Add signal to scene tree when a node entering or exiting group

[qt911025]

Describe the project you are working on

A game.

Describe the problem or limitation you are having in your project

Godot can call methods or set values via some group calls, but it only affects nodes in a group currently. In the circumstance of changeful group, new nodes can't be affected while joining a group or enter a tree(with group joined already) for lacking of corresponding event, thus making new nodes complicated to do decorations like adding child or connecting signal.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

"enter_group" signal for scene tree happens when a node (already in scene tree) is added to a group, or a node (already in group) enters scene tree, and "exit_group" does the opposite.

The 2 signals emit with 2 parameters: target node and group name.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

If this enhancement will not be used often, can it be worked around with a few lines of script?

Is there a reason why this should be core and not an add-on in the asset library?

To fit with native godot interface, otherwise the add on should implement a whole wrapper to wrap functions already implemented.

[AThousandShips]

Already tracked in:

• Add SceneTree signals for adding/removing a Node to/from a group #1259

[Calinou]

Thanks for the proposal! Consolidating in #1259.