co-sign-pr.sh

#!/usr/bin/env bash
set -eou pipefail

TMPDIR=""
GREEN=$'\033[32m'
RESET=$'\033[0m'

msg() { echo "${GREEN}==> $1${RESET}"; }

main() {
    local local_repo="${1:?Usage: co-sign-pr <path-to-local-clone> <pr-number>}"
    local pr="${2:?Usage: co-sign-pr <path-to-local-clone> <pr-number>}"

    local_repo="$(cd "$local_repo" && pwd)"
    local remote_url
    remote_url="$(git -C "$local_repo" remote get-url origin)"

    TMPDIR="$(mktemp -d)"
    trap 'rm -rf "$TMPDIR"' EXIT

    msg "Cloning from '${local_repo}' -> '${TMPDIR}'..."
    git clone --quiet --reference-if-able "$local_repo" "$remote_url" "$TMPDIR"
    cd "$TMPDIR"

    local gh_repo
    gh_repo="$(gh repo view --json nameWithOwner --jq .nameWithOwner)"

    local head_branch
    head_branch="$(gh pr view "$pr" --repo "$gh_repo" --json headRefName --jq .headRefName)"

    msg "Checking out PR #${pr} (${head_branch})..."
    git checkout --quiet -B "$head_branch" "origin/$head_branch"
    git branch --quiet --set-upstream-to="origin/$head_branch"

    local base merge_base count
    base="$(gh pr view "$pr" --repo "$gh_repo" --json baseRefName --jq .baseRefName)"
    merge_base="$(git merge-base HEAD "origin/${base}")"
    count="$(git rev-list --count "${merge_base}..HEAD")"

    msg "Re-signing ${count} commit(s)..."
    git rebase --quiet --exec 'git commit --amend --no-edit' "$merge_base"

    msg "Pushing..."
    git push --quiet --force-with-lease

    msg "Done. PR #${pr} commits re-signed."
}

main "$@"