This is an experimental plugin to test the liveupdate feature of neovim.

Install with your preferred plugin manager, and then drop something like this in your .vimrc:

fun! <SID>Hiwords()
  if exists(':Hiword')
    syntax off
    Hiword Conditional if
    Hiword Conditional else
    Hiword Conditional elseif
    Hiword Statement elseif
    " and so on
  endif
endfun
" run Hiword commands when vim has finished loading the plugin
au! VimEnter * call <SID>Hiwords()
" run Hiword commands right now if they are ready (for example when the
" user sources this file)
call <SID>Hiwords()

Each Hiword command spawns a new python process using jobstart(). Each python process will monitor the contents of every buffer using the live update feature and highlighting for a single word. E.g., if you call Hiword with 20 different words then 20 python processes will be spawned, all of them watching every single buffer for updates.

So this tool has a pretty obvious race condition where it can receive a LiveUpdate notification, spend some time working out the new highlights for the line that needs changing, and then by the time it sends API calls to neovim specifying which lines to modify hl for, the user has already added a new line above the one that was originally changed meaning the line numbers in the API call are all wrong. :-(

The solution is to write out the main loop logic like this:

def mainloop():
    pending_highlights = []
    while pending_highlights or nvim.wait_for_message():
        while nvim.have_messages():
            # process any LiveUpdate messages coming in from neovim
            pending_highlights += handle_notifications()
        # lock nvim so the user can't make any buffer changes
        with nvim.lock_buffer(bufnr):
            if not nvim.have_messages():
                # send the HL updates to neovim now
                send_highlights(pending_highlights)
                pending_highlights = []