bug#33992: 27.0.50; xref-find-definitions wastes too much space

[Dmitry Gutov <dgutov@yandex.ru>]

On 07.04.2019 0:03, Juri Linkov wrote:
>>>> Does it feel the same way to you?
>>>
>>> The difference is that completions pop up in a small unobtrusive window.
>>
>> Small window? I usually have a side-by-side fullscreen split, and if
>> I initiate completion in one of the windows, *Completion* takes up the
>> whole other window. Temporarily, of course.
> 
> The key word here is 'Temporarily'.  Unlike *Completions*,
> the *xref* buffer doesn't go out easily.

I can understand that. So yes, I can see myself preferring some 
different behavior for a particular command.

>>>     (defun display-buffer-condition-from-xref (_buffer-name _action)
>>>       (string-match-p "\\`\\*\\(xref\\)\\*\\(\\|<[0-9]+>\\)\\'"
>>>                       (buffer-name (current-buffer))))
>>
>> This function seems unused.
> 
> It's unused because it would be useful only in the *xref* buffer
> created by the xref-find-definitions command, so xref needs to
> provide a way to distinguish such case.

Shouldn't it be referenced somewhere else in your patch as well?

>>>     (setq display-buffer-alist
>>>        '((display-buffer-condition-xref
>>>           display-buffer-in-direction
>>
>> And this function is undefined in my Emacs.
> 
> This function is implemented by Martin in bug#33870.

OK, found it, tried it. Seems to work okay-ish for 
xref-find-definitions, except xref-quit-and-goto-xref doesn't seem to be 
functioning too well together with your customization (every other time 
it seemed to use a different window to display the location, not the one 
I called xref-find-definitions from).

>>>     (with-eval-after-load 'xref
>>>       (define-key xref--button-map [(control ?m)] #'xref-quit-and-goto-xref))
>>>
>>> How do you like that?
>>
>> I might, but since I can't really try your customization myself yet, I'll
>> repeat a question you might be familiar with already:
>>
>>    Will this also affect xref-find-references and project-find-regexp?
> 
> It should not affect them due to (memq this-command '(xref-find-definitions))
> above.

It would affect them due to the modification of xref--button-map above, 
though. This part I don't like.

> But also to not affect commands active in the *xref* buffer,
> xref should provide a way to check if the *xref* buffer was created
> by xref-find-definitions.

Yes, we should retain some extra information, e.g. to support revert-buffer.