(next|previous)-buffer no longer fail silently (bug#38384)

* lisp/window.el (next-buffer, previous-buffer):
Signal 'user-error' if there is no buffer to switch to.

* etc/NEWS: Document it.

2 files changed, 8 insertions, 2 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 2a14eb2ecfc..d3331daf17f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2620,6 +2620,10 @@ scrolling.
 ** help-follow-symbol now signals 'user-error' if point (or the
 position pointed to by the argument POS) is not in a symbol.
 
+---
+*** next-buffer and previous-buffer now signal 'user-error' if there
+is no buffer to switch to.
+
 
 * Lisp Changes in Emacs 27.1
 
diff --git a/lisp/window.el b/lisp/window.el
index 49fad75d3cd..c8a5816b8c9 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -4850,7 +4850,8 @@ minibuffer window or is dedicated to its buffer."
     (user-error "Window is strongly dedicated to its buffer"))
    (t
     (dotimes (_ (or arg 1))
-      (switch-to-next-buffer)))))
+      (unless (switch-to-next-buffer)
+        (user-error "No next buffer"))))))
 
 (defun previous-buffer (&optional arg)
   "In selected window switch to ARGth previous buffer.
@@ -4864,7 +4865,8 @@ minibuffer window or is dedicated to its buffer."
     (user-error "Window is strongly dedicated to its buffer"))
    (t
     (dotimes (_ (or arg 1))
-      (switch-to-prev-buffer)))))
+      (unless (switch-to-prev-buffer)
+        (user-error "No previous buffer"))))))
 
 (defun delete-windows-on (&optional buffer-or-name frame)
   "Delete all windows showing BUFFER-OR-NAME.