Report a bug

I've been playing with arktype and trying to compose validators using preexisting types with type.declare .
When adding undefined this falls apart during compilation.

🔎 Search Terms

I didn't I asked a question on the discord server and it turned out to be a bug.
@ssalbdivad prompted me to create an Issue

🧩 Context

• ArkType version: 2.1.25
• TypeScript version (5.1+): 5.9.3

🧑‍💻 Repro

Playground Link: https://arktype.io/playground?code=import%2520%257B%2520type%2520%257D%2520from%2520%2522arktype%2522%250A%250A%250Atype%2520Member%2520%253D%2520%27a%27%2520%257C%2520%27b%27%2520%257C%2520undefined%253B%2520%252F%252F%2520withough%2520undefined%2520it%2520works%250Aconst%2520memberValidator%2520%253D%2520type.declare%253CMember%253E%28%29.type%28%2560%2522a%2522%2520%257C%2520%2522b%2522%2520%257C%2520undefined%2560%29%253B%250A%250Atype%2520Object%2520%253D%2520%257B%250A%2520%2520m%253A%2520Member%253B%250A%257D%253B%250Aconst%2520Thing%2520%253D%2520type.declare%253CObject%253E%28%29.type%28%257B%250A%2520%2520m%253A%2520memberValidator%252C%250A%257D%29%253B%250A%250Aconst%2520out%2520%253D%2520Thing%28%257B%2520m%253A%2520%27a%27%2520%257D%29%253B

import { type } from 'arktype';

type Member = 'a' | 'b' | undefined; // withough undefined it works
const memberValidator = type.declare<Member>().type(`"a" | "b" | undefined`);

type Object = {
  m: Member;
};
const objectValidator = type.declare<Object>().type({
  m: memberValidator,
});

const output = objectValidator({ m: 'a' });

Note

In the repro link the compilation issue is not visible, the behaviour can be observed here:
https://stackblitz.com/edit/vitejs-vite-cpr8tkpa?file=src%2Fmain.ts