improve logging if evaluation is not present in github

nixpkgs_review/github.py

@@ -9,7 +9,7 @@
 from pathlib import Path
 from typing import IO, Any, override
 
-from .utils import System
+from .utils import System, warn
 
 
 def pr_url(pr: int) -> str:
@@ -175,16 +175,26 @@ def get_github_action_eval_result(
                 workflow_run["artifacts_url"],
             )["artifacts"]
 
+            found_comparison = False
             for artifact in artifacts:
                 if artifact["name"] != "comparison":
                     continue
+                found_comparison = True
                 changed_paths: Any = self.get_json_from_artifact(
                     workflow_id=artifact["id"],
                     json_filename="changed-paths.json",
                 )
                 if changed_paths is None:
+                    warn(f"Found comparison artifact, but no changed-paths.json in workflow {workflow_run['html_url']}")
                     continue
                 if (path := changed_paths.get("rebuildsByPlatform")) is not None:
                     assert isinstance(path, dict)
                     return path
+
+            if not found_comparison:
+                if workflow_run["status"] == "queued":
+                    warn(f"Found eval workflow run, but evaluation is still work in progress: {workflow_run['html_url']}")
+                else:
+                    warn(f"Found eval workflow run, but no comparison artifact in {workflow_run['html_url']}.")
+
         return None