"Parent node is busy setting up children" error on focusing out with "Save on Focus Lost" enabled

[trollusk]

Godot version

Godot 4.0.2

System information

Windows 11

Issue description

Sprite3D nodes always produce the following red error message:

Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.
scene/main/window.cpp:1459 - Condition "!is_inside_tree()" is true.

This occurs even if the scene contains nothing but the Sprite3D node, and is run in an otherwise empty project.

The error message gives no information about its origin (i.e. which node is producing the error).

Steps to reproduce

Create a new scene containing only a Sprite3D node. Run the scene.

Minimal reproduction project

N/A

[Calinou]

I can't reproduce this on 4.0.2.stable or 4.1.dev d6dde81 (Linux) with the following scene setups using the Forward+ or Compatibility rendering methods:

Please upload a minimal reproduction project to make this easier to troubleshoot.

[trollusk]

Run the scene in this project:
Test.zip

[Calinou]

Run the scene in this project: Test.zip

I've tried that project and still don't get any messages in the Output panel (or terminal) when running the project.

[09silverware]

This happens on my setup, it is not related to Sprite3D.

  Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.
  scene/main/window.cpp:1459 - Condition "!is_inside_tree()" is true.

4.0.2.stable [7a0977c] via Steam on Windows 10.

This happens when I have Save on Focus Lost enabled in the editor.
I think it's trying to do something with the current focus item when it auto saves.
The save does seem to work fine.

Normal saves are perfectly fine.

Happens even with Overlay Disabled...

[kleonc]

This happens when I have Save on Focus Lost enabled in the editor.

Can confirm this is the cause. Specifically it fails to add_child in here:

godot/editor/progress_dialog.cpp

Lines 158 to 168 in 1becfea

	EditorNode *ed = EditorNode::get_singleton();
	if (ed && !is_inside_tree()) {
	Window *w = ed->get_window();
	while (w && w->get_exclusive_child()) {
	w = w->get_exclusive_child();
	}
	if (w && w != this) {
	w->add_child(this);
	popup_centered(ms);
	}
	}

because the Window w seems to be currently propagating the focus out notification (which trigerred the scene saving / creating progress dialog) and hence it's blocking child addition:

godot/scene/main/node.cpp

Lines 1949 to 1957 in 1becfea

	void Node::propagate_notification(int p_notification) {
	data.blocked++;
	notification(p_notification);
	for (KeyValue<StringName, Node *> &K : data.children) {
	K.value->propagate_notification(p_notification);
	}
	data.blocked--;
	}

godot/editor/editor_node.cpp

Lines 733 to 737 in 1becfea

	case NOTIFICATION_APPLICATION_FOCUS_OUT: {
	// Save on focus loss before applying the FPS limit to avoid slowing down the saving process.
	if (EDITOR_GET("interface/editor/save_on_focus_loss")) {
	_menu_option_confirm(FILE_SAVE_SCENE, false);
	}

godot/scene/main/node.cpp

Line 1156 in 1becfea

ERR_FAIL_COND_MSG(data.blocked > 0, "Parent node is busy setting up children, `add_child()` failed. Consider using `add_child.call_deferred(child)` instead.");

Deferring these seems like the most straighforward thing to do, not sure if that's a proper fix though, might be just a workaround. cc @bruvzg who added this in #71209.

[Calinou]

Thanks for the confirmation. This is a duplicate of #73765.