Merge branch '98-add-util-git-replay-merge.sh' into 'master'

Put git-replay-merge in source tree

Closes #98

See merge request !83

util/git-replay-merge.sh

+#!/bin/bash
+#
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+set -e
+
+SELF="$(basename $0)"
+SELF="${SELF/-/ }"
+
+STATE_FILE=".git/REPLAY_MERGE"
+
+die() {
+	for MESSAGE in "$@"; do
+		echo -e "${MESSAGE}" >&2
+	done
+	exit 1
+}
+
+die_with_usage() {
+	die "Usage:"								\
+	    ""									\
+	    "	${SELF} <merge_commit_id> <target_remote> <target_branch>"	\
+	    "	${SELF} --continue"						\
+	    "	${SELF} --abort"
+}
+
+die_with_continue_instructions() {
+	die ""								\
+	    "Replay interrupted.  Conflicts need to be fixed manually."	\
+	    "When done, run \"${SELF} --continue\"."			\
+	    "Use \"${SELF} --abort\" to abort the replay."
+}
+
+die_if_wrong_dir() {
+	if [[ ! -d ".git" ]]; then
+		die "You need to run this command from the toplevel of the working tree."
+	fi
+}
+
+die_if_not_in_progress() {
+	die_if_wrong_dir
+	if [[ ! -f "${STATE_FILE}" ]]; then
+		die "No replay-merge in progress?"
+	fi
+}
+
+die_if_in_progress() {
+	die_if_wrong_dir
+	if [[ -f "${STATE_FILE}" ]]; then
+		die "Another replay-merge in progress.  Use --continue or --abort."
+	fi
+}
+
+die_if_local_behind_target() {
+	TARGET_REF_HEAD="$(git rev-list --max-count=1 "${TARGET_REF}")"
+	if [[ "$(git merge-base "${TARGET_REF}" "${TARGET_BRANCH}")" != "${TARGET_REF_HEAD}" ]]; then
+		die "Local branch ${TARGET_BRANCH} is behind ${TARGET_REF}, cannot merge into it."	\
+		    "Update or remove the local branch, then run \"${SELF} --continue\"."		\
+		    "Use \"${SELF} --abort\" to abort the replay."
+	fi
+}
+
+branch_exists() {
+	ESCAPED_BRANCH_NAME=${1//\//\\\/}
+	BRANCH_REGEX="/^(remotes\/)?${ESCAPED_BRANCH_NAME}$/"
+	if [[ -n "$(git branch -a | awk "\$NF ~ ${BRANCH_REGEX} {print \$NF}")" ]]; then
+		return 0
+	else
+		return 1
+	fi
+}
+
+go() {
+	# Process parameters.
+	SOURCE_COMMIT="$1"
+	TARGET_REMOTE="$2"
+	TARGET_BRANCH="$3"
+	TARGET_REF="${TARGET_REMOTE}/${TARGET_BRANCH}"
+	# Establish the range of commits comprising the source branch.
+	REPLAY_COMMIT_RANGE="$(
+		git show --format="%P" "${SOURCE_COMMIT}" 2>&1 |
+		sed -n "1s/\([0-9a-f]\{40\}\) \([0-9a-f]\{40\}\)/\1..\2/p;"
+	)"
+	if [[ -z "${REPLAY_COMMIT_RANGE}" ]]; then
+		die "${SOURCE_COMMIT} is not a valid merge commit ID."
+	fi
+	# Extract the name of the source branch.
+	SOURCE_BRANCH="$(
+		git log --max-count=1 --format="%B" "${SOURCE_COMMIT}" |
+		sed -n "s/^Merge branch '\([^'][^']*\).*/\1/p;" |
+		head -n 1
+	)"
+	if [[ -z "${SOURCE_BRANCH}" ]]; then
+		die "Unable to extract source branch name from ${SOURCE_COMMIT}."
+	fi
+	# Ensure the target ref is valid.
+	if ! branch_exists "${TARGET_REF}"; then
+		die "${TARGET_REF} is not a valid replay target."
+	fi
+	# Abort if a local branch with the name about to be used for replaying
+	# the merge already exists.
+	REPLAY_BRANCH="${SOURCE_BRANCH}-${TARGET_BRANCH}"
+	if branch_exists "${REPLAY_BRANCH}"; then
+		die "Local branch with name ${REPLAY_BRANCH} already exists."	\
+		    "Cannot use it for replaying a merge."
+	fi
