Tab or complete when in insert mode in vim

tab-or-complete.vim

" Auto-Completion --------------------------------------------------------- {{{

" Use TAB to complete when typing words, else inserts TABs as usual.
function! Tab_Or_Complete(move_to_next_word) abort
  " If auto-complete menu is not open and we are in the middle of typing a
  " word OR if auto-complete menu is already open the `tab` cycles through
  " suggested completions.
  if pumvisible() || (col('.')>1 && strpart( getline('.'), col('.')-2, 3 ) =~ '^\w')
    return a:move_to_next_word
  else
    " If we aren't typing a word and we press `tab` simply do the normal `tab`
    " action.
    return "\<Tab>"
  endif
endfunction

inoremap <expr> <Tab> Tab_Or_Complete("\<C-N>")
inoremap <expr> <S-Tab> Tab_Or_Complete("\<C-P>")

" }}}