Generalizing merging/ extending in a function

[czottmann]

Hi. I use zod to validate incoming API calls. Many of these calls are similar, all share this common foundation:

const incomingBaseParams = z.object({
  action: z.string(),
  "x-error": z.string().url().optional(),
  "x-success": z.string().url().optional(),
})

On top of that, a few of the API endpoints accept one of three parameters, file, uid, or periodic-note. Depending on the passed-in parameter, an internal object is looked up. So I figured I could write a function which extends the foundation, implements the one-of-three-params check, and enhances the output with a _computed key that stores a reference to the aforementioned internal object. Different endpoints have different additional parameters.

function targetedNoteSchema(additionalParams: z.AnyZodObject) {
  return incomingBaseParams
    .merge(additionalParams)
    .extend({
      file: z.string().optional(),
      uid: z.string().optional(),
      "periodic-note": z.enum(["daily", "weekly"]).optional(),
    })
    .refine(
      (obj) =>
        ["file", "uid", "periodic-note"]
          .filter((key) => key in obj).length === 1,
      { message: "Either 'file', 'uid', or 'periodic-note' must be provided" },
    )
    .transform((incoming) => {
      // Transformation happening here (this works)

      return {
        ...incoming,
        _computed: {
          someValue: "sure",
        },
      };
    });
}

The problem I can't figure out: when I use the function, neither the keys from incomingBaseParams nor these of obj are part of the result's type.

const additionalParams = z.object({
  silent: z.boolean(),
  "x-error": z.string().url(),
  "x-success": z.string().url(),
});
const getParams = targetedNoteSchema(additionalParams);
type GetParams = z.output<typeof getParams>;

// type GetParams = {
//     _computed: {
//         inputKey: string;
//         path: string;
//         pathExists: boolean;
//     };
//     file?: unknown;
//     uid?: unknown;
//     "periodic-note"?: unknown;
// }

I suspect that I'm just holding it hilariously wrong, nevertheless, I'm stuck. It's been a long week already, and I'd appreciate any help you folks might be able to give. Thanks in advance!