Immer modifies `readonly` properties of nested instances that are not immerable

import { immerable, produce } from "immer";

class Address {
  constructor(public readonly streetName: string) {
    this.streetName = streetName;
  }
}

class ImmerableAddress {
  [immerable] = true;

  constructor(public readonly streetName: string) {
    this.streetName = streetName;
  }
}

class ImmerablePerson {
  [immerable] = true;

  constructor(public readonly address: Address) {
    this.address = address;
  }
}

describe("immer", () => {
  const immerableAddress = new ImmerableAddress("foo");
  it("works fine with immerable nested class instance", () => {
    const produced = produce(new ImmerablePerson(immerableAddress), (draft) => {
      draft.address.streetName = "bar";
    });
    expect(produced.address.streetName).toBe("bar");
    expect(produced.address).toBeInstanceOf(ImmerableAddress);
    expect(produced.address).not.toBe(immerableAddress);
  });

  const address = new Address("foo");
  it("allows illegal modification of non-immerable nested class instance", () => {
    const produced = produce(new ImmerablePerson(address), (draft) => {
      draft.address.streetName = "bar"; // works unexpectedly
    });
    expect(produced.address.streetName).toBe("bar");
    expect(produced.address).toBeInstanceOf(Address);
    expect(produced.address).toBe(address);
  });
});