core/proxywindow: fix ProxiedWindow proxy pointer after reload

Previously was not updated after reload, causing QsWindowAttached to
use the old window pointer after it had been freed.

src/window/proxywindow.cpp

@@ -131,6 +131,8 @@ void ProxyWindowBase::connectWindow() {
 		generation->registerIncubationController(this->window->incubationController());
 	}
 
+	this->window->setProxy(this);
+
 	// clang-format off
 	QObject::connect(this->window, &QWindow::visibilityChanged, this, &ProxyWindowBase::visibleChanged);
 	QObject::connect(this->window, &QWindow::xChanged, this, &ProxyWindowBase::xChanged);

src/window/proxywindow.hpp

@@ -168,6 +168,7 @@ public:
 	    , mProxy(proxy) {}
 
 	[[nodiscard]] ProxyWindowBase* proxy() const { return this->mProxy; }
+	void setProxy(ProxyWindowBase* proxy) { this->mProxy = proxy; }
 
 signals:
 	void exposed();

src/window/test/windowattached.cpp

@@ -2,6 +2,7 @@
 
 #include <qobject.h>
 #include <qquickitem.h>
+#include <qscopedpointer.h>
 #include <qsignalspy.h>
 #include <qtest.h>
 #include <qtestcase.h>
@@ -36,6 +37,33 @@ void TestWindowAttachment::attachedBeforeReload() {
 	QCOMPARE(spy.length(), 1);
 }
 
+void TestWindowAttachment::earlyAttachReloaded() {
+	auto window1 = QScopedPointer(new ProxyWindowBase());
+	auto item1 = QScopedPointer(new QQuickItem());
+	item1->setParentItem(window1->contentItem());
+	window1->reload(nullptr);
+
+	auto window2 = ProxyWindowBase();
+	auto item2 = QQuickItem();
+	item2.setParentItem(window2.contentItem());
+
+	auto* attached = WindowInterface::qmlAttachedProperties(&item2);
+	QCOMPARE_NE(attached, nullptr);
+	QCOMPARE(attached->window(), nullptr);
+
+	auto spy = QSignalSpy(attached, &QsWindowAttached::windowChanged);
+	window2.reload(window1.get());
+
+	QCOMPARE(attached->window(), &window2);
+	QCOMPARE(spy.length(), 1);
+
+	item1.reset();
+	window1.reset();
+
+	QCOMPARE(attached->window(), &window2);
+	QCOMPARE(spy.length(), 1);
+}
+
 void TestWindowAttachment::owningWindowChanged() {
 	auto window1 = ProxyWindowBase();
 	auto window2 = ProxyWindowBase();

src/window/test/windowattached.hpp

@@ -9,6 +9,7 @@ class TestWindowAttachment: public QObject {
 private slots:
 	static void attachedAfterReload();
 	static void attachedBeforeReload();
+	static void earlyAttachReloaded();
 	static void owningWindowChanged();
 	static void nonItemParents();
 };