.NET: Failed to unload assemblies when using `TweenMethod`/`TweenCallback` in tool script

[beicause]

Tested versions

Reproducible in 4.2.stable, 4.3.stable, 4.4.dev

System information

Godot v4.4.beta.mono - EndeavourOS SMP PREEMPT_DYNAMIC Sun, 02 Feb 2025 01:02:29 +0000 on Wayland - X11 display driver, Multi-window, 1 monitor - Vulkan (Mobile) - integrated AMD Radeon Graphics (RADV RENOIR) - AMD Ryzen 7 4800U with Radeon Graphics (16 threads)

Issue description

The error occurs .NET: Failed to unload assemblies. Please check #78513 for more information when using TweenMethod/TweenCallback in tool script and building and reloading scene several times.

Steps to reproduce

Add a node and attach the script to it ( see also MRP ). Make changes to code, build and reload scene several times.

using Godot;

[Tool]
public partial class TweenAnim : Node2D
{
    public override void _Ready()
    {
        Position = Vector2.Zero;
        var tween = CreateTween();

        // with this:
        tween.TweenMethod(
            Callable.From((Vector2 p) => { Position = p; }), Vector2.Zero, new Vector2(200, 200), 1);

        // or with this:
        // tween.TweenCallback(
        //     Callable.From(() => { Position = new(200, 200); })
        // ).SetDelay(1);

        // comment out/modify the code, build, and *reload* the scene several times
        // GD.Print("ready");
    }
}

Error log

.NET: Reloading assemblies...
ERROR: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'TweenAnim'.
   at Godot.GodotObject.GetPtr(GodotObject instance) in /home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/GodotObject.base.cs:line 93
   at Godot.GodotObject.GetInstanceId() in /home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Generated/GodotObjects/GodotObject.cs:line 539
   at Godot.DelegateUtils.TrySerializeSingleDelegate(Delegate delegate, Byte[]& buffer) in /home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/DelegateUtils.cs:line 174
   at Godot.DelegateUtils.TrySerializeDelegate(Delegate delegate, Array serializedData) in /home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/DelegateUtils.cs:line 134
   at Godot.DelegateUtils.TrySerializeDelegateWithGCHandle(IntPtr delegateGCHandle, godot_array* nSerializedData) in /home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/DelegateUtils.cs:line 325
   at: void Godot.NativeInterop.ExceptionUtils.LogException(System.Exception) (/home/luo/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/NativeInterop/ExceptionUtils.cs:113)
Failed to serialize delegate
Unloading assembly load context...
Assembly unloading is taking longer than expected...
Failed to unload assemblies. Possible causes: Strong GC handles, running threads, etc.

Minimal reproduction project (MRP)

dotnet-tween-reload.zip

[beicause]

The problem may come from Callable.From. I found a workaround by using new Callable(this, "xxx"), but the limitation is that can't capture other variables.

[beicause]

I think I found the reason. It is a legacy issue mentioned in #83217 that hasn't been solved yet. Callables capturing Object or variables that cannot be serialized (such as C# types that don't belong to Godot) will lead to this issue.
Workaround:

	var instId = GetInstanceId();
	tween.TweenMethod(
	Callable.From((Vector2 pos) =>
	{
		if (InstanceFromId(instId) is Node2D node)
		{
			node.Position = pos;
		}
	}), Vector2.Zero, new Vector2(200, 200), 1);

[Delsin-Yu]

It might be worth notifying @paulloz , the original PR author.

[BrahRah]

Here is what I've come up with to fix the assembly disconnect issue:

Godot will emit a pre-build signal, allowing subscribed addons to unload .NET resources if needed. Once all have confirmed unloading, the build starts. After completion, a post-build signal is sent, prompting addons to reload their resources. This ensures only necessary addons pause the build, preventing .NET disconnection issues efficiently.

Someone with the skills please implement this! I've got 3 addons to release which I can't as long as this issue is around.

[beicause]

Notably, after I migrate my script to the parent node and capture and tween the child node instead of itself, it seems to work well. I'm not sure about the reason.

	var child = GetNode<Node2D>("Node2D");
	var tween = CreateTween(); ;
	tween.TweenMethod(
		Callable.From((Vector2 pos) =>
		{
		child.Position = pos;
		}), Vector2.Zero, new Vector2(200, 200), 1);

[Delsin-Yu]

@BrahRah Please do not spam the same message all over the place; you have already posted the identical message in #78513