git-merge-pr

#!/bin/bash

PRUNE_FLAG=off
BRANCH_TO_MERGE=""
DESTINATION_BRANCH=""

function usage() {
	echo "usage: git merge-pr [--no-prune] <src> <dest>"
}

if [ "$#" -lt 2 ] || [ "$#" -gt 3 ]; then
	usage
	exit
fi

while :
do
	case "$1" in
		-h | -help )
			usage
			exit 0
			;;
		--no-prune )
			PRUNE_FLAG=on
			shift
			;;
		-* )
			usage
			exit 0
			;;
		* )
			if [ -z $BRANCH_TO_MERGE ]; then
				BRANCH_TO_MERGE="$1"
				shift
			elif [ -z $DESTINATION_BRANCH ]; then
				if [ -n "$1" ]; then
					DESTINATION_BRANCH="$1"
					shift
				else
					usage
					exit 0
				fi
			else
				break
			fi
	esac
done

CURRENT_BRANCH="$(git symbolic-ref --short HEAD)"
WORKING_DIRECTORY=$(pwd)

unstash_changes() {
	if [ "$STASH_OUTPUT" != "No local changes to save" ]; then
		echo "Attempting to unstash local changes"
		POP_STASH="$(git stash pop)"
		if [ $? != 0 ]; then
			echo "ERROR:"
			echo "$POP_STASH"
			exit 9
		fi
	fi
}


restore_original_state() {
	echo "Attempting to return to branch $CURRENT_BRANCH"
	CLEAR_INDEX="$(git reset --hard HEAD)"
	if [ $? != 0 ]; then
		echo "ERROR:"
		echo "$CLEAR_INDEX"
	fi
	CHECKOUT_ORIGINAL_OUTPUT="$(git checkout -q $CURRENT_BRANCH)"
	if [ $? != 0 ]; then
		echo "ERROR:"
		echo "$CHECKOUT_ORIGINAL_OUTPUT"
		exit 8
	fi
    unstash_changes
    cd $WORKING_DIRECTORY
}

run_command()
{
	output=$(eval $1 2>&1)
	if [ $? != 0 ]; then
		printf "ERROR: %s\n" "$output"
		return 1
	else
		return 0
	fi
}

echo "Attempting to securely merge branch 'origin/$BRANCH_TO_MERGE' into 'origin/$DESTINATION_BRANCH'"

# prevent running on branch to be merged without --no-prune
if [ $CURRENT_BRANCH = $BRANCH_TO_MERGE ] &&  [ $PRUNE_FLAG = off ]; then
    echo "ERROR: You are checked out on the branch you are trying to merge."
	echo "         This will prevent the tool from auto-pruning after merging."
	echo "         If you want to keep a local copy of this branch, please consider the --no-prune flag."
	echo "         Otherwise, check out a different branch and try again."
	exit 10
fi

echo "Stashing any local changes and checking out remote branch 'origin/$DESTINATION_BRANCH'"
STASH_OUTPUT="$(git -c commit.gpgSign=false stash save -a)" || exit 1;
cd $(git rev-parse --show-toplevel)

echo "Securely fetching remote branches and revisions:"
echo "    Fetching $DESTINATION_BRANCH..."
echo "    <---- GPG signature required to commit RSL fetch entry"
run_command "git secure-fetch origin $DESTINATION_BRANCH" || { restore_original_state && exit 2; }
echo "    Fetching $BRANCH_TO_MERGE..."
echo "    <---- GPG signature required to commit RSL fetch entry"
run_command "git secure-fetch origin $BRANCH_TO_MERGE" || { restore_original_state && exit 2; }


echo "Cleaning up local repository"
run_command "git gc"

echo "Checking out $DESTINATION_BRANCH"
run_command "git checkout --detach origin/$DESTINATION_BRANCH" || { unstash_changes && exit 3; }

echo "Merging $BRANCH_TO_MERGE into $DESTINATION_BRANCH"
MERGE_MESSAGE="\"Merge 'origin/$BRANCH_TO_MERGE' into $DESTINATION_BRANCH\""
run_command "git merge -S --no-ff -m $MERGE_MESSAGE origin/$BRANCH_TO_MERGE" || { restore_original_state && exit 4; }
echo "Merge Successful!"

echo "Pushing to remote repository 'origin'"
echo "    clearsigning RSL push entry and signing RSL push commit"
echo "    <---- 2 GPG signatures required" 
run_command "git secure-push origin HEAD:$DESTINATION_BRANCH" || { restore_original_state && exit 5; }
echo "Push Successful!"


if [ "$PRUNE_FLAG" = off ]; then
	run_command "git push origin :$BRANCH_TO_MERGE" || { restore_original_state && exit 6; }
	BRANCH_EXISTS="$(git show-ref refs/heads/$BRANCH_TO_MERGE)"
	if [ -n "$BRANCH_EXISTS" ]; then
		run_command "git branch -d $BRANCH_TO_MERGE" || { restore_original_state && exit 7; }
	fi
fi

restore_original_state

exit 0