2 files changed, 40 insertions, 4 deletions

diff --git a/modules/ui-navigation.el b/modules/ui-navigation.el
index e9c9eaf26..d8d7162e2 100644
--- a/modules/ui-navigation.el
+++ b/modules/ui-navigation.el
@@ -118,15 +118,30 @@ window.  Return the new window."
       (set-window-buffer new buffer))
     new))
 
+(defun cj/--split-from-dashboard-p (buffer-name)
+  "Return non-nil when BUFFER-NAME is the dashboard.
+Splitting from the dashboard shows *scratch* in the new window instead of
+the dashboard again."
+  (equal buffer-name "*dashboard*"))
+
+(defun cj/--split-companion-buffer ()
+  "Buffer to show in the new window after a C-x 2 / C-x 3 split.
+The dashboard, or the *scratch* buffer when splitting from the dashboard."
+  (if (cj/--split-from-dashboard-p (buffer-name))
+      (get-scratch-buffer-create)
+    (cj/--dashboard-buffer)))
+
 (defun cj/split-below-with-dashboard ()
-  "Split below and show the dashboard in the new window; stay in this one."
+  "Split below and show the companion buffer in the new window; stay in this one.
+The companion is the dashboard, or *scratch* when splitting from the dashboard."
   (interactive)
-  (cj/--split-show-buffer #'split-window-below (cj/--dashboard-buffer)))
+  (cj/--split-show-buffer #'split-window-below (cj/--split-companion-buffer)))
 
 (defun cj/split-right-with-dashboard ()
-  "Split right and show the dashboard in the new window; stay in this one."
+  "Split right and show the companion buffer in the new window; stay in this one.
+The companion is the dashboard, or *scratch* when splitting from the dashboard."
   (interactive)
-  (cj/--split-show-buffer #'split-window-right (cj/--dashboard-buffer)))
+  (cj/--split-show-buffer #'split-window-right (cj/--split-companion-buffer)))
 
 (keymap-global-set "C-x 2" #'cj/split-below-with-dashboard)
 (keymap-global-set "C-x 3" #'cj/split-right-with-dashboard)
diff --git a/tests/test-ui-navigation--split-dashboard.el b/tests/test-ui-navigation--split-dashboard.el
index b815a4c59..407335f80 100644
--- a/tests/test-ui-navigation--split-dashboard.el
+++ b/tests/test-ui-navigation--split-dashboard.el
@@ -54,6 +54,27 @@
     (should (eq (car captured) #'split-window-right))
     (should (eq (cadr captured) 'dashboard))))
 
+(ert-deftest test-ui-navigation-split-from-dashboard-p ()
+  "Normal/Boundary: only the dashboard buffer routes the companion to *scratch*."
+  (should (cj/--split-from-dashboard-p "*dashboard*"))
+  (should-not (cj/--split-from-dashboard-p "todo.org"))
+  (should-not (cj/--split-from-dashboard-p "*scratch*")))
+
+(ert-deftest test-ui-navigation-split-companion-scratch-from-dashboard ()
+  "Normal: splitting from the dashboard yields the *scratch* buffer, not the
+dashboard again."
+  (cl-letf (((symbol-function 'cj/--split-from-dashboard-p) (lambda (_) t))
+            ((symbol-function 'get-scratch-buffer-create) (lambda () 'scratch))
+            ((symbol-function 'cj/--dashboard-buffer) (lambda () 'dashboard)))
+    (should (eq (cj/--split-companion-buffer) 'scratch))))
+
+(ert-deftest test-ui-navigation-split-companion-dashboard-otherwise ()
+  "Normal: splitting from any other buffer yields the dashboard."
+  (cl-letf (((symbol-function 'cj/--split-from-dashboard-p) (lambda (_) nil))
+            ((symbol-function 'get-scratch-buffer-create) (lambda () 'scratch))
+            ((symbol-function 'cj/--dashboard-buffer) (lambda () 'dashboard)))
+    (should (eq (cj/--split-companion-buffer) 'dashboard))))
+
 (ert-deftest test-ui-navigation-dashboard-buffer-returns-existing ()
   "Boundary: cj/--dashboard-buffer returns an existing *dashboard* without opening."
   (let ((db (get-buffer-create "*dashboard*"))