LookDevX crashing on connection break

[dgovil]

Describe the bug
We are seeing an issue with LookDevX that is replicable when building against the latest commits that have been staged for Maya USD 0.29 as well as latest top of tree for 0.30. If we build against the commits for 0.28, we do not see this issue. It seems like an incompatibility that has arisen in between those tags. However we haven't bisected further.

The crash occurs in the graph below if I try to delete the connection between standard_surface1 and Output

Steps to reproduce
Steps to reproduce the behavior:

1. Create a Standard Surface shader connected to the Output
2. Disconnect the standard surface shader from the output

We get the following crash. I believe this is a regression since 0.28.

Thread 0 Crashed:: CrBrowserMain Dispatch queue: com.apple.main-thread
0   libunwind.dylib               	       0x18e9d4a68 libunwind::UnwindCursor<libunwind::LocalAddressSpace, libunwind::Registers_arm64>::step(bool) + 796
1   libobjc.A.dylib               	       0x1819dd140 objc_addExceptionHandler + 84
2   AppKit                        	       0x18590216c -[NSApplication _commonBeginModalSessionForWindow:relativeToWindow:modalDelegate:didEndSelector:contextInfo:] + 748
3   libqcocoa.dylib               	       0x1045f3464 QCocoaEventDispatcherPrivate::currentModalSession() + 356
4   libqcocoa.dylib               	       0x1045f2ab8 QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 688
5   libExtensionLayer.dylib       	       0x10c72f8fc 0x10c6f4000 + 243964
6   libExtensionLayer.dylib       	       0x10c72b534 0x10c6f4000 + 226612
7   libsystem_platform.dylib      	       0x181dcb584 _sigtramp + 56
8   ???                           	0xffff80010c66cec8 ???
9   libLookdevXVnn_1_4.dylib      	       0x3c1fd0fb0 LookdevX::UfeCommandHook::deleteConnection(VNN_lookdevx_v1::AddRefWrapper<VNN_lookdevx_v1::Port> const&, VNN_lookdevx_v1::AddRefWrapper<VNN_lookdevx_v1::Port> const&) + 936
10  libvnnUI_lookdevx_1_0.dylib   	       0x3eb411f7c TVNNnodeGEModelManager::deleteConnection(VNN_lookdevx_v1::AddRefWrapper<VNN_lookdevx_v1::Port> const&, VNN_lookdevx_v1::AddRefWrapper<VNN_lookdevx_v1::Port> const&, bool) + 244
11  libvnnUI_lookdevx_1_0.dylib   	       0x3eb415778 TVNNnodeGEModelManager::deleteItems(QList<TmodelNode> const&, QList<TmodelEdge> const&) + 1260
12  libvnnUI_lookdevx_1_0.dylib   	       0x3eb38ca84 TnodeGEContainerScene::deleteSelectedItems() + 2120
13  QtCore                        	       0x10f3c70c0 void doActivate<false>(QObject*, int, void**) + 1388
14  QtGui                         	       0x10d4ea920 QAction::activate(QAction::ActionEvent) + 368
15  libvnnUI_lookdevx_1_0.dylib   	       0x3eb45a828 CmpEdImpl::handleShortcut(QKeyEvent*, NodeEditor::TnodeGraphEditorView*) + 768
16  libvnnUI_lookdevx_1_0.dylib   	       0x3eb3b5320 TnodeGraphEditorNavigationContext::handleKeyPressEvent(QKeyEvent*) + 404
17  QtCore                        	       0x10f37d1b4 QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject*, QEvent*) + 228
18  QtWidgets                     	       0x10df5b244 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 80
19  QtWidgets                     	       0x10df5c368 QApplication::notify(QObject*, QEvent*) + 1044
20  libExtensionLayer.dylib       	       0x10c73277c 0x10c6f4000 + 255868
21  QtCore                        	       0x10f37d004 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 292
22  QtWidgets                     	       0x10dfb7e40 QWidgetWindow::event(QEvent*) + 204
23  QtWidgets                     	       0x10df5b304 QApplicationPrivate::notify_helper(QObject*, QEvent*) + 272
24  QtWidgets                     	       0x10df5c154 QApplication::notify(QObject*, QEvent*) + 512
25  libExtensionLayer.dylib       	       0x10c73277c 0x10c6f4000 + 255868
26  QtCore                        	       0x10f37d004 QCoreApplication::notifyInternal2(QObject*, QEvent*) + 292
27  QtGui                         	       0x10d1decf8 QGuiApplicationPrivate::processKeyEvent(QWindowSystemInterfacePrivate::KeyEvent*) + 260
28  QtGui                         	       0x10d2357bc QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 396
29  QtGui                         	       0x10d2353a0 QWindowSystemInterface::flushWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 496
30  libqcocoa.dylib               	       0x10463b158 -[QNSView(Keys) handleKeyEvent:] + 1868
31  libqcocoa.dylib               	       0x10463c014 -[QNSView(Keys) keyDown:] + 92
32  AppKit                        	       0x1857fbfec -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 480
33  AppKit                        	       0x1857fbc38 -[NSWindow(NSEventRouting) sendEvent:] + 284
34  libqcocoa.dylib               	       0x1046446b8 -[QNSWindow sendEvent:] + 884
35  AppKit                        	       0x185ec1e70 -[NSApplication(NSEventRouting) sendEvent:] + 1604
36  libqcocoa.dylib               	       0x1045e716c -[QNSApplication sendEvent:] + 76
37  AppKit                        	       0x185b0f8cc -[NSApplication _handleEvent:] + 60
38  AppKit                        	       0x1856c3cdc -[NSApplication run] + 512
39  libqcocoa.dylib               	       0x1045f2f28 QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 1824
40  QtCore                        	       0x10f386c5c QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 532
41  QtCore                        	       0x10f37d690 QCoreApplication::exec() + 112
42  libExtensionLayer.dylib       	       0x10c72cc70 Tapplication::start() + 724
43  Maya                          	       0x10401d35c 0x104008000 + 86876
44  Maya                          	       0x10401cc48 0x104008000 + 85064
45  dyld                          	       0x181a120e0 start + 2360

Specs (if applicable):

• OS: macOS 14 and macOS 15
• Compiler & version: Apple clang version 15 and 16
• Maya version: Maya 2025.1
• Maya USD commit SHA: fdb1dd6
• Pixar USD commit SHA: Using the USD Inside Maya