fix(provider-utils): handle anyOf/allOf/oneOf and definitions in addAdditionalPropertiesToJsonSchema

[ellis-driscoll]

Background

#11078 updated z4. toJSONSchema() in packages/provider-utils/src/schema.ts to use io: 'input' instead of io: 'output'

With io: 'input', zod does not automatically set additionalProperties: false, so addAdditionalPropertiesToJsonSchema was added as a post-processor.

The current implementation only handles objects and arrays of object, so more complex schemas fail with errors like:

error: {
  message: "Invalid schema for response_format 'response': In context=('properties', 'response', 'anyOf', '0'), 'additionalProperties' is required to be supplied and to be false.",
  type: 'invalid_request_error',
  param: 'text.format.schema',
  code: 'invalid_json_schema'
}

Summary

With heavy inspiration from @Jeto143's comment on #11369, this change adds support for schemas with:

• multiple types e.g., "type": ["object", "null"]
• anyOf e.g., from z.union()
• allOf e.g., from z.intersection()
• oneOf
• definitions e.g, for recursive schemas

Note, multiple types and oneOf are not currently produced by zod, but I figured it made sense to future proof.

Manual Verification

Running the script below from packages/ai will fail with the error above on main, but runs successfully with this change.

import { generateText, Output } from './src/index.js';
import { createOpenAI } from '../openai/src/index.js';
import { z } from 'zod/v4';

const OPENAI_API_KEY = 'sk-svcacct-...';
const openai = createOpenAI({ apiKey: OPENAI_API_KEY });

const responseSchema = z.object({
  payload: z.discriminatedUnion('kind', [
    z.object({
      kind: z.literal('foo'),
      message: z.string(),
    }),
    z.object({
      kind: z.literal('bar'),
      reason: z.string(),
    }),
  ]),
});

async function main() {
  const { output } = await generateText({
    model: openai('gpt-5-mini'),
    prompt: 'Pick one',
    output: Output.object({ schema: responseSchema }),
  });

  console.log(output);
}

main();

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

Fixes #11369

[Copilot]

Pull request overview

This PR fixes a critical issue where schemas with complex structures like anyOf, allOf, oneOf, and definitions were failing validation with OpenAI's API due to missing additionalProperties: false requirements. The fix extends the addAdditionalPropertiesToJsonSchema function to recursively process these schema constructs.

• Adds support for handling union types (e.g., ["object", "null"])
• Adds recursive processing of anyOf, allOf, oneOf, and definitions schema constructs
• Introduces a helper visit function to handle JSONSchema7Definition types (which can be boolean or schema objects)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/provider-utils/src/add-additional-properties-to-json-schema.ts	Extended function to handle complex schema structures including union types, composition operators, and schema definitions with recursive processing
packages/provider-utils/src/add-additional-properties-to-json-schema.test.ts	Added three new test cases covering union types, anyOf, and recursive references via definitions
packages/provider-utils/src/__snapshots__/schema.test.ts.snap	Updated snapshots to reflect additionalProperties: false now being added to schemas in definitions

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