Object destructuring with default empty object generates wrong type

TypeScript Version: 4.0.3

Search Terms:

destructuring
object destructuring
object destructuring default

Code

const random = () =>
	new Date().getTime() % 2 === 0 ? { prop1: 1, prop2: 2, prop3: 3 } : undefined;
const obj = random();
// the type of obj is { prop1: number; prop2: number; prop3: number; } | undefined

const test = { testProp: obj };
const { testProp } = test;
// the type of testProp is { prop1: number; prop2: number; prop3: number; } | undefined
const { testProp: testProp2 = {} } = test;
// the type of testProp2 is: {}

const { prop1 } = obj ?? {}; // works
const { prop2 } = testProp ?? {}; // works
const { prop3 } = testProp2; // error

Expected behavior:

const { prop3 } = testProp2 should work.

Actual behavior:

const { prop3 } = testProp2 returns the error: Property 'prop3' does not exist on type '{}'. ts(2339).

Additional information:

const { prop3 } = testProp2 should work, just like const { prop2 } = testProp ?? {}, because the only difference is that the default {} was assigned during the object destructuring to get testProp2 while, for testProp, the default was assigned during the destructuring of the object itself.

If obj type is Type | undefined, I would expect testProp2 type to be Partial<Type>, as long as Type is not a primitive, but an object (which it is in the above code, so testProp2 should be Partial<{ prop1: number; prop2: number; prop3: number; }>).

Related Issues:

https://github.com/microsoft/TypeScript/issues/41080 (similar, but not the same, already fixed)

Comienza con la reproducción en TypeScript 4.0.3 del issue y compara las dos formas de desestructuración; después, revisa el issue relacionado #41080 para obtener contexto. Se considera terminado cuando testProp2, al tener un valor predeterminado, conserva las propiedades del objeto, de modo que la desestructuración de prop3 ya no informa de un error.