ZodSchema not strictly parsing union types

[simeng-li]

I was trying to infer a ZodType from a well-defined typescript type: e.g.

type Temp = {
 a?: string | null;
}

The following ZodType definition is considered as a valid ZodSchema type.

const guard: ZodSchema<Temp> = z.object({
 a: z.string();
})

What I am expected is it should throw an error like ZodString type is not assignable to ZodOptional<ZodNullable<ZodString>>

only

const guard: ZodSchema<Temp> = z.object({
 a: z.string().nullable().optional();
})

Is strictly allowed.

Wondering whether this is by design or not?

Thanks~

[JacobWeisenburger]

I can't speak to if this was by design or not, but this code might help you.

type ShapeFromType<Type extends Record<string, any> | undefined> =
    Type extends undefined ? never : {
        [ key in keyof Type ]-?:
        unknown extends Type[ key ] ? z.ZodType<Type[ key ]> | z.ZodOptional<z.ZodType<Type[ key ]>> :
        undefined & null extends Type[ key ] ?
        z.ZodNullable<z.ZodOptional<z.ZodType<Type[ key ]>>> | z.ZodOptional<z.ZodNullable<z.ZodType<Type[ key ]>>> :
        undefined extends Type[ key ] ? z.ZodOptional<z.ZodType<Type[ key ]>> :
        null extends Type[ key ] ? z.ZodNullable<z.ZodType<Type[ key ]>> :
        z.ZodType<Type[ key ]>
    }

type Temp = {
    a?: string | null
}

const guard = z.object<ShapeFromType<Temp>>( {
    a: z.string().nullable().optional()
} )