fix(tvix/glue): reject unknown attrset args for fetch builtins r/8315

This now uses UnexpectedArgumentBuiltin in case builtins.fetchurl or
builtins.fetchTarball are called with the wrong arguments:

```
note: while evaluating this Nix code
 --> [code]:1:1
  |
1 | builtins.readDir (builtins.fetchTarball { url = "https://git"; hash = "sha1-NKNeU1csW5YJ4lCeWH3Z/apppNU=";})
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error[E040]: Unexpected agrument `"hash"` passed to builtin
 --> [code]:1:19
  |
1 | builtins.readDir (builtins.fetchTarball { url = "https://git"; hash = "sha1-NKNeU1csW5YJ4lCeWH3Z/apppNU=";})
  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ while calling this builtin

```

Change-Id: I51124255a46b78d3cf4dc89a1eca9e68750858d4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11878
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Reviewed-by: flokli <flokli@flokli.de>
Reviewed-by: Simon Hauser <simon.hauser@helsinki-systems.de>
Tested-by: BuildkiteCI

1 files changed, 8 insertions, 1 deletions

diff --git a/tvix/glue/src/builtins/fetchers.rs b/tvix/glue/src/builtins/fetchers.rs
index 47da71fb922b..1ad43b383353 100644
--- a/tvix/glue/src/builtins/fetchers.rs
+++ b/tvix/glue/src/builtins/fetchers.rs
@@ -60,7 +60,14 @@ async fn extract_fetch_args(
         Err(cek) => return Ok(Err(cek)),
     };
 
-    // TODO: disallow other attrset keys, to match Nix' behaviour.
+    // Disallow other attrset keys, to match Nix' behaviour.
+    // We complain about the first unexpected key we find in the list.
+    const VALID_KEYS: [&[u8]; 3] = [b"url", b"name", b"sha256"];
+    if let Some(first_invalid_key) = attrs.keys().find(|k| !&VALID_KEYS.contains(&k.as_bytes())) {
+        return Err(ErrorKind::UnexpectedArgumentBuiltin(
+            first_invalid_key.clone(),
+        ));
+    }
 
     // parse the sha256 string into a digest.
     let sha256 = match sha256_str {