Question

I use the following code to make cc preserve the existing indentation when the line is not empty, and to use the calculated indentation (using indentexpr) when the line is empty.

function SmartCC()
  if getline('.') !~# '\S'
    return 'cc'
  else
    let spaces = repeat(' ', indent('.'))
    return '0d$i' . spaces
  endif
endfunction
nnoremap <expr> cc SmartCC()

The only problem I have with it is that, unlike the built-in cc, this inserts “real” spaces and not “tentative” spaces that get deleted automatically if nothing is typed on that line.

Is there a way to insert such tentative spaces?

Or maybe what I’m trying to achieve is already available by setting some secret option?

To make it clear, a plugin that removes all trailing spaces is not a solution.

Answer 1

Try the following hack:

function SmartCC_IndentExpr(indent, savedindentexpr)
    let &l:indentexpr=a:savedindentexpr
    return a:indent
endfunction
function SmartCC()
    if getline('.')=~#'\S'
        let &l:indentexpr='SmartCC_IndentExpr('.indent('.').', '.string(&l:indentexpr).')'
    endif
    return 'cc'
endfunction
nnoremap <expr> cc SmartCC()

. The idea is to set &l:indentexpr only for the period of evaluation cc. As it is known that cc checks indent only once and nothing triggers the check before cc under such circumstances then the &l:indentexpr itself can be used to restore &l:indentexpr back before indent is checked for the second time for another reason.