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display-buffer-reuse-frames tells Emacs to re-use frames for displaying buffers. However, as of 24.3 this variable is obsolete (emphasis mine):

display-buffer-reuse-frames is a variable defined in window.el.
Its value is t
Original value was nil

This variable is obsolete since 24.3; use a reusable-frames alist entry in display-buffer-alist.

Documentation:
Non-nil means display-buffer should reuse frames. If the buffer in question is already displayed in a frame, raise that frame.

I understand that I am supposed to replace that variable with display-buffer-alist. I'm familiar with the latter, and use it at many different places in my configuration, but nonetheless this docstring is a mystery to me.

What entry exactly do I need to add to display-buffer-alist to replicate this variable? IOW, what entry do I need to add to display-buffer-alist to make Emacs reuse frames for all buffers, while still using the default display actions?

And please, dear Emacs developers, write less hand-wavy docstrings for obsolete options…

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  • I suspect you cannot easily reproduce the original functionality of that obsoleted variable as the code suggests you can only enable it for specific display-buffer-alist items otherwise.
    – wasamasa
    Jul 21, 2015 at 9:17
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    The doc (doc string and manual) for display-buffer-alist is a hard nut to crack, indeed. Consider filing a doc bug report, if you can say something concrete about a problem you encounter with it or you have a suggestion for improving it: M-x report-emacs-bug. FWIW, the doc, although still difficult to fathom, is better than it was at first.
    – Drew
    Jul 21, 2015 at 13:46
  • @Drew Thanks, but as I said I'm familiar with display-buffer-alist, and I'm fine with its docstring. My remark refers to the deprecation notice in the docstring of display-buffer-reuse-frames, which doesn't tell me the proper alternative instead.
    – user227
    Jul 21, 2015 at 13:50
  • Same comment applies in that case. A deprecation notice should make clear what to replace the deprecated construct with. Or if there is no replacement then it should say that. (IMHO.)
    – Drew
    Jul 21, 2015 at 14:31
  • It may behoove the original poster to clarify the question by explaining why the (2) two examples in the documentation that utilize a display-buffer-alist entry of (reusable-frames . 0) do not address the issue at hand: gnu.org/software/emacs/manual/html_node/elisp/… In other words, explain why neither of these examples replicates the behaviour of display-buffer-reuse-frames, and shows how to reuse frames for all buffers, using the default display actions.
    – lawlist
    Jul 21, 2015 at 15:26

1 Answer 1

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display-buffer merges the various alists. Something like this should apply reuse-frames to all buffers.

(add-to-list 'display-buffer-alist
             '("." nil (reusable-frames . t)))

Alternatively use display-buffer-overriding-action or even display-buffer-function (as a wrapper), if feasible.

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  • Thanks, that's what I needed. I didn't know that nil was an acceptable value at this place. Still, it's not perfect, though. It must be the last entry in display-buffer-alist, because it overrides any later entry with more specific actions. Apparently, display-buffer merges alists, but not actions.
    – user227
    Jul 22, 2015 at 7:39
  • Yes, that's a problem. Replacements of deperecations rarely provide the exact same functionality, I guess.
    – politza
    Jul 22, 2015 at 14:03
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    Looking at the code, it doesn't even merge alists, as I thought for some reason. At least not the ones from display-buffer-alist, i.e. first match wins.
    – politza
    Jul 22, 2015 at 16:10

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