bug#54133: 29.0.50; Buffer-menu-visit-tags-table disrupts non-tags buffers

[Bob Rogers <rogers@rgrjr.com>]

   From: Eli Zaretskii <eliz@gnu.org>
   Date: Thu, 24 Feb 2022 19:42:14 +0200

   > From: Bob Rogers <rogers@rgrjr.com>
   > Date: Thu, 24 Feb 2022 12:30:53 -0500
   > 
   > . . .
   > 
   > This does ineed work, and I had considered something similar, but
   > was concerned that it would not be as robust . . .

   Maybe we should have a more thorough implementation in
   etags-verify-tags-table, then.  But that function's purpose is to do
   what we need here.

That would require disentangling detection and initialization.  Which
shouldn't be all that hard; it just seemed like more work than necessary
to scratch this particular itch.

   > In short, I thought checking the major mode was the better choice,
   > since the file was already present in a buffer.

   But what if the file is already in a buffer, but not under the right
   major-mode?  E.g., what if the file was visited literally?

Ah, so you mean that Buffer-menu-visit-tags-table is normally meant to
introduce tags-table-mode in buffers not already there.  I see now that
is implied by "Visit the tags table ..." in the command documentation.
In which case I withdraw my reservations.

   And maybe I'll have a look at cleaning up etags initialization when I
get a chance . . .

					-- Bob