Zod coerce does not work with remote function form

[regnstr]

Describe the bug

The example from the documentation (changed to zod instead of valibot):

import { z } from 'zod';
import { form } from '$app/server';

export const setCount = form(
	v.object({
		// Zod:
		count: z.coerce.number()
	}),
	async ({ count }) => {
		// ...
	}
);

Gives the following typescript error in my editor (VS Code):

No overload matches this call.
  Overload 1 of 3, '(validate: "unchecked", fn: (data: RemoteFormInput) => unknown): RemoteForm<RemoteFormInput, unknown>', gave the following error.
    Argument of type 'ZodObject<{ count: ZodCoercedNumber<unknown>; }, $strip>' is not assignable to parameter of type '"unchecked"'.
  Overload 2 of 3, '(validate: StandardSchemaV1<RemoteFormInput, Record<string, any>>, fn: (data: Record<string, any>) => unknown): RemoteForm<RemoteFormInput, unknown>', gave the following error.
    Argument of type 'ZodObject<{ count: ZodCoercedNumber<unknown>; }, $strip>' is not assignable to parameter of type 'StandardSchemaV1<RemoteFormInput, Record<string, any>>'.
      The types of '"~standard".types' are incompatible between these types.
        Type 'Types<{ count: unknown; }, { count: number; }> | undefined' is not assignable to type 'Types<RemoteFormInput, Record<string, any>> | undefined'.
          Type 'Types<{ count: unknown; }, { count: number; }>' is not assignable to type 'Types<RemoteFormInput, Record<string, any>>'.
            Types of property 'input' are incompatible.
              Type '{ count: unknown; }' is not assignable to type 'RemoteFormInput'.
                Property 'count' is incompatible with index signature.
                  Type 'unknown' is not assignable to type 'RemoteFormInput | FormDataEntryValue | FormDataEntryValue[] | RemoteFormInput[]'.ts(2769)

I'm not sure if this is an issue with zod or SvelteKit though...

Reproduction

Unfortunately I don't know how to reproduce this since the bug is just in typescript. Pasting the code above into a new sveltekit project .remote file should reproduce it.

Logs

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (16) x64 AMD Ryzen 7 7800X3D 8-Core Processor
    Memory: 33.79 GB / 63.22 GB
  Binaries:
    Node: 22.13.1 - C:\Program Files\nodejs\node.EXE
    npm: 10.9.2 - C:\Program Files\nodejs\npm.CMD
    pnpm: 10.10.0 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Chromium (140.0.3485.54)
    Internet Explorer: 11.0.26100.1882

Severity

annoyance

Additional Information

No response

[Rich-Harris]

Looking at the Zod docs I suspect it needs to be this:

z.coerce.number<string>()

Does that work?

[regnstr]

Yes, that works 👍. It's a little inconvenient to have to specify the input type but if that's how it has to be, then that's ok!

[dummdidumm]

we should adjust the documentation accordingly

[jippi]

Unfortunately, Zod 3 do not support the z.coerce.number<string> syntax, so svelte forms do not work with zod3 coerce, which might be worth calling out

The suggested syntax only works for Zod4, which might be worth calling out

Though I am curious why everything but form() have no problem with coerce calls 🤔

[sillvva]

Other remote functions receive JSON as an input, whereas form receives FormData which only has types: string | File | Blob. SvelteKit automatically coerces number and boolean checkbox fields, so your schema must have the following input types: string | string[] | number | boolean | File | File[].

Without specifying a type, z.coerce.number() has an input type of unknown.