bug#25946: 26.0.50; display-buffer ignores ignores reusable-frames in display-buffer-alist

[martin rudalics <rudalics@gmx.at>]

 > I fail to get display-buffer-alist working.
 >
 > Recipe starting from 'emacs -Q':
 > Eval this expression:
 > (customize-set-variable
 >   'display-buffer-alist
 >   '(("\\*shell\\*"
 >      . (display-buffer-pop-up-frame . '((reusable-frames . t))))))
 > M-x shell
 > A shell frame opens as expected.
 > M-x shell
 > A new frame is opened, while I expected the existing one to be
 > reused.

Please try with

(customize-set-variable
  'display-buffer-alist
  '(("\\*shell\\*"
     (display-buffer-reuse-window display-buffer-pop-up-frame)
     (reusable-frames . t))))

 > Actually, I'm sure that I do not understand the documentation for
 > display-buffer (redirected from display-buffer-alist).  Maybe that
 > is a separate bug.

I think that

  -- Function: display-buffer-pop-up-frame buffer alist
      This function creates a new frame, and displays the buffer in that
      frame's window.

is quite clear in the sense that it does not talk about reusing windows
or frames.  But please feel free to suggest improvements.

 > In previous versions of Emacs, I used special-display-buffer-names,
 > which is obsolete now and points to the variable used above,
 > display-buffer-alist.  It would be great if the documentation for
 > that variable explained what to do.  In particular, I would like the
 > frame to be special/dedicated such that it disappears if the buffer
 > is killed.  Is that lack of documentation a separate bug?

Please read also this

      If ALIST contains a `pop-up-frame-parameters' entry, the associated
      value is added to the newly created frame's parameters.

martin