Force UTF-8 locale to keep tab-separated parsing intact

[vivek8031]

Problem

When any script in this repo (save.sh, restore.sh, the helpers they share) runs in an environment with no LC_ALL or LANG set, tmux 3.x's -F format substitution renders tab characters (0x09) as underscores (0x5f). Because this script uses IFS=$'\t' read everywhere (pane_format, window_format, state_format, …), every line collapses into a single field, the parser bails out, and save_all writes a near-empty resurrect file containing only the trailing state line — about 8 bytes.

Common environments that hit this on macOS:

• launchd LaunchAgents (TMPDIR/PATH are set but LC_ALL/LANG are not)
• minimal cron environments
• a few CI runners

The result is silent: save.sh exits 0, last symlink updates to the broken file, and the next auto-restore brings back nothing.

Reproduction (macOS, tmux 3.6a)

$ unset LC_ALL LANG LC_CTYPE
$ tmux list-panes -a -F "pane\t#{session_name}\t#{pane_pid}" | head -1 | xxd
00000000: 7061 6e65 5f34 5f31 3335 3934 0a   pane_4_13594.   ← underscores

$ export LC_ALL=C.UTF-8
$ tmux list-panes -a -F "pane\t#{session_name}\t#{pane_pid}" | head -1 | xxd
00000000: 7061 6e65 0934 0931 3335 3934 0a   pane.4.13594.   ← tabs

This pairs nastily with tmux-continuum: a LaunchAgent / status-bar driven continuum_save overwrites the last symlink with the 8-byte file right before auto-restore runs on next boot. Discussed at length in tmux-continuum issues #90 / #94 and at https://joeywrites.dev/posts/fixing-broken-tmux-resurrect-save/, where the documented workaround is to ln -sf a known-good save back into place by hand.

Fix

In scripts/helpers.sh (sourced by every script in the repo), set LC_ALL=C.UTF-8 if and only if the user has no locale configured at all:

if [ -z "${LC_ALL:-}${LANG:-}" ]; then
    export LC_ALL=\"C.UTF-8\"
fi

C.UTF-8 is available on glibc (≥ 2.13) and macOS (Big Sur+), and is a sensible neutral default. Existing LC_ALL or LANG are left alone, so users who have explicitly chosen a locale see no change.

Verification

# unpatched, no locale: 8-byte file, parsing broken
$ unset LC_ALL LANG LC_CTYPE
$ bash /path/to/installed/plugin/scripts/save.sh quiet
$ wc -l ~/.local/share/tmux/resurrect/last
       1
$ ls -la ~/.local/share/tmux/resurrect/last
… 8 …

# patched, no locale: full 2 KB save with all sessions
$ unset LC_ALL LANG LC_CTYPE
$ bash /path/to/fork/scripts/save.sh quiet
$ wc -l ~/.local/share/tmux/resurrect/last
      23
$ awk '$1==\"pane\"{print $2}' ~/.local/share/tmux/resurrect/last | sort -u
4
demo
main
property-mastering-engine
$ head -1 ~/.local/share/tmux/resurrect/last | xxd | head -1
00000000: 7061 6e65 0934 0931 0931 093a 2a09 …   pane.4.1.1.:*. …   ← tabs

Compatibility

• No new tmux options, no behaviour change for users with LC_ALL or LANG already set.
• Falls back to a locale that exists on every platform this plugin supports.
• Single 9-line addition in helpers.sh.