Dev container cache image generation

.devcontainer/cache/restore-diff.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# This file restores the results of the "prepare.sh" into their proper locations
+# once the container has been created. It runs as a postCreateCommand which
+# in GitHub Codespaces occurs parallel to other startup activities and does not
+# really add to the overal startup time given how quick the operation ends up being.
+
+set -e
+
+SOURCE_FOLDER="$(cd "${1:-"."}" && pwd)"
+CACHE_FOLDER="${2:-"/usr/local/etc/devcontainer-cache"}"
+
+if [ ! -d "${CACHE_FOLDER}" ]; then
+	echo "No cache folder found."
+	exit 0
+fi
+
+echo "[$(date)] Expanding $(du -h "${CACHE_FOLDER}/cache.tar") file to ${SOURCE_FOLDER}..."
+cd "${SOURCE_FOLDER}"
+tar -xf "${CACHE_FOLDER}/cache.tar"
+rm -f "${CACHE_FOLDER}/cache.tar"
+echo "[$(date)] Done!"
+