a jj/git prompt command

.vcs_prompt.sh

# vim: ft=sh
# shellcheck shell=bash

# jj/git prompt command
#
# For jj, uses the script from jj's wiki:
# https://github.com/jj-vcs/jj/wiki/Shell-Prompt
#
# For git, uses the "git-prompt.sh" contrib script:
# https://github.com/git/git/blob/master/contrib/completion/git-prompt.sh
#
# ---
#
# 1. Download this scirpt, save it as ~/.vcs_prompt
# 2. Download the git-prompt.sh script, save it as ~/.git_prompt
# 3. In .bashrc, add:
#
# ```sh
# . ~/.vcs_prompt
# PROMPT_COMMAND=__vcs_prompt
# ```
#
# Dedicated to the Public Domain under the Unlicense:
# https://unlicense.org/UNLICENSE

if [ -f ~/.git_prompt ]; then
    # shellcheck source=/dev/null
    . ~/.git_prompt
fi

# echo "jj" or "git" if either is found in $PWD or its parents
__pwd_in_vcs() {
    # using the shell is much faster than
    # `git rev-parse --git-dir` or `jj root`
    local D="/$PWD"
    while test -n "$D" ; do
        test -e "$D/.jj" && { echo jj ; return; }
        test -e "$D/.git" && { echo git ; return; }
        D="${D%/*}"
    done
}

# Print Git or jj repository information
__vcs_prompt() {
    local jjgit

    jjgit="$(__pwd_in_vcs)"  # results in "jj", "git" or ""

    if test "$jjgit" = jj ; then
        # --ignore-working-copy: avoid inspecting $PWD and concurrent
        # snapshotting which could create divergent commits
        jj --ignore-working-copy --no-pager log --no-graph --color=always -r @ -T \
           ' "jj[@ " ++ concat( separate(" ", format_short_change_id_with_hidden_and_divergent_info(self), format_short_commit_id(commit_id),
                           bookmarks, if(conflict, label("conflict", "conflict")) ) ) ++ "]\n" ' 2>/dev/null
    elif test "$jjgit" = git ; then
        # __git_ps1 *sets* the PS1 var, so we save and restore later
        local pps1=$PS1
        __git_ps1 'git[' ']' '%s'
        echo "${PS1@P}"
        PS1=$pps1
    fi
}