backport

#!/usr/bin/env bash

set -euo pipefail

if ! which gh &>/dev/null;
then
   echo "gh cli tool is required in order to continue"
   echo "MacOS install via: brew install gh"
   echo "https://github.com/cli/cli#installation"
   exit 1
fi

if ! which jq &>/dev/null;
then
   echo "jq tool is required in order to continue"
   echo "MacOS install via: brew install jq"
   echo "https://stedolan.github.io/jq/"
   exit 1
fi

usage () {
    echo "Usage:"
    echo "  $0 PR_NUMBER BRANCH_NAME [, BRANCH_NAME, ...]"
    echo ""
    echo "  PR_NUMBER     - the GitHub PR number to backport. example: 4376"
    echo "  BRANCH_NAME   - the name of the branch to backport PR_NUMBER to. example: 1.8"
    echo ""
    echo "Examples:"
    echo ""

    echo "  Backport PR #3489 to branch 0.61"
    echo "    $0 3489 0.61"
    echo ""
    echo "  Backport PR #4376 to branches 1.8, 1.7, and 1.5"
    echo "    $0 4376 1.8 1.7 1.5"
}

if [ $# -lt 2 ];
then
    echo "Error:"
    echo "  Too few arguments, must supply at least PR_NUMBER and 1 BRANCH_NAME"
    echo ""
    usage
    exit 1
fi


PR_NUMBER="${1}"
shift 1
TO_BRANCHES="$@"

# Determine the remote to use
# DEV: If anything here fails, then default to 'origin'
# DEV: We might have https://github.com/DataDog/dd-trace-py, or git@github.com:DataDog/dd-trace-py.
REMOTE=origin

if git remote -v show | grep -qe "[Dd]ata[Dd]og/dd-trace-py\(\.git\)\? (push)" > /dev/null
then
    REMOTE=$(git remote -v show | grep -e "[Dd]ata[Dd]og/dd-trace-py\(\.git\)\? (push)" | awk '{print $1}')
else
    echo "🟠 Failed to automatically determine the remote to use, falling back to 'origin'"
    REMOTE="origin"
fi


if [[ -z "${PR_NUMBER}" ]];
then
    echo "Error:"
    echo "  Must supply a PR number to backport"
    echo ""
    usage
    exit 1
fi

if [[ -z "${TO_BRANCHES}" ]];
then
    echo "Error:"
    echo "  Must supply at least 1 branch to backport to"
    echo ""
    usage
    exit 1
fi


# Download data about the PR
echo "Fetching data for PR ${PR_NUMBER}"
pr_data="$(gh pr view --json "state,title,mergeCommit,author,labels,body" ${PR_NUMBER})"

# Verify that we are going to have a merge commit
if "$(echo "${pr_data}" | jq -e '.state != "MERGED"')";
then
    echo "PR ${PR_NUMBER} has not been merged yet"
    exit 1
fi

# Extract data from the original PR
merge_commit_sha="$(echo "${pr_data}" | jq -r '.mergeCommit.oid')"
original_title="$(echo "${pr_data}" | jq -r '.title')"
original_body="$(echo "${pr_data}" | jq -r '.body')"
original_author="$(echo "${pr_data}" | jq -r '.author.login')"
original_labels="$(echo "${pr_data}" | jq -r '[.labels[].name] | join(",")')"

# Get the current branch so we can switch back to it when we are done
current_branch="$(git rev-parse --abbrev-ref HEAD)"

# Try to make sure we have the latest data from remote
git fetch --all &>/dev/null || true

for base_branch in "$@";
do
  echo "Backporting ${PR_NUMBER} (sha: ${merge_commit_sha}) to ${base_branch}"
  branch_name="backport-${PR_NUMBER}-to-${base_branch}"
  if ! git switch --detach "${REMOTE}/${base_branch}"
  then
    echo "🟠 Cannot switch to base branch ${base_branch}, skipping ..."
    continue
  fi
  git switch -C "${branch_name}"

  echo "Cherry-picking ${merge_commit_sha} (git commit signing required here)"
  if ! git cherry-pick -x "${merge_commit_sha}";
  then
      echo "Cherry-pick failed. In a separate shell, please:"
      echo "  1. Manually resolve merge conflicts"
      echo "  2. git add resolved files"
      echo "  3. Run git cherry-pick --continue to complete the merge"
      echo ""
      read -p "Press any key to continue once conflict is manually resolved..." -n1 -s
      echo ""
  fi
  echo "Pushing branch ${branch_name}"
  git push --set-upstream ${REMOTE} "${branch_name}"

  echo "Creating pull request"
  IFS='' read -r -d '' new_body <<EOF || true
Backport of #${PR_NUMBER} to ${base_branch}

${original_body}
EOF
  new_title="${original_title} [backport #${PR_NUMBER} to ${base_branch}]"
  gh pr create --base "${base_branch}" --title "${new_title}" --body "${new_body}" --assignee "@me,${original_author}" --label "${original_labels}"

  echo "Enabling auto-merge on PR"
  gh pr merge --auto "${branch_name}"

  echo "Opening PR in the browser for review"
  gh pr view --web "${branch_name}"

  # Back to the original branch and delete the temporary branch
  echo "Switching back to ${current_branch} and deleting temporary branch ${branch_name}"
  git switch "${current_branch}"
  git branch -D "${branch_name}"
done

echo "✨ 🍰 ✨ All done! ✨ 🍰 ✨"