tmux-outer-border

tmux built from a pinned upstream commit (74b91d6, reports next-3.7) with a patch adding a pane-outer-border window option.

When enabled, tmux draws a border around the outside of the whole pane area — top, left, right and bottom — in addition to the usual borders between splits. The pane area is inset by one cell on each side to make room for it.

# ~/.tmux.conf
set -gw pane-outer-border on

┌──────────────────┬──────────────────┐
│                  │                  │
│  pane 0          │  pane 1          │
│                  │                  │
├──────────────────┼──────────────────┤
│                  │                  │
│  pane 2          │  pane 3          │
│                  │                  │
└──────────────────┴──────────────────┘

The option is a standard window option (default off), so it composes with status-position, pane splits, and all of the select-layout presets (tiled, even-horizontal, main-vertical, …).

Install (Arch Linux)

From the AUR

yay -S tmux-outer-border
# or
paru -S tmux-outer-border

Manually with makepkg

git clone https://github.com/al3rez/tmux-outer-border.git
cd tmux-outer-border
makepkg -si

This package provides/conflicts tmux, so it replaces the official tmux package and installs the binary at /usr/bin/tmux.

What the patch changes

File	Change
options-table.c	Adds the pane-outer-border window flag (default off).
layout.c	Insets the layout by one cell on each side when the option is on (layout_fix_offsets is the single authoritative spot; layout_init/layout_resize reserve the size).
layout-set.c	Re-applies the inset after select-layout presets, which build at full size.
screen-redraw.c	Treats x==0/y==0 as border cells, fixes corner/edge glyph classification, and suppresses the off-screen window-edge border so the right/bottom frame draws correctly.

The full diff lives in pane-outer-border.patch.

Updating the pinned commit

1. Update _commit and pkgver in PKGBUILD.
2. Refresh the patch against the new tree if needed.
3. updpkgsums && makepkg --printsrcinfo > .SRCINFO.

License

tmux is distributed under the ISC license. The patch is provided under the same terms.