Pre-push hook for LLVM monorepo

pre-push

#!/bin/sh

# Pre-push hook making sure there is no merge commit in the set of commits
# being pushed upstream. This hooks works by walking the set of commits being
# pushed and making sure that none of them has two parents or more (which is
# the definition of a merge commit).
#
# This hook is called with the following parameters:
#
# ${1} -- Name of the remote to which the push is being done
# ${2} -- URL to which the push is being done
#
# Information about the commits which are being pushed is supplied as lines to
# the standard input in the form:
#
#   <local ref> <local sha1> <remote ref> <remote sha1>

set -e

remote="${1}"
url="${2}"

while read local_ref local_sha remote_ref remote_sha; do
	range="${remote_sha}..${local_sha}"
	new_commits="$(git rev-list "${range}")"

	for commit in ${new_commits}; do
		parents=$(git cat-file -p "${commit}" | grep 'parent' | wc -l)
		if (( ${parents} >= 2 )); then
			short="$(git rev-parse --short "${commit}")"
			echo "commit ${short} appears to be a merge commit: aborting the push" >&2
			exit 1
		fi
	done
done

exit 0