git-shallow

#!/usr/bin/env bash
set -euo pipefail
set -x

TMP_GIT_SHALLOW=$(mktemp -d -t yplatform.XXXXXXXXXX)
function on_exit() {
    rm -rf ${TMP_GIT_SHALLOW}
}
trap on_exit EXIT

GIT_BRANCH=$(git -C $1 rev-parse --abbrev-ref HEAD)
GIT_BRANCH_TRACKING_REF=
GIT_TAG=
if [[ -n "${GIT_BRANCH#HEAD}" ]]; then
    GIT_BRANCH_TRACKING_REF=$(git -C $1 for-each-ref --format="%(upstream)" "$(git -C $1 symbolic-ref -q HEAD)")
else
    GIT_TAG=$(git -C $1 tag --points-at HEAD | head -1)
    GIT_BRANCH="${GIT_TAG}"
fi
[[ -n "${GIT_BRANCH#HEAD}" ]] || {
    # attach temporarily
    >&2 echo "$(date +"%H:%M:%S")" "[INFO] Creating temporary branch yp-git-shallow."
    git -C $1 checkout -B yp-git-shallow
    GIT_BRANCH=$(git -C $1 rev-parse --abbrev-ref HEAD)
    [[ "${GIT_BRANCH}" = "yp-git-shallow" ]]
}

>&2 echo "$(date +"%H:%M:%S")" "[INFO] Shallow-cloning branch/tag ${GIT_BRANCH}."
# file:/// or else no shallow clone. see https://stackoverflow.com/a/40383231/465684
git clone \
    --depth 1 \
    --branch ${GIT_BRANCH} \
    --recurse-submodules \
    --shallow-submodules \
    file:///$1 ${TMP_GIT_SHALLOW}

git -C ${TMP_GIT_SHALLOW} branch --unset-upstream
git -C ${TMP_GIT_SHALLOW} config --unset remote.origin.fetch
git -C ${TMP_GIT_SHALLOW} remote set-url origin "$(git -C $1 remote get-url origin)"
git -C ${TMP_GIT_SHALLOW} pack-refs
rm -rf ${TMP_GIT_SHALLOW}/.git/refs/remotes

rm -rf ${1}/.git
mv ${TMP_GIT_SHALLOW}/.git ${1}/

if [[ "${GIT_BRANCH}" != "yp-git-shallow" ]]; then
    if [[ -n "${GIT_TAG}" ]]; then
        >&2 echo "$(date +"%H:%M:%S")" "[INFO] Set up fetching tag ${GIT_TAG}."
        git -C $1 config remote.origin.fetch "+refs/tags/${GIT_TAG}:refs/tags/${GIT_TAG}"
    elif [[ -n "${GIT_BRANCH_TRACKING_REF}" ]]; then
        if [[ "${GIT_BRANCH_TRACKING_REF#refs/remotes/origin/}" = "${GIT_BRANCH_TRACKING_REF}" ]]; then
            >&2 echo "$(date +"%H:%M:%S")" "[SKIP] Set up fetching branch ${GIT_BRANCH} to ${GIT_BRANCH_TRACKING_REF}."
        else
            >&2 echo "$(date +"%H:%M:%S")" "[INFO] Set up fetching branch ${GIT_BRANCH} to ${GIT_BRANCH_TRACKING_REF}."
            git -C $1 config remote.origin.fetch "+refs/heads/${GIT_BRANCH}:${GIT_BRANCH_TRACKING_REF}"
        fi
    fi
else
    >&2 echo "$(date +"%H:%M:%S")" "[INFO] Set up fetching all branches."
    git -C $1 config remote.origin.fetch "+refs/heads/*:refs/remotes/origin/*"
    # detach again
    >&2 echo "$(date +"%H:%M:%S")" "[INFO] Detach from yp-git-shallow."
    GIT_BRANCH=yp-git-shallow
    git -C $1 checkout $(git -C $1 rev-parse HEAD)
    git -C $1 branch -D ${GIT_BRANCH}
    git -C $1 branch -r -D origin/${GIT_BRANCH}
fi