Fastify Swagger not managing enumerators as expected

August 2, 2024

We are working on a backend with Fastify, declaring schemas with Typebox and generating OpenApi definitions with Fastify Swagger
We are facing some problems with enums or similar during docs generation

Let’s say we declare a typebox enumerator in one of the following ways

export const ProviderType = Type.Union([
  Type.Literal("sms"),
  Type.Literal("email"),
]);

//OR

enum Providers {
  SMS = "sms",
  EMAIL = "email",
}

export const ProviderType = Type.Enum(Providers);

When the open api docs are generated we get this

- schema:
    anyOf:
        - type: string
          enum:
              - sms
        - type: string
          enum:
              - email

That is not what we expect, but something like

schema:
    type: string
    enum: [sms, email]

Otherwise, the places where the enum is used are not correctly rendered by the various packages.

Did you already face this problem?

>Solution :

The TypeBox project does not support enum ATM as said by the lead maintainer.

It suggests a workaround:

const StringEnum = <T extends string[]>(items: [...T]) =>
  Type.Unsafe<T[number]>({ type: "string", enum: items });

export const ProviderType = StringEnum(["email", "sms"]);

// BECOMES
 - schema:
            type: string
            enum:
              - email
              - sms

So the fastify-swagger would be using the enum keyword.