additional DevContainer Improvements (#6)

Author: opajonk

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

@@ -11,6 +11,7 @@
         },
         "ghcr.io/devcontainers/features/git-lfs": {
             // Installs the latest version from the Distribution
+            "autoPull": "false" // do not automatically pull LFS files when creating the container
         },
         "ghcr.io/devcontainers/features/common-utils": {
             // Installs latest version from the Distribution

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

@@ -30,7 +30,7 @@
             "description": "sha256sums of Bazel Compile Commands to verify the download; format: <codename>:<sha256sum>;<codename>:<sha256sum>;..."
         }
     },
-    "postCreateCommand": "/devcontainer/features/s-core-local/post_create_command.sh",
+    "onCreateCommand": "/devcontainer/features/s-core-local/on_create_command.sh",
 	"mounts": [ {
             "source": "${localEnv:HOME}/.cache/bazel", // default Bazel cache directory
             "target": "/var/cache/bazel",

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

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# ensure that the Bazel cache directory exists
+if [ ! -d /var/cache/bazel ]; then
+  echo "Creating /var/cache/bazel directory..."
+  # yes, mkdir -p is idempotent, but we want to see the log message
+  mkdir -p /var/cache/bazel
+fi
+
+# If /var/cache/bazel is not a mountpoint, we assume it is a container-local cache.
+# This is the case in codespaces, for example.
+# Here, we must ensure that the directory has the correct permissions
+# so that Bazel can write to it.
+if ! mountpoint -q /var/cache/bazel; then
+    echo "/var/cache/bazel is not mounted. Using container-local cache and setting permissions."
+    chown -R "$(id -un):$(id -gn)" /var/cache/bazel
+fi
+
+# Configure Bazel to use the cache directory
+# This way, Bazel can re-use an existing cache on the host machine, if mounted.
+# Note that in some scenarios (like codespaces), it is not and hence resides in the container.
+echo "startup --output_user_root=/var/cache/bazel" >> ~/.bazelrc
+
+# Configure clangd to remove the -fno-canonical-system-headers flag, which is
+# GCC-specific. If not done, there is an annoying error message on the first
+# line of every C++ file when being displayed in Visual Studio Code.
+mkdir -p ~/.config/clangd
+cat > ~/.config/clangd/config.yaml <<EOF
+CompileFlags:
+  Remove:
+    - -fno-canonical-system-headers
+EOF