bug#51016: 28.0.50; 'diff-font-lock-prettify' breaks display of outline headers

[Juri Linkov <juri@linkov.net>]

>> Yep, I already tried `(re-search-forward diff-hunk-header-re)' too,
>> and it works.  But still typing TAB on the hunk heading
>> with outline-minor-mode-cycle=t does nothing, whereas typing TAB
>> on the file heading correctly cycles the file diff.
>
> Oh yeah, now I'm seeing the problem.  I don't really use outline mode
> daily, so I'm not sure how it's supposed to work, but -- TAB in these
> buffers are bound to diff-hunk-next, and as far as I can tell, outline
> mode has just placed a keymap property on the file headings, not the
> hunk headings.
>
> Or is that the actual bug here?  😀  I should probably have read the
> entire thread before getting involved.

Actually, ‘outline-font-lock-keywords’ extends the outline regexp
to (concat "^\\(?:" outline-regexp "\\).+").  And indeed,

  (re-search-forward (concat "^\\(?:" diff-hunk-header-re "\\).+"))

fails in diff buffers.  Don't ask me why outline.el adds ".+"
at the end, I don't know 🤐  To circumvent this idiosyncrasy
for headings in ‘describe-bindings’, I had to use a different regexp
in ‘outline-minor-mode-highlight-buffer’ (not based on font-lock):

  (concat "^\\(?:" outline-regexp "\\).*$")))

where ".+" is replaced with less-strict ".*".