Does not generate from opds2 schema

[asm0dey]

First of all, thank you very much for your work! I usually use an excellent app.quicktype.io to create quick demonstrations! Your language support is just outstanding!

However, today I wanted to use it for my pet project and wasn't able to generate classes from https://raw.githubusercontent.com/opds-community/drafts/master/schema/feed.schema.json.

I had to fix several things in external schemas to make it correct, but now it should generate and, for example, https://www.jsonschema2pojo.org/ can generate classes for Java, which makes me think that it should be possible to generate classes for other languages too.

Could you check it please?

[asm0dey]

Folks, I would appreciate any input on this. Is it even fixable?

[schani]

Triage sweep note (assisted by Claude): confirmed reproducible on current master (v23.3.0, 68ecb284).

Root cause

quicktype crashes with Error: Maximum call stack size exceeded on the OPDS 2.0 feed schema (and the Readium webpub-manifest schema it pulls in) for every target language (tried java/typescript/csharp/python).

The overflow is unbounded recursion in the graph-rewriting fixpoint used to resolve intersections/flatten unions (Run.ts:310 drives resolveIntersections/flattenUnions, which call into GraphRewriteBuilder's reconstitute* methods in packages/quicktype-core/src/Type/GraphRewriting.ts and packages/quicktype-core/src/Type/TypeBuilder.ts). The cyclic allOf/anyOf structure in this schema graph makes that recursion effectively unbounded — raising --stack-size to 50000/100000 doesn't help; it just delays the crash past a 300s timeout instead of resolving. This is the same architectural class of bug as the still-open #1376 (FHIR schemas), not something specific to OPDS.

Secondary bug found while investigating: quicktype's own remote-URL fetching is also broken on master independent of this schema — pointing --src at a URL now fails earlier with Internal error: Defined value expected, because NodeIO's readableFromFileOrURL passes undici's WHATWG stream to getStream (inputStream.once is not a function), and FetchingJSONSchemaStore swallows the resulting error. That's worth a separate issue if it isn't tracked already — it means nobody can currently repro this one straight from the URL in the OP without hitting a different, more confusing error first.

Assessment

• Severity: high — total failure (crash, not just wrong output) on a real-world, non-pathological schema; same root cause likely affects other schemas with cyclic composition.
• Difficulty: hard — fixing requires bounding/memoizing the reconstitute recursion in the graph rewriter, which is core architecture shared by every input path (JSON Schema, GraphQL, TypeScript). Not a local patch.

Reproduction

node dist/index.js --lang java --src-lang schema --src feed.schema.json

Original source: https://raw.githubusercontent.com/opds-community/drafts/master/schema/feed.schema.json (plus its $refed Readium webpub-manifest sub-schemas). Because of the remote-fetch bug above, and because fetching resolves $refs against $id/base URLs that make an isolated repro fiddly, I mirrored the current schema graph locally with $refs localized to sibling files and $ids stripped, and confirmed the crash persists on that mirror: gist with the mirrored schema files (base64 tar.gz — base64 -d file | tar xzf -, then run quicktype with --src feed.schema.json from that directory).

[asm0dey]

This is a nice assessment, but it doesn't give much hope, does it?

[asm0dey]

The schema is not a draft anymore, so it is stored here: https://github.com/opds-community/specs/tree/master/schema

[asm0dey]

It seems my Claude found a solution, will verify and contribute soon