[UInputDate] Unable to distinguish between empty and incomplete date (no partial value emitted)

Environment

Operating system	Linux 6.6.87.2-microsoft-standard-WSL2
CPU	Intel(R) Core(TM) i7-10610U CPU @ 1.80GHz (4 cores)
Node.js version	v24.13.0
nuxt/cli version	3.34.0
Package manager	npm@10.9.7
Nuxt version	4.4.2
Nitro version	2.13.2
Builder	vite@7.3.1
Config	app, compatibilityDate, css, devtools, extends, i18n, modules, runtimeConfig, ssr, ui
Modules	@nuxt/eslint@1.15.2, @nuxt/ui@4.6.0, @nuxtjs/i18n@10.2.4

Is this bug related to Nuxt or Vue?

Nuxt

Package

v4.x

Version

v4.4.2

Reproduction

https://play.ui.nuxt.com/#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

Description

The UInputDate component only emits a value when all three fields (day, month, year) are fully filled in. If only one or two fields are populated, the component emits no value at all — behaving identically to a completely empty input.

Use case

I have an optional date field with the following validation rules:

✅ No error if the field is completely empty (since it's optional)
❌ Show an "invalid" error if the date is incomplete (e.g., only day and month are filled)
❌ Show a "future" error if the date is after today

Problem

When a user partially fills in the date (e.g., enters a day and a month but leaves the year empty), the component emits undefined / no value — exactly the same as if nothing had been entered at all.

This makes it impossible to differentiate between:

The user hasn't entered anything → no error (optional field)
The user has started entering a date but left it incomplete → should show a validation error
Similarly, if a user fills in all three fields and then clears one of them, the value is completely lost, as if the input was never touched.

Expected behavior

It would be helpful if UInputDate could emit some kind of partial/incomplete state (e.g., a partial object, an "incomplete" flag, or an invalid Date) so that consumers can distinguish between "no input" and "incomplete input" for validation purposes.

Question

Is this behavior (only emitting a value when the date is fully complete) intentional by design? If so, is there a recommended workaround to handle the "incomplete date" validation case?

Additional context

No response

Logs

Start with the UInputDate implementation and the linked Nuxt UI reproduction, comparing emitted values for empty, partially filled, and cleared fields. Done means the component behavior or an agreed workaround lets consumers distinguish a completely empty optional date from an incomplete date.