EXPERIMENTAL: jj pin – Guard the tree at a bookmark during history cleanup

jj-pin.bash

# jj pin – guard the tree at a bookmark during history cleanup
# Source in .bashrc / .zshrc:  source ~/.jj-pin.sh
#
# Pins the closest bookmark to @ by storing a git ref at
# refs/jj-pin/<bookmark> pointing to the bookmark's current commit.
# jj only imports refs/heads, refs/tags, and refs/remotes, so a
# custom ref namespace is invisible to jj and won't affect
# immutable_heads() or jj log.  Requires a colocated repo.
#
# Status and diff always compare the pinned commit to the bookmark's
# current commit, regardless of where @ is.

_JJ_PIN_PREFIX=refs/jj-pin

_jj_pin_read() {
  local ref
  ref=$(git for-each-ref --format='%(refname)' "$_JJ_PIN_PREFIX/" 2>/dev/null | head -1)
  [ -n "$ref" ] || return 1

  _jj_pin_bookmark="${ref#"$_JJ_PIN_PREFIX/"}"
  _jj_pin_commit=$(git rev-parse "$ref" 2>/dev/null) || return 1
}

_jj_pin_clear() {
  local ref
  for ref in $(git for-each-ref --format='%(refname)' "$_JJ_PIN_PREFIX/" 2>/dev/null); do
    git update-ref -d "$ref" 2>/dev/null
  done
}

jj-pin() {
  local bookmark
  bookmark=$(jj log -r 'heads(::@ & bookmarks())' --no-graph -T 'local_bookmarks.map(|b| b.name()).join("\n")' 2>/dev/null | head -1)

  if [ -z "$bookmark" ]; then
    echo "error: no bookmark found at or before @" >&2; return 1
  fi

  local commit_id
  commit_id=$(jj log -r "$bookmark" --no-graph -T 'commit_id' 2>/dev/null) || {
    echo "error: could not resolve bookmark '$bookmark'" >&2; return 1
  }

  _jj_pin_clear

  git update-ref "$_JJ_PIN_PREFIX/$bookmark" "$commit_id" 2>/dev/null || {
    echo "error: could not create ref (colocated git repo required)" >&2; return 1
  }

  echo "📌 pinned $bookmark (${commit_id:0:12})"
}

jj-unpin() {
  _jj_pin_read || { echo "error: no pin set" >&2; return 1; }
  _jj_pin_clear
  echo "📌 unpinned $_jj_pin_bookmark"
}

# Short string for prompt integration.
#
#   no pin            → empty (prints nothing)
#   pin set, matches  → "📌"
#   pin set, changed  → "📌✗"
#   pin set, error    → "📌?"
#
# Usage: PS1='... $(jj-pin-status) $ '
jj-pin-status() {
  _jj_pin_read || return

  local pin_tree
  pin_tree=$(git rev-parse "${_jj_pin_commit}^{tree}" 2>/dev/null) || {
    printf '📌?'; return
  }

  local current_commit current_tree
  current_commit=$(jj log -r "$_jj_pin_bookmark" --no-graph -T 'commit_id' 2>/dev/null) || {
    printf '📌?'; return
  }
  current_tree=$(git rev-parse "${current_commit}^{tree}" 2>/dev/null) || {
    printf '📌?'; return
  }

  if [ "$pin_tree" = "$current_tree" ]; then
    printf '📌'
  else
    printf '📌✗'
  fi
}

jj-pin-diff() {
  _jj_pin_read || {
    echo "error: no pin set (run jj-pin first)" >&2; return 1
  }

  local current_commit
  current_commit=$(jj log -r "$_jj_pin_bookmark" --no-graph -T 'commit_id' 2>/dev/null) || {
    echo "error: could not resolve bookmark '$_jj_pin_bookmark'" >&2; return 1
  }

  jj diff --from "$_jj_pin_commit" --to "$current_commit" "$@"
}

# --- Convenience aliases (optional) ---
# alias jp='jj-pin'
# alias jpu='jj-unpin'
# alias jpd='jj-pin-diff'