omnicomplete in vim with shift-tab not working?

Question

Im trying to get vim to allow me to circle through the autocomplete popup list with the tab key. It works fine for tab but not for s-tab (shift-tab). It seems like shift-tab somehow canceles the autocomplete menu before applying C-P

Anyone got any ideas?

function InsertTabWrapper(direction)
  if pumvisible()
    if "forward" == a:direction
      return "\<C-N>"
    else
      return "\<C-P>"
    endif
  endif
  let col = col('.') - 1
  if !col || getline('.')[col - 1] !~ '\k' 
    return "\<tab>"
  else
    return "\<c-x>\<c-o>"
  endif
endfunction

inoremap <tab> <c-r>=InsertTabWrapper("forward")<cr>
inoremap <s-tab> <c-r>InsertTabWrapper("backward")<cr>

Answer 1

You missed the equal sign "=" after <c-r> for the <s-tab> mapping.

However, I would suggest doing it like this:

function! InsertTabWrapper()
  if pumvisible()
    return "\<c-n>"
  endif
  let col = col('.') - 1
  if !col || getline('.')[col - 1] !~ '\k'
    return "\<tab>"
  else
    return "\<c-x>\<c-o>"
  endif
endfunction
inoremap <expr><tab> InsertTabWrapper()
inoremap <expr><s-tab> pumvisible()?"\<c-p>":"\<c-d>"

1. Use <expr> mapping. It's nicer to see and clearer (many people don't know about <c-r>= things.
2. Mapping <s-tab> like this and you can do unindent in insertmode.