Fix reference tracking in ObjWriter::add_element

[CUB3D]

Description

When writing primitive values, we currently increment the reference value for some primitive types. We shouldn't do that. Lets also support CacheKeys for XML and Date kinds as well as they can be referenced. As long as add_element is only used for adding primitives this is correct, it would be ideal to enforce this somehow but I don't see a way to handle that while also not duplicating the logic of date() and xml() for each writer.
Also added tests for the XML and Date cases.

Lets check if the Value kind in add_element is something that should be reference-able instead.

Checklist

• I, a human, have self-reviewed this PR and fully understand the changes within.
• I have added or updated tests where possible.
• This PR builds, has no outstanding failing lints, and passes all tests.
• An LLM was NOT involved in the authoring of this code.
  Closes AMF0 obj_writer increments its reference index for every property #115, In AMF0, XML objects should reference the cache #124, AMF0 Reference generation seems broken #72

[evilpie]

Could we assert that the Value type is primitive?

[danielhjacobs]

Thinking more about it, it feels like there may be a possibility that reference indexes may be used for XML Documents and Dates. I feel like that may have to be tested.

[evilpie]

Thinking more about it, it feels like there may be a possibility that reference indexes may be used for XML Documents and Dates. I feel like that may have to be tested.

#72

[danielhjacobs]

Thinking more about it, it feels like there may be a possibility that reference indexes may be used for XML Documents and Dates. I feel like that may have to be tested.

#72

Well, that proves the Date case, XML Document shows this:

var payload = new Object();
payload.n_xml = new XML("<root><child id='avm1'>test</child></root>");
payload.n_xml_ref = payload.n_xml;
var nc = new NetConnection();
nc.connect("http://localhost:8000/");
var responder = new Object();
nc.call("test.avm1", responder, payload);

Flash output:

Navigator::fetch:
  URL: http://localhost:8000/
  Method: POST
  Mime-Type: application/x-amf
  Body: [00, 00, 00, 00, 00, 01, 00, 09, 74, 65, 73, 74, 2E, 61, 76, 6D, 31, 00, 02, 2F, 31, 00, 00, 00, 4D, 0A, 00, 00, 00, 01, 03, 00, 05, 6E, 5F, 78, 6D, 6C, 0F, 00, 00, 00, 2A, 3C, 72, 6F, 6F, 74, 3E, 3C, 63, 68, 69, 6C, 64, 20, 69, 64, 3D, 22, 61, 76, 6D, 31, 22, 3E, 74, 65, 73, 74, 3C, 2F, 63, 68, 69, 6C, 64, 3E, 3C, 2F, 72, 6F, 6F, 74, 3E, 00, 09, 6E, 5F, 78, 6D, 6C, 5F, 72, 65, 66, 07, 00, 02, 00, 00, 09]

[danielhjacobs]

That said, this isn't correct in Ruffle currently either:

running 1 test
2026-07-28T18:52:38.084378Z ERROR ruffle_core::net_connection: Couldn't submit AMF Packet to http://localhost:8000/: FetchError("Could not get metadata for '/localhost': The file or directory could not be found")
test avm1/xml_ref ... FAILED

failures:

---- avm1/xml_ref ----
assertion failed: `(ruffle_actual == flash_expected)`

Diff < left / right > :
 Navigator::fetch:
   URL: http://localhost:8000/
   Method: POST
   Mime-Type: application/x-amf
<  Body: [00, 00, 00, 00, 00, 01, 00, 09, 74, 65, 73, 74, 2E, 61, 76, 6D, 31, 00, 02, 2F, 31, 00, 00, 00, 79, 0A, 00, 00, 00, 01, 03, 00, 05, 6E, 5F, 78, 6D, 6C, 0F, 00, 00, 00, 2A, 3C, 72, 6F, 6F, 74, 3E, 3C, 63, 68, 69, 6C, 64, 20, 69, 64, 3D, 22, 61, 76, 6D, 31, 22, 3E, 74, 65, 73, 74, 3C, 2F, 63, 68, 69, 6C, 64, 3E, 3C, 2F, 72, 6F, 6F, 74, 3E, 00, 09, 6E, 5F, 78, 6D, 6C, 5F, 72, 65, 66, 0F, 00, 00, 00, 2A, 3C, 72, 6F, 6F, 74, 3E, 3C, 63, 68, 69, 6C, 64, 20, 69, 64, 3D, 22, 61, 76, 6D, 31, 22, 3E, 74, 65, 73, 74, 3C, 2F, 63, 68, 69, 6C, 64, 3E, 3C, 2F, 72, 6F, 6F, 74, 3E, 00, 00, 09]
>  Body: [00, 00, 00, 00, 00, 01, 00, 09, 74, 65, 73, 74, 2E, 61, 76, 6D, 31, 00, 02, 2F, 31, 00, 00, 00, 4D, 0A, 00, 00, 00, 01, 03, 00, 05, 6E, 5F, 78, 6D, 6C, 0F, 00, 00, 00, 2A, 3C, 72, 6F, 6F, 74, 3E, 3C, 63, 68, 69, 6C, 64, 20, 69, 64, 3D, 22, 61, 76, 6D, 31, 22, 3E, 74, 65, 73, 74, 3C, 2F, 63, 68, 69, 6C, 64, 3E, 3C, 2F, 72, 6F, 6F, 74, 3E, 00, 09, 6E, 5F, 78, 6D, 6C, 5F, 72, 65, 66, 07, 00, 02, 00, 00, 09]

failures:
    avm1/xml_ref

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 5 filtered out; finished in 0.20s

error: test failed, to rerun pass `--test tests`

var payload = new Object();
payload.n_xml = new XML("<root><child id='avm1'>test</child></root>");
payload.n_xml_ref = payload.n_xml;
var nc = new NetConnection();
nc.connect("http://localhost:8000/");
var responder = new Object();
nc.call("test.avm1", responder, payload);

[danielhjacobs]

#124