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

[martin rudalics via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

 > I meant switching to the window to instruct display-buffer what window
 > to use as mru, then switch back to the rgrep window.

Who would switch to the window?  The user or 'display-buffer' itself?

 > We already have 'previous-window' that I'm using for a long time,
 > and it works nicely with such configuration:
 >
 > (defvar-local display-buffer-previous-window nil)
 >
 > (defun display-buffer-from-grep-p (_buffer-name _action)
 >    (with-current-buffer (window-buffer)
 >      (and (memq this-command '(compile-goto-error))
 >           (derived-mode-p '(compilation-mode)))))
 >
 > (add-to-list 'display-buffer-alist
 >               '(display-buffer-from-grep-p
 >                 display-buffer-in-previous-window
 >                 (previous-window . display-buffer-previous-window)
 >                 (inhibit-same-window . nil))
 >               ;; Append to not override display-buffer-same-window
 >               'append)
 >
 > (define-advice compile-goto-error (:around (ofun &rest args) previous-window)
 >    (let ((buffer (current-buffer)))
 >      (apply ofun args)
 >      (with-current-buffer buffer
 >        (setq-local display-buffer-previous-window (selected-window)))))
 >
 > But this is very complicated configuration.  So I wanted to help people
 > to do basically the same with much simpler setting that overrides
 > the hard-coded 'lru' with just '(some-window . mru)'.

I think that's what we want here and it should cover all sorts of
'next-error-function' too.  But 'get-mru-window' won't cut it.

 > The only problem with '(some-window . mru)' is that its NOT-SELECTED is t,
 > so this excludes the very useful case of displaying the buffer
 > in the same selected window.  For example, with 'previous-window'
 > I often visit rgrep results in the same window where the rgrep buffer
 > was displayed.  This keeps everything confined to one window.

We could provide two basic modes: One mode where the compilation, grep,
or occur buffer is always kept visible and the file buffers are
displayed in one or a few other windows.  And a mode where only one
window is used.

In either case we could use a window parameter, say 'next-window', that
indicates that this window shall be used for the next 'display-buffer'
call with a non-nil 'next-window' alist entry.  The value could be
'grep', 'occur' 'compile' or whatever we want so a user could do, for
example, a grep within the outer context of analyzing compilation
output.

I see the following problems:

- How to set up the 'next-window' parameter in the first call of a given
   context.  IIUC we don't have a unique starting function for
   establishing a suitable context of a series of related calls.  So
   both, 'compile-goto-error' and 'next-error', would have to call
   'display-buffer' with an appropriate 'next-window' entry.  For me,
   it's been always confusing that 'compilation-next-error' does not
   display the source buffer while 'next-error' does.

- How to remove/reset the parameter after the last call.  'quit-window'
   should probably do that, but I'm not sure.

- How to "nest" contexts when windows are shared.  If the same window
   were used for displaying grep results within a compilation results
   context, the 'next-window' parameter would have to become a list and
   'quit-window' should probably pop an entry from it.

martin