bug#33870: 27.0.50; xref-goto-xref not configurable

[Juri Linkov]

>> * But by using less space it is also less useful.  You don't get to see,
>>    at a glance, a great deal of xrefs.  And xrefs are different from
>>    completions, they're closer to grep hits.  You wouldn't put*grep*
>>    hits in such a potentially tiny window, would you?
>
> This would be my main objection as well.

Actually the window is not tiny.  It gets more than a half window
from the window there is was called.  But now I propose to do this
only for xref-find-definitions.

>> Then again, perhaps you would, and the whole point of this patch is to
>> make the UI configurable.  If so, I'd make the original UI the default,
>> or at least very very easy to bring back.
>
> Making it configurable on a high level is something I might agree with (and
> indeed, the find-definitions command probably should behave differently
> from the rest), but the way it's done should be transparent and not
> strongly coupled to a particular commands.
>
> Maybe via two different xrefs-show-function values. I'm not sure.

Or maybe better xrefs-display-buffer-alist.