SyntaxError when using zod `.preprocess()`

[binajmen]

Describe the bug

SyntaxError when using zod .preprocess().

Schema seems to work correctly when using zod .parse(). I noticed the same schema doesn't seem to be supported when used with getParamsOrFail().

Steps to Reproduce the Bug or Issue

const schema = z.object({
  id: z.string(),
  intervals: z.preprocess(
    (val) => (typeof val === "string" ? JSON.parse(val) : []),
    z.array(
      z.object({
        // id: z.number(),
        day: z.number().min(0).max(6),
        from: z.string().regex(/^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/),
        to: z.string().regex(/^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/),
      })
    )
  ),
  intervalIds: z.preprocess(
    (val) => (typeof val === "string" ? JSON.parse(val) : []),
    z.array(z.number())
  ),
});

const intervals = formData.get("intervals");
const intervalIds = formData.get("intervalIds");
console.log({ intervals, intervalIds });

// works ✅ 
const dataZod = schema.parse({ id: "test", intervals, intervalIds });
console.log({ dataZod });

// throws error 🔴 
const data = await getParamsOrFail(formData, schema);
console.log({ data });

Output:

{
  intervals: '[{"id":1,"day":1,"from":"07:00","to":"23:30"},{"id":2,"day":2,"from":"07:00","to":"23:30"},{"id":3,"day":3,"from":"07:00","to":"23:30"},{"id":4,"day":4,"from":"07:00","to":"23:30"},{"id":5,"day":5,"from":"07:00","to":"23:30"},{"id":6,"day":6,"from":"07:00","to":"23:30"}]',
  intervalIds: '[1,2,3,4,5,6]'
}
{
  dataZod: {
    id: 'test',
    intervals: [ [Object], [Object], [Object], [Object], [Object], [Object] ],
    intervalIds: [ 1, 2, 3, 4, 5, 6 ]
  }
}
SyntaxError: Unexpected token U in JSON at position 0
    at JSON.parse (<anonymous>)

Expected behavior

{
  data: {
    id: 'test',
    intervals: [ [Object], [Object], [Object], [Object], [Object], [Object] ],
    intervalIds: [ 1, 2, 3, 4, 5, 6 ]
  }
}

[binajmen]

FYI, the root error is:

Error: Unexpected type ZodObject for key intervals

From what I read, I believe .preprocess() is not supported (yet)? https://github.com/kiliman/remix-params-helper/blob/76115b81a20f1779fec9bfe9f6ac37d4e02a8228/src/helper.ts#L206-L236

First param of .preprocess() is a type coercion function: https://github.com/colinhacks/zod#preprocess

[kiliman]

I see. Looks like it's not handled properly. Thanks for your test case. I'll work to support it.

[binajmen]

Thank you, I'm not quite sure how to handle this case, otherwise I would have tried to make a PR.