+	# Get the name of the currently checked out branch so that it can be
+	# checked out again once the replay is finished.
+	CHECKED_OUT_BRANCH="$(git branch | awk "\$1 == \"*\" {print \$2}")"
+	# Store state in case it needs to be restored later.
+	cat <<-EOF > "${STATE_FILE}"
+		CHECKED_OUT_BRANCH="${CHECKED_OUT_BRANCH}"
+		SOURCE_COMMIT="${SOURCE_COMMIT}"
+		SOURCE_BRANCH="${SOURCE_BRANCH}"
+		REPLAY_BRANCH="${REPLAY_BRANCH}"
+		TARGET_REMOTE="${TARGET_REMOTE}"
+		TARGET_BRANCH="${TARGET_BRANCH}"
+		TARGET_REF="${TARGET_REF}"
+	EOF
+	# Announce the plan.
+	echo "Attempting to replay ${REPLAY_COMMIT_RANGE} on top of ${TARGET_REF} in ${REPLAY_BRANCH}..."
+	# Switch to the replay branch.
+	git checkout -t -b "${REPLAY_BRANCH}" "${TARGET_REF}" >/dev/null
+	# Try replaying the branch.  If there is any conflict, the command will
+	# fail, which means we need to bail and let the user fix the current
+	# cherry-pick manually, expecting "git replay-merge --continue" to be
+	# used afterwards.  If there is no conflict, just proceed with what
+	# --continue would do.
+	if ! git cherry-pick -x "${REPLAY_COMMIT_RANGE}"; then
+		die_with_continue_instructions
+	fi
+	resume
+}
+
+resume() {
+	# If cherry-picking has not yet been completed, resume it.  If it
+	# fails, bail.  If if succeeds, we can proceed with merging.
+	if [[ -f ".git/sequencer/todo" ]]; then
+		if ! git cherry-pick --continue; then
+			die_with_continue_instructions
+		fi
+	fi
+	# Announce the plan.
+	echo "Attempting to merge ${REPLAY_BRANCH} into ${TARGET_BRANCH}..."
+	# Check if a local branch with the same name as the target branch
+	# exists.  If it does not, switch to a new local branch with the same
+	# name as the target branch.  Otherwise, ensure the local branch is not
+	# behind the target branch at the target remote, then switch to it.
+	if ! branch_exists "${TARGET_BRANCH}"; then
+		git checkout -t -b "${TARGET_BRANCH}" "${TARGET_REF}" >/dev/null
+	else
+		die_if_local_behind_target
+		git checkout "${TARGET_BRANCH}" &>/dev/null
+	fi
+	# Use the original commit message with a modified subject line.
+	COMMIT_MSG="$(
+		git log --max-count=1 --format="%B" "${SOURCE_COMMIT}" |
+		sed "1s/.*/Merge branch '${REPLAY_BRANCH}' into '${TARGET_BRANCH}'/;"
+	)"
+	# Merge the replay branch into the local target branch.
+	git merge --no-ff -m "${COMMIT_MSG}" "${REPLAY_BRANCH}"
+	cat <<-EOF
+
+	Replayed ${SOURCE_BRANCH} onto ${TARGET_BRANCH}.
+	To push the replay, use:
+
+	        git push ${TARGET_REMOTE} ${TARGET_BRANCH}:${TARGET_BRANCH}
+
+	EOF
+	cleanup
+}
+
+cleanup() {
+	# Restore working copy state from before the replay was started,
+	# ignoring any potential errors to prevent "set -e" from interfering.
+	{
+		git merge --abort
+		git cherry-pick --abort
+		git checkout "${CHECKED_OUT_BRANCH}"
+		git branch -D "${REPLAY_BRANCH}"
+	} &>/dev/null || true
+	rm -f "${STATE_FILE}"
+}
+
+case "$1" in
+	"--abort")
+		die_if_not_in_progress
+		source "${STATE_FILE}"
+		cleanup
+		;;
+	"--continue")
+		die_if_not_in_progress
+		source "${STATE_FILE}"
+		resume
+		;;
+	*)
+		if [[ $# -ne 3 ]]; then
+			die_with_usage
+		fi
+		die_if_in_progress
+		go "$@"
+		;;
+esac