ament-cmake-core: use build platform Python

distros/ament-cmake-core-setup-hook/default.nix

@@ -0,0 +1,9 @@
+{ makeSetupHook, python }:
+
+makeSetupHook {
+  name = "ament-cmake-core-setup-hook";
+  substitutions = {
+    python_major = python.sourceVersion.major;
+    python_executable = python.pythonForBuild.interpreter;
+  };
+} ./setup-hook.sh

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

@@ -0,0 +1,33 @@
+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 "$targetOffset" _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:BOOL=OFF"
+  # Point CMake at build platform Python so it can run it at build time
+  cmakeFlags+=" -DPython@python_major@_EXECUTABLE:FILEPATH=@python_executable@"
+}
+preConfigureHooks+=(_amentCmakeCorePreConfigureHook)