Crash on C# exception while reloading assemblies

[codecat]

Godot version

v4.0.alpha.mono.custom_build [0b8a63e]

System information

Windows 11, Vulkan, 3080

Issue description

When I build a C# project that generates an exception in the editor, it crashes the editor inside of godotsharp_internal_script_debugger_send_error because EngineDebugger::get_script_debugger() returns null, and this is not checked.

Steps to reproduce

1. Open the reproduction project
2. Make sure the "crash_test" addon is enabled
3. You should see a gizmo drawing a line in the 3D view
4. In addons/crash_test/CrashGizmoPlugin.cs, change if (true) { to if (false) {
5. Click "Build" in Godot

Minimal reproduction project

CrashTest20220829.zip

[raulsntos]

EngineDebugger::get_script_debugger() returns null, and this is not checked.

You are not entirely correct about this, it's true that this method can return null but we do guard calls to this method with a call to EngineDebugger::is_active() which would return false if the debugger is null so it would never call that method:

godot/modules/mono/glue/GodotSharp/GodotSharp/Core/NativeInterop/ExceptionUtils.cs

Lines 106 to 109 in 8c7be63

	if (NativeFuncs.godotsharp_internal_script_debugger_is_active())
	{
	SendToScriptDebugger(e);
	}

The NativeFuncs.godotsharp_internal_script_debugger_is_active method calls EngineDebugger::is_active() to check that the script debugger is not null, then we call the SendToScriptDebugger method which ends up calling EngineDebugger::get_script_debugger() but this only happens if the previous check passed.

---

I have been unable to reproduce the crash (with Godot built from commit 3cf16c959) but I do get an error in the console with the C# exception:

modules/mono/glue/runtime_interop.cpp:1241 - System.InvalidCastException: Unable to cast object of type 'Godot.EditorNode3DGizmoPlugin' to type 'CrashGizmoPlugin'.
     at crash_test.RestoreGodotObjectData(GodotSerializationInfo info) in /media/raulsntos/Data/GodotProjects/TESTS/CrashGizmo/Godot.SourceGenerators/Godot.SourceGenerators.ScriptSerializationGenerator/crash_test_ScriptSerialization_Generated.cs:line 15
     at Godot.Bridge.CSharpInstanceBridge.DeserializeState(IntPtr godotObjectGCHandle, godot_dictionary* propertiesState, godot_dictionary* signalEventsState) in /media/raulsntos/Data/Godot/src/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/Bridge/CSharpInstanceBridge.cs:line 239

This is caused by the generated code that handles the restoring of a class when reloading assemblies. When reloading assemblies we replace script instances with placeholders to keep their state while we dispose of the old instance, when the assemblies have been reloaded we can instantiate the script again but if the class is not a [Tool] it can't be instantiated by the editor so that's probably what causes the exception here. I understand that the documentation examples are missing the [Tool] attribute so sorry about that.

[raulsntos]

@codecat Are you still able to reproduce this issue in Godot 4.0 RC2 or any later release?

[codecat]

I am not working on the particular project that I was anymore, but I just tested the reproduction project on RC2 and it doesn't seem to crash anymore for me. 👍