Weird type error with nested objects with index type

[G-Rath]

I'm not too sure why this error is happening, and was hoping you could shed some light on if this is a bug with this library, or something I just have to work around:

interface Mx {
  data: {
    prop: string | null;

    [K: string]: unknown;
  };
}

const f = makeFactory<Mx>({ data: { prop: null } });

const f1 = f.build();
const f2 = f.build({
  ...f1,
  data: {
    ...f1.data,
    v: 'hello world'
  }
});

The above code gives the following error:

TS2345: Argument of type '{ data: { v: string; prop: string | null; }; }' is not assignable to parameter of type 'RecPartial<Mx>'.
  Types of property 'data' are incompatible.
    Type '{ v: string; prop: string | null; }' is not assignable to type 'RecPartial<{ [K: string]: unknown; prop: string | null; }>'.
      Property 'prop' is incompatible with index signature.
        Type 'string | null' is not assignable to type 'RecPartial<unknown> | undefined'.
          Type 'null' is not assignable to type 'RecPartial<unknown> | undefined'.

If I change the index type to be any, v becomes the problem:

TS2345: Argument of type '{ data: { v: string; prop: string | null; }; }' is not assignable to parameter of type 'RecPartial<Mx>'.
  Types of property 'data' are incompatible.
    Type '{ v: string; prop: string | null; }' is not assignable to type 'RecPartial<{ [K: string]: any; prop: string | null; }>'.
      Property 'v' is incompatible with index signature.
        Type 'string' is not assignable to type 'RecPartial<any> | undefined'.

The error goes away when I do the following:

• Remove the ...f1.data
• Add prop: <string> (but not prop: null)
• Add prop: undefined
• Change the signature of prop to string | undefined

None of these work if I use any instead of unknown, nor if I use a subfactory:

const f2 = f.build({
  ...f1,
  data: makeFactory<Mx['data']>({ prop: null }).build({
    ...f1.data,
    v: 'string'
  })
});

Overall, I'm pretty confused by this 😂
Let me know if there's anything else I can provide!

[sashashakun]

I see similar error

[willryan]

@G-Rath @sashashakun What version of Typescript, and what version of factory.ts are you using? I can't seem to repro. I don't see any compile errors with the example code. Thanks.

[G-Rath]

@willryan Sorry I thought I'd included a minimal repo, but guess I didn't.

I can repo it w/ the above code + npm i -D typescript factory.ts.

[G-Rath]

Here are the versions:

"factory.ts": "^0.5.0",
"typescript": "^3.4.2"

(This is still a problem in typescript@3.5.2)