Description

Problem

When generating Zod schemas for OpenAPI specs with union/oneOf types, the current implementation creates unions that can cause unexpected data loss. Zod's default union behavior returns the first successfully matching schema, which means less specific schemas can "steal" matches from more specific ones, silently dropping valid properties.

Example

Given these generated schemas:

typescriptconst schema = z.union([
    z.object({ value: z.number() }),                    // Schema A
    z.object({ value: z.number(), value2: z.number() }) // Schema B
]);

const data = { value: 5, value2: 10 };
const result = schema.parse(data); // Returns: { value: 5 } - value2 is lost!

Schema A matches first and returns incomplete data, even though Schema B would be a complete match.

Proposed Solution

Add a configuration option to generate Zod schemas with .strict() mode for union members, which would reject objects with extra properties:

const schema = z.union([
    z.object({ value: z.number() }).strict(),
    z.object({ value: z.number(), value2: z.number() }).strict()
]);

const data = { value: 5, value2: 10 };
const result = schema.parse(data); // Now correctly returns: { value: 5, value2: 10 }