private GroupAssignment assignHomogenous(
        GroupSpec groupSpec,
        SubscribedTopicDescriber subscribedTopicDescriber
    ) {
        Set<Uuid> subscribeTopicIds = groupSpec.memberSubscription(groupSpec.memberIds().iterator().next())
            .subscribedTopicIds();
        if (subscribeTopicIds.isEmpty())
            return new GroupAssignment(Collections.emptyMap());

        Map<Uuid, Set<Integer>> targetPartitions = computeTargetPartitions(
            subscribeTopicIds, subscribedTopicDescriber);

        return new GroupAssignment(groupSpec.memberIds().stream().collect(Collectors.toMap(
            Function.identity(), memberId -> new MemberAssignmentImpl(targetPartitions))));
    }
A simple partition assignor that assigns each member all partitions of the subscribed topics.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/assignor/SimpleAssignor.java