[RFC]: Add auto-completion preview for REPL

[tudor-pagu]

Description

This RFC proposes adding a gray preview for auto-completion in the cases where the completer decides that there is only one valid completion. This aims to be similar to the behaviour of the node.js REPL:

After seeing the preview, the user can press tab for the completion to be filled in normally. Additionally, to mimic the node.js REPL, if the user presses the up arrow, the completion should also be filled in, and if the user presses enter the completion should be filled in and the line should be executed.

Related Issues

Related issue stdlib-js/google-summer-of-code#1
This issue also involves adding a listener for every key press in the REPL: #1672

Questions

Is the behaviour I proposed when pressing up/enter good? Are there any other interactions which I've missed that I should implement?

Other

No.

Checklist

• I have read and understood the Code of Conduct.
• Searched for existing issues and pull requests.
• The issue name begins with RFC:.

[tudor-pagu]

Hi @kgryte @Planeshifter, if the issue is accepted I would like to be assigned to it, please. I have made some progress on it.

[kgryte]

@tudor-pagu This would be a welcome addition. Feel free to open a PR.