Subject: bug#78999: 31.0.50; [wishlist] window-divider-mode: option to show the bottom divider only when the mode line is hidden

From: Dani Moncayo <[email-masked]>
Date: Sat, 12 Jul 2025 12:13:36 +0200

Severity: wishlist.

With the current master branch, it's now easy to hide the mode line in
specific buffers/windows, with the new 'mode-line-invisible-mode'.

But then, in a multi-window layout with some windows stacked
vertically, it becomes important to have a window divider at the
bottom edge of each window, to visually distinguish them.  This can be
achieved with:
  (setq window-divider-default-places t)
  (window-divider-mode 1)

But that setup isn't entirely satisfactory to me, because I don't want
_every_ window to show a bottom divider; I'd like to have the bottom
divider _only_ in windows where the mode line is hidden.

In other words, I’d prefer _not_ to have a window displaying both its
mode line and bottom divider -- I don't need/want both of them.

So, would it be possible to add a feature to window-divider-mode
whereby a window's bottom divider is shown only when its mode-line is
hidden?

TIA.

-- 
Dani Moncayo

In GNU Emacs 31.0.50 (build 59, x86_64-pc-linux-gnu, GTK+ Version
 3.24.41, cairo version 1.18.0) of 2025-07-12 built on C11-Q8YAKWONJX0
Repository revision: f746762e74adeac8beaa73abcf20ee5e74298597
Repository branch: master
Windowing system distributor 'Microsoft Corporation', version 11.0.12010000
System Description: Ubuntu 24.04.2 LTS

Configured features:
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LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINERAMA
XINPUT2 XPM XRANDR GTK3 ZLIB

Important settings:
  value of $LANG: C.UTF-8
  locale-coding-system: utf-8-unix