feat(tvix/eval): implement builtins.toJSON r/5652

Implements `Serialize` for `tvix_eval::Value`. Special care is taken
with serialisation of attribute sets, and forcing of thunks.

The tests should cover both cases well.

Change-Id: I9bb135bacf6f87bc6bd0bd88cef0a42308e6c335
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7803
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Autosubmit: tazjin <tazjin@tvl.su>

1 files changed, 20 insertions, 1 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index c6b274f0b7..d413f0073f 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -9,7 +9,8 @@ use std::iter::FromIterator;
 
 use imbl::{ordmap, OrdMap};
 use serde::de::{Deserializer, Error, Visitor};
-use serde::Deserialize;
+use serde::ser::SerializeMap;
+use serde::{Deserialize, Serialize};
 
 use crate::errors::ErrorKind;
 use crate::vm::VM;
@@ -140,6 +141,24 @@ impl TotalDisplay for NixAttrs {
     }
 }
 
+impl Serialize for NixAttrs {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        match &self.0 {
+            AttrsRep::Empty => serializer.serialize_map(Some(0))?.end(),
+            AttrsRep::KV { name, value } => {
+                let mut map = serializer.serialize_map(Some(2))?;
+                map.serialize_entry("name", name)?;
+                map.serialize_entry("value", value)?;
+                map.end()
+            }
+            AttrsRep::Im(map) => map.serialize(serializer),
+        }
+    }
+}
+
 impl<'de> Deserialize<'de> for NixAttrs {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where