Re: xref backends for elisp-related modes Was: Re: Bad moves with xref-find-definitions

[Dmitry Gutov]

On 04/26/2015 02:51 PM, address@hidden (João Távora) wrote:

> BTW the necessary level of indirection is already present with
> `advice-add': we needn't necessarily add more variables. I mean:
>
>     (advice-add 'elisp-xref-find :override #'etags-xref-find)

Looks good enough to me. Indeed, maybe xref-etags-mode should be 
replaced by a function that applies these advices.

> Should be enough and quite readable. Conversely, I wouldn't be very
> annoyed if etags were the default method of finding elisp xrefs. Then I
> would use advice-add to set my behaviour, perhaps by doing

I think elisp-xref-find is a better default.

>     (advice-add 'elisp-xref-find :override
>     #'elisp-compiled-identifier-locations) ; better name pending

This cannot be done globally (or it'll affect all buffers).

> Additionally, if `add-function' allowed `:append' for its WHERE arg,
> like Common Lisp's method combinations, it would be even cleaner to get
> the behaviour desired by Eli (and Vitalie, I think), of multiple
> backends.
>
>     (advice-add 'elisp-xref-find :append #'etags-xref-find)

a: If we want it to do appending, that could be implemented in 
`elisp-xref-find'. Or there could be a variant of it doing that.

b: This doesn't deal with duplicates, which I think is the main problem 
if we were to go that way.

> It does, I know, but it would be a lot simpler, especially for functions
> spawning *Help* buffers, to just assume we're in an elisp-related
> context. Packages like SLIME or SLY or CIDER that make use of these
> major modes should be the ones overriding the backend.

Can we be sure that languages using the default backend (etags) and 
expecting it to work in their help buffers, will be a negligible minority?

> +(defun elisp--setup-xref-backend ()
> +  (setq-local xref-find-function #'elisp-xref-find)
> +  (setq-local xref-identifier-completion-table-function
> +              #'elisp--xref-identifier-completion-table))

Shouldn't this also include the dynamic declarations removed from 
`emacs-lisp-mode'?