bug#81624: New command: xref-find-by-kind

Dmitry Gutov <[email protected]> writes:

> Regarding obarray, I think you're either describing a caching scheme
> (indefinite or timed) or a more complex return value for
> xref-backend-xref-kinds.

The latter.  But sort of simpler, not more complex.  To illustrate, in
Common Lisp, a dedicated package could hold the handful of kind symbols.
So the database lives there instead of a list of plists.

   (defpackage :eglot-kinds
      (:export "DECLARATION" "IMPLEMENTATION" "TYPE-DEFINITION"))
   (in-package :eglot-kinds)
    
   (cl:setf
    (cl:get 'declaration 'xref-kind)     '(:name "declaration"     :key #\c)
    (cl:get 'type-definition 'xref-kind) '(:name "type definition" :key #\t)
    (cl:get 'implementation 'xref-kind)  '(:name "implementation"  :key #\i))
    
   (in-package :eglot)
    
   (defmethod xref:xref-kinds ((backend (eql :eglot))) (find-package "EGLOT-KINDS"))
    
   (defun eglot:find-type-definition (identifier)
     (interactive (xref:read-identifier "Find declarations of"))
     (xref:find-by-kind identifier 'eglot-kinds:declaration))

   ...

You get the idea... You can do this mostly in Elisp if you really want
to, but I admit it's a bit awkward, because there's no named obarrays
and no read syntax for them.  So the elegant last line would become an
odd intern-soft with an extra arg.  Now that I think of it, not sure the
Elisp version really avoids your "coin-flip" problem, because
intern-soft does a runtime lookup anyway, whereas in CL that job is done
at read-time and the right symbol reference is already compiled in.

Anyway, this is just academic, these lookups are super cheap, don't do
it :-)

João