`enumValues` + `immutable` generates broken `FlattenedDeepRequired` for readonly arrays

[Cippas]

openapi-typescript version

7.13.0

Node.js version

24.x.x

OS + version

macOS 26.3.1

Description

When using enumValues: true together with immutable: true, the generated FlattenedDeepRequired utility type fails to flatten readonly arrays, producing type errors on the enum value exports.

immutable: true generates readonly arrays (readonly T[]). The FlattenedDeepRequired utility checks:

T[K] extends unknown[] | undefined | null

But in TypeScript, readonly unknown[] does not extend unknown[] — readonly arrays are not assignable to mutable arrays. So the array-to-element flattening never triggers, and the indexed path (e.g. ["fields"]["name"]) fails because fields remains typed as an array instead of being flattened to its element type.

Related: PR #2139 improved FlattenedDeepRequired for optional props and arrays but didn't account for readonly arrays generated by immutable: true.

Reproduction

Given a schema with an enum nested inside an array property:

MatchingRuleFilterMetadata:
  type: object
  properties:
    fields:
      type: array
      items:
        type: object
        properties:
          name:
            type: string
            enum: [description, merchant_name, amount]

Running with immutable: true and enumValues: true generates:

type FlattenedDeepRequired<T> = {
    [K in keyof T]-?: FlattenedDeepRequired<T[K] extends unknown[] | undefined | null ? Extract<T[K], unknown[]>[number] : T[K]>;
};

export const matchingRuleFilterMetadataFieldsNameValues: ReadonlyArray<
  FlattenedDeepRequired<components>["schemas"]["MatchingRuleFilterMetadata"]["fields"]["name"]
> = ["description", "merchant_name", "amount"];

This produces:

error TS2339: Property 'name' does not exist on type 'readonly FlattenedDeepRequired<{ readonly name?: "description" | "merchant_name" | "amount" | undefined; ... }>[]'

Expected result

The generated enum value exports should compile without errors when immutable: true and enumValues: true are used together. FlattenedDeepRequired should correctly flatten readonly arrays to their element type, so that paths like ["fields"]["name"] resolve through the array to the element's properties.

Required

• My OpenAPI schema is valid and passes the Redocly validator (npx @redocly/cli@latest lint)

Extra

• I’m willing to open a PR (see CONTRIBUTING.md)