fix(tvix/eval): implement cppnix JSON-serialisation semantics r/5979

This drops the usage of serde::Serialize, as the trait can not be used
to implement the correct semantics (function colouring!).

Instead, a manual JSON serialisation function is written which
correctly handles toString, outPath and other similar weirdnesses.

Unexpectedly, the eval-okay-tojson test from the C++ Nix test suite
now passes, too.

This fixes an issue where serialising data structures containing
derivations to JSON would fail.

Change-Id: I5c39e3d8356ee93a07eda481410f88610f6dd9f8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8209
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

2 files changed, 0 insertions, 14 deletions

diff --git a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.exp b/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.exp
deleted file mode 100644
index e92aae3235f2..000000000000
--- a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.exp
+++ /dev/null
@@ -1 +0,0 @@
-"{\"a\":123,\"b\":-456,\"c\":\"foo\",\"d\":\"foo\\n\\\"bar\\\"\",\"e\":true,\"f\":false,\"g\":[1,2,3],\"h\":[\"a\",[\"b\",{\"foo\\nbar\":{}}]],\"i\":3,\"j\":1.44,\"k\":\"foo\"}"
diff --git a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.nix b/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.nix
deleted file mode 100644
index ce67943bead5..000000000000
--- a/tvix/eval/src/tests/nix_tests/notyetpassing/eval-okay-tojson.nix
+++ /dev/null
@@ -1,13 +0,0 @@
-builtins.toJSON
-  { a = 123;
-    b = -456;
-    c = "foo";
-    d = "foo\n\"bar\"";
-    e = true;
-    f = false;
-    g = [ 1 2 3 ];
-    h = [ "a" [ "b" { "foo\nbar" = {}; } ] ];
-    i = 1 + 2;
-    j = 1.44;
-    k = { __toString = self: self.a; a = "foo"; };
-  }