Is it possible to detect missing Object.freeze() with Flow? - flowtype

Question

Flow has $ReadOnly utility type [1] that represents a read-only view of T. Unfortunately, as Flow allows to assign a mutable T to its read-only version, it cannot be used to model the usage of Object.freeze(). In particular, it cannot detect missing calls to the latter. For example, given
type Foo = { field: string };
// frozen is assumed to be immutable with no way to change it
type WithFrozenFoo = { +frozen: $ReadOnly<Foo> }
Flow type-checks the following code:
let foo = { field: "test" };
foo.field = "new value";
let bar = { frozen: foo };
...
foo.field = "changed"; // Also changes bar.frozen.field
when the correct code should be:
let foo = { field: "test" };
foo.field = "new value";
let bar = { frozen: Object.freeze(foo) };
...
foo = { ...foo, field: "changed" }
Ideally Flow should have provided a separated $Frozen which instances can only be assigned from T via Object.freeze().
But given the lack of this, is it possible to model it in a different way even if this would involve a utility function that uses any internally?
[1] - https://flow.org/en/docs/types/utilities/#toc-readonly

Answer 1

It turned out just by using read-only fields we can solve the problem which also made frozen unnecessary. The drawback is cloning objects on updates, but as Object.freeze() can be slower then object creation [1], this was a useful compromise.
type Foo = { +field: string };
let foo: Foo = { field: "test" };
foo = {...foo, field: "new value"};
let bar = { frozen: foo };
...
// Now flow complain
foo.field = "changed";
[1] - https://jsitor.com/jwRCuqLFN