feat(tvix/eval): implement binary comparison operators r/4478

This is accomplished by simply delegating to the Rust implementations
of (Partial)Ord and (Partial)Eq, which are implemented for Value and
underlying wrapper types to behave like they do in Nix.

To ease the implementation overhead, a new comparison operator macro
has been added to the VM module.

Incomparable types will raise a new error variant when a comparison is
attempted, containing both supplied types. This mimics the information
carried in the error thrown by C++ Nix.

Change-Id: Ia19634d69119d40722f3ca672387bc3a80096998
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6143
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

1 files changed, 5 insertions, 0 deletions

diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index fb9f3b6ec5..f7f64f4e68 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -14,6 +14,11 @@ pub enum Error {
         expected: &'static str,
         actual: &'static str,
     },
+
+    Incomparable {
+        lhs: &'static str,
+        rhs: &'static str,
+    },
 }
 
 impl Display for Error {