Misleading error message when interface tries to extend constrained type parameter

🔎 Search Terms

"statically known members."
"could be instantiated with a different subtype of constraint 'object'."

🕗 Version & Regression Information

• This changed between versions 3.6.2 and 3.7.5

⏯ Playground Link

https://www.typescriptlang.org/play?ts=3.7.5#code/JYOwLgpgTgZghgYwgAgKIA84FsAOAbCAHgBVkJ1IQATAZ2QHsAjAKwgTAD4yKJq7SA3gF8AUEA

💻 Code

interface Example<T extends object> extends T {}

🙁 Actual behavior

I get the following message:

Interface 'Example' incorrectly extends interface 'T'.
'Example' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'object'.

This error message is misleading. The interface does not vary with T and since it declares no new members, is completely compatible with T.

🙂 Expected behavior

I expect a descriptive message. Prior to 3.6.2, the error message was more helpful:

An interface can only extend an object type or intersection of object types with statically known members.

This is still the error you get if the type variable T does not have the extends constraint.

Additional information about the issue

No response

Beginne mit dem TypeScript 3.7.5 Playground-Beispiel: interface Example extends T {}. Vergleiche dessen Diagnose mit dem Fall eines uneingeschränkten Typparameters und der Formulierung vor 3.6.2. Als erledigt gilt die Aufgabe, wenn der eingeschränkte Fall eine beschreibende Diagnose meldet, ohne das bestehende Verhalten zu beeinträchtigen.