Add a QmlSingleton decorator

Add a simple decorator function that stores the type in a list
for the QmlElement decorator to use singleton registration.

Task-number: PYSIDE-1709
Change-Id: I075d583404bd60dc52b84c23a3d09e50d32a5a3a
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 671f9ed73ee174fe2ba96d7a1c2b267455ef367e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

8 files changed, 95 insertions, 12 deletions

diff --git a/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.cpp b/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.cpp
index 1dd0507f7..b3d2b31fe 100644
--- a/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.cpp
+++ b/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.cpp
@@ -370,7 +370,8 @@ static int getGlobalInt(const char *name)
 enum class RegisterMode {
     Normal,
     Anonymous,
-    Uncreatable
+    Uncreatable,
+    Singleton
 };
 
 static PyObject *qmlElementMacroHelper(PyObject *pyObj,
@@ -411,21 +412,36 @@ static PyObject *qmlElementMacroHelper(PyObject *pyObj,
     if (minorVersion == -1)
         minorVersion = 0;
 
-    if (PySide::qmlRegisterType(pyObj, importName.c_str(), majorVersion, minorVersion,
-                                mode != RegisterMode::Anonymous ? typeName : nullptr,
-                                noCreationReason,
-                                mode == RegisterMode::Normal) == -1) {
-       PyErr_Format(PyExc_TypeError, "Failed to register type %s.", typeName);
+    const char *uri = importName.c_str();
+    const int result = mode == RegisterMode::Singleton
+        ? PySide::qmlRegisterSingletonType(pyObj, uri, majorVersion, minorVersion,
+                                          typeName, nullptr,
+                                          PySide::isQObjectDerived(pyObjType, false),
+                                          false)
+        : PySide::qmlRegisterType(pyObj, uri, majorVersion, minorVersion,
+                                  mode != RegisterMode::Anonymous ? typeName : nullptr,
+                                  noCreationReason,
+                                  mode == RegisterMode::Normal);
+
+    if (result == -1) {
+        PyErr_Format(PyExc_TypeError, "%s: Failed to register type %s.",
+                     decoratorName, typeName);
     }
 
     return pyObj;
 }
 
+// FIXME: Store this in PySide::TypeUserData once it is moved to libpyside?
+static QList<PyObject *> decoratedSingletons;
+
 PyObject *PySide::qmlElementMacro(PyObject *pyObj)
 {
-    auto *noCreationReason = PySide::qmlNoCreationReason(pyObj);
-    const auto mode = noCreationReason != nullptr
-                      ? RegisterMode::Uncreatable : RegisterMode::Normal;
+    const char *noCreationReason = nullptr;
+    RegisterMode mode = RegisterMode::Normal;
+    if (decoratedSingletons.contains(pyObj))
+        mode = RegisterMode::Singleton;
+    else if ((noCreationReason = PySide::qmlNoCreationReason(pyObj)))
+        mode = RegisterMode::Uncreatable;
     return qmlElementMacroHelper(pyObj, "QmlElement", mode, noCreationReason);
 }
 
@@ -434,3 +450,10 @@ PyObject *PySide::qmlAnonymousMacro(PyObject *pyObj)
     return qmlElementMacroHelper(pyObj, "QmlAnonymous",
                                  RegisterMode::Anonymous);
 }
+
+PyObject *PySide::qmlSingletonMacro(PyObject *pyObj)
+{
+    decoratedSingletons.append(pyObj);
+    Py_INCREF(pyObj);
+    return pyObj;
+}
diff --git a/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.h b/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.h
index e8105eb94..643033237 100644
--- a/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.h
+++ b/sources/pyside6/PySide6/QtQml/pysideqmlregistertype.h
@@ -100,6 +100,10 @@ PyObject *qmlElementMacro(PyObject *pyObj);
 /// \param pyObj Python type to be registered
 PyObject *qmlAnonymousMacro(PyObject *pyObj);
 
+/// PySide implementation of the QML_SINGLETON macro
+/// \param pyObj Python type to be registered
+PyObject *qmlSingletonMacro(PyObject *pyObj);
+
 } // namespace PySide
 
 #endif // PYSIDEQMLREGISTERTYPE_H
diff --git a/sources/pyside6/PySide6/QtQml/typesystem_qml.xml b/sources/pyside6/PySide6/QtQml/typesystem_qml.xml
index 02fcb222f..d1664f1ed 100644
--- a/sources/pyside6/PySide6/QtQml/typesystem_qml.xml
+++ b/sources/pyside6/PySide6/QtQml/typesystem_qml.xml
@@ -111,6 +111,10 @@
         <inject-code class="target" file="../glue/qtqml.cpp" snippet="qmlanonymous"/>
     </add-function>
 
