Nathan Shively-Sanders 64ff195426
Set-only accessors spread to undefined (#28213)
* Set-only accessors spread to undefined

Previously they were skipped. The runtime behaviour is to create a
property of type undefined, unlike (for example) spreading numbers or
other primitives. So now spreading a set-only accessor creates a
property of type undefined:

```ts
const o: { foo: undefined } = { ...{ set foo(v: number) { } } }
```

Notably, `o.foo: undefined` not `number`.

Fixes #26337

* Fix isSpreadableProperty oversimplification
2018-10-29 14:51:12 -07:00
..