fix(tvix/eval): handle toJSON on attribute sets with `outPath` r/5977

These are serialised as the serialisation of the value of that field.

Change-Id: Ida51708b1f43ce09b0ec835f4e265918aa31dd09
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8205
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

1 files changed, 23 insertions, 6 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index a9d04ba7c3fb..535bf8b2a305 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -359,13 +359,30 @@ mod pure_builtins {
 
     #[builtin("toJSON")]
     async fn builtin_to_json(co: GenCo, val: Value) -> Result<Value, ErrorKind> {
-        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()));
+        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