Bug (CVS HEAD): highlight-changes-mode with auto-revert-tail-mode edit buffer

[Denis Bueno]

I realise the subject line is pretty obscure.  The symptom is that when I
enable both of those modes in a buffer with a background appending process,
eventually I get asked if I'm sure I want to modify the buffer, which of
course I don't.

Here's a recipe for GNU Emacs 22.1.50.2 (i386-apple-darwin8.9.1, Carbon
Version 1.6.0) of 2007-07-06:

    1. emacs -Q
    2. Visit an existing file, say /tmp/foo
    3. M-x auto-revert-tail-mode
    4. Execute appending process in a shell like so:

       $ while true; do echo "Hello, number $RANDOM." >> /tmp/crap.log;
sleep 4; done

    (Buffer at this point should revert once at least.)
    5. M-x highlight-changes-mode
    6. M-x highlight-changes-rotate-faces  (n times)

I wrote "n times" on step 6 because you have to execute it until the "really
edit the buffer?" message appears in the minibuffer.  It only took me two
executions to get it to appear, but, I think the error is caused by
auto-revert-tail-mode and highlight-changes-mode stepping on each other's
feet, which might take more than one execution of step 6 to occur.

I'm not sure.

Anyway, that's the best I can muster for a bug report.  I have no idea how
to investigate this further.

Thank you.

-Denis