+    <add-function signature="QmlSingleton(PyObject*)" return-type="PyObject*">
+        <inject-code class="target" file="../glue/qtqml.cpp" snippet="qmlsingleton"/>
+    </add-function>
+
     <function signature="qjsEngine(const QObject*)">
         <modify-function>
             <modify-argument index="return" pyi-type="Optional[PySide6.QtQml.QJSEngine]"/>
diff --git a/sources/pyside6/PySide6/glue/qtqml.cpp b/sources/pyside6/PySide6/glue/qtqml.cpp
index 2d4a69a0e..27834e2a7 100644
--- a/sources/pyside6/PySide6/glue/qtqml.cpp
+++ b/sources/pyside6/PySide6/glue/qtqml.cpp
@@ -90,3 +90,7 @@ return %CONVERTTOPYTHON[%RETURN_TYPE](retval);
 // @snippet qmlanonymous
 %PYARG_0 = PySide::qmlAnonymousMacro(%ARGUMENT_NAMES);
 // @snippet qmlanonymous
+
+// @snippet qmlsingleton
+%PYARG_0 = PySide::qmlSingletonMacro(%ARGUMENT_NAMES);
+// @snippet qmlsingleton
diff --git a/sources/pyside6/doc/extras/QtQml.QmlSingleton.rst b/sources/pyside6/doc/extras/QtQml.QmlSingleton.rst
new file mode 100644
index 000000000..d3d3bf4a7
--- /dev/null
+++ b/sources/pyside6/doc/extras/QtQml.QmlSingleton.rst
@@ -0,0 +1,25 @@
+.. currentmodule:: PySide6.QtQml
+.. _QmlSingleton:
+
+QmlSingleton
+************
+
+.. py:decorator:: QmlSingleton
+
+Declares the decorated type to be a singleton in QML. This only takes effect if
+the type is a Q_OBJECT and is available in QML (by having a QmlElement decorator).
+The QQmlEngine will try to create a singleton instance using the type's default
+constructor.
+
+.. code-block:: python
+
+    QML_IMPORT_NAME = "com.library.name"
+    QML_IMPORT_MAJOR_VERSION = 1
+    QML_IMPORT_MINOR_VERSION = 0 # Optional
+
+    @QmlElement
+    @QmlSingleton
+    class ClassForQml(QObject):
+        # ...
+
+.. note:: The order of the decorators matters; ``QmlSingleton`` needs to be preceded by ``QmlElement``.
diff --git a/sources/pyside6/doc/extras/QtQml.qmlRegisterSingletonType.rst b/sources/pyside6/doc/extras/QtQml.qmlRegisterSingletonType.rst
index 83102bf86..32231a391 100644
--- a/sources/pyside6/doc/extras/QtQml.qmlRegisterSingletonType.rst
+++ b/sources/pyside6/doc/extras/QtQml.qmlRegisterSingletonType.rst
@@ -15,6 +15,8 @@ qmlRegisterSingletonType
 
    This function registers a Python type as a singleton in the QML system.
 
+   Alternatively, the :ref:`QmlSingleton` decorator can be used.
+
 .. py:function:: qmlRegisterSingletonType(pytype: type, uri: str, versionMajor: int, versionMinor: int, typeName: str, callback: object) -> int
 
    :param type pytype: Python class
diff --git a/sources/pyside6/tests/QtQml/registersingletontype.py b/sources/pyside6/tests/QtQml/registersingletontype.py
index a939628cf..6ebc0004c 100644
--- a/sources/pyside6/tests/QtQml/registersingletontype.py
+++ b/sources/pyside6/tests/QtQml/registersingletontype.py
@@ -39,7 +39,8 @@ from helper.helper import quickview_errorstring
 
 from PySide6.QtCore import Property, Signal, QTimer, QUrl, QObject
 from PySide6.QtGui import QGuiApplication
-from PySide6.QtQml import qmlRegisterSingletonType, qmlRegisterSingletonInstance
+from PySide6.QtQml import (qmlRegisterSingletonType, qmlRegisterSingletonInstance,
+                           QmlElement, QmlSingleton)
 from PySide6.QtQuick import QQuickView
 
 finalResult = 0
@@ -70,6 +71,25 @@ def singletonQJSValueCallback(engine):
     return engine.evaluate("new Object({data: 50})")
 
 
+QML_IMPORT_NAME = "Singletons"
+QML_IMPORT_MAJOR_VERSION = 1
+
+@QmlElement
+@QmlSingleton
+class DecoratedSingletonQObject(QObject):
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self._data = 200
+
+    def getData(self):
+        return self._data
+
+    def setData(self, data):
+        self._data = data
+
+    data = Property(int, getData, setData)
+
+
 class TestQmlSupport(unittest.TestCase):
     def testIt(self):
         app = QGuiApplication([])
@@ -99,7 +119,7 @@ class TestQmlSupport(unittest.TestCase):
         view.show()
         QTimer.singleShot(250, view.close)
         app.exec()
-        self.assertEqual(finalResult, 299)
+        self.assertEqual(finalResult, 499)
 
 
 if __name__ == '__main__':
diff --git a/sources/pyside6/tests/QtQml/registersingletontype.qml b/sources/pyside6/tests/QtQml/registersingletontype.qml
index 2365cf201..16defa867 100644
--- a/sources/pyside6/tests/QtQml/registersingletontype.qml
+++ b/sources/pyside6/tests/QtQml/registersingletontype.qml
@@ -33,6 +33,7 @@ Item {
     Component.onCompleted: {
         SingletonQObjectCallback.data += SingletonQObjectNoCallback.data
             + SingletonQJSValue.data
-            + SingletonInstance.data;
+            + SingletonInstance.data
+            + DecoratedSingletonQObject.data;
     }
 }