nix-required-mounts: support new versions of Nix (#442389)

pkgs/by-name/ni/nix-required-mounts/nix_required_mounts.py

@@ -61,11 +61,19 @@ def symlink_parents(p: Path) -> List[Path]:
     return out
 
 
-def get_strings(drv_env: dict, name: str) -> List[str]:
+def get_required_system_features(parsed_drv: dict) -> List[str]:
+    # Newer versions of Nix (since https://github.com/NixOS/nix/pull/13263) store structuredAttrs
+    # in the derivation JSON output.
+    if "structuredAttrs" in parsed_drv:
+        return parsed_drv["structuredAttrs"].get("requiredSystemFeatures", [])
+
+    # Older versions of Nix store structuredAttrs in the env as a JSON string.
+    drv_env = parsed_drv.get("env", {})
     if "__json" in drv_env:
-        return list(json.loads(drv_env["__json"]).get(name, []))
-    else:
-        return drv_env.get(name, "").split()
+        return list(json.loads(drv_env["__json"]).get("requiredSystemFeatures", []))
+
+    # Without structuredAttrs, requiredSystemFeatures is a space-separated string in env.
+    return drv_env.get("requiredSystemFeatures", "").split()
 
 
 def validate_mounts(pattern: Pattern) -> List[Tuple[PathString, PathString, bool]]:
@@ -140,8 +148,7 @@ def entrypoint():
     )
 
     parsed_drv = parsed_drv[canon_drv_path]
-    drv_env = parsed_drv.get("env", {})
-    required_features = get_strings(drv_env, "requiredSystemFeatures")
+    required_features = get_required_system_features(parsed_drv)
     required_features = list(filter(known_features.__contains__, required_features))
 
     patterns: List[Pattern] = list(