[zod-openapi] unable to infer response type from c.status()

[fumieval]

When the response schemas are heterogeneous depending on the status code, the typechecker erroneously forces the response type to one of them.

Here's a reproducing example:

/*
JSONRespondReturn<{ id string; }, 200 | 404>' is not assignable to type 'TypedResponse<{ message string; }, 404, "json">
*/
import { describe, it } from 'vitest'
import { OpenAPIHono, createRoute, z } from '../src/index'

describe('createRoute', () => {
  const config = {
    method: 'get',
    path: '/',
    request: {},
    responses: {
      200: {
        content: {
          'application/json': {
            schema: z.object({
              id: z.string(),
            }),
          },
        },
        description: 'Retrieve a value',
      },
      404: {
        content: {
          'application/json': {
            schema: z.object({
              message: z.string(),
            }),
          },
        },
        description: 'Not found',
      },
    },
  } as const
  const route = createRoute(config)

  const app = new OpenAPIHono()
  app.openapi(route, async (c) => {
    if (Math.random() > 0.5) {
      c.status(404)
      return c.json({ message: 'Not found' })
    } else {
      c.status(200)
      return c.json({ id: '42' })
    }
  })

  it('should compile', () => {})
})

The workaround is to specifying the status code via the second argument.

  // this works
  app.openapi(route, async (c) => {
    if (Math.random() > 0.5) {
      return c.json({ message: 'Not found' }, 404)
    } else {
      return c.json({ id: '42' }, 200)
    }
  })

If it's a known limitation, perhaps it's worth documenting it somewhere in https://hono.dev/examples/zod-openapi

[yusukebe]

Hi @fumieval

It's not a bug. You should specify the status number explicitly. It's the same as RPC mode:

https://hono.dev/docs/guides/rpc#status-code