Super lightweight autocomplete using vim's built-in <C-n> completion

minimal-autocomplete.vim

set cot=menu,menuone

ino <BS> <BS><C-r>=getline('.')[col('.')-3:col('.')-2]=~#'\k\k'?!pumvisible()?"\<lt>C-n>\<lt>C-p>":'':pumvisible()?"\<lt>C-y>":''<CR>
ino <CR> <C-r>=pumvisible()?"\<lt>C-y>":""<CR><CR>
ino <Tab> <C-r>=pumvisible()?"\<lt>C-n>":"\<lt>Tab>"<CR>
ino <S-Tab> <C-r>=pumvisible()?"\<lt>C-p>":"\<lt>S-Tab>"<CR>

augroup MyAutoComplete 
    au!
    au InsertCharPre * if
    \ !exists('s:complete') &&
    \ !pumvisible() &&
    \ getline('.')[col('.')-2].v:char =~# '\k\k' |
        \ let s:complete = 1 |
        \ noautocmd call feedkeys("\<C-n>\<C-p>", "nt") |
    \ endif
    au CompleteDone * if exists('s:complete') | unlet s:complete | endif
augroup END