Zod resolver infered types are incorect since 4.1.0

[vanwalj]

Describe the bug
zodResolver now infer schema type which is great but unfortunately produces invalid typings

To Reproduce
Setup a project using zod, typescript and react-hook-form, create a simple form such as

const FORM_SCHEMA = z.object({
  s: z.string(),
});

const App = () => {
  const form = useForm({
    resolver: zodResolver(FORM_SCHEMA),
  });

  const [s] = form.watch(["s"]);

  console.log(s);
  ...
};

Codesandbox link (Required)
https://codesandbox.io/p/sandbox/wispy-wildflower-fk7ymp?file=%2Fsrc%2Findex.js%3A11%2C4

Expected behavior
s is typed as string but should be typed as string | undefined

Screenshots

Desktop (please complete the following information):

• OS: macOS 15.3
• Browser any
• Versions: zod 3.24.2, react-hook-form 7.54.2, @hookform/resolvers 4.1.0

Additional context

I personally used to provide useForm both TFieldValues and TTransformedValues typings so that everything is properly typed such as

const form = useForm<
    DeepPartial<z.input<typeof SCHEMA>>,
    unknown,
    z.output<typeof SCHEMA>
  >({
    resolver: zodResolver(SCHEMA),
  });

but even this is now impossible since types are clashing: Types of parameters 'values' and 'values' are incompatible

Thank you 🙇

[ruiaraujo012]

I'm facing the same issue but for the valibot resolver, the cause is probably the same.

[an-tran511]

I have similar issue

[pgjones]

I think react-hook-form/react-hook-form#11951 is required before this repository can be updated in a similar manner to fix this bug.

Edit: I've written up how I type zod form validators here which should give context to why I think the input and output types are required in react-hook-form and in this repo.

[jorisre]

Got it, thanks for reporting this. I'm looking into it.

[AnderssonPeter]

@jorisre I'm not 100% sure but woulden't it be more correct to use z.input instead of z.infer?
Let's say i have the following schema:

const schema = z
    .object({
        title: z
            .string()
            .optional()
            .transform(v => v ?? "")
            .pipe(
                z
                    .string()
                    .nonempty("Required"))
    });

    // { title: string; }
    type infer = z.infer<typeof schema>;
    // { title: string | undefined; }
    type input = z.input<typeof schema>;
    // { title: string; }
    type output = z.output<typeof schema>;

The idea here is that undefined is allowed as input value but not as output.

Not 100% sure this is the same issue but it might be?

[Omelyan]

Because the authors after the years still do not understand what a Form is.
A Form is the transformation (and possibly validation) of an Input into an Output!

Why is this code logically absolutely correct, yet contains a TypeScript error?!

and, on the other hand, why does the following code, despite having no errors, not work?!

I'm over it. Just don't use the lib.

[diegotraid]

Because the authors after the years still do not understand what a Form is. A Form is the transformation (and possibly validation) of an Input into an Output!

Why is this code logically absolutely correct, yet contains a TypeScript error?!

and, on the other hand, why does the following code, despite having no errors, not work?!

I'm over it. Just don't use the lib.

Maybe helping out the useForm function by definining input and output types would help:

const schema = z
  .object({
    id: z.number(),
  })
  .transform((v) => ({
    name: `my id is ${v.id}`,
  }));

type SchemaInput = z.input<typeof schema>;
type SchemaOutput = z.output<typeof schema>;

const form = useForm<SchemaInput, unknown, SchemaOutput>({
  resolver: zodResolver(schema),
  values: {
    id: 1, // No TS error since id is part of the input schema
  },
});

form.handleSubmit((output) => console.log(output))();

Outputs: {name: 'my id is 1'}

const schema = z
  .object({
    id: z.number(),
  })
  .transform((v) => ({
    name: `my id is ${v.id}`,
  }));

type SchemaInput = z.input<typeof schema>;
type SchemaOutput = z.output<typeof schema>;

const form = useForm<SchemaInput, unknown, SchemaOutput>({
  resolver: zodResolver(schema),
  values: {
    name: 'yeah right', // TS Error: Object literal may only specify known properties, and 'name' does not exist in type '{ id: number; }'
  },
});

form.handleSubmit((output) => console.log(output))(); // No output since submitting fails

[Omelyan]

@diegotraid
how about that..? :))

[jorisre]

Hello everyone, as I mentioned earlier, I'm currently working on it. I kindly ask for your patience, and if you have suggestions, feel free to open a pull request instead of expressing dissatisfaction.