TERM in bash and nushell

.bashrc

setup-TERM() {
  # vte-256color messes up emacs with solarized, so use xterm-256color
  # instead.
  declare vte=xterm-256color
  declare -a terms

  case $TERM:$COLORTERM in
    ansi:*)
      # probably Windows telnet
      TERM=vt100 ;;

    screen*|tmux*:*)
      # leave it alone! don't trip on the following vte checks
      ;;

    *:roxterm|xterm:)
      if [[ $ROXTERM_PID == "$PPID" ]]; then
        TERM=$vte
      elif [[ -e /etc/crouton ]]; then
        # https://groups.google.com/a/chromium.org/forum/#!topic/chromium-hterm/2EmfR2Mac88
        TERM=xterm-256color
      elif [[ $(xargs -0 < /proc/$PPID/cmdline) == *gnome-terminal* ]] 2>/dev/null; then
        # gnome-terminal stopped setting COLORTERM=gnome-terminal
        # https://github.com/GNOME/gnome-terminal/commit/1d5c1b6ca6373c1301494edbc9e43c3e6a9c9aaf
        TERM=$vte
      fi
      ;;

    *:Terminal|*:gnome-terminal)
      TERM=$vte ;;
  esac

  case $TERM in
    alacritty)
      terms=("$TERM" xterm-256color xterm) ;;
    rxvt-*)
      terms=("$TERM" rxvt xterm) ;;
    xterm-256color|xterm-kitty)
      terms=("$TERM" xterm-256color xterm) ;;
    screen*)
      terms=(screen-256color "$TERM" screen) ;;
    tmux*)
      terms=(tmux-256color screen-256color "$TERM" tmux screen) ;;
  esac

  if [[ -n $terms ]]; then
    # toe on gentoo searches only /usr/share/terminfo.
    # toe on debian/unbuntu searches only ~/.terminfo and /etc/terminfo.
    # both appear to be broken, so we search explicitly.
    declare -a toes
    toes=($(
      for d in ~/.terminfo /etc/terminfo /lib/terminfo /usr/share/terminfo; do
        [[ -d $d ]] && toe "$d"
      done | awk '{print $1}'
    ))
    for term in "${terms[@]}"; do
      for toe in "${toes[@]}"; do
        if [[ $term == "$toe" ]]; then
          TERM=$term
          return
        fi
      done
    done
  fi
}

setup-TERM

unset -f setup-TERM

env.nu

$env.TERM = (
  # Start with whatever is in TERM already.
  ($env | get -i 'TERM' | default-empty 'xterm') |

  # Do some replacements, optimistically upgrading xterm to xterm-256color for
  # the moment.
  (
    if $in == 'ansi' {'vt100'}
    else if ($in == 'xterm') {'xterm-256color'}
    else if ($in | find -r '^screen|^tmux' | is-not-empty) {$in}
    else if ($env | get -i 'COLORTERM' | default '' |
      find -r '^roxterm$|^Terminal$|^gnome-terminal$' | is-not-empty)
      {'xterm-256color'}
    else {$in}
  ) |

  # Convert to list with fallbacks, for example:
  #   xterm-kitty -> [xterm-kitty xterm-256color xterm]
  (
    if (['alacritty' 'xterm-256color' 'xterm-kitty'] | any {|it| str contains $it}) {
      [$in 'xterm-256color' 'xterm']
    } else if ($in | str starts-with 'rxvt-') {
      [$in 'rxvt' 'xterm']
    } else if ($in | str starts-with 'screen') {
      ['screen-256color' $in 'screen']
    } else if ($in | str starts-with 'tmux') {
      ['tmux-256color' 'screen-256color' $in 'tmux' 'screen']
    } else {
      [$in]
    }
  ) |

  # Now that we have a prioritized list with fallbacks, choose the first that
  # is available on the current system.
  (do {
    let terms = $in
    # Don't call external toe command. It's slow and doesn't work the same on
    # all Linux distros.
    let toes = (
      ['~/.terminfo' '/etc/terminfo' '/lib/terminfo' '/usr/share/terminfo'] |
      reduce -f [] {|d, acc|
        $acc ++ (
          try {ls ([$d * *] | path join) | get name | path basename}
          catch {[]}
        )
      }
    )
    for term in $terms {
      if ($toes | any {|toe| $term == $toe}) {
        return $term
      }
    }
    return ($terms | last) # most conservative
  })
)