Plugins not recognized by QT tools

[semtexzv]

I've been playing around, trying to get Rust plugins recognized by Qt Designer Studio, but failing miserably.
After some investigation, I have tracked it down to this:

It seems that the generated metadata is incomplete.

Test case:

1. Simple cdylib crate, lib.rs with:

use std::ffi::CStr;
use cstr::cstr;
use qmetaobject::*;

#[derive(Default, QObject)]
struct QTTest {
    base: qt_base_class!(trait QObject),
}

#[derive(Default, QObject)]
struct QExampleQmlPlugin {
    base: qt_base_class!(trait QQmlExtensionPlugin),
    plugin: qt_plugin!("org.qt-project.Qt.QQmlExtensionInterface/1.0"),
}

impl QQmlExtensionPlugin for QExampleQmlPlugin {
    fn register_types(&mut self, uri: &CStr) {
        assert_eq!(uri, cstr!("XFlow"));
        qml_register_type::<QTTest>(uri, 1, 0, cstr!("XFlow"));
    }
}

Running

cd target/debug
QT_PLUGIN_PATH=`pwd` qtplugininfo ./lib<whatever>.so

results in

IID "org.qt-project.Qt.QQmlExtensionInterface/1.0" Qt 5.1.0 (debug)
qtplugininfo: ./libxflow_gui.so: invalid metadata, user data is not a JSON object

And running

cd target/debug
QT_PLUGIN_PATH=`pwd`  qmlplugindump -v XFlow 1.0  ./libxflow_gui.so

fails outright with

QQmlComponent: Component is not ready