additionalProperties option incorrectly applied to enum/union schemas → Ajv strictTypes error

[tsegreto]

When the Prismabox generator option additionalProperties = false is enabled, Prismabox applies additionalProperties: false to non-object schemas generated for Prisma enums (TypeBox Type.Union of literals). Ajv strict mode (strictTypes) rejects additionalProperties unless the schema is type: "object", causing schema compilation to fail.

Example error:

strict mode: missing type "object" for keyword "additionalProperties" at "#/properties/status" (strictTypes)

Reproduction

Prisma schema

generator prismabox {
  provider             = "prismabox"
  additionalProperties = false
}

enum Status {
  active
  inactive
}

model User {
  id     String @id
  status Status
}

Generated output (excerpt)

status: Type.Union([Type.Literal("active"), Type.Literal("inactive")], {
  additionalProperties: false,
}),

Using with Ajv

import Ajv from "ajv";
import { UserPlain } from "./generated/User.js";

const ajv = new Ajv({ strict: true }); // strictTypes enabled by default in strict mode
ajv.compile(UserPlain); // throws

Expected behavior

additionalProperties should only be applied to object schemas, not enums/unions/literals/arrays. Enums should be generated without it:

status: Type.Union([Type.Literal("active"), Type.Literal("inactive")]),

Suggested fix

When emitting TypeBox options, apply additionalProperties only for Type.Object(...) (and other object-like schemas, if any), not for unions/enums/literals/arrays.

Workaround

import { Type } from "@sinclair/typebox";
import { UserPlain } from "./generated/User.js";
import { Status } from "./generated/enums.js";

// Manual enum
export const status = Type.Enum(Status);

// Override in usage
export const UserSchema = Type.Composite([
  Type.Omit(UserPlain, ["status"]),
  Type.Object({ status }),
]);

[giuvincenzi]

I'm also affected by this issue.
Using prismabox 1.1.26 with Fastify + Ajv strict mode, I get strictTypes warnings for all Prisma enums because additionalProperties: false is applied to Type.Union().

Any updates on a fix?

[tsegreto]

This has been workaround:

import { type TSchema } from "@sinclair/typebox";

export function stripAdditionalProperties<T extends TSchema>(schema: T): T {
	const seen = new WeakSet<object>();

	const walk = (node: unknown): void => {
		if (!node || typeof node !== "object" || seen.has(node)) return;
		seen.add(node);

		const n = node as Record<string, unknown>;

		if (n.type === "array" && Object.prototype.hasOwnProperty.call(n, "additionalProperties")) {
			delete n.additionalProperties;
		}

		// Arrays
		const items = n.items;
		if (items) (Array.isArray(items) ? items : [items]).forEach(walk);

		const prefixItems = n.prefixItems;
		if (Array.isArray(prefixItems)) prefixItems.forEach(walk);

		// Schema maps
		for (const key of ["properties", "patternProperties", "definitions", "$defs", "dependentSchemas"] as const) {
			const v = n[key];
			if (v && typeof v === "object") {
				Object.values(v as Record<string, unknown>).forEach(walk);
			}
		}

		// Schema arrays
		for (const key of ["anyOf", "oneOf", "allOf"] as const) {
			const v = n[key];
			if (Array.isArray(v)) v.forEach(walk);
		}

		// Single schemas
		for (const key of [
			"not",
			"if",
			"then",
			"else",
			"contains",
			"additionalItems",
			"propertyNames",
			// optional: traverse object.additionalProperties if it's a schema
			"additionalProperties",
		] as const) {
			const v = n[key];
			if (v && typeof v === "object") walk(v);
		}
	};

	walk(schema);
	return schema;
}

I think PrismaBox is great, I really hope it's not abandoned.