Can't get method on CallableCustom "Delegate::Invoke" error when using a lambda function in UndoRedo.AddDoMethod and UndoRedo.AddUndoMethod

[robbertzzz]

Tested versions

Tested on v4.2.1.stable.mono.official [b09f793]

System information

Windows 11

Issue description

I'm converting a tool written in C# from a plugin to a runtime tool and have an undo function where a variable is being bound to the Callable. In C# this can only be done through a lambda, which is what I'm doing. However, unfortunately UndoRedo's AddDoMethod() and AddUndoMethod() throw the error Can't get method on CallableCustom "Delegate::Invoke" which from a quick look in the engine codebase means the function name isn't accessible (which is isn't, it's a lambda function).

Note that this is not the same issue as #70026 because it only happens when the UndoRedo functions are actually called, but it seems to be similar to #80434 except that that's in GDScript.

Steps to reproduce

Use any lambda function when calling UndoRedo.AddDoMethod or UndoRedo.AddUndoMethod, i.e., UndoRedo.AddUndoMethod(Callable.From(() => GD.Print("Hello World!")))

Minimal reproduction project (MRP)

UndoRedoLambdaBug.zip

Run the project, click the button, check the error log.

[raulsntos]

It looks like UndoRedo tries to get the Callable's method name with Callable::get_method() and then falls back to Callable::operator String():

godot/core/object/undo_redo.cpp

Lines 162 to 166 in 83b916b

	do_op.name = p_callable.get_method();
	if (do_op.name == StringName()) {
	// There's no `get_method()` for custom callables, so use `operator String()` instead.
	do_op.name = static_cast<String>(p_callable);
	}

The error can safely be ignored, but maybe we should implement CallableCustom::get_method like they did for GDScript in #80506.

[4d49]

The problem also affects GDScript.

func _ready() -> void:
	var undo_redo := UndoRedo.new()

	var callable: Callable = func() -> void:
		pass

	undo_redo.add_do_method(callable)

I got error: Can't get method on CallableCustom "<anonymous lambda>(lambda)"

[KoBeWi]

I got error: Can't get method on CallableCustom "(lambda)"

This doesn't seem to happen on master.

[4d49]

This doesn't seem to happen on master.

I'm sorry! I must have made a mistake. Here's the correct example.

var undo_redo := UndoRedo.new()
var value: bool = false

func _ready() -> void:
	var do = func() -> void:
		value = true

	var undo = func() -> void:
		value = false

	undo_redo.create_action("test")
	undo_redo.add_do_method(do)
	undo_redo.add_undo_method(undo)
	undo_redo.commit_action()