Use rsync to cache intermediate build artifacts with Docker buildkit

rsync_cache.sh

#!/bin/bash

set -ue

# Sync the cache back to the source path.
# Use --times to preserve timestamps
# Use --update to make sure that newer files in the source path
# aren't overwritten by older files in the cache.

cache_root_path=$1
cacheable_source_paths=$2
command=$3

for path in $cacheable_source_paths; do
  echo "Restoring cache from $cache_root_path/${path} to $path"
  mkdir -p $cache_root_path/${path}
  mkdir -p $path
  rsync --archive --times --update $cache_root_path/${path}/ $path
done

echo "Running: ${command}"
$command

# Sync the working tree back to the cache.
# Use --times to preserve timestamps
# Use --delete to remove files from the cache that aren't present in the source path

for path in $cacheable_source_paths; do
  echo "Saving $path to cache at $cache_root_path"
  rsync --archive --times --delete $path/ $cache_root_path/$path
done