Make fold feature act like Emacs's org-mode fold

Question

In Emacs org-mode, folds use * at the start of the lines, and any * added consecutively, will add a level of indentation to the header.

Furthermore, the header text placed after * or any number of it, will be the only thing shown when folded/folding (in contrast, Vim's fold show part of the text that was folded, instead of only showing the header's text).

Here a gif (roughly 2 seconds) with one fold level.

And here another one (roughly 5 seconds) with more than one fold level (three levels).

Any way/or existing plugin to do this?

Answer 1

You can accomplish this kind of folding fairly easily by using a file expression, using a function to calculate the fold level of the current line.

You can start a new fold of level n on a line that starts with n *s (possibly followed by whitespace.) For a line that doesn't start with *, simply use the fold level of the most recent * line above it.

That's easily implemented with:

 function OrgFold(lnum)
  let level = strlen(matchstr(getline(a:lnum), '\v^\s*\zs\*+'))
  if level > 0
    return '>'.level
  else
    return '='
  endif
endfunction

The folding function can return something like >2 to start a level 2 fold on the current line. Returning = means use the fold level of the preceding line which had the fold level explicitly set.

Enable this folding with:

set foldmethod=expr foldexpr=OrgFold(v:lnum)

You can customize the text displayed when the block is folded. For example, to simply display the first line followed by three dots, you can use:

set foldtext=getline(v:foldstart).'...'.repeat('\ ',999)

This expression also suppresses the dashes to the right of the fold text, by padding the string with enough spaces to fully hide them.