How do you *actually* run a Snap package when your home directory isn't under /home?

It seems that snap gets its information on where your home directory is straight from /etc/passwd and not from any other source. One workaround that I've been able to get mostly working involves using a Docker container to replace /etc/passwd from snap's point of view, with one that says my home directory is /home/$USER.

I'm sure there's a lighter-weight way to do this (maybe just a chroot?) that would negate the need for some of the other workarounds I needed to get snap to work inside a container, and I haven't tried it with minetest, but here's the script I put together that runs the teatime Snap without me having to actually move my home directory. Basically it starts a container with snapd in it, with all the places that snapd keeps state mounted in from outside, but initialized with the base state of a freshly installed snapd (which is what it needs the local-persist Docker volume driver for). Then it runs snap in the container, as you, with all the X11 and DBUS plumbing wired up so that teatime can show its windows and desktop notifications.

#!/usr/bin/env bash

# teatime.sh: Run the teatime snap in a Docker container
# Requires local-persist driver installed in Docker: https://github.com/MatchbookLab/local-persist
# Installs it if not available.

set -ex

IMAGE_NAME="snapdock"
CONTAINER_NAME="snaphost"
STORAGE_ROOT="/var/lib/snapdock"
PASSWD_FILE="$HOME/etc/passwd.docker"

if [[ ! -f "${PASSWD_FILE}" ]] ; then
    # The /etc/passwd that claims we have a normal home directory doesn't exist.
    # We need to make it.
    mkdir -p "$(dirname "${PASSWD_FILE}")"

    cat "/etc/passwd" | sed "s_${HOME}_/home/${USER}_g" > "${PASSWD_FILE}"
fi


if ! (docker images "${IMAGE_NAME}" | grep "${IMAGE_NAME}" >/dev/null) ; then
    # There's no image ready. We need to make one
    WORKDIR="$(mktemp -d)"
    cd "${WORKDIR}"
    cat >Dockerfile <<EOF
FROM ubuntu:18.04
# Based on https://github.com/ogra1/snapd-docker/blob/master/build.sh
ENV container docker
ENV PATH "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin"
ENV LANG C.UTF-8
ENV LC_ALL C.UTF-8
RUN DEBIAN_FRONTEND=noninteractive apt-get -q -y update && \
    DEBIAN_FRONTEND=noninteractive apt-get -q -y upgrade && \
    DEBIAN_FRONTEND=noninteractive apt-get -q -y install \
        fuse \
        snapd \
        snap-confine \
        squashfuse \
        sudo && \
    apt-get clean && \
    dpkg-divert --local --rename --add /sbin/udevadm && \
    ln -s /bin/true /sbin/udevadm
VOLUME ["/sys/fs/cgroup"]
STOPSIGNAL SIGRTMIN+3
CMD ["/sbin/init"]
EOF
    docker build . -t "${IMAGE_NAME}"
    cd -
    rm -Rf "${WORKDIR}"
fi

if ! which docker-volume-local-persist >/dev/null ; then
    # We need the local-persist driver installed into Docker.

    WORKDIR="$(mktemp -d)"
    cd "${WORKDIR}"
    curl -fsSL "https://raw.githubusercontent.com/MatchbookLab/local-persist/45c5c344d5dfd358c28d7148be48302d20456fac/scripts/install.sh" >install.sh
    chmod +x install.sh
    cat install.sh
    sudo install.sh
    cd -
    rm -Rf "${WORKDIR}"
fi

if ! (docker ps --filter "name=${CONTAINER_NAME}" | grep "${CONTAINER_NAME}" >/dev/null) ; then
    # Container is not running. Start it.

    if [[ ! -e "${STORAGE_ROOT}" ]] ; then
        # Make sure we have the directories to mount          
        mkdir -p "${STORAGE_ROOT}/lib"
        mkdir -p "${STORAGE_ROOT}/cache"
        mkdir -p "${STORAGE_ROOT}/systemd"
        mkdir -p "${STORAGE_ROOT}/snap"
        sudo chown -R root:root "${STORAGE_ROOT}"
    fi

    # Start the container
    docker run --rm --network=host --cap-add SYS_ADMIN --security-opt apparmor:unconfined --security-opt seccomp:unconfined --volume="$(echo ~:/home/${USER})"  --volume="${PASSWD_FILE}:/etc/passwd:ro" --volume="/etc/group:/etc/group:ro" --volume="/etc/shadow:/etc/shadow:ro" --volume="/etc/sudoers.d:/etc/sudoers.d:ro" --volume="/tmp/.X11-unix:/tmp/.X11-unix:rw" --volume="/sys/fs/cgroup:/sys/fs/cgroup:ro" --volume="/lib/modules:/lib/modules:ro" --device=/dev/fuse --tmpfs /run --tmpfs /run/lock --volume="/run/user/$(id -u):/run/user/$(id -u):rw" --tmpfs /tmp --volume="${STORAGE_ROOT}/lib/:/var/lib/snapd:rw" --volume="${STORAGE_ROOT}/cache/:/var/cache/snapd:rw" --mount "type=volume,volume-driver=local-persist,src=installed-snaps-systemd,target=/etc/systemd/system,volume-opt=mountpoint=${STORAGE_ROOT}/systemd" --mount "type=volume,volume-driver=local-persist,src=installed-snaps-snap,target=/snap,volume-opt=mountpoint=${STORAGE_ROOT}/snap" -it --name="${CONTAINER_NAME}" -d "${IMAGE_NAME}" >/dev/null

    # Wait for it to come up
    sleep 5

fi

# Make sure the snap is installed
docker exec snaphost snap install teatime
# Try and fail to run it as root to avoid complaints about not being able to capture mountpoints when we run it as us.
docker exec snaphost teatime || true
# Run it as us with X11 and Dbus set up
docker exec -d --user="$(id -u ${USER})" --env="DISPLAY" --env="DBUS_SESSION_BUS_ADDRESS" snaphost teatime