How to convert leading spaces to tabs? - vim

Question

Many people use spaces rather than tabs. I use both of them. Tabs at the beginning of line and spaces from the first non-whitespace character. No problem for starting new document and in case I have to modify one better adapt to using format. Still sometimes I need to fix the spaces issue anyway.
According to Search and replace I can just do :%s/spaces_for_tab/tab/g. It is simple and it will work for many cases. Anyway I want to refactor only spaces at the beginning of line.

Answer 1

This is more of a regex issue. To anchor at the beginning of the line, use the caret, e.g.
s/^ /\t/
Or do it using vim's builtin functionality:
:set tabstop=4 "four spaces will make up for one tab
:set noexpandtab "tell vim to keep tabs instead of inserting spaces
:retab "let vim handle your case
By the way, I too prefer tabs for indentation and spaces for alignment. Unfortunately, vim doesn't handle this well (and I don't know what other editors do), so I mostly use :set expandtab (maybe see :set softtabstop).

Answer 2

I've written a simple func for it. Anyway it will work only for 4-space tab.
fu! Fixspaces()
while search('^\t* \{4}') != 0
execute ':%s/^\t*\zs \{4}/\t/g'
endwhile
endfu
You can suggest better solution, if exists, and I will use it with pleasure.
The issue is that this func replaces spaces in strings as well.

Answer 3

David's response is very elegant but it doesn't address leading whitespace that has a mixture of tabs and spaces. For example to convert a line like:
<SPACE><SPACE><TAB>something...
you have to know the position of the tab to determine the number of spaces needed to replace the <TAB> and reach the next tabstop. My solution below, although not as compact as David's, addresses this. It also allows me to select which way to use leading whitespace without depending upon &expandtab. I would appreciate any suggestions to improve my code...
function! TabsToSpaces(...)
let ts = &tabstop
let pos = getpos('.')
while search('^ *\zs\t', "w") != 0
let l:curpos = getcharpos('.')
" The number of spaces needed depends upon the position of the <TAB>
let numsp = 1 + ts - ( curpos[2] % ts )
if numsp == 9
let numsp = 1
endif
silent execute ':s/^ *\zs\t/'.repeat(' ', numsp).'/'
endwhile
if a:0 == 0
echo 'Changed leading tabs to spaces'
endif
call setpos('.', pos)
endfunction
function! SpacesToTabs(...)
let ts = &tabstop
let pos = getpos('.')
" First normalize all tabs to spaces
call TabsToSpaces("quiet")
while search('^\t* \{'.ts.'}') != 0
silent execute ':%s/^\t*\zs \{'.ts.'}/\t/g'
endwhile
if a:0 == 0
echo 'Changed leading spaces to tabs'
endif
call setpos('.', pos)
endfunction
" Some keystrokes to implement the spaces/tabs functions
nmap <Leader>st :execute SpacesToTabs()<CR>
nmap <Leader>ts :execute TabsToSpaces()<CR>

Answer 4

I took Martin's answer and improved on it a bit if anyone's interested:
function Fixspaces()
let ts = &tabstop
let pos = getpos('.')
if &expandtab
while search('^ *\t') != 0
silent execute ':%s/^ *\zs\t/'.repeat(' ', ts).'/g'
endwhile
echo 'Changed tabs to spaces'
else
while search('^\t* \{'.ts.'}') != 0
silent execute ':%s/^\t*\zs \{'.ts.'}/\t/g'
endwhile
echo 'Changed spaces to tabs'
endif
call setpos('.', pos)
endfunction
This function does the appropriate thing depending on the values of the expandtab and tabstop settings and also remembers where the cursor is.