bug#19392: Emacs searches for dabbrevs in archive buffers

[Eli Zaretskii]

> Cc: 19392@debbugs.gnu.org
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sat, 07 May 2022 13:20:47 +0200
> 
> Paul Pogonyshev <pogonyshev@gmail.com> writes:
> 
> > $ emacs -Q random.zip
> >
> > 1. Switch to buffer "*scratch*"
> > 2. Type "P" (without quotes)
> > 3. Press M-/
> > 4. Here it finds expansion "PK" from buffer "random.zip".  Cycling
> >    with M-/ finds a few more, which are more binary-like.
> 
> I've now fixed this in Emacs 29.  Instead of making some kind of
> framework for letting modes specify this themselves, it seems more user
> friendly to just introduce a new dabbrev-ignored-buffer-modes variable,
> so I did that.

Does tar-mode really belong to the list of those modes?  Unlike
archive-mode, where each file is separately compressed into binary
garbage, tar-mode shows the original files, and the only "binary"
parts are the headers, most of which are also plain text.  So I'd
suggest to remove tar-mode for the default list of modes.