CompletableFuture.cancel vs Future.cancel bug?

Hi,

I noticed that the CompletableFuture.cancel method breaks the contract for
Future.cancel.
The spec says "This attempt will fail if the task ... has already been
cancelled..." but at the same time CompletableFuture will return true even
if someone else has cancelled the future.

I see that it can be workarounded by completeExceptionally(new
CancellationException()) but this inconsistency is neither obvious nor even
documented and IMO should be fixed.

To be clear I'm extending CompletableFuture.cancel with my own cancellation
logic and obviously I want this logic to be executed only once thus using
super.cancel() would be wrong. On another hand I want my future to behave
consistently with the original CompletableFuture and of course I can
emulate that but this all gets ugly...

Please advise.

Sergi

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