clan-config: introduce --machine + add tests

pkgs/clan-cli/clan_cli/nix.py

@@ -1,8 +1,34 @@
 import os
+import tempfile
 
 from .dirs import flake_registry, unfree_nixpkgs
 
 
+def nix_eval(flags: list[str]) -> list[str]:
+    if os.environ.get("IN_NIX_SANDBOX"):
+        with tempfile.TemporaryDirectory() as nix_store:
+            return [
+                "nix",
+                "eval",
+                "--show-trace",
+                "--extra-experimental-features",
+                "nix-command flakes",
+                "--flake-registry",
+                str(flake_registry()),
+                # --store is required to prevent this error:
+                # error: cannot unlink '/nix/store/6xg259477c90a229xwmb53pdfkn6ig3g-default-builder.sh': Operation not permitted
+                "--store",
+                nix_store,
+            ] + flags
+    return [
+        "nix",
+        "eval",
+        "--show-trace",
+        "--extra-experimental-features",
+        "nix-command flakes",
+    ] + flags
+
+
 def nix_shell(packages: list[str], cmd: list[str]) -> list[str]:
     # we cannot use nix-shell inside the nix sandbox
     # in our tests we just make sure we have all the packages