Tab Vs Space preferences in Vim

Creating a stab option in Vim itself would not be easy, but I've whipped up this command/function that you can drop in your .vimrc (or a plugin file if you're super-organized). Use :Stab and you will be prompted for an indent level and whether or not to use expandtab. If you hit enter without giving it a new indent level, it will just print the current settings.

" put all this in your .vimrc or a plugin file
command! -nargs=* Stab call Stab()
function! Stab()
  let l:tabstop = 1 * input('set shiftwidth=')

  if l:tabstop > 0
    " do we want expandtab as well?
    let l:expandtab = confirm('set expandtab?', "&Yes\n&No\n&Cancel")
    if l:expandtab == 3
      " abort?
      return
    endif

    let &l:sts = l:tabstop
    let &l:ts = l:tabstop
    let &l:sw = l:tabstop

    if l:expandtab == 1
      setlocal expandtab
    else
      setlocal noexpandtab
    endif
  endif

  " show the selected options
  try
    echohl ModeMsg
    echon 'set tabstop='
    echohl Question
    echon &l:ts
    echohl ModeMsg
    echon ' shiftwidth='
    echohl Question
    echon &l:sw
    echohl ModeMsg
    echon ' sts='
    echohl Question
    echon &l:sts . ' ' . (&l:et ? '  ' : 'no')
    echohl ModeMsg
    echon 'expandtab'
  finally
    echohl None
  endtry
endfunction

This is my first attempt at writing VimScript, but here goes:

function! Stab(value)
    let &shiftwidth  = a:value
    let &softtabstop = a:value
    let &tabstop     = a:value
endfunc

If I put this in my .vimrc file, I can call it by running :call Stab(X), where X is the desired tab width. This is an adequate solution for now, but if anyone can suggest a way of making it easier to call I would be grateful.

I've also created a function that quickly summarizes the current settings, which I have mapped to ctrl-Tab:

nmap <C-Tab> :call TabParams()<CR>
function! TabParams()
    echo "tabstop:     ".&tabstop
    echo "shiftwidth:  ".&shiftwidth
    echo "softtabstop: ".&softtabstop
endfunc

Well, I put up a 100 point bounty for this answer, and now I've half solved it myself. Not sure if I can accept my own answer...

You can in edit mode also use Ctrl-T to indent and Ctrl-D to deindent to the next indentation level as set by shiftwidth, regardless of the tabstop, softtabstop or expandtab settings. Vim will automatically add/remove spaces or tabs to bring you to the right column.

If you use these commands to control indentation instead of Tab/Backspace you don't have to worry about all these tab settings fitting together and always get to the correct indentation level.

If expandtab is set then (as too much php points out), softtabstop becomes redundant. The only reason you might set shiftwidth differently from tabstop would be to cater to an odd habit; for instance, you use four-space indents but you prefer tab to insert eight spaces.

If expandtab is unset then things get fuzzier. If you want your code to look the same in with cat and non-vim editors as it does in vim, then tabstop should always be set at 8; in this case you would set softtabstop and shiftwidth both to your preferred indent level. If you instead prefer that every "physical tab" in the file represents one indent level, you would set tabstop and shiftwidth to your preferred indent level and leave softtabstop at zero (setting it equal to tabstop is equivalent except that if you change tabstop it will get out of sync, while zero just means "ignore this please").

Your understanding of softtabstop and expandtab is wrong - so the stab option you suggest wouldn't be very useful.

expandtab is for when you want to use spaces instead of tabs for everything. If you set expandtab, then Vim ignores the softtabstop option and uses tabstop and shiftwidth to work out how many spaces to insert.

softtabstop is only for when you would like to use a mix of tabs and spaces, allowing you to indent with fine control (2 or 4 spaces), while keeping tab width at a higher value (usually 8) so that text appears in the other applications. Setting softtabstop=tabstop doesn't accomplish anything because Vim will always use tabs for indenting.

Update: As kaizer.se has pointed out, if you are using expandtab, then you still need to set softtabstop if you want Vim to backspace multiple spaces as though they are a tab.

Are you changing your white space settings so often you really need a function to manage that? If you are messing with tabstop a lot and also setting expandtab, you are probably going to have a mess over time as you change files with different values passed to stab. Today I use :call stab (4), tomorrow it's :call stab (2) and last week it was :call stab (8). Sounds like even if you write it, you'll soon stop using it.

If you plan to always pass the same value to stab, why not just edit your global settings? In vim:

:e $MYVIMRC

and add the following:

set tabstop=4
set shiftwidth=4  "tabs are 4 spaces wide (default = 8)
set expandtab     "Convert tabs to spaces

This is how my .vimrc is setup.

One useful option is softtabstop=-1 which will set it to the value of shiftwidth.
You can also set shiftwidth to 0, in which case the tabstop value will be used.