valid json, unable to convert to C# or nothing seems to happen, default settings

[stuyckp]

sync.txt
Hi,

I have used your online conversion tool for large json files successfully with sometimes minor modifications to the converters.
But the one attached does not convert. Or it seems so, because nothing happens.

Also when an enum conversion fails, I have modified the code to allow the exception pass the position where it fails :

using Newtonsoft.Json;

namespace StarTrekDataLibrary.Converters;

internal class JsonUnMarshalException : Exception
{
private readonly JsonReader _reader;
private readonly Type _type;
private readonly string? _value;

public JsonUnMarshalException(JsonReader reader,Type type,string? value)
{
    _reader = reader;
    _type = type;
    _value = value;
}

public override string Message => $"{Description} {Location}".TrimEnd();

private string Description => $"Cannot unmarshal type {_type} with value {_value}";
private string Location => _reader is IJsonLineInfo lineInfo && lineInfo.HasLineInfo() ? $"on line:{lineInfo.LineNumber}/{lineInfo.LinePosition}" : "";

}

Feel free to use that code or something similar. When processing large files it is really useful.

Thank you.

regards,
philip

[schani]

Triage note (systematic backlog sweep, assisted by Claude): confirmed reproducible on current master (v23.3.0, 68ecb284) with the attached sync.txt. The CLI crashes outright (the web app just swallows the error, which is why "nothing seems to happen").

Root cause: the input has sibling map-typed fields where one has entries and a nested one is empty, which trips map-type inference. UnifyClasses.ts:191 — the map branch of makeObject calls this.typeBuilder.getMapType(...) without passing along the pending forwardingRef, unlike the class/object branches a few lines below which do pass it. This trips the assertion in GraphRewriting.ts:370 during inferMaps, producing:

Error: Internal error: Type creator didn't return its forwarding ref.

Minimized repro (240 bytes) below. I verified a one-line fix (pass forwardingRef through to getMapType) against a patched build and both the minimized input and the full 1.1MB sync.txt then convert successfully.

Workaround: --no-maps.

Possibly a duplicate of #1320 and #1509 (same internal error, same code path).

Assessment:

• Severity: high — outright crash on valid JSON with no workaround-free path, and the web UI gives no feedback at all.
• Difficulty: easy — one-argument fix confirmed to resolve it, though the surrounding graph-rewriting machinery is brittle enough that it deserves a regression test.

Reproduction:

node quicktype --lang csharp --src-lang json min.json

{"mission_specs":{"1":{"objectives":{"1":{"rewards":{"11":{},"5":{}}}}},"2":{"objectives":{"1":{"rewards":{}}}}}}

The original attachment is here: https://github.com/quicktype/quicktype/files/10254254/sync.txt

(Separately, the enum-value line-number request in the issue is a minor, unrelated enhancement — NewtonSoftCSharpRenderer.ts:1103.)