Apparent properties in union of primitive and object causes incorrect error

[bjornstar]

TypeScript Version: 3.5.1

Search Terms: sub blink sup bold HTML Element String.prototype methods

Code

type sign = (payload: string | object) => void;
const sign: sign = (payload) => { console.log(payload)}
sign({ sub: null })

Expected behavior: Ok

Actual behavior:

$ ./node_modules/.bin/tsc --version
Version 3.5.1
$ ./node_modules/.bin/tsc --lib es2015 --strict ./repro.ts
repro.ts:5:6 - error TS2326: Types of property 'sub' are incompatible.
  Type 'null' is not assignable to type '(() => string) | undefined'.

5 sign({ sub: null })
       ~~~~~~~~~~~~~


Found 1 error.

$ ./node_modules/.bin/tsc --version
Version 3.6.0-dev.20190530
$ ./node_modules/.bin/tsc --lib es2015 --strict ./repro.ts
repro.ts:5:6 - error TS2326: Types of property 'sub' are incompatible.
  Type 'null' is not assignable to type '(() => string) | undefined'.

5 sign({ sub: null })
       ~~~~~~~~~~~~~


Found 1 error.

[RyanCavanaugh]

@weswigham reduced

type Thing = number | object;
const k: Thing = { toFixed: null };

Looks like the discriminating logic gets tripped up

[weswigham]

Looks like the discriminating logic gets tripped up

Hm, I guess we probably shouldn't look at apparent types for discriminators when object is involved in the union (since we only want to discriminate against other real object types, not primitive apparent types).