fix(tvix/eval): implement cppnix JSON-serialisation semantics r/5979

This drops the usage of serde::Serialize, as the trait can not be used
to implement the correct semantics (function colouring!).

Instead, a manual JSON serialisation function is written which
correctly handles toString, outPath and other similar weirdnesses.

Unexpectedly, the eval-okay-tojson test from the C++ Nix test suite
now passes, too.

This fixes an issue where serialising data structures containing
derivations to JSON would fail.

Change-Id: I5c39e3d8356ee93a07eda481410f88610f6dd9f8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8209
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

1 files changed, 1 insertions, 20 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index e4584e3aa2..bacfd22217 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -10,8 +10,7 @@ use std::iter::FromIterator;
 use imbl::{ordmap, OrdMap};
 use lazy_static::lazy_static;
 use serde::de::{Deserializer, Error, Visitor};
-use serde::ser::SerializeMap;
-use serde::{Deserialize, Serialize};
+use serde::Deserialize;
 
 use super::string::NixString;
 use super::thunk::ThunkSet;
@@ -151,24 +150,6 @@ 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