Issue with Dates and zod (loadVendor)

[jofflin]

Hi,
I automatically generate my schema for my endpoints. My issue: The types are dates and the toJsonSchema for zod v4 doesnt allow Dates (https://zod.dev/json-schema#unrepresentable)
There is a workaround to convert Dates to string date-time (https://zod.dev/json-schema#override) But i don't know understand on how to use the loadVendor correctly.
Currently my loadVendor looks like this:
loadVendor('zod', { toOpenAPISchema: (schema, context) => convertToOpenAPISchema( toJSONSchema(schema, { io: 'input', override: (ctx) => { const def = ctx.zodSchema._zod.def; logger.info('def', { def }); if (def.type === 'date') { ctx.jsonSchema.type = 'string'; ctx.jsonSchema.format = 'date-time'; } }, }) as Omit<ReturnType<typeof toJSONSchema>, 'exclusiveMaximum'> & { exclusiveMaximum?: number; }, context ), });

I also need to make the type casting because the JsonSchemas dont align.
Current versions:
zod 4.1.12
hono 4.9.8
hono-openapi 1.1.0

What I need:
Instructions on how to use loadVendor correctly (Do I need to inject is somewhere?)

Ideal solution:
A option for hono-openapi to automatically convert specific types to something else.
Something like
openAPIRouteHandler(app, { overrides: { date: (d) => {} } }

[jofflin]

I managed to get it working by adding unrepresentable: 'any', To it.
I wasnt reading the zod documentation correctly
https://zod.dev/json-schema#override:~:text=Note%20that%20unrepresentable%20types%20will%20throw%20an%20Error%20before%20this%20functions%20is%20called.%20If%20you%20are%20trying%20to%20define%20custom%20behavior%20for%20an%20unrepresentable%20type%2C%20you%27ll%20need%20to%20use%20set%20the%20unrepresentable%3A%20%22any%22%20alongside%20override.

For anyone with the same issue:
loadVendor('zod', { toOpenAPISchema: (schema, context) => convertToOpenAPISchema( toJSONSchema(schema, { io: 'input', unrepresentable: 'any', override: (ctx) => { const def = ctx.zodSchema._zod.def; if (def.type === 'date') { logger.info('def', { def }); ctx.jsonSchema.type = 'string'; ctx.jsonSchema.format = 'date-time'; } }, }) as Omit<ReturnType<typeof toJSONSchema>, 'exclusiveMaximum'> & { exclusiveMaximum?: number; }, context ), });

However, maybe someone can help me with getting the TS types to work

[feychenie]

depending on your use-case, you could use z.iso.date() (or z.iso.datetime()) instead.
https://zod.dev/json-schema?id=string-formats

[jofflin]

Yeah, that is what i thought. But i want to work with dates after validate safeParse on the schema in the backend. Having the instantiate all Date() is annoying since the api gives me Date already and then zod thinks that it is a string.
FYI:

z.coerce
  .date<Date>()
  .transform((date) => new Date(date))

This is my current workaround

[nemvince]

@jofflin
Could you please expand a bit on where and how loadVendor is used within the app? Thanks!

[jofflin]

@nemvince sure.
I use it in the root app.ts (my entry point of hono)

[imports]

loadVendor('zod', {
  toOpenAPISchema: (schema, context) =>
    convertToOpenAPISchema(
      // biome-ignore lint/suspicious/noExplicitAny: THis is a library version mismatch
      toJSONSchema(schema as any, {
        io: 'input',
        unrepresentable: 'any',
        override: (ctx) => {
          const def = ctx.zodSchema._zod.def;
          if (def.type === 'unknown') {
            ctx.jsonSchema.type = 'boolean';
          }
          if (def.type === 'date') {
            ctx.jsonSchema.type = 'string';
            ctx.jsonSchema.format = 'date-time';
          }
        },
      }) as Omit<ReturnType<typeof toJSONSchema>, 'exclusiveMaximum'> & {
        exclusiveMaximum?: number;
      },
      context
    ),
});
const app = new Hono()
app.use(...)
app.route(...)

serve({
  fetch: app.fetch,
  port,
});

export default app;

I think my issue can be solved using zod (v4) codecs (https://zod.dev/api#codecs). But somehow that doesnt work as expected.
I need the above overrides for boolean (queryparams are always strings) and date to isodate.