don't modify spack.yaml if no site-specific spack.yaml exists

install_spack_env.sh

@@ -57,8 +57,6 @@ spack env activate $EBRAINS_SPACK_ENV
 # update environment site-configs
 rm -rf $SPACK_ENV/site-config && cp -r $EBRAINS_REPO/site-config $SPACK_ENV
 # update spack.yaml: merge top-level and site-specific spack.yaml files
-# TODO: find a more robust way to do this (maybe with yq? but we need to download the binary)
-# TODO: or add pyyaml to dependencies and use python script
 spack-python $EBRAINS_REPO/site-config/ymerge.py $EBRAINS_REPO/spack.yaml $EBRAINS_REPO/site-config/$SYSTEMNAME/spack.yaml > /tmp/spack.yaml
 cp /tmp/spack.yaml $SPACK_ENV/
 

site-config/ymerge.py

-import sys
+# spack-python script that merges two environment configuration files (spack.yaml) into one
+# Usage: spack-python /path/to/first/spack.yaml /path/to/second/spack.yaml
+# (note: if the second file does not exist, the output is the first file
+
+import sys, os
 from spack.config import merge_yaml, read_config_file, syaml
 
-print(syaml.dump(merge_yaml(read_config_file(sys.argv[1]), read_config_file(sys.argv[2]))))
+if not os.path.exists(sys.argv[2]):
+    merged = syaml.dump(read_config_file(sys.argv[1]))
+else:
+    merged = syaml.dump(merge_yaml(read_config_file(sys.argv[1]), read_config_file(sys.argv[2])))
+
+print(merged)
+