CMake: Allow building pure QML modules not backed by C++ sources

When no C++ sources are passed to qt_internal_add_qml_plugin (a pure
QML module), create a C++ backed Qt plugin anyway.

In such a case, generate a dummy plugin.cpp containing a
QQmlEngineExtensionPlugin subclass.

The class name is autogenerated from the QML import URI.
The class constructor will call the qmltyperegistrar generated
void qml_register_types_foo() function, to ensure the needed module
versions are registered for the QML module.

Change-Id: I19959dafdf0dc837c6037e7dc1d549b7420110a7
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/qml/Qt6QmlPluginTemplate.cpp.in b/src/qml/Qt6QmlPluginTemplate.cpp.in
new file mode 100644
index 0000000000..9788932743
--- /dev/null
+++ b/src/qml/Qt6QmlPluginTemplate.cpp.in
@@ -0,0 +1,23 @@
+// This file is autogenerated by CMake.
+// It facilitates usage of a pure QML module as a static QML plugin.
+
+#include <QtQml/qqmlextensionplugin.h>
+
+@qt_qml_plugin_intro@
+
+class @qt_qml_plugin_class_name@ : public QQmlEngineExtensionPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID QQmlEngineExtensionInterface_iid)
+
+public:
+    @qt_qml_plugin_class_name@(QObject *parent = nullptr) : QQmlEngineExtensionPlugin(parent)
+    {
+        Q_UNUSED(parent);
+        @qt_qml_plugin_constructor_content@
+    }
+};
+
+@qt_qml_plugin_outro@
+
+#include "@qt_qml_plugin_moc_include_name@"