sync-branch

#!/usr/bin/env bash
# Merge the given release tags.
set -Eeuo pipefail

if [[ $# -lt 1 ]]; then
	echo "usage: $0 TAG..." >&2
	exit 1
fi

tags_to_sync=("$@")

for tag_to_sync in "${tags_to_sync[@]}"; do
	if git merge --no-ff "$tag_to_sync"; then
		continue
	fi

	if ! git rev-parse --verify --quiet MERGE_HEAD > /dev/null || git diff --quiet --diff-filter=U; then
		exit 1
	fi

	git checkout "$tag_to_sync" -- '.'
	git add --all
	git merge --continue
done

# Check that every tag is in the branch.
# This catches cases where a merge did not actually incorporate one of the
# requested release tags.
for tag_to_sync in "${tags_to_sync[@]}"; do
	if ! git merge-base --is-ancestor "$tag_to_sync" HEAD; then
		echo "tag $tag_to_sync is not contained in $(git rev-parse --abbrev-ref HEAD)" >&2
		exit 1
	fi
done