feat(tvix/eval): Implement comparison for lists r/5221

Lists are compared lexicographically in C++ nix as of [0], and our
updated nix test suites depend on this. This implements comparison of
list values in `Value::nix_cmp` using a very similar algorithm to what
C++ does - similarly to there, this requires passing in the VM so we can
force thunks in the list elements as we go.

[0]: https://github.com/NixOS/nix/commit/09471d2680292af48b2788108de56a8da755d661#

Change-Id: I5d8bb07f90647a1fec83f775243e21af856afbb1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7070
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

1 files changed, 10 insertions, 0 deletions

diff --git a/tvix/eval/src/value/list.rs b/tvix/eval/src/value/list.rs
index 8ea3db7aecf3..236a654ad88d 100644
--- a/tvix/eval/src/value/list.rs
+++ b/tvix/eval/src/value/list.rs
@@ -1,4 +1,6 @@
 //! This module implements Nix lists.
+use std::ops::Deref;
+
 use crate::errors::ErrorKind;
 use crate::vm::VM;
 
@@ -125,3 +127,11 @@ impl<'a> IntoIterator for &'a NixList {
         self.0.iter()
     }
 }
+
+impl Deref for NixList {
+    type Target = Vec<Value>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}