Typing arktype with morphs

[tpetry]

Hi,
I am migrating a complex zod validation to arktype and use that opportunity to refactor some stuff. The basic premise is that some module is creating parsers to be consumed by other modules.

In some cases the inference with morphs does not work. A parser is always meant to parse unknown types into something. But here the typing of the morph (which extends the succeeded validation?) is used as the input type instead of the regular unknown.

import { type } from "arktype"
import type { Type, Out } from "arktype";

type NullableStr = string | null;

// TS2322: Type Type<(In: string | null) => Out<NullableStr>, {}> is not assignable to type Type<(input: unknown) => Out<NullableStr>, {}>
//   Types of property t are incompatible.
//     Type (In: string | null) => Out<NullableStr> is not assignable to type (input: unknown) => Out<NullableStr>
//       Types of parameters In and input are incompatible.
//         Type unknown is not assignable to type string | null
const parseStr: Type<(input: unknown) => Out<NullableStr>> = type("string.trim | null").pipe((value: NullableStr): NullableStr => value === '' ? null : value);