Avoid type widening with enum-typed values in FormValue

[tmcw]

The current generic type for FormValue is this:

export type FormValue<Schema> = Schema extends
	| string
	| number
	| boolean
	| Date
	| bigint
	| null
	| undefined
	? string | undefined

In this, if you have an enum or constant string type, then it will get widened into a string type. Turning Date and null types into string | undefined makes sense, but it is kind of just inconvenient to lose type information if you have an enum.

This tweaks the generic type so that if you have a type that extends string, then the FormValue generic uses that type instead of widening to string.

[edmundhung]

This is tricky... because conform does not validate the form value. The type you got is more or less a faith that the type should be mostly correct if you are using Conform properly. But it couldn't stop you from putting a hidden input with an invalid enum which will be reflected on form value regardless. 😅

Maybe it is alright to made the same assumption with enum here... What do you think?

[jansedlon]

I think that that's what typescript's about, constraining things to be something we want even though Javascript allows to do about anything. If you use typescript incorrectly or if you make a mistake and mistakenly widen a type to things you don't want to, you will fuck yourself up anyway :D

On the other hand since inputs are strings / files by design.. I would slightly incline to have it widened and put the responsibility on the developer. I know, I also don't like not having the convenience but.. It forces the developer to put more checks in place.

[lifeiscontent]

might be worth using the string interpolation type:

https://www.typescriptlang.org/play?#code/C4TwDgpgBAYg9gJwLYDUCGAbArhAPAZQGMALCJNAPigF4ojTyoIAPYCAOwBMBnAKCigAfKN2AIAluwDm-IVHZYkAIwgJZwpeKmTg6qErhwMENOz0KMGPVi4QAZpIidZAfigADACQBvemTQAvu5yNpz2js4CAFx0JP5MrBw8sOLGrinGIbYO7E6yMbkAbqoA3Ly8oJAZEOjY0LTwyLU4uDCpEBRlldD4YpJSzfWwiKiYLaIS0p0V4D190gCq7OJw7IM0w01jeABEAIw7cjsATDvT3VAAcooqCOsNI4O4Csqq57NXN6pLK2vbG41RnVcHs5MdprwAPSQqA2bhYBDQcR2KDAYjibhQADucCwGE4+mgLEghDYnAANPosMAoCBcVApBAaWjoNpRAA6GZVABCWgAkuxgPdNkCWpptIL3jz+YKfqthYCnnt2GD2FLoEswjknArHttcKFwrlOOrPpZdVtgRYMNMgA