JSON compatibility of Option

[florianbepunkt]

🚀 Feature request

Current Behavior

import { Json, stringify } from "fp-ts/lib/Json.js";
import * as O from "fp-ts/lib/Option.js";

type A = O.Option<string>;
const a = O.none;
const serialize = <V extends Json>(value: V) => stringify(value);
serialize(a); // <-- type signature does not match

a does not extend Json

Argument of type 'Option<never>' is not assignable to parameter of type 'Json'.
  Type 'None' is not assignable to type 'Json'.
    Type 'None' is not assignable to type 'JsonRecord'.
      Index signature for type 'string' is missing in type 'None'.

But obviously the object is json-serializable

export interface None {
  readonly _tag: 'None'
}

Desired Behavior

Suggested Solution

Who does this impact? Who is this for?

Describe alternatives you've considered

Additional context

Your environment

Software	Version(s)
fp-ts
TypeScript

[viell-dev]

The interface would need to have an index signature for type string for that to be possible.
As noted by Index signature for type 'string' is missing in type 'None'.

Seems to me at least that this is better solved in userland by just adding an index signature with a predicate function or some such.

Relevant discussion: microsoft/TypeScript#15300