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/vm/generators.rs b/tvix/eval/src/vm/generators.rs
index d5b5f1de4979..79de6886923a 100644
--- a/tvix/eval/src/vm/generators.rs
+++ b/tvix/eval/src/vm/generators.rs
@@ -493,7 +493,7 @@ where
                         VMRequest::ToJson(value) => {
                             self.reenqueue_generator(name, span.clone(), generator);
                             self.enqueue_generator("to_json", span, |co| {
-                                value.into_json_generator(co)
+                                value.into_contextful_json_generator(co)
                             });
                             return Ok(false);
                         }
@@ -778,9 +778,9 @@ pub(crate) async fn request_span(co: &GenCo) -> LightSpan {
 pub(crate) async fn request_to_json(
     co: &GenCo,
     value: Value,
-) -> Result<serde_json::Value, CatchableErrorKind> {
+) -> Result<(serde_json::Value, NixContext), CatchableErrorKind> {
     match co.yield_(VMRequest::ToJson(value)).await {
-        VMResponse::Value(Value::Json(json)) => Ok(*json),
+        VMResponse::Value(Value::Json(json_with_ctx)) => Ok(*json_with_ctx),
         VMResponse::Value(Value::Catchable(cek)) => Err(*cek),
         msg => panic!(
             "Tvix bug: VM responded with incorrect generator message: {}",