Misleading EPC error on deferred generic type when assigning any object literal, but empty object is also not assignable

🔎 Search Terms

N/A (bug report forked from #56388)

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBAylC8UDeAPAXFA5AQwEYGNMBfAKADMBXAO32AEsB7KqMgHgBUoIVgIqATAM6wAfAAoAlMhJQo+JoOBR0yANoBrKHWbtVmFJgC6hjFQoBbXBABORBMjz4MARjsB6N1ACiABQDCXNbWDNYANCwhUNhUIFrm2ADm2ngANtDqECAycgpKIBhIGlo6egbGphZWtvZI7p7yQRC0UKCQgcHWJKRAA

💻 Code

type S = {x: 'abc'}
function f<T extends S>() {
  const x: {[k in T['x']]: number} = {abc: 1} // EPC error, for any imaginable key
  const y: {[k in T['x']]: number} = {} // ...but this is also a (correct!) type error
}

🙁 Actual behavior

EPC diagnostic on any non-empty object literal, but {} is also not assignable.

🙂 Expected behavior

No EPC diagnostic; should just be a straight assignability failure.

Additional information about the issue

Producing an EPC (excess property check) error for any non-empty object literal here is misleading since that ultimately implies {} would be a legal value (it is not). 5.3 exacerbates this because it removes the "X is not assignable to Y" text from EPC diagnostics, which further implies that the value would be legal if assigned indirectly (also not true; the type is generic and might have other properties).

Führe das verlinkte TypeScript Playground-Beispiel aus und vergleiche die Diagnosen für die nicht leeren und leeren Objekt-Literale im generic mapped-type-Fall. Verfolge das excess property checking des Compilers und seine assignability-Entscheidung für dieses Muster; erledigt ist die Aufgabe, wenn das nicht leere Literal einen regulären assignability-Fehler statt einer EPC-Diagnose erhält.