Types for helper functions for working with schemas?

[msakrejda]

I'm trying to write a helper function for wrapping schema parsing in my app, and I'm having some trouble understanding how to handle type definitions. My function is something like

function parseInput(input, schema) {
  const processedInput = ... // some pre-processing omitted

  return schema.safeParse(processedInput);
}

I tried a type definition like

function parseInput<S extends ZodRawShape, T extends ZodObject<S>>(input: MyInputType, schema: T): ReturnType<T['safeParse']> {
  const processedInput = ... // some pre-processing omitted

  return schema.safeParse(processedInput);
}

(my schema is always an object and I need to access some ZodObject fields during this step), but I get the rather cryptic

Type 'SafeParseReturnType<{ [k in keyof addQuestionMarks<{ [k in keyof S]: S[k]["_input"]; }>]: addQuestionMarks<{ [k in keyof S]: S[k]["_input"]; }>[k]; }, { [k in keyof addQuestionMarks<{ [k in keyof S]: S[k]["_output"]; }>]: addQuestionMarks<...>[k]; }>' is not assignable to type 'ReturnType<T["safeParse"]>'.
  Type 'SafeParseSuccess<{ [k in keyof addQuestionMarks<{ [k in keyof S]: S[k]["_output"]; }>]: addQuestionMarks<{ [k in keyof S]: S[k]["_output"]; }>[k]; }>' is not assignable to type 'ReturnType<T["safeParse"]>'.ts(2322)

Any ideas?

[JacobWeisenburger]

I can't figure out why you are getting that error. But if you are wanting to do some preprocessing I would recommend using z.preprocess

const schema = z.object( {
    foo: z.string(),
    bar: z.literal( 'bar' ),
} )
type Schema = z.infer<typeof schema>
// type Schema = {
//     foo: string
//     bar: "bar"
// }

const preprocessedSchema = z.preprocess( input => {
    const processedInput = ... // some pre-processing omitted
    return processedInput
}, schema )
type PreprocessedSchema = z.infer<typeof preprocessedSchema>
// type PreprocessedSchema = {
//     foo: string
//     bar: "bar"
// }

[msakrejda]

Great, thanks for the suggestion.