Add autocompletion for scene unique nodes

[KoBeWi]

Describe the project you are working on

A couple of big projects. I started adapting the scene unique nodes into them.

Describe the problem or limitation you are having in your project

Scene Unique Names are a cool feature and works really good. There is one minor gripe though - no autocompletion. When you type $, you get autocompletion for nodes on the scene. But it only includes full paths. If I have e.g. 10 unique nodes, at different levels in the scene, I can't easily type them; I need to copy the name at best, which might be problematic in big scenes.

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

When typing $"%, script editor should list all unique nodes on the current scene, so they can be easily selected.

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

When doing normal path autocompletion and % is used, fetch the list of unique node names in the current scene and list them for autocompletion.

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

Not really, although script editor plugins are a thing. Maybe.

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

It completes a cool existing feature.

[hsandt]

And of course, when using shorthand $% too (works when node names have no spaces in them).

I tried to auto-complete with full path from root, but even that didn't work: it only detected path for autoloaded singleton + child nodes (it makes sense, how could a script know in which scene context it can appear at runtime? but I think it used to work with the currently opened scene for convenience anyway)

so I cannot even use the trick of showing full path then deleting the part before. Copy-pasting the node name seems the fastest workaround.

And just a screenshot to illustrate the current case, where no auto-completion popup shows at all after adding %:

[aXu-AP]

I'm not sure what was the state of this when this issue was first written, but currently (4.3) situation is as follows:

• $ gives suggestions for unique nodes, but they are in quotes (eg $ -> $"%MyNode") made a pr to fix this: Remove unneeded quotes from autocomplete % nodes godot#96666
• % gives suggestions after you write first letter (eg %m -> %MyNode)
  • It seems that this extra letter problem was discussed at least here: Fix autocompletion after DOLLAR token godot#84706 (comment)
• $% is a bit broken; it gives the same suggestions as $ operator, and also waits for extra letter (eg $%m -> $%"%MyNode" [note the extra %, which is a bug] or $%MyNonUniqueNode)
• get_node works, no problems here (since the path is anyways in quotes).

So all in all, some support is there, but it's not perfect yet. It seems that godotengine/godot#85384 is where the current support came to be.

Another thing is, paths like %MyUniqueNode/Child aren't supported at all by autocompletion, altough I'm not sure how widely used nodepaths relative to unique nodes are...