Fix Qt3D.Core type registration to be called in static builds

The automatically generated type registrations function
qml_register_types_Qt3D_Core was not called in static builds, because
the quick3dcoreplugin target is using a custom
qt3dquick3dcoreplugin.cpp file instead of an auto-generated one.

Types were found correctly in a shared Qt build because the 3DQuick
backing library was loaded by the dynamic plugin at runtime and the
static initializer calling qml_register_types_Qt3D_Core was executed.

In a static build, the linker would discard the
qml_register_types_Qt3D_Core function (and the static initializer)
because nothing was referencing it.

Modify qt3dquick3dcoreplugin.cpp to manually reference the type
registration file, just like an auto-generated source file would do
it.
A Q_IMPORT_PLUGIN(Qt3DQuick3DCorePlugin) which is link directly to
applications via an object file then ensures that registrations
succeeds.

Compared to 6.4, the type registration symbol lives outside of
QT_BEGIN_NAMESPACE because
e2b4226abfb1f1b43f8ecc5f9df40787e3d574b6 was not picked for < 6.4.

Amends 59fc9cacce5eca68c9dece3c30d6f11ee7693d4e

Fixes: QTBUG-102328
Change-Id: I371b272c7c3a1d21aeeb68f45a26e4186c39c5c9
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
(cherry picked from commit 57fbc3b60f6ade591713092a723dcf696ced734b)

2 files changed, 11 insertions, 1 deletions

diff --git a/src/quick3d/imports/core/qt3dquick3dcoreplugin.cpp b/src/quick3d/imports/core/qt3dquick3dcoreplugin.cpp
index 14987e764..de476918d 100644
--- a/src/quick3d/imports/core/qt3dquick3dcoreplugin.cpp
+++ b/src/quick3d/imports/core/qt3dquick3dcoreplugin.cpp
@@ -62,8 +62,18 @@
 
 #include <QtQml/qqml.h>
 
+extern void qml_register_types_Qt3D_Core();
+Q_GHS_KEEP_REFERENCE(qml_register_types_Qt3D_Core);
+
 QT_BEGIN_NAMESPACE
 
+Qt3DQuick3DCorePlugin::Qt3DQuick3DCorePlugin(QObject *parent)
+    : QQmlExtensionPlugin(parent)
+{
+    volatile auto registration = &qml_register_types_Qt3D_Core;
+    Q_UNUSED(registration);
+}
+
 void Qt3DQuick3DCorePlugin::registerTypes(const char *uri)
 {
     Q_UNUSED(uri);
diff --git a/src/quick3d/imports/core/qt3dquick3dcoreplugin.h b/src/quick3d/imports/core/qt3dquick3dcoreplugin.h
index afc092bbb..ebedb22a4 100644
--- a/src/quick3d/imports/core/qt3dquick3dcoreplugin.h
+++ b/src/quick3d/imports/core/qt3dquick3dcoreplugin.h
@@ -49,7 +49,7 @@ class Qt3DQuick3DCorePlugin : public QQmlExtensionPlugin
     Q_OBJECT
     Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
 public:
-    Qt3DQuick3DCorePlugin(QObject *parent = nullptr) : QQmlExtensionPlugin(parent) { }
+    Qt3DQuick3DCorePlugin(QObject *parent = nullptr);
     ~Qt3DQuick3DCorePlugin();
     void registerTypes(const char *uri) override;
 };