I wanted to improve the standard Vim foldtext both to look better in GUI versions of Vim, and to make the folding work better with C-like languages (such as C++, Java and pov).

The foldtext function below does three things:

• Is less intrusive when displaying code, and right-aligns the number of lines in the fold.
• Collapses folds that start and end on braces with everything between the braces replaced with {...}.
• Tries to collapse multiline comments with the first non-blank line in the comment.

Outstanding issues:

• Right alignment may not work with signs turned on.
• Tabs mess up the in-place display of the initial '{'.

" Set a nicer foldtext function
set foldtext=MyFoldText()
function! MyFoldText()
  let line = getline(v:foldstart)
  if match( line, '^[ \t]*\(\/\*\|\/\/\)[*/\\]*[ \t]*$' ) == 0
    let initial = substitute( line, '^\([ \t]\)*\(\/\*\|\/\/\)\(.*\)', '\1\2', '' )
    let linenum = v:foldstart + 1
    while linenum < v:foldend
      let line = getline( linenum )
      let comment_content = substitute( line, '^\([ \t\/\*]*\)\(.*\)$', '\2', 'g' )
      if comment_content != ''
        break
      endif
      let linenum = linenum + 1
    endwhile
    let sub = initial . ' ' . comment_content
  else
    let sub = line
    let startbrace = substitute( line, '^.*{[ \t]*$', '{', 'g')
    if startbrace == '{'
      let line = getline(v:foldend)
      let endbrace = substitute( line, '^[ \t]*}\(.*\)$', '}', 'g')
      if endbrace == '}'
        let sub = sub.substitute( line, '^[ \t]*}\(.*\)$', '...}\1', 'g')
      endif
    endif
  endif
  let n = v:foldend - v:foldstart + 1
  let info = " " . n . " lines"
  let sub = sub . "                                                                                                                  "
  let num_w = getwinvar( 0, '&number' ) * getwinvar( 0, '&numberwidth' )
  let fold_w = getwinvar( 0, '&foldcolumn' )
  let sub = strpart( sub, 0, winwidth(0) - strlen( info ) - num_w - fold_w - 1 )
  return sub . info
endfunction

I also use the following highlights with white backgrounded source to visually set the folds apart from non-folded lines, while trying to keep a nice aesthetic.

highlight FoldColumn  gui=bold    guifg=grey65     guibg=Grey90
highlight Folded      gui=italic  guifg=Black      guibg=Grey90
highlight LineNr      gui=NONE    guifg=grey60     guibg=Grey90

See alsoEdit

• Folding presents an overview of how to use folding

ReferencesEdit

• :help 'foldtext'

CommentsEdit

Here's what I use. I think that some of it might be good to merge in (especially the 'diff' folding section) but I'm not up do doing it right now. My goal was to have a very similar fold pattern for things like C code, but provide a good fallback for all other folds, and define something special for diff folding. I really like the way the author of this tip treats comments in a special way—I might need to use that idea.

In my $HOME/vimfiles/ftplugin directory, I set up different file-types to use my different fold patterns. For example, in c.vim, I have 'let b:foldpat=1'.

