From 939cebd0f17b8e8ec6a4664f9f7e0a5e1c6e3957 Mon Sep 17 00:00:00 2001
From: Vincent Ambo <mail@tazj.in>
Date: Sat, 4 Mar 2023 02:12:06 +0300
Subject: fix(tvix/eval): implement cppnix JSON-serialisation semantics

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
---
 tvix/eval/src/builtins/mod.rs    | 32 ++------------------------------
 tvix/eval/src/builtins/to_xml.rs |  3 ++-
 2 files changed, 4 insertions(+), 31 deletions(-)

(limited to 'tvix/eval/src/builtins')

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 535bf8b2a3..e24285f5c2 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -359,36 +359,8 @@ mod pure_builtins {
 
     #[builtin("toJSON")]
     async fn builtin_to_json(co: GenCo, val: Value) -> Result<Value, ErrorKind> {
-        let mut val = val; // shadow mutably, not supported by macro
-        loop {
-            if let Value::Attrs(attrs) = &val {
-                // Attribute sets with a callable `__toString` attribute
-                // serialise to the string-coerced version of the result of
-                // calling that.
-                if let Some(s) = attrs.try_to_string(&co, CoercionKind::Weak).await {
-                    return Ok(Value::String(serde_json::to_string(&s)?.into()));
-                }
-
-                // Attribute sets with an `outPath` attribute
-                // serialise to a JSON serialisation of that inner
-                // value (regardless of what it is!).
-                if let Some(out_path) = attrs.select("outPath") {
-                    val = out_path.clone();
-                    continue;
-                }
-
-                // Attribute set should be serialised normally (by
-                // traversing it and serialising keys/values).
-                break;
-            }
-
-            break;
-        }
-
-        // All thunks need to be evaluated before serialising, as the
-        // data structure is fully traversed by the Serializer.
-        let val = generators::request_deep_force(&co, val, SharedThunkSet::default()).await;
-        let json_str = serde_json::to_string(&val)?;
+        let json_value = val.to_json(&co).await?;
+        let json_str = serde_json::to_string(&json_value)?;
         Ok(json_str.into())
     }
 
diff --git a/tvix/eval/src/builtins/to_xml.rs b/tvix/eval/src/builtins/to_xml.rs
index 750bb27aa2..375785b7a6 100644
--- a/tvix/eval/src/builtins/to_xml.rs
+++ b/tvix/eval/src/builtins/to_xml.rs
@@ -126,7 +126,8 @@ fn value_variant_to_xml<W: Write>(w: &mut EventWriter<W>, value: &Value) -> Resu
         Value::AttrNotFound
         | Value::Blueprint(_)
         | Value::DeferredUpvalue(_)
-        | Value::UnresolvedPath(_) => {
+        | Value::UnresolvedPath(_)
+        | Value::Json(_) => {
             return Err(ErrorKind::TvixBug {
                 msg: "internal value variant encountered in builtins.toXML",
                 metadata: Some(Rc::new(value.clone())),
-- 
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