Scroll floating win in insert mode (creds to @oblitum)

scroll_float

function! FloatScroll(forward) abort
  let float = coc#util#get_float()
  if !float | return '' | endif
  let buf = nvim_win_get_buf(float)
  let buf_height = nvim_buf_line_count(buf)
  let win_height = nvim_win_get_height(float)
  if buf_height < win_height | return '' | endif
  let pos = nvim_win_get_cursor(float)
  if a:forward
    if pos[0] == 1
      let pos[0] += 3 * win_height / 4
    elseif pos[0] + win_height / 2 + 1 < buf_height
      let pos[0] += win_height / 2 + 1
    else
      let pos[0] = buf_height
    endif
  else
    if pos[0] == buf_height
      let pos[0] -= 3 * win_height / 4
    elseif pos[0] - win_height / 2 + 1  > 1
      let pos[0] -= win_height / 2 + 1
    else
      let pos[0] = 1
    endif
  endif
  call nvim_win_set_cursor(float, pos)
  return ''
endfunction

inoremap <silent><expr> <down> coc#util#has_float() ? FloatScroll(1) : "\<down>"
inoremap <silent><expr>  <up>  coc#util#has_float() ? FloatScroll(0) :  "\<up>"