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, 23 insertions, 0 deletions

diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
index 918061b8b861..41e7f207b9e8 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
@@ -93,4 +93,27 @@ in
   (preserveContext other-drv (builtins.concatStringsSep "${other-drv}" [ "abc" "def" ]))
   # `attrNames` will never ever produce context.
   (preserveContext "abc" (toString (builtins.attrNames { a = { }; b = { }; c = { }; })))
+  # `toJSON` preserves context of its inputs.
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a = [ drv ];
+    b = [ other-drv ];
+  }))
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a.deep = [ drv ];
+    b = [ other-drv ];
+  }))
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a = "${drv}";
+    b = [ other-drv ];
+  }))
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a.deep = "${drv}";
+    b = [ other-drv ];
+  }))
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a = "${drv} ${other-drv}";
+  }))
+  (preserveContexts [ drv other-drv ] (builtins.toJSON {
+    a.b.c.d.e.f = "${drv} ${other-drv}";
+  }))
 ]