Fix SHLVL in tmux

dotfiles/.bashrc

@@ -185,12 +185,7 @@ bashrc_customize_terminal_colors() {
 
 bashrc_set_prompt() {
     local exit_code=$?
-
     local level=$SHLVL
-    if [[ -n "$TMUX" ]]; then
-        level=$(($SHLVL - 2))
-    fi
-
     local prompt=$(printf '\$%.0s' $(seq 1 $level))
     local color="$cyan"
     if [ $EUID -eq 0 ]; then

dotfiles/.tmux.conf

@@ -44,8 +44,10 @@ set -g status-justify        centre
 set -g status-left           '@#h ⧉ #S'              # @host ⧉session
 set -g status-right          '%Y-%m-%d %a %H:%M'    # date, weekday, time
 
-# Make sure we always start at 1, even when invoked from a wrapper script
-set-environment -g SHLVL 1
+# The shell will increment SHLVL by one when it is started -> unsetting this
+# variable here removes any memory of nesting before tmux was executed and will
+# cause shells to start with level 1 again within the session.
+set-environment -gu SHLVL
 
 #
 # Colors