1 files changed, 46 insertions, 5 deletions

diff --git a/modules/ui-navigation.el b/modules/ui-navigation.el
index d8d7162e2..c099e0834 100644
--- a/modules/ui-navigation.el
+++ b/modules/ui-navigation.el
@@ -75,14 +75,55 @@ resize -- each moves the active window's divider in the arrow's direction
   "<up>"    #'windsize-up
   "<down>"  #'windsize-down)
 
+(defun cj/window-pull-side (key)
+  "Map a `C-; b' arrow KEY to the side the revealed window opens on.
+The arrow names the edge the current window shrinks toward, so the new
+window opens on the *opposite* side and the current window keeps the
+arrow's edge: <down> -> above, <up> -> below, <left> -> right,
+<right> -> left.  Returns nil for anything else."
+  (pcase key
+    ("<down>"  'above)
+    ("<up>"    'below)
+    ("<left>"  'right)
+    ("<right>" 'left)
+    (_ nil)))
+
+(defun cj/window--pull-away (side)
+  "Split the sole window so the previous buffer opens on SIDE.
+SIDE is one of above/below/left/right -- opposite the pressed arrow, so
+the current window keeps the arrow's edge.  The new window is minimized
+to a sliver (the current window keeps almost the whole frame) and shows
+`other-buffer'; focus stays on the current window so the sticky arrows
+then shrink it step by step via `windsize', exactly as resizing an
+existing split does.  No-op when SIDE is nil."
+  (when side
+    (let ((new (split-window (selected-window) nil side)))
+      (set-window-buffer new (other-buffer (current-buffer) t))
+      ;; Shrink the reveal to the smallest window Emacs allows (~2 lines, the
+      ;; mode line) so the current window keeps almost the whole frame; the
+      ;; sticky `windsize' arrows grow the reveal from there.  `minimize-window'
+      ;; floors at `window-min-height' (4 by default), so bind it down to 1.
+      (let ((window-min-height 1))
+        (minimize-window new))
+      new)))
+
 (defun cj/window-resize-sticky ()
   "Resize the active window's divider in the just-pressed arrow's direction
-(via `windsize'), then keep `cj/window-resize-map' active so bare arrows keep
-nudging until any other key.  Bound to `C-; b <left>/<right>/<up>/<down>'."
+\(via `windsize'), then keep `cj/window-resize-map' active so bare arrows keep
+nudging until any other key.  Bound to `C-; b <left>/<right>/<up>/<down>'.
+
+When the selected window is the sole window in the frame there is no
+divider to move, so the first arrow instead splits a sliver away on the
+side opposite the arrow (`cj/window--pull-away'), revealing the previous
+buffer; the current window keeps almost the whole frame and the following
+arrows shrink it via `windsize', so it reads the same as resizing an
+existing split."
   (interactive)
-  (let ((cmd (keymap-lookup cj/window-resize-map
-                            (key-description (vector last-command-event)))))
-    (when cmd (call-interactively cmd)))
+  (let ((key (key-description (vector last-command-event))))
+    (if (one-window-p)
+        (cj/window--pull-away (cj/window-pull-side key))
+      (let ((cmd (keymap-lookup cj/window-resize-map key)))
+        (when cmd (call-interactively cmd)))))
   (set-transient-map cj/window-resize-map t))
 
 ;; ------------------------------ Window Splitting -----------------------------