Online (real-time) spell checking

[jmcphers]

RStudio has a built-in spell checker which can be invoked with e.g. F7. However, many users have requested online spell checking in RStudio; that is, words spelled incorrectly are highlighted in some way as soon as they're typed, without the need to manually invoke the checker.

https://community.rstudio.com/t/underline-misspelled-words-in-rstudio/8235/2

https://stackoverflow.com/questions/31653319/spell-check-in-rstudio/

Our editor, Ace, doesn't itself doesn't embed a spell checker; although it can integrate with the browser's spell checker, it can't do context-sensitive checking, which is what we'd need since the most relevant place for spell checking in RStudio is in R Markdown documents, which contain a mix of content that requires spell checking (prose) and content that doesn't (R code).

See also this old project to add spell check to Ace and typo.js.

One of the reasons we haven't done this yet is that the F7 spell check, if simply turned into an online spell checker, probably wouldn't be satisfactory, as there are a number of rough edges that would suddenly become very abrasive. In particular:

1. we need to spell check the correct regions of each file type; for example, we don't check headings right now (#1588), and spelling in comments of R files would be nice too
2. many domain specific terms aren't in the default dictionary
3. the UX for suggestions/ignoring/adding to a dictionary would need some polish and would also need to be added to a context menu.

[mcfrank]

Thanks @adamconroy for working on this - let me know if you need alpha testing. :) I am a big advocate for RStudio + RMarkdown as the reproducible writing solution and would love to see this feature as it's a key part of convincing people to write in RStudio rather than say word or gdocs.

[benmarwick]

I recently spotted live, on-the-fly spell checking in OSX v.1.3.118 and later, which can be downloaded from https://dailies.rstudio.com/ Thanks, @adamconroy ! (#4762)

[jmcphers]

This is implemented now. If anyone would like to try it, you can do so using our daily builds:

https://dailies.rstudio.com/

Check the "Real time spellchecking" preference here:

This preference is currently off by default in the daily builds, but will be on by default when we release a preview with this functionality.

[mcfrank]

👏 👏 👏