if has("folding")
  set foldtext=MyFoldText()
  function! MyFoldText()
    " for now, just don't try if version isn't 7 or higher
    if v:version < 701
      return foldtext()
    endif
    " clear fold from fillchars to set it up the way we want later
    let &l:fillchars = substitute(&l:fillchars,',\?fold:.','','gi')
    let l:numwidth = (v:version < 701 ? 8 : &numberwidth)
    if &fdm=='diff'
      let l:linetext=''
      let l:foldtext='---------- '.(v:foldend-v:foldstart+1).' lines the same ----------'
      let l:align = winwidth(0)-&foldcolumn-(&nu ? Max(strlen(line('$'))+1, l:numwidth) : 0)
      let l:align = (l:align / 2) + (strlen(l:foldtext)/2)
      " note trailing space on next line
      setlocal fillchars+=fold:\ 
    elseif !exists('b:foldpat') || b:foldpat==0
      let l:foldtext = ' '.(v:foldend-v:foldstart).' lines folded'.v:folddashes.'|'
      let l:endofline = (&textwidth>0 ? &textwidth : 80)
      let l:linetext = strpart(getline(v:foldstart),0,l:endofline-strlen(l:foldtext))
      let l:align = l:endofline-strlen(l:linetext)
      setlocal fillchars+=fold:-
    elseif b:foldpat==1
      let l:align = winwidth(0)-&foldcolumn-(&nu ? Max(strlen(line('$'))+1, l:numwidth) : 0)
      let l:foldtext = ' '.v:folddashes
      let l:linetext = substitute(getline(v:foldstart),'\s\+$','','')
      let l:linetext .= ' ---'.(v:foldend-v:foldstart-1).' lines--- '
      let l:linetext .= substitute(getline(v:foldend),'^\s\+','','')
      let l:linetext = strpart(l:linetext,0,l:align-strlen(l:foldtext))
      let l:align -= strlen(l:linetext)
      setlocal fillchars+=fold:-
    endif
    return printf('%s%*s', l:linetext, l:align, l:foldtext)
  endfunction
endif

Another suggestion (less elaborated than above, tested for 7.2/7.3):

set foldtext=MyFoldText()
function MyFoldText()
  let nucolwidth = &fdc + &number*&numberwidth
  let winwd = winwidth(0) - nucolwidth - 5
  let foldlinecount = foldclosedend(v:foldstart) - foldclosed(v:foldstart) + 1
  let prefix = " _______>>> "
  let fdnfo = prefix . string(v:foldlevel) . "," . string(foldlinecount)
  let line =  strpart(getline(v:foldstart), 0 , winwd - len(fdnfo))
  let fillcharcount = winwd - len(line) - len(fdnfo)
  return line . repeat(" ",fillcharcount) . fdnfo
endfunction

This will display javadoc summaries in a fold and will skip over multiple single line comments and C-style comments to display a method signature as the foldtext. I make heavy use of syntax folding and fold javadoc comments and function definitions separately, so I can see both doc summaries and method signatures. I generally want to skip over non-javadoc comments which precede a method decl when I fold a method, so this does both, shows javadoc summary and skips other comments to just show method signature.

This will also align the fold text portion after the number of lines being folded is displayed, so it cleans up the fold display significantly.

function! GetFoldedHeader()
  let numlines_folded = v:foldend - v:foldstart + 1
  let line_num = v:foldstart
  let firstline = getline(v:foldstart)

  let charline = matchstr(firstline, '^\s*\(<[^!]\|\w\+\)[^{}]*')

  " Handle javadoc style comments, display the javadoc summary as the foldtext
  if match(firstline, '^\s*\/\*\*') == 0
    if match(firstline, '^\s*\/\*\*\s*$') == 0
      let charline = substitute(getline(v:foldstart+1), '^\s*\**\s*', '(doc) ', '')
      let charline = substitute(charline, '\..*$', '.', '')
    else
      let charline = substitute(firstline, '\s*\/\*\*\s*', '', '')
    endif
  else
    " handle the special case of multiple single line comments
    if match(firstline, '^\s*\/\/') == 0
      if match(getline(v:foldend), '^\s*\/\/') == 0
        let charline = substitute(firstline, '\s*\/*\s*', '', '')
      endif
    else
      let charline = matchstr(firstline, '^\s*\(<[^!]\|\w\+\)[^{}]*')
      while strlen(charline) == 0 && line_num < v:foldend
        let line_num = line_num + 1
        let charline = matchstr(getline(line_num), '^\s*\(<[^!]\|\w\+\)[^{}]*')
      endw
    endif
  endif

  let preamble = printf("[%d lines folded]:", numlines_folded)
  return printf("%-20s%s", preamble, substitute(charline, '^\s*', '', ''))