Reduce ROS2 closure sizes and make example work out of the box

distros/ament-cmake-core-setup-hook.sh

@@ -0,0 +1,31 @@
+isAmentPackage() {
+  [ -d "$1/share/ament_index" ]
+}
+
+declare -gA _amentPackagesSeen
+
+_findAmentPackages() {
+  local pkg="$1"
+  # Deduplicate the packages
+  if [ -z "${_amentPackagesSeen["$pkg"]:-}" ] \
+    && isAmentPackage "$pkg" \
+    && [ -n "$(shopt -s nullglob; echo $pkg/share/*/local_setup.sh)" ]
+  then
+    # ROS scripts use unbound variables
+    set +u
+    for setup in "$pkg"/share/*/local_setup.sh; do
+      source "$setup"
+    done
+    set -u
+  fi
+  _amentPackagesSeen["$pkg"]=1
+}
+addEnvHooks "$hostOffset" _findAmentPackages
+
+_amentCmakeCorePreConfigureHook() {
+  # Don't create share/ament_index/resource_index/parent_prefix_path resource
+  # that contains references to all dependencies. This file isn't used with Nix
+  # and just bloats the closure.
+  cmakeFlags+=" -DAMENT_CMAKE_ENVIRONMENT_PARENT_PREFIX_PATH_GENERATION=OFF"
+}
+preConfigureHooks+=(_amentCmakeCorePreConfigureHook)