Improve instantiating nodes in the editor with unnamed script classes

[harrison-munitz]

Instancing nodes from scripts which include a class_name is very easy. You open the Create New Node window, select your class in the list, and you're done. It creates a new node, attaches the correct script to it and sets the correct base-class that your script inherits from.

However, when the script doesn't include a class_name the process is a bit more manual. It's by no means complicated, but it has more potential for mistakes and represents a "gotcha" in the engine. Specifically, since unnamed classes don't appear in the Create New Node window, you have to make sure to manually choose the correct base-class of node to attach the script to (or remember to change it after) since adding the script will not automatically change the node's type. This can lead to all sorts of weird and undesirable behavior or more likely, instant errors and crashes.

For example: If you add a Node2D to your scene and then give it a script which inherits from Control it will still be a Node2D, but with all of the additional behavior and properties from that script. It will typically cause the game to crash as soon as the script tries to access a member or method of Control since it doesn't have them.

I propose two different solutions, either or both would improve the user experience around unnamed classes:

1. Adding a script to a node should change its type to the one which that script extends. Ideally it should also rename the node if it wasn't already given a custom name.
   • Related to this change but unrelated to the post, changing the inheritance of a script should also change the type of the node.
2. There should be a way to instantiate nodes with unnamed scripts directly, such as one of the following:
   1. Unnamed scripts should appear in the Create New Node window and displayed using the file name/path. A checkbox could be used to hide or show these since it could be annoying if you have dozens or hundreds of one-off scripts. Alternatively or additionally, if searching in the window returns no results, it could extend the search to include unnamed scripts.
   2. Dragging a script to the empty space in the node-hierarchy in the inspector, i.e. not to an existing node, should create a new instance of that script.