Object member completions are offered from all union constituents even after union has been discriminated

[aloifolia]

TypeScript Version: 3.9.5 (probably more)

Search Terms:

Code

type Choice = {
    kind: number, x: 42
} | {
    kind: undefined, y: 42
}

const c: Choice = {kind: undefined, X_OR_Y: 42} // X_OR_Y is a placeholder

Expected behavior:
When you use autocompletion to replace X_OR_Y by x or y, the editor should suggest y, only:

Actual behavior:
The editor suggests both x or y:

Of course, if you choose x, the compiler will then complain about the wrongly typed assignment.

Playground Link:
Playground

Related Issues:

[andrewbranch]

Changed the title because this happens even when undefined is not the discriminant: https://www.typescriptlang.org/play?#code/C4TwDgpgBAwgFgewJYGNoF4oG8BQV9QDWSAdgCYBcUJArgLYBGEATgDRQAeVALAEw4BfKAB9seAsXJUARAGcIKBOSgpEqCNPYge-AThyKSs4CqrxkaKJiyTKUOQqVkVatJvwCgA