Xref Fallback

["Philip K." <philipk@posteo.net>]

Hi,

a few weeks ago, I managed to port "dumb-jump"[0] to use Xref instead of
it's own custom interface[1]. Part of the transition was to deprecate
the old commands[2], that has lead to some complaints among
"lsp-mode"[3] users, because lsp-mode doesn't fall back on dumb-jump if
it has no results[4].

Part of the issue is that LSP's Xref activation function just returns
"'xref-lsp", the symbol that is specializes it's xref methods on,
without any checking -- which is fairly common from what I see. But if
that fails, Xref won't go on searching, even though the next backend
could have more to offer.

Before writing this message, I was fairly sure that there were some
discussions on this issue, but I couldn't find them in the archives
anymore, so just to be safe, I re-iterated the problem.

What I would want to know, is if there have been discussion on this
issue, what the status is, and if not what would have to be done. I can
imagine, that falling back onto the next backend isn't always desirable
(especially if etags is next, and it demands a TAGS file that doesn't
exist).

[0] For those unfamiliar, dumb-jump is a package for finding places
    where functions or variables are defined, but without any permanent
    external tools such as etags or indexing servers, but by using grep
    or grep-like tools and a search-database
    (https://github.com/jacktasia/dumb-jump).
[1] https://github.com/jacktasia/dumb-jump/pull/343
[2] https://github.com/jacktasia/dumb-jump/pull/349
[3] https://github.com/emacs-lsp/lsp-mode/
[4] https://github.com/jacktasia/dumb-jump/issues/353#issuecomment-671462247
[5] https://github.com/emacs-lsp/lsp-mode/blob/00fcee92ae2e57055fdb31d25741b9637fe96215/lsp-mode.el#L6174