Add nullableInput

[ArnaudBarre]

Hello and thanks for this lib that has completely changed my way of doing client and server side validations.

One pattern that I'm missing is the ability to change the input type while keeping the output type strict. This PR includes my most needed one: Adding nullable type on the input.

Why?

I'm using schema["_input"] type to strongly type the initial values of my form, and some values are required but can't have a meaningful default (like choosing an entity from a list) and are set to null.

Current solution

export const addNullInput = <A, B, C>(value: ZodType<A, B, C>) =>
  value
    .nullable()
    .refine((v) => v !== null, "Required")
    .transform((v) => v!);

The problem is it creates some runtime and type-checking overhead that could be simplified with a support from the lib.

Related

#213

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[colinhacks]

Interesting use case! This was a tricky one but I found a good approach. It recently because possible to add issues inside transforms, similar to superRefine, which unlocks a cleaner approach to this problem:

  const noNull = <T>(val: T | null, ctx: z.RefinementCtx) => {
    if (val === null) {
      ctx.addIssue({
        code: z.ZodIssueCode.invalid_type,
        expected: z.ZodParsedType.string,
        received: z.ZodParsedType.null,
        message: "Required",
      });
    }
    return val!;
  };
  const schema = z.number().nullable().transform(noNull);

You can define noNull somewhere and import it wherever it's needed. Because it's generic, it can be used on any nullable schema and the input/output types will be what you expect. I think this is cleaner than adding an additional method.