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, 4 deletions

diff --git a/tvix/glue/src/builtins/derivation.rs b/tvix/glue/src/builtins/derivation.rs
index 078cb0e1ffd1..1a8d18943ebe 100644
--- a/tvix/glue/src/builtins/derivation.rs
+++ b/tvix/glue/src/builtins/derivation.rs
@@ -372,14 +372,13 @@ pub(crate) mod derivation_builtins {
                             return Ok(val);
                         }
 
-                        // TODO(raitobezarius): context for json values?
-                        // input_context.mimic(&val);
-
-                        let val_json = match val.into_json(&co).await? {
+                        let (val_json, mut context) = match val.into_contextful_json(&co).await? {
                             Ok(v) => v,
                             Err(cek) => return Ok(Value::from(cek)),
                         };
 
+                        input_context = input_context.join(&mut context);
+
                         // No need to check for dups, we only iterate over every attribute name once
                         structured_attrs.insert(arg_name.to_owned(), val_json);
                     } else {