Zod error messages are always "Invalid Input" in dev mode

[Gerschtli]

• Before posting an issue, read the FAQ and search the previous issues.

Description

When updating the zod library in the official example in https://github.com/ciscoheat/superforms-examples/tree/zod to any version >= 4.0.0 (tested right now with 4.1.5), the error messages are always "Invalid Input" when starting the application with pnpm dev.

Setting the locale explicitly with

import z from 'zod';

z.config(z.locales.de());

does not change this behaviour.

To see that this locale configuration has the correct effect, you can add

console.log(z.prettifyError(schema.safeParse({ name: '', email: '' }).error!));

at the start of the action.

Full +page.server.ts:

import { fail, message, superValidate } from 'sveltekit-superforms';
import { zod4 } from 'sveltekit-superforms/adapters';
import z from 'zod';
import { schema } from './schema.js';

z.config(z.locales.de());

export const load = async () => {
	return { form: await superValidate(zod4(schema)) };
};

export const actions = {
	default: async ({ request }) => {
		console.log(z.prettifyError(schema.safeParse({ name: '', email: '' }).error!));

		const form = await superValidate(request, zod4(schema));
		console.log(form);

		if (!form.valid) return fail(400, { form });

		return message(form, 'Form posted successfully!');
	}
};

This logs the following when submitting with empty form fields:

✖ Zu klein: erwartet, dass string >=2 Zeichen hat
  → at name
✖ Ungültig: E-Mail-Adresse
  → at email
{
  id: '9yawuu',
  valid: false,
  posted: true,
  errors: { name: [ 'Invalid input' ], email: [ 'Invalid input' ] },
  data: { name: '', email: '' }
}

What is kind of confusing to me is the fact, that this behaviour only appears when running pnpm dev. When served by pnpm build && pnpm preview, the logs (and also the frontend) show the correct messages:

✖ Zu klein: erwartet, dass string >=2 Zeichen hat
  → at name
✖ Ungültig: E-Mail-Adresse
  → at email
{
  id: '9yawuu',
  valid: false,
  posted: true,
  errors: {
    name: [ 'Zu klein: erwartet, dass string >=2 Zeichen hat' ],
    email: [ 'Ungültig: E-Mail-Adresse' ]
  },
  data: { name: '', email: '' }
}

[ghtx280]

@Gerschtli same issue, did you find a solution?

[Gerschtli]

Downgrading to latest zod v3 was the only fix. I still use the zod/v4 imports.