add flake evaluator, make hydraJob outputs optional

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

flupdt/flake_eval.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+
+import logging
+from typing import Optional
+from flupdt.common import bash_wrapper
+import re
+
+drv_re = re.compile(r'.*(/nix/store/.*\.drv).*')
+
+def evaluate_output(path:str, output: str) -> Optional[str]:
+    logging.info(f"evaluating {output}")
+    out = bash_wrapper(f"nix eval {path}#{output}")
+    logging.debug(out[0])
+    logging.debug(out[1])
+    logging.debug(out[2])
+    if out[2] != 0:
+        logging.warning(f"output {output} did not evaluate correctly")
+        return None
+    else:
+        drv_match = drv_re.match(out[0])
+        if drv_match is None:
+            out_msg = "derivation succeeded but output derivation does not contain a derivation"
+            raise RuntimeError(out_msg)
+        drv = drv_match.group(1)
+        logging.debug(f"derivation evaluated to {drv}")