fold.vim

set nofoldenable
set foldlevel=99
set fillchars=fold:\
set foldtext=CustomFoldText()
setlocal foldmethod=expr
setlocal foldexpr=GetPotionFold(v:lnum)

function! GetPotionFold(lnum)
  if getline(a:lnum) =~? '\v^\s*$'
    return '-1'
  endif
  let this_indent = IndentLevel(a:lnum)
  let next_indent = IndentLevel(NextNonBlankLine(a:lnum))
  if next_indent == this_indent
    return this_indent
  elseif next_indent < this_indent
    return this_indent
  elseif next_indent > this_indent
    return '>' . next_indent
  endif
endfunction

function! IndentLevel(lnum)
    return indent(a:lnum) / &shiftwidth
endfunction
function! NextNonBlankLine(lnum)
  let numlines = line('$')
  let current = a:lnum + 1
  while current <= numlines
      if getline(current) =~? '\v\S'
          return current
      endif
      let current += 1
  endwhile
  return -2
endfunction

function! CustomFoldText()
  " get first non-blank line
  let fs = v:foldstart
  while getline(fs) =~ '^\s*$' | let fs = nextnonblank(fs + 1)
  endwhile
  if fs > v:foldend
      let line = getline(v:foldstart)
  else
      let line = substitute(getline(fs), '\t', repeat(' ', &tabstop), 'g')
  endif
  let w = winwidth(0) - &foldcolumn - (&number ? 8 : 0)
  let foldSize = 1 + v:foldend - v:foldstart
  let foldSizeStr = " " . foldSize . " lines "
  let foldLevelStr = repeat("+--", v:foldlevel)
  let expansionString = repeat(" ", w - strwidth(foldSizeStr.line.foldLevelStr))
  return line . expansionString . foldSizeStr . foldLevelStr
endfunction