Environment

• Operating System: Darwin
• Node Version: v24.5.0
• Nuxt Version: 4.1.2
• CLI Version: 3.28.0
• Nitro Version: 2.12.5
• Package Manager: pnpm@10.15.0
• Builder: -
• User Config: compatibilityDate, ssr, alias, typescript, nitro, vite, modules, i18n, css, hooks, icon, runtimeConfig, $development, $test
• Runtime Modules: @nuxt/icon@2.0.0, @nuxt/ui@4.0.0, @nuxtjs/i18n@10.1.0, nuxt-auth-utils@0.5.24
• Build Modules: -

Is this bug related to Nuxt or Vue?

Nuxt

Package

v4.x

Version

4.0.0

Reproduction

https://codesandbox.io/p/devbox/epic-shamir-l5ccfm

Description

The code as simple as this:

<script setup lang="ts">
import * as z from "zod"
import { reactive } from "vue"

const fields = reactive({
  // In UI, the file may be selected or not.
  file: null as File | null,
})

const schema = z.object({
  // But the form is only considered valid when the file is selected.
  file: z.file(),
})
</script>

<template>
  <u-form :state="fields" :schema="schema">
    <u-file-upload v-model="fields.file" />
  </u-form>
</template>

Triggers type error:

Type '{ file: { readonly lastModified: number; readonly name: string; readonly webkitRelativePath: string; readonly size: number; readonly type: string; arrayBuffer: () => Promise<ArrayBuffer>; slice: (start?: number | undefined, end?: number | undefined, contentType?: string | undefined) => Blob; stream: () => ReadableSt...' is not assignable to type 'Partial<{ file: File; }>'

Expected: it's allowed to have a form with a schema that requires a file to be selected.

Additional context

In fact, I believe this is a much broader problem. Why is the state typed as Partial<InferInput<S>> in the first place? The type of the fields does not always match the schema. Basically, that's the point of schema in the first place, to perform validation — and not only value, but also the type. Consider number input value:

<script setup lang="ts">
import * as z from "zod"

const fields = reactive({
  // Type used by <input v-model="..." type="number">
  // It saves empty string for non-numbers.
  foo: "" as number | "",
})

const schema = z.object({
  // But we need the actual number for the input data.
  foo: z.number(),
})
</script>

<template>
  <u-form :state="fields" :schema="schema">
    <input v-model="fields.foo" type="number" />
  </u-form>
</template>

This leads to similar type error:

Type '{ foo: number | ""; }' is not assignable to type 'Partial<{ foo: number; }>'.
  Types of property 'foo' are incompatible.
    Type 'number | ""' is not assignable to type 'number | undefined'.
      Type 'string' is not assignable to type 'number'.

As I see it, state should be untyped/unknown.

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