bug#57534: 29.0.50; Highlighting lost after auto-revert-mode triggers

[Dima Kogan <dima@secretsauce.net>]

Hi. I'm seeing this:

1. seq 10 > /tmp/file

2. emacs -Q /tmp/file

3. (highlight-lines-matching-regexp "3")

   This is bound to "M-s h l". I see the line containing "3" highlighted
   in yellow, as expected

4. M-x auto-revert-mode

5. Back in the shell: seq 20 > /tmp/file


auto-revert-mode kicks in, updating the buffer with the results of 'seq
20' (possibly updating to an empty buffer first, if we react immediately
to the file truncation). At this point I would expect either:

1. The buffer being fully reverted, with all the highlighting
   disappearing. This is what happens if we did M-x revert buffer

2. The buffer contents being reverted, but the highlighting being
   reapplied

In this auto-revert scenario, we get something in-between: after the
auto-revert hi-lock-interactive-patterns still contains the highlighting
regex, but no highlighting actually happens. It'd be really nice and
useful if the highlighting stayed.

Thanks!