undo_merge.sh

#!/usr/bin/env bash
eval "$(/opt/homebrew/bin/brew shellenv)"
GERRIT_ROOT="$HOME/gerrit"
cd "$GERRIT_ROOT/git"

strike() {
	echo "=================================="
}

export GERRIT_REPO

# Step 1
cd "$GERRIT_REPO.git/"

echo "Garbage collecting $GERRIT_REPO"
git gc
strike

$GERRIT_ROOT/bin/gerrit.sh stop

# Step 2
echo
echo "Exporting Merged Commits"
export_merged() {
    for i in $(grep meta packed-refs | cut -d' ' -f2)
    do
        echo "$i:$(git log --oneline $i --grep='autogenerated:gerrit:merged')" | grep patch
    done | cut -d' ' -f1
}

export_merged | tee /tmp/export_merged.txt
strike

# Step 3
echo
echo "Updating Merged Commits to previous HEAD"
cp packed-refs /tmp/packed-refsback
for i in $(cat /tmp/export_merged.txt); do
    REF="$(echo $i | cut -d':' -f1)"
    MERGED="$(echo $i | cut -d':' -f2)"
    NEWREF="$(git rev-parse $MERGED~1)"
    git update-ref $REF $NEWREF
done
git gc
strike

# Step 3
echo
echo "Refreshing gerrit UI to reflect latest status"
$GERRIT_ROOT/bin/gerrit.sh start
CHANGE_URL=$(printf %s "$GERRIT_REPO" | jq -sRr @uri)
for i in $(grep meta packed-refs| cut -d' ' -f2)
do
    CHANGE_NUM=$(basename $(dirname $i))
    screen -d -m curl -s "https://localhost:8443/changes/$CHANGE_URL~$CHANGE_NUM/revisions/current/mergeable" -k -o /tmp/log
    sleep 0.1
done