Juri Linkov <juri@linkov.net> writes:

Thanks for your comments!

>> +(autoload 'outline-minor-mode "outline")
>
> Actually, outline-minor-mode is already autoloaded, so no special
> handling is needed for it.

Ok, I'll improve this.

> But the problem is that too many outline functions are used in
> diff-mode.el in your patch.  This is a clear indication that
> some part should be moved to outline.el.

You're right. 

> Note that the following function has no diff-specific code, so it could
> be refactored and some generalized function added to outline.el.  Such
> function could be like `outline-map-region' to accept arguments `beg', `end'
> and a predicate function that defines whether to hide or show the
> body.

Ok. I'll make a try.

In the meantime, here is a new version that implements both:

- Outline based on presence of long lines (using `so-long-detected-long-line-p'
predicate)

- Outline based on file names matching a regexp (well, truly file
  heading matching a regexp).