prettier/tests/typescript_conditional_types/conditonal-types.ts

export type DeepReadonly<T> = T extends any[] ? DeepReadonlyArray<T[number]> : T extends object ? DeepReadonlyObject<T> : T;

type NonFunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? never : K }[keyof T];

interface DeepReadonlyArray<T> extends ReadonlyArray<DeepReadonly<T>> {}

type DeepReadonlyObject<T> = {
    readonly [P in NonFunctionPropertyNames<T>]: DeepReadonly<T[P]>;
};