bug#53749: 29.0.50; [PATCH] Xref backend for TeX buffers

[Dmitry Gutov]

Hi!

Let us first discuss whether we could make do without an additional Xref 
backend. Just to make sure.

On 03.02.2022 17:09, David Fussner via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Similarly, any xref command on 'my:citekey' will only search by default
> for the half of the symbol under point, stopping at the colon.

etags's implementation of 'xref-backend-identifier-at-point' calls 
'find-tag--default', which consults 'find-tag-default-function' and
(get major-mode 'find-tag-default-function).

So if your main goal was to alter which string gets searched for (based 
on text around point), you can define a function which returns the 
necessary string (as you did in the patch) and then either set 
'find-tag-default-function' to that function, or put it on the 
'find-tag-default-function' property for the respective major mode 
functions.

> There are many other behaviors that are suboptimal, as well, so in the
> end I wrote a new xref backend for TeX buffers (cloning large portions
> of the default etags backend), and wondered whether it might be welcome
> in GNU Emacs.

Could you point out the other changes which were required?