fancy_tab_completion.vim

" Remap the tab key to do snippets, autocompletion or indentation depending on
" the context (cobbled together by Gary Bernhardt; partly based on
" http://www.vim.org/tips/tip.php?tip_id=102)
"
" Because this uses the private 'Jumper' function in snippetsEmu, you'll need
" to edit '/.vim/plugin/snippetsEmu.vim' to make it public. To do that, just
" replace all occurrences of '<SID>Jumper' with just 'Jumper'. There were only
" two occurrences in my copy.
" 
" The g:snippetsEmu_key variable must be defined, but not to a function key.
" (I have no idea why function keys break it.) "  I recommend something on the
" leader prefix that you don't use.
let g:snippetsEmu_key = '<leader>]'
function ContextualTabCompletion()
    " If we're at the beginning of a line or on whitespace, indent
    let col = col('.') - 1
    if !col || getline('.')[col - 1] !~ '\k'
        return "\<tab>"
    else
        " We're completing something. Try snippets first. If they don't do
        " anything, try autocompletion
        let jumper_result = Jumper()
        let snippets_key = substitute(g:snippetsEmu_key, '^<', "\\<","")
        let no_snippet_completed = (jumper_result == snippets_key)
        if no_snippet_completed
            return "\<c-p>"
        else
            return jumper_result
    endif
endfunction
inoremap <tab> <c-r>=ContextualTabCompletion()<cr>