bug#29206: Make xref-show-xrefs-function a defcustom

[Dmitry Gutov]

On 11/18/17 12:14 PM, Eli Zaretskii wrote:

> > -(defvar xref-show-xrefs-function 'xref--show-xref-buffer
> > -  "Function to display a list of xrefs.")
> > +(defcustom xref-show-xrefs-function 'xref--show-xref-buffer
> > +  "Function to display a list of xrefs."
> > +  :type 'function)
> >   
> >   (defvar xref--read-identifier-history nil)
>
> Dmitry, any comments on this?  (If accepted, the defcustom should have
> a :version tag.)

I don't really see the point, yet: we don't offer any alternative 
functions, and if the user is going to write one, `setq' is just as easy 
to do.

Further, applying this kind of minor change (and finding it important) 
seems like it would indicate that xref is kind of "stable", which it is 
not, so far.