[WIP][Completion] Configurable Completers

[saurfang]

Improve reconfigurability of completers:

1. Completers can be selectively enabled and disabled. snippet and keywords completers source completions from Ace's language mode definition. text completer completes with local words.
2. R language completer now receives full text in addition to the current line buffer due to full-text lags due to debouncing.
3. R language completer now provides full completion object such that fields can be customized: name, value, description, and meta.

@vnijs This is based on my work in progress SQL editor. As far as I can tell, it works fine but I have not done extensive testing. Feel free to work off of this branch or even merge if you wish. I have left a few TODOs in the code for ideas.

For your case, I think you need

updateAceEditor("editor", autoCompleters = "rlang")

and with value <- session$input[[paste0("shinyAce_", inputId, "_hint")]] you can get full document with value$document to parse yaml with.

p.s. The js injection in aceEditor horrifies me a little and it's also unfortunate to have a duplicated logic in aceEditor and updateAceEditor.

[vnijs]

For the yaml processing example I mentioned autoCompleters = "static" works perfectly. Really nice. I'll look at the others tomorrow.

[vnijs]

@saurfang and @GregorDeCillia: I ended up using paste0(inputId, "_shinyAce_hint").