darkrc/vim/plugin/annotate.vim

let s:namespace = nvim_create_namespace("annotate_cursor")
let s:callbacks = []

if has("nvim")
	function! Blame()
		if exists("b:blame")
			let l:lineblame = b:blame[line('.')-1]
			return l:lineblame['author'] . ' @ ' . l:lineblame['time']
		end
	endfun

	function! Annotate(callback)
		call insert(s:callbacks, a:callback)
		call s:update()
	endfun
	com! -nargs=1 Annotate call Annotate(funcref(<q-args>))

	function! Deannotate(callback)
		let s:callbacks = filter(s:callbacks, { idx, value -> value != a:callback })
		call s:update()
	endfun
	com! -nargs=1 Deannotate call Deannotate(funcref(<q-args>))

	function! Annotated(callback)
		for l:Callback in s:callbacks
			if l:Callback == a:callback
				return 1
			end
		endfor
		return 0
	endfun

	function! s:update()
		call nvim_buf_clear_namespace(0, s:namespace, 1, -1)
		for l:Callback in s:callbacks
			call nvim_buf_set_virtual_text(0, s:namespace, line('.')-1, [[l:Callback(), "comment"]], {})
		endfor
		redraw!
	endfun

	au CursorMoved * call <SID>update()
	au CursorMovedI * call <SID>update()
end