enum { QmlCurrentSingletonTypeRegistrationVersion = 3 };
 template <typename T>
 inline int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName,
                                 QObject *(*callback)(QQmlEngine *, QJSEngine *))
@@ -642,7 +642,26 @@ inline int qmlRegisterSingletonType(const char *uri, int versionMajor, int versi
 
         uri, versionMajor, versionMinor, typeName,
 
-        nullptr, callback, &T::staticMetaObject, qRegisterNormalizedMetaType<T *>(pointerName.constData()), 0
+        nullptr, nullptr, &T::staticMetaObject, qRegisterNormalizedMetaType<T *>(pointerName.constData()), 0, callback
+    };
+
+    return QQmlPrivate::qmlregister(QQmlPrivate::SingletonRegistration, &api);
+}
+
+template <typename T, typename F, typename std::enable_if<std::is_convertible<F, std::function<QObject *(QQmlEngine *, QJSEngine *)>>::value
+                                                 && !std::is_convertible<F, QObject *(*)(QQmlEngine *, QJSEngine *)>::value, void>::type* = nullptr>
+inline int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName,
+                                    F&& callback)
+{
+
+    QML_GETTYPENAMES
+
+    QQmlPrivate::RegisterSingletonType api = {
+        QmlCurrentSingletonTypeRegistrationVersion,
+
+        uri, versionMajor, versionMinor, typeName,
+
+        nullptr, nullptr, &T::staticMetaObject, qRegisterNormalizedMetaType<T *>(pointerName.constData()), 0, callback
     };
 
     return QQmlPrivate::qmlregister(QQmlPrivate::SingletonRegistration, &api);
diff --git a/src/qml/qml/qqmlmetatype.cpp b/src/qml/qml/qqmlmetatype.cpp
index c6858780a1..a2c2ae47af 100644
--- a/src/qml/qml/qqmlmetatype.cpp
+++ b/src/qml/qml/qqmlmetatype.cpp
@@ -107,7 +107,7 @@ static QQmlTypePrivate *createQQmlType(QQmlMetaTypeData *data, const QString &el
     d->version_maj = type.versionMajor;
     d->version_min = type.versionMinor;
 
-    if (type.qobjectApi) {
+    if (type.qobjectApi || (type.version >= 3 && type.generalizedQobjectApi)) {
         if (type.version >= 1) // static metaobject added in version 1
             d->baseMetaObject = type.instanceMetaObject;
         if (type.version >= 2) // typeId added in version 2
@@ -118,10 +118,14 @@ static QQmlTypePrivate *createQQmlType(QQmlMetaTypeData *data, const QString &el
 
     d->extraData.sd->singletonInstanceInfo = new QQmlType::SingletonInstanceInfo;
     d->extraData.sd->singletonInstanceInfo->scriptCallback = type.scriptApi;
-    d->extraData.sd->singletonInstanceInfo->qobjectCallback = type.qobjectApi;
+    if (type.version >= 3) {
+        d->extraData.sd->singletonInstanceInfo->qobjectCallback = type.generalizedQobjectApi;
+    } else {
+        d->extraData.sd->singletonInstanceInfo->qobjectCallback = type.qobjectApi;
+    }
     d->extraData.sd->singletonInstanceInfo->typeName = QString::fromUtf8(type.typeName);
     d->extraData.sd->singletonInstanceInfo->instanceMetaObject
-            = (type.qobjectApi && type.version >= 1) ? type.instanceMetaObject : nullptr;
+            = ((type.qobjectApi || (type.version >= 3 && type.generalizedQobjectApi) ) && type.version >= 1) ? type.instanceMetaObject : nullptr;
 
     return d;
 }
diff --git a/src/qml/qml/qqmlprivate.h b/src/qml/qml/qqmlprivate.h
index ae84803648..a07736c6fc 100644
--- a/src/qml/qml/qqmlprivate.h
+++ b/src/qml/qml/qqmlprivate.h
@@ -51,6 +51,8 @@
 // We mean it.
 //
 
+#include <functional>
+
 #include <QtQml/qtqmlglobal.h>
 
 #include <QtCore/qglobal.h>
@@ -276,6 +278,7 @@ namespace QQmlPrivate
         const QMetaObject *instanceMetaObject; // new in version 1
         int typeId; // new in version 2
         int revision; // new in version 2
+        std::function<QObject*(QQmlEngine *, QJSEngine *)> generalizedQobjectApi; // new in version 3
         // If this is extended ensure "version" is bumped!!!
     };
 
diff --git a/src/qml/qml/qqmltype_p.h b/src/qml/qml/qqmltype_p.h
index 1d65a08c8f..158fefad2c 100644
--- a/src/qml/qml/qqmltype_p.h
+++ b/src/qml/qml/qqmltype_p.h
@@ -51,6 +51,8 @@
 // We mean it.
 //
 
+#include <functional>
+
 #include <private/qtqmlglobal_p.h>
 #include <private/qqmlrefcount_p.h>
 
@@ -145,7 +147,7 @@ public:
     struct Q_QML_PRIVATE_EXPORT SingletonInstanceInfo
     {
         QJSValue (*scriptCallback)(QQmlEngine *, QJSEngine *) = nullptr;
-        QObject *(*qobjectCallback)(QQmlEngine *, QJSEngine *) = nullptr;
+        std::function<QObject *(QQmlEngine *, QJSEngine *)> qobjectCallback = {};
         const QMetaObject *instanceMetaObject = nullptr;
         QString typeName;
         QUrl url; // used by composite singletons
diff --git a/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp b/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
index 0cb6753020..8d0106b92c 100644
--- a/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
+++ b/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
@@ -1015,6 +1015,25 @@ void tst_qqmlengine::singletonInstance()
     }
 
     {
+        int data = 30;
+        auto id = qmlRegisterSingletonType<CppSingleton>("Qt.test",1,0,"CapturingLambda",[data](QQmlEngine*, QJSEngine*){ // register qobject singleton with capturing lambda
+                auto o = new CppSingleton;
+                o->setProperty("data", data);
+                return o;
+        });
+        QJSValue value = engine.singletonInstance<QJSValue>(id);
+        QVERIFY(!value.isUndefined());
+        QVERIFY(value.isQObject());
+        QObject *instance = value.toQObject();
+        QVERIFY(instance);
+        QCOMPARE(instance->metaObject()->className(), "CppSingleton");
+        QCOMPARE(instance->property("data"), data);
+    }
+    {
+        qmlRegisterSingletonType<CppSingleton>("Qt.test",1,0,"NotAmbiguous", [](QQmlEngine* qeng, QJSEngine* jeng) -> QObject* {return CppSingleton::create(qeng, jeng);}); // test that overloads for qmlRegisterSingleton are not ambiguous
+    }
+
+    {
         // Invalid types
         QJSValue value;
         value = engine.singletonInstance<QJSValue>(-4711);