RFC: Improved (?) tab completion for symbols

[mpastell]

This changes the REPL to show latex and emoji symbols as tab completions and complete names starting with that symbol as well:

This a very initial to implementation to get some feedback whether this is a good idea at all. See some discussion at: JuliaLang/IJulia.jl#634

[JeffBezanson]

I don't like this because I want to know what I can actually type, not just what characters are available. We could potentially show both what to type and what the resulting character would look like.

I don't think we should complete both character names and full identifiers at once. It doesn't make sense to suggest α1 if we don't yet know whether you want to type an alpha.

[mpastell]

I actually also think that showing full completions makes more sense in Jupyter as there you can choose the completion from a menu.

[JeffBezanson]

That's true, but I think even there I'd also like to see the character name so I know what to type in the future.

[mpastell]

I'd be happy with adding character preview to the REPL and using JuliaLang/IJulia.jl#634 for IJulia.

I'm not sure how I could add the character names to Jupyter completetions, I think it would require changes in Jupyter protocol. @stevengj any thoughts? In Jupyter lab this could be added to completer metadata, but at least currently the colors of compeletions would be messed up.

[ChristianKurz]

This could be improved by using a TerminalMenu for tab-completion.

It would be nice to have a multi-column terminal menu for that, though.

[KristofferC]

The IPython preview is nice:

[StefanKarpinski]

Having graphical selection for tab completion would be ideal. As @ChristianKurz said, we've got all the bits and pieces now that TerminalMenus is included in the REPL code, we just need to integrate it and iterate on the features more.