Union gives errors on last type only

[rsinohara]

Let's say I have a Union of two types. I expect my value to match the first type, but something is wrong.
The problem is Zod only reports the error on the second type, so that doesn't help me to debug what is wrong in my first type.

Am I missing something? Right now (just starting) I remove the union just for debugging, but that will not be possible at scale.

[scotttrinh]

@rsinohara it's a little confusing because it's an array of arrays, but you should see something from your target schema reporting errors in the list of issues. feel free to post an example here!

[rsinohara]

I see, it does get complex.
I was only thinking of the errors I encountered so far (and I am parsing many already existing objects).

But just out of curiosity. To me the annotation there wouldn't be con C, but on the object itself, something line

{
  c: 42 
} // Could not match to any union type

I will get back to thinking about this once I learn more about what types of errors can happen.

[scotttrinh]

I guess the point is that error doesn't tell you anything. Why didn't it match? It's about as helpful as result.success === false. Is it just missing an a or a b property?

[rsinohara]

True.
My main idea was to place the error inside the evaluated object. Mostly because in a large object, even the non specific error message is better close to where it happens. For sure improving the intelligence around the errors would also be great.

Thanks for looking into it. I'll keep it in mind and see if something comes out of it.

[colinhacks]

There is detailed error reporting with unions that describes exactly why each element failed to parse the input. @rsinohara you'll have to provide a code example if you still think something is behaving unexpectedly.

const schema = z.union([
  z.object({ a: z.string() }),
  z.object({ b: z.string() }),
]);

console.log(schema.safeParse({ c: 42 }));
/*
ZodError: [
  {
    "code": "invalid_union",
    "unionErrors": [
      {
        "issues": [
          {
            "code": "invalid_type",
            "expected": "string",
            "received": "undefined",
            "path": [
              "a"
            ],
            "message": "Required"
          }
        ],
        "name": "ZodError"
      },
      {
        "issues": [
          {
            "code": "invalid_type",
            "expected": "string",
            "received": "undefined",
            "path": [
              "b"
            ],
            "message": "Required"
          }
        ],
        "name": "ZodError"
      }
    ],
    "path": [],
    "message": "Invalid input"
  }
]
*/

[rsinohara]

Hi Colin, that is what I see, all good.
I was just asking if there was any other way to format the error. To me, they would be more useful if shown as 'annotation' in the original object being parsed, so I wanted to make sure there were no other formatting options available.

I will be doing a lot of huge object schemas, so if there is a chance this could work let me know and I can play with it.

[rsinohara]

Actually @colinhacks I have one specific case where I only get errors on the second union type.

Is this behavior known or expected?

This schema is defined by export const ProductRowListSchema = z.array(z.array(CiSchema.or(ProductSchema)));
Funny enough, changing the order of the union doesn't help.
This particular element was expected to be a 'product'. It fails because a nested schema should be nullable. But I only ever see errors for the CISchema part.

{
    "issues": [
        {
            "code": "invalid_union",
            "unionErrors": [
                {
                    "issues": [
                        {
                            "code": "invalid_type",
                            "expected": "content_infusion",
                            "received": "product",
                            "path": [0, 0, "type"],
                            "message": "Expected content_infusion, received product"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "string",
                            "received": "undefined",
                            "path": [0, 0, "id"],
                            "message": "Required"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "ci_collage",
                            "received": null,
                            "path": [0, 0, "subtype"],
                            "message": "Expected ci_collage, received null"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "object",
                            "received": "undefined",
                            "path": [0, 0, "image"],
                            "message": "Required"
                        }
                    ],
                    "name": "ZodError"
                },
                {
                    "issues": [
                        {
                            "code": "invalid_type",
                            "expected": 3,
                            "received": 1,
                            "path": [0, 0, "width"],
                            "message": "Expected 3, received 1"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "string",
                            "received": "object",
                            "path": [0, 0, "content"],
                            "message": "Expected string, received object"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "content_infusion",
                            "received": "product",
                            "path": [0, 0, "type"],
                            "message": "Expected content_infusion, received product"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "string",
                            "received": "undefined",
                            "path": [0, 0, "id"],
                            "message": "Required"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "ci_image",
                            "received": null,
                            "path": [0, 0, "subtype"],
                            "message": "Expected ci_image, received null"
                        },
                        {
                            "code": "invalid_type",
                            "expected": "object",
                            "received": "undefined",
                            "path": [0, 0, "image"],
                            "message": "Required"
                        }
                    ],
                    "name": "ZodError"
                }
            ],
            "path": [0, 0],
            "message": "Invalid input"
        }
    ],
    "name": "ZodError"
}

[colinhacks]

Looks like unionErrors contains two elements, the first corresponds to CiSchema and the second corresponds to ProductSchema.

[rsinohara]

The two errors are from content infusion schema error, there are just two of them. CiSchema is itself an union. The error for product is really not there.

This is consistent, I am constantly running the same check but filtering only products, then I get the correct errors.