Re: Xref/Eglot feature requests and a question

[Dmitry Gutov <dmitry@gutov.dev>]

On 24/08/2023 16:33, Gerd Möllmann wrote:
> I have a couple of feature requests regarding Xref and/or Eglot, after
> switching from Lsp-mode to Eglot yesterday, which BTW went really
> well. Thanks to João!
> 
> 1.
> 
> I'm in a C buffer with Eglot running, and I want to go to the definition
> of something whose name I know, but point is not on an identifier naming
> that thing.  For instance, I want to go the definition of Lisp_Package
> (in an obsure branch having a struct Lisp_Package), while point is
> somewhere.
> 
> C-u M-. offers some completions, but Lisp_Package is not among them.
> Not using a completion and entering Lisp_Package works.
> 
> Feature request: Could the completions be made to contain all workspace
> symbols?  Lsp-mode has something doing that, and I found it quite useful
> with Helm.
> 
> C-M-. Lisp_Package RET works fine, but entering a word list as
> advertised in the prompt, say "Li Pa", does not.
> 
> Question: Bug or limitation?

Both of these are up to Eglot, I think. Or the underlying language server.

> 3.
> 
> In C mode, Xref works using Eglot, in ELisp mode it uses something else
> (I have no tags tables).  Both work really well, but I apparently have
> to be in an ELisp buffer to use one and in a C buffer to use the other.
> 
> Feature request: Is it possible to use more than one backend at the same
> time?  So that I could C-M-. to find an ELisp function while being in a
> C file?  I couldn't find something like that mentioned in the docs, so I
> guess it's not yet possible.

No such capability at the moment, but we indeed have an ELPA package 
xref-union which implements the "merging" feature that has been 
requested in the past.

You are asking for something a little different, though: to be able to 
switch to a different language/project that's also present in the 
current Emacs session. Its backend function cannot be found in the 
xref-backend-functions in the current buffer (local or global), unlike 
the examples with mixing in etags or imenu results, like mentioned by 
Visuwesh.

A naive approach, or for the new code to search across different open 
buffers and look for different available xref-backend-functions 
elements. And then prompt the user, and then call (?) the said function 
in one of the buffers it was found in, because in all likelihood it 
would fail in unrelated ones.

Perhaps the solution is to add a new facility to Xref, where different 
"projects" would be able to register globally in. A feature request indeed.