Tell macOS' Time Machine to ignore the files Git ignores

git-tmutil-ignore.bash

#!/bin/bash
# shellcheck enable=all disable=SC2030,SC2249,SC2250
function git-tmutil-ignore() (
    set -euo pipefail
    case $=${ZSH_NAME-${BASH-other}} in
        */bash) shopt -s lastpipe ;;
    esac

    attr_name=com.apple.metadata:com_apple_backup_excludeItem
    attr_value=bplist00_com.apple.backupd

    function init-for() {
        last=''
        header=${1?need HEADER}
    }

    function print-item() {
        if [[ -n $header ]]; then
            echo >&2 "$header"
            header=''
        fi
        echo >&2 "- ${1?need ITEM}"
        printf '%s\0' "${repo?}/$1"
    }

    function directories-to-reset() (
        init-for "Resetting tracked directories in $repo..."
        local last='////'
        while IFS= read -r line; do
            case $line in
                "$last"/*) continue ;;                           # skip last dir's contents
                */*) last=${line//\/*/} && print-item "$last" ;; # print top-most parent dir
            esac
        done
    )

    function directories-to-exclude() (
        init-for "Excluding ignored directories in $repo..."
        local last='////'
        while IFS= read -r line; do
            case $line in
                "$last"/*) continue ;;                         # skip last dir's contents
                */) last=${line/%\//} && print-item "$last" ;; # print dirs
            esac
        done
    )

    (($#)) || set -- "$PWD"
    while (($#)); do
        repo=$1
        shift

        LC_ALL=C git -C "$repo" ls-files --cached |
            directories-to-reset |
            xargs -r0 xattr -rd "$attr_name"

        LC_ALL=C git -C "$repo" ls-files --others --directory --ignored --exclude-standard --deduplicate |
            directories-to-exclude |
            xargs -r0 xattr -w "$attr_name" "$attr_value"
    done
)

if ! (return 0 2> /dev/null); then
    git-tmutil-ignore "$@"
fi