Type.Recursive does not work with Type.Transform for StaticDecode

[joshuaavalon]

import { Type } from "@sinclair/typebox";

import type { StaticDecode, StaticEncode, TSchema } from "@sinclair/typebox";

const schema = Type.Recursive(self => Type.Object({
  a: Type.Number(),
  b: Type.Transform(Type.Union([self, Type.Null(), Type.Undefined()]))
    .Decode(v => v ?? undefined)
    .Encode(v => v)
}));

/**
type A = {
    a: number;
    b: ... | null | undefined;
}
 */
type A = StaticEncode<typeof schema>;

/**
type B = {
    a: number;
    b: undefined;
}
 */
type B = StaticDecode<typeof schema>;

You can see b is resolved to undefined even though it should be B | undefined.

[dearlordylord]

Hey, I worked on reproduction and my own report before finding there's a report already.

My issue seems to be the same. There's an additional issue reproduction I've prepared https://github.com/dearlordylord/typebox-recursion-transform-bug/blob/master/libs%2Ftypebox%2Fsrc%2Flib%2Ftypebox.ts

mport { Type, StaticDecode, Static } from '@sinclair/typebox';
import { Value } from '@sinclair/typebox/value';

const Recursion = Type.Recursive(Self => Type.Object({
  id: Type.String(),
  children: Type.Transform(
    Type.Array(Self)
  ).Decode((v/*inferred as never[];*/) => v).Encode(v => v),
}));

type Recursion = StaticDecode<typeof Recursion>;

const r: {children: never[]} = Value.Decode(Recursion, {
  children: [
    { children: [] },
    { children: [{ children: [] }] },
  ],
});

function test(node: Recursion) {
  const a: never[] = node.children[0];
  // @ts-expect-error
  const b = node.children[0].children[0].id;
}

when it comes to .Transform inside .Recursive, the type seems to be erased to never