C extends A but C does not extend A | B

[jer-sen]

C extends A but C does not extend A | B

[jer-sen]

Maybe the fallback match could be improved a bit. The repro is very simple and should be handle correctly IMHO.

[Andarist]

This is a fallout of an extra attempt to match combinations in typeRelatedToDiscriminatedType. The normal union-based match fails here in both cases and it's just that fallback match that even allows Works to work.

I'd probably call it a design limitation as that fallback match is something that, IIRC, breaks some general rules. { prop: A } | { prop: B } isn't always interchangeable with { prop: A | B }. This fallback match also only works to a certain number of combinations so it's already not something that works universally.

[ethanresnick]

Possibly related? #36969