bug#70949: display-buffer-choose-some-window

[martin rudalics]

> The same way as the condition function allows to check
> the original buffer, e.g. customization to show
> outgoing 'vc-diff' buffers in the same window
> where the 'vc-dir' was displayed:
>
>    (defun display-buffer-from-vc-dir-p (_buffer-name _action)
>      (with-current-buffer (window-buffer)
>        (derived-mode-p '(vc-dir-mode))))

This means that the user has to always go back from the *vc-diff* window
back to a *vc-dir* window in order to tell what to show next in the
*vc-diff* window.  It completely defeats the idea of the advanced
mechanics of 'next-error' which autonomously would guess what to show
next in the *vc-diff* window without having to continuously hop back to
the *vc-dir* buffer.

I hardly use 'vc-diff' because I'm not good at reading diffs.  When I
want to view the differences of a fileset controlled by git I first run
git status in a shell window and, based on its output, ediff on all
involved files.  The crucial aspect here is that whenever I'm done with
watching the differences of one file, I'd never want to go back to the
shell window because that would disrupt my ediff layout with two side by
side windows and the ediff status window on bottom.  Rather I use a
mechanism that gets me directly from a layout showing the (presumably
last) diff for the current file to a layout showing the first diff for
the next file listed by git status.

martin