feat(tvix/eval): contextful JSON operations r/7899

`toJSON` transform a Nix structure into a JSON string.

For each context in that Nix structure, the JSON string must possess it.

Thus, it is necessary to take the union of all contexts and attach it to
the final structure.

Unfortunately, the return type of `into_json` is a serde's JSON object,
not a string. Therefore, it is not possible to reuse `NixString`
machinery.

Context tests are reinforced as Nix does not test those behaviors.

Fixes b/393.

Change-Id: I5afdbc4e18dd70469192c1aa657d1049ba330149
Signed-off-by: Ryan Lahfa <tvl@lahfa.xyz>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11266
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 3 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index cb55894b6c7e..3d24e495efa3 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -453,11 +453,11 @@ mod pure_builtins {
 
     #[builtin("toJSON")]
     async fn builtin_to_json(co: GenCo, val: Value) -> Result<Value, ErrorKind> {
-        match val.into_json(&co).await? {
+        match val.into_contextful_json(&co).await? {
             Err(cek) => Ok(Value::from(cek)),
-            Ok(json_value) => {
+            Ok((json_value, ctx)) => {
                 let json_str = serde_json::to_string(&json_value)?;
-                Ok(json_str.into())
+                Ok(NixString::new_context_from(ctx, json_str).into())
             }
         }
     }