v0.96.1 cause typescript errors in generated zod schemas because of extend() on z.object({}).and()

[amarant]

Description

Following probably this PR : #3780
v0.96.1 cause typescript errors in generated zod schemas because of the usage extends() on z.object({}).and()

I have errors in :

  zUserNotificationDeleteContentRunning.extend({ status: z.literal('running') }),

Reproducible example or configuration

using this typespec reproduction :

import "@typespec/http";
import "@typespec/openapi";
import "@typespec/openapi3";

using Http;

model UserNotificationDeleteContentBase {
  name: string;
}

model UserNotificationDeleteContentRunning extends UserNotificationDeleteContentBase {
  startedAt: utcDateTime;
}

model UserNotificationDeleteContentSuccess extends UserNotificationDeleteContentBase {
  finishedAt: utcDateTime;
}

model UserNotificationDeleteContentError extends UserNotificationDeleteContentBase {
  finishedAt: utcDateTime;
  error: string;
}

@discriminated(#{ envelope: "none", discriminatorPropertyName: "status" })
union UserNotificationDeleteContent {
  running: UserNotificationDeleteContentRunning,
  success: UserNotificationDeleteContentSuccess,
  error: UserNotificationDeleteContentError,
}


@route("/notification")
@get
op getNotification() : UserNotificationDeleteContent;

And this example :

https://stackblitz.com/edit/hey-api-client-fetch-example-penlxfm1?file=openapi-ts.config.ts

OpenAPI specification (optional)

openapi: 3.0.0
info:
  title: (title)
  version: 0.0.0
tags: []
paths:
  /notification:
    get:
      operationId: getNotification
      parameters: []
      responses:
        '200':
          description: The request has succeeded.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/UserNotificationDeleteContent'
components:
  schemas:
    UserNotificationDeleteContent:
      type: object
      oneOf:
        - $ref: '#/components/schemas/UserNotificationDeleteContentRunning'
        - $ref: '#/components/schemas/UserNotificationDeleteContentSuccess'
        - $ref: '#/components/schemas/UserNotificationDeleteContentError'
      discriminator:
        propertyName: status
        mapping:
          running: '#/components/schemas/UserNotificationDeleteContentRunning'
          success: '#/components/schemas/UserNotificationDeleteContentSuccess'
          error: '#/components/schemas/UserNotificationDeleteContentError'
    UserNotificationDeleteContentBase:
      type: object
      required:
        - name
      properties:
        name:
          type: string
    UserNotificationDeleteContentError:
      type: object
      required:
        - finishedAt
        - error
      properties:
        finishedAt:
          type: string
          format: date-time
        error:
          type: string
      allOf:
        - $ref: '#/components/schemas/UserNotificationDeleteContentBase'
    UserNotificationDeleteContentRunning:
      type: object
      required:
        - startedAt
      properties:
        startedAt:
          type: string
          format: date-time
      allOf:
        - $ref: '#/components/schemas/UserNotificationDeleteContentBase'
    UserNotificationDeleteContentSuccess:
      type: object
      required:
        - finishedAt
      properties:
        finishedAt:
          type: string
          format: date-time
      allOf:
        - $ref: '#/components/schemas/UserNotificationDeleteContentBase'

System information (optional)

No response

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• hey-api-client-fetch-example-penlxfm1 (Open reproduction)

[pullfrog]

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[dosubot]

Hi @amarant! I'm Dosu and I’m helping the openapi-ts team.

This looks like a bug introduced by PR #3780, which added native z.discriminatedUnion() support. The issue is that z.discriminatedUnion() requires each member to be a ZodObject, and .extend() only exists on ZodObject — not on ZodIntersection types created by .and().

In your case, the TypeSpec extends keyword produces an allOf in the OpenAPI output, which the Zod plugin renders as z.object({}).and(baseRef) (a ZodIntersection). When the discriminated union logic then tries to call .extend({ status: z.literal('running') }) on that intersection result, TypeScript rightfully errors because ZodIntersection doesn't have an .extend() method [1].

The tryBuildDiscriminatedUnion helper is supposed to fall back to z.union() when the schema structure doesn't fit the discriminated union pattern, but it appears the fallback isn't triggering correctly for schemas where union members use allOf/inheritance rather than being plain $refs [1].

As a workaround until this is fixed, you could pin to v0.96.0 to avoid the regression.

To reply, just mention @dosu.

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