Cancellation error

[EdmondDantes]

At the moment, the RFC uses inheritance from \Error for the cancellation exception in order to make cancellation errors safe.
In the initial implementations, however, a new root class was used directly in the PHP core. I later removed that implementation to reduce the amount of coordination required for the code. However, it now seems to me that it was 100% correct.

[SerafimArts]

Maybe it makes sense to inherit from RuntimeException, like CancellationException extends RuntimeException?

[EdmondDantes]

Maybe it makes sense to inherit from RuntimeException, like CancellationException extends RuntimeException?

Throwable
└─ Exception
└─ RuntimeException

One of the reasons why CancellationException is so special is legacy code that is used to catching the \Exception class.
If old code simply does not catch CancellationException, this is actually a good thing, because in most cases it will behave correctly.
Therefore, it is highly desirable that CancellationException does not inherit from \Exception.

[bwoebi]

Yep, that.
Code which aims to handle general exceptions, shall handle \Exception. Code which aims to cleanup after something is thrown, shall handle \Throwable. This is true already now, and neatly fits with the expectations of Cancellation.

[bwoebi]

Given that there can be classes inheriting from Cancellation, I propose to prefer Cancellation extends \Throwable.

CancellationException is, in my opinion a bad choice for two reasons:

1. It suggests to be inheriting Exception (it doesn't).
2. Classes inheriting Cancellation should be called <something>Cancellation and not <something>CancellationException. E.g. TimeoutCancellation.

I don't know who voted here, but I really think this isn't a matter of just preference, but CancellationException seems actively wrong to me.