[BUG] 1.4.12 regression on ArkType: TypeError: Cannot read properties of undefined (reading 'target')

[dcitron]

After upgrading to 1.4.12, hitting /docs/json on my elysia app spits out dozens of errors like this:

TypeError: Cannot read properties of undefined (reading 'target')
    at Object.output (/workspace/node_modules/@ark/schema/out/roots/root.js:45:67)
    at unwrapSchema (/workspace/node_modules/@elysiajs/openapi/dist/index.mjs:2959:48)
    at toOpenAPISchema (/workspace/node_modules/@elysiajs/openapi/dist/index.mjs:3268:26)
    at openAPISchema (/workspace/node_modules/@elysiajs/openapi/dist/index.mjs:10240:9)
    at handle (eval at composeHandler (file:///workspace/vgback/elysia.init.js:399:52), <anonymous>:26:13)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)

Reproduction

import { Elysia } from 'elysia';
import { openapi } from '@elysiajs/openapi';
import { type } from 'arktype';

const ResponseType = type({
  items: type({ id: 'string', name: 'string' }).array(),
});

new Elysia()
  .use(openapi())
  .get('/test', () => ({ items: [] }), {
    response: ResponseType,
  })
  .listen(3000);

Then visit http://localhost:3000/openapi/json

Error

TypeError: undefined is not an object (evaluating 'opts.target')
      at output (@ark/schema/out/roots/root.js:45:62)
      at unwrapSchema (@elysiajs/openapi/dist/index.mjs:2959:48)
      at toOpenAPISchema (@elysiajs/openapi/dist/index.mjs:3268:26)
      at openAPISchema @elysiajs/openapi/dist/index.mjs:10240:9)
      at handle (node_modules/elysia/dist/bun/index.js:6:76)
      at handle (elysia/dist/bun/index.js:6:80)

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🔗 Similar Issues

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• Typebox [0.34.38] is not compatible with Elysia elysia#1296
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• gabrieljablonski
• DaxServer

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[dcitron]

This could be the cause:

The unwrapSchema function (introduced in the "support standalone schema" commits on Dec 18) calls schema.input(opts) / schema.output(opts) expecting TypeBox-style schemas.

ArkType schemas have .input() and .output() methods, but they expect different arguments — they're accessors for the schema's input/output types, not transformation functions that take an opts object with a target property.

So perhaps it could be fixed by adding ArkType detection before calling .input()/.output():

// Check if this is an ArkType schema (has ~standard property)
if ('~standard' in schema) {
  // ArkType - use toJSONSchema() directly
  return schema.toJSONSchema?.() ?? schema;
}

// Otherwise proceed with existing TypeBox/Elysia logic

Or check if input/output are functions before calling them with arguments?

[dcitron]

FYI I added simple reproduction steps in the original description.