Arktype does not work in Expo, when Disjoint.withPrefixKey is called internally

[davisriedel]

Report a bug

The same issue that was reported in issue #1027 and fixed in arktype version 2.1.4 for Disjoint.invert is also present in Disjoint.withPrefixKey (and not yet fixed, as of version 2.2.3). Hermes does not preserve Array subclasses through Array.prototype.map.

🔎 Search Terms

Expo, React Native, Hermes

🧩 Context

Arktype 2.2.3
Typescript 7.0.2
Expo SDK 57
React Native 0.86.2
Hermes 0.16

🧑‍💻 Repro

The issue can be reproduced with any union of two object literals whose branches are disjoint at a key. For example:

import { type } from "arktype"

// TypeError: undefined is not a function
const result = type({
      results: "Record<string, unknown>[][]",
      success: "true"
}).or({
      errors: "string[]",
      results: "Record<string, unknown>[][]",
      success: "false"
})

On Expo SDK 57 / React Native 0.86.2 / Hermes 0.16, this throws TypeError: undefined is not a function at the .or(...) call at runtime.

Suggested fix

We can use a similar fix/workaround like @dolgim suggested in #1027. I patched arktype locally with the following, and can confirm that it works:

withPrefixKey(key: PropertyKey, kind: Prop.Kind): Disjoint {
      const result = this.map(entry => ({
              ...entry,
              path: [key, ...entry.path],
              optional: entry.optional || kind === "optional"
      }))

      // Workaround for Hermes
      if (!(result instanceof Disjoint)) return new Disjoint(...result)

      return result
}

However, we might need a solution that avoids any similar issues. E.g. we could make Disjoint no longer extend Array.

[pullfrog]

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