pr-number

#!/bin/sh
# Print the number of the GitHub pull request whose head is the current branch.
# Works whether the pull request is within one repository or is from a fork to
# the fork's parent repository, and whether or not the branch that the pull
# request was made from is the one that the local branch tracks.
# With --url, prints the pull request's URL instead of its number.

set -eu

field=number
if [ "${1:-}" = "--url" ]; then
  field=url
  shift
fi
if [ $# -ne 0 ]; then
  echo "Usage: pr-number [--url]" >&2
  exit 2
fi

branch=$(git rev-parse --abbrev-ref HEAD)
if [ "$branch" = "HEAD" ]; then
  echo "pr-number: detached HEAD, no branch to look up" >&2
  exit 1
fi

# The pushed branch name can differ from the local branch name.
if upstream=$(git rev-parse --abbrev-ref --symbolic-full-name '@{u}' 2> /dev/null); then
  remote=${upstream%%/*}
  head_branch=${upstream#*/}
else
  remote=origin
  head_branch=$branch
fi

# Append a word to a space-separated list, if the list does not contain it.
# Arguments: the current list, the word.  Prints the new list.
add_word() {
  case " $1 " in
    *" $2 "*) printf '%s' "$1" ;;
    *) printf '%s' "${1:+$1 }$2" ;;
  esac
}

# The same branch may exist in several of the repositories that this clone has
# remotes for, and the pull request may have been made from any of them.  Search
# every remote's repository, plus the parent of each that is a fork, starting
# with the repository of the remote that the branch tracks.
# Resolving from each remote's URL avoids gh's base-repo guessing.
repos=
owners=
for r in "$remote" $(git remote | grep -v -x "$remote"); do
  if ! remote_url=$(git remote get-url "$r" 2> /dev/null); then
    continue
  fi
  if ! repo_json=$(gh repo view "$remote_url" --json nameWithOwner,parent 2> /dev/null); then
    continue
  fi
  for repo in \
    $(printf '%s' "$repo_json" \
      | jq -r '.nameWithOwner, (if .parent then .parent.owner.login + "/" + .parent.name else empty end)'); do
    repos=$(add_word "$repos" "$repo")
    owners=$(add_word "$owners" "${repo%%/*}")
  done
done

if [ -z "$repos" ]; then
  echo "pr-number: no GitHub repository found among this clone's remotes" >&2
  exit 1
fi

# gh does not accept the "owner:branch" form for --head, so match the head
# repository's owner afterward.  Otherwise a same-named branch in an unrelated
# fork could be reported.
for repo in $repos; do
  result=$(gh pr list --repo "$repo" --head "$head_branch" --state all \
    --json "$field",headRepositoryOwner \
    | jq -r --arg owners "$owners" --arg field "$field" \
      '[.[] | select(.headRepositoryOwner.login as $o | $owners | split(" ") | index($o)) | .[$field]] | first // empty')
  if [ -n "$result" ]; then
    echo "$result"
    exit 0
  fi
done

echo "pr-number: no pull request found for branch $head_branch in $repos" >&2
exit 1