bug#28407: 26.0.50; xref should use imenu

[Visuwesh <visuweshm@gmail.com>]

[சனி ஜூன் 25, 2022] Eli Zaretskii wrote:

>> Cc: Tom Tromey <tom@tromey.com>, 28407@debbugs.gnu.org
>> From: Visuwesh <visuweshm@gmail.com>
>> Date: Sat, 25 Jun 2022 19:34:48 +0530
>> 
>> [ To elaborate, say that I visited the TAGS residing in Emacs' src/
>>   directory then switched to another project.  Now, if I do C-u
>>   M-. Fplist_get RET, then it will take me to the Emacs project!!  This
>>   seems to be a general problem with the etags backend tho.  ]
>
> In general, when you visit a new TAGS file, etags asks you whether to
> replace the previous one or to keep them both.  Maybe the way you
> "switch to another project" somehow hides that prompt/decision?

It does ask me to replace the previous one but I expected Emacs to
restrict the TAGS file to the buffer I selected it from, mostly because
I was mislead to believe the check (or tags-table-files tags-file-name)
would work that way.
[ The check is from a previous revision of my patch.  ]