Vim retab spaces at the beginning of lines only

Question

I'm currentling using

:set noet|retab!

But the problem I'm running into is it's replacing all instances of 4 spaces to tabs throughout the entire file. I need vim to only replace instances of 4 spaces at the beginning of lines only.

If I remove the ! at the end of retab, spaces are not replaced anywhere.

I've tried using a custom function that somebody created:

" Retab spaced file, but only indentation
command! RetabIndents call RetabIndents()

" Retab spaced file, but only indentation
func! RetabIndents()
    let saved_view = winsaveview()
    execute '%s@^\( \{'.&ts.'}\)\+@\=repeat("\t", len(submatch(0))/'.&ts.')@'
    call winrestview(saved_view)
endfunc

but I get a nice little error message when I run:

:RetabIndents

Error detected while processing function RetabIndents:

line 2:

E486: Pattern not found: ^( {4})+

Answer 1

After talking with some other people about this, I needed to add the silent! command before execute. So this is what I have working now:

autocmd BufWritePre * :RetabIndents
command! RetabIndents call RetabIndents()

func! RetabIndents()
    let saved_view = winsaveview()
    execute '%s@^\(\ \{'.&ts.'\}\)\+@\=repeat("\t", len(submatch(0))/'.&ts.')@e'
    call winrestview(saved_view)
endfunc

So now this function will automatically replace spaces with tabs at the beginning of each line only.