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

4 files changed, 35 insertions, 2 deletions

diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.exp b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.exp
index 3f8905e9bd0d..a136b0035e0a 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.exp
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.exp
@@ -1 +1 @@
-[ true true true true true true true true true true true ]
+[ true true true true true true true true true true true true true ]
diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
index 1b645b1a2607..ecd8ab0073d0 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
@@ -41,6 +41,13 @@ let
   reconstructed-path = appendContextFrom combo-path
     (builtins.unsafeDiscardStringContext combo-path);
 
+  an-str = {
+    a = "${drv}";
+  };
+  an-list = {
+    b = [ drv ];
+  };
+
   # Eta rule for strings with context.
   etaRule = str:
     str == appendContextFrom
@@ -70,4 +77,7 @@ in
   (etaRule "foo")
   (etaRule drv.drvPath)
   (etaRule drv.foo.outPath)
+  # `toJSON` tests
+  (builtins.hasContext (builtins.toJSON an-str))
+  (builtins.hasContext (builtins.toJSON an-list))
 ]
diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.exp b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.exp
index 8bb828e36a42..ff56f6ca18e7 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.exp
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.exp
@@ -1 +1 @@
-[ true true true true true true true true true true true true true true true true true true true true true true true true true true true true ]
+[ true true true true true true true true true true true true true true true true true true true true true true true true true true true true true true true true true true ]
diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
index 918061b8b861..41e7f207b9e8 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-propagation.nix
@@ -93,4 +93,27 @@ in
   (preserveContext other-drv (builtins.concatStringsSep "${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}";
+  }))
 ]