Shows softabs (spaces instead of tabs) as real tabs, but still saves spaces. I don't get it. Don't worry - neither do I.

vim-ruby-listchars-spaces.vim

" shows expanded tabs (2 spaces) using
" vim's listchars (which only work with
" hard tabs) but still saves spaces instead of tabs
" needds following settings:
" set softtabstop=2
" set shiftwidth=2
" set tabstop=2
" set expandtab
" set list
" set listchars=tab:▸\ ,eol:.
" but it can be made more flexible
function! g:ShowIndents()
  let line_num = line(".")
  setlocal noexpandtab
  " FIXME this regex needs to work only with
  " something like ^(\ \ )*"
  silent exe '%s=  =\t=g'
  setlocal nomodified
  exe "goto ".line_num
endfunction

function! g:HideIndents()
  let line_num = line(".")
  setlocal expandtab
  retab
  setlocal nomodified
  exe "goto ".line_num
endfunction

"auto commands
autocmd BufWritePre *.rb call g:HideIndents()
autocmd BufWritePost *.rb call g:ShowIndents()
autocmd BufRead *.rb call g:ShowIndents()
autocmd BufNewFile *.rb call g:ShowIndents()