From bb43055ef08049fa3a1694b7769adbade762c17d Mon Sep 17 00:00:00 2001
From: Phil Sainty <psainty@orcon.net.nz>
Date: Thu, 1 Jan 2026 21:28:59 +1300
Subject: [PATCH] Support the `reusable-frames' value 0 for
 `display-buffer-in-tab'

* lisp/tab-bar.el (tab-bar--reusable-frames): Implement support for the
`reusable-frames' value 0, for better consistency with other buffer
display actions. (bug#80092)
---
 doc/lispref/windows.texi |  2 ++
 lisp/tab-bar.el          | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/doc/lispref/windows.texi b/doc/lispref/windows.texi
index dd0d925ed7e..09d58c17c01 100644
--- a/doc/lispref/windows.texi
+++ b/doc/lispref/windows.texi
@@ -3580,6 +3580,8 @@ which already displays the buffer.  The possible values of
 means consider all existing frames.
 @item @code{visible}
 means consider all visible frames.
+@item 0
+means consider all frames on the current terminal.
 @item A frame
 means consider that frame only.
 @item Any other non-@code{nil} value
diff --git a/lisp/tab-bar.el b/lisp/tab-bar.el
index 5c63de5e39f..f9df4110757 100644
--- a/lisp/tab-bar.el
+++ b/lisp/tab-bar.el
@@ -2865,9 +2865,20 @@ with those specified by the selected window configuration."
 
 
 (defun tab-bar--reusable-frames (all-frames)
+  "Process the `reusable-frames' buffer display action alist entry.
+Return a frame list.  Used with the `display-buffer-in-tab' action."
   (cond
    ((eq all-frames t) (frame-list))
    ((eq all-frames 'visible) (visible-frame-list))
+   ;; The standard behavior for a `reusable-frames' value of 0 is implemented in
+   ;; candidate_window_p() in window.c, and we have to go via `window-list-1' to
+   ;; utilize this.  We list the selected frame first.
+   ((eq all-frames 0) (let (frames)
+                        (dolist (w (window-list-1 nil nil 0))
+                          (let ((f (window-frame w)))
+                            (unless (memq f frames)
+                              (push f frames))))
+                        (nreverse frames)))
    ((framep all-frames) (list all-frames))
    (t (list (selected-frame)))))
 
@@ -2883,6 +2894,9 @@ The optional argument ALL-FRAMES specifies the frames to consider:
 
 - `visible' means consider all tabs on all visible frames.
 
+- 0 (the number zero) means consider all tabs on all visible and
+  iconified frames.
+
 - A frame means consider all tabs on that frame only.
 
 - Any other value of ALL-FRAMES means consider all tabs on the
@@ -2941,6 +2955,7 @@ displays BUFFER.  The possible values of `reusable-frames' are:
 
   t -- all existing frames;
   `visible' -- all visible frames;
+  0 -- all frames on the current terminal;
   A frame -- that frame only;
   Any other non-nil value -- the selected frame;
   nil -- do not search any frames (equivalent to omitting the entry).