Reflect.has fails to act as type guard (should act same as "in" operator)

TypeScript Version: ^3.4.0-dev.20190330

Search Terms:
Reflect.has
in operator

Code

const test1 = (a: { field: number } | {}) => (("field" in a) ? a.field : 0);

const test2 = (a: { field: number } | {}) => Reflect.has(a, "field") ? a.field : 0;

Expected behavior:
Both compile successfully. "in" operator acts as a type guard per https://github.com/Microsoft/TypeScript/issues/10485. Reflect.has should act the same as "in" operator here.

We'd like to use Reflect.has a lot more and this case holds us back. Thank you!

Actual behavior:
"in" operator line compiles; Reflect.has line does not compile. Error:

allPasos.ts:445:31 - error TS2339: Property 'field' does not exist on type '{} | { field: number; }'.
Property 'field' does not exist on type '{}'.

445 Reflect.has(a, "field") ? a.field : 0;

Playground Link:

https://goo.gl/2R4dkS

Related Issues:

https://github.com/Microsoft/TypeScript/issues/10485

Inizia dalla riproduzione collegata in Playground e confronta il comportamento esistente di narrowing dell’operatore in con Reflect.has; leggi la issue correlata #10485 per il contesto. Il lavoro è completato quando l’espressione Reflect.has mostrata compila e si comporta come previsto dalla issue, con una copertura per la regressione.