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)

Start with the TypeScript 4.0.3 reproduction in the issue and compare the two destructuring forms, then review related issue #41080 for context. Done means the defaulted testProp2 retains the object properties so that destructuring prop3 no longer reports an error.