Replace bind-mount with volume as Bazel Cache

Since bind-mounting the Bazel cache from the host causes various problems (problematic access rights; incompatibilities with CodeSpaces) without major benefits, we use now a regular named volume as persistent cache.

Author: opajonk

src/s-core-devcontainer/.devcontainer/s-core-local/devcontainer-feature.json

@@ -36,9 +36,9 @@
     "postCreateCommand": "if [ -f .bazelversion ] && [ \"$(cat .bazelversion)\" != \"$(dpkg --list | grep 'ii  bazel   ' | awk '{print $3}')\" ]; then sudo apt-get update && sudo apt-get install -y --allow-downgrades bazel=$(cat .bazelversion); fi",
     "mounts": [
         {
-            "source": "${localEnv:HOME}/.cache/bazel", // default Bazel cache directory
+            "source": "eclipse-s-core-bazel-cache",
             "target": "/var/cache/bazel",
-            "type": "bind"
+            "type": "volume"
         }
     ]
 }

src/s-core-devcontainer/.devcontainer/s-core-local/on_create_command.sh

@@ -1,15 +1,24 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# In some scenarios (like CodeSpaces), apparently not all (or even any?)
-# bind mounts to the host are done and /var/cache/bazel does not exist.
-# See devcontainer-feature.json, where this mount is defined.
-# Hence, if /var/cache/bazel exists, it was mounted from the host,
-# and we configure Bazel to use /var/cache/bazel as cache.
-# This way, Bazel re-uses a bind-mounted cache from the host machine, while
-# still using the default cache (${HOME}/.cache/bazel) if no such cache exists.
+# Enable persistent Bazel cache
+#
+# Usually, a volume is mounted to /var/cache/bazel (see
+# devcontainer-feature.json). This shall be used as Bazel cache, which is then
+# preserved across container re-starts. Since the volume has a fixed
+# name ("eclipse-s-core-bazel-cache"), it is even used across all Eclipse
+# S-CORE DevContainer instances.
 if [ -d /var/cache/bazel ]; then
-  echo "Configuring Bazel to use /var/cache/bazel as cache..."
+  echo "Bazel Cache: /var/cache/bazel exists. Checking ownership and configuring Bazel to use it as cache..."
+  current_owner_group=$(stat -c "%U:%G" /var/cache/bazel)
+  current_user_group="$(id -un):$(id -gn)"
+  if [ "${current_owner_group}" = "${current_user_group}" ]; then
+    echo "Bazel Cache: /var/cache/bazel is already owned by ${current_user_group}. "
+  else
+    echo "Bazel Cache: /var/cache/bazel is not owned by ${current_owner_group}. Setting ownership (this may take a few seconds) ..."
+    sudo chown -R "${current_user_group}" /var/cache/bazel
+  fi
+  echo "Bazel Cache: Configuring Bazel to use /var/cache/bazel as cache..."
   echo "startup --output_user_root=/var/cache/bazel" >> ~/.bazelrc
 fi