Tab to align cursor with next non-whitespace character in the line above (in insert mode)

Question

How can we do this with vim?

set hlsearch                        " Highlight search matches
set incsearch                       " Highlight search matches as you type
set visualbell                      " Use visual bell instead of beeping
set shortmess+=I                    " Disable vim intro message
set lazyredraw      █...............x<-- Put the cursor here

In particular:

• Should work without changing normal Tab functionality
• Solution doesn't necessarily have to use the Tab key

Update:

I've got a pretty well working 'supertab' key based on Maxim Kim's posted solution.

A modified tabbing behavior that jumps to align with the next word on the previous line can be achieved by including this in your vimrc:

" Tab that will advance to align with next word on the previous line
fun! SuperTab() abort
  let spaces = matchstr(getline(line('.')-1)[col('.')-1:], '^\s*')

  return len(spaces) ? spaces : "\<tab>"
endfun

inoremap <expr> <C-t> SuperTab()

For a more succinct solution if backwards compatibility is not a concern (since support for a regular expression anchor \%.c that represents the current cursor position has been introduced into vim in version 8.2.3110):

" Tab that will advance to align with next word on the previous line (needs vim >= 8.2.3110)
fun! SuperTab() abort
  let spaces = matchstr(getline(line('.')-1), '\%.c\s*')

  return len(spaces) ? spaces : "\<tab>"
endfun

inoremap <expr> <C-t> SuperTab()

Although binding this to something like CtrlTab could feel intuitive, that happens to be one of the key combinations that doesn't have universal support across terminal emulators. For this reason, I've currently got it bound to CtrlT in normal mode.

Answer 1

Well, you can do it with vimscript, here is the proof of concept:

func! MyTab() abort
    let spaces = matchstr(getline(line('.')-1), '\%.c\s*')
    if len(spaces)
        return spaces
    else
        return "\<Tab>"
    endif
endfunc
inoremap <expr> <tab> MyTab()

NOTE though, the example uses quite recent vim that has added \%.c for regexes -- match at the current column position. With older vim you have to substitute it with real column position taken from either col('.') or getpos() functions.

Upd

If you don't want to change "normal" tab functionality do not remap tab, do

inoremap <expr> <C-j> MyTab()

instead.

Still if you look for some very simple solution, like existing built-in setting to change -- there is none atm afaik.

Answer 2

You already have a working solution, not sure what your question is about now, since you updated it :/

Anyhow, here is another simple solution. On the line above, where you want the cursor to be positioned, put the cursor at the exact stop and remember the value echoed by :echo col('.')-1. Now enter :setlocal varsofttabstop=<number> where <number> is the result of what col('.')-1 returned.

This makes use of the vartab feature, that allows you to specify how far to stretch the tab. By default a <Tab> usually spans multiples of 8, but with the vartabs feature, you can specify a different amount for several different stop. See the help at :help 'varsofttabstop' for more information.

Note: this can be made a bit more automatic, by creating a function, that analyzes the buffer content and sets the vartabs setting accordingly (My CSV plugin does this for tab delimited files).