[Feature] External cancellation of ...WaitFor... methods where feasible

[maw136]

Add external cancellation of ...WaitFor... methods where feasible.

Reasoning:
Wait for style methods have a timeout, but there are circumstances where external events could be the cause to cancel specific waits.
The current solution doesn't provide any cancellation except default/custom timouts.

[mxschmitt]

Thanks for the feature request, unfortunately this is not compatible with the way Playwright, the driver and calls to the browser are working. If you sent once something to the browser, it can't be canceled. Since we don't plan on implementing this, I will close it for now.

[maw136]

Could you take another look at this?
The set of APIs that 'WaitFor' events are dotnet-side.
My PR implements the bread and butter of this specific kind of scenario.
The exact use case is like waiting for multiple different Request/Responses and cancelling some waits under some specific circumstances.
The cancellation is not at the level at which the driver calls the browser, the cancellation is at the listening for specific kind of events.
In the current state of Playwright there is no way to stop listening to these events. It is just an early exit.

[mxschmitt]

Yup sorry for closing this before, re-opening by that.

[pavelfeldman]

Could you provide a complete example where you benefit from the cancellation token? I'd like to understand the use case better.

[mxschmitt]

We discussed this feature in our team and came to the conclusion that this change might confuse users. While event handlers, aka. WaitFor* methods can be cancelled, the code you have inside, can not. Often these are clicks, evaluates, etc. To keep a clear boundary about this, we decided to not go forward with this API proposal.

I apologise for being slow on this PRs/issues, since some of our coworkers were out of office. Thank you!

[maw136]

But it's all about cancelling the wait/listen for event, not the action. There is no way for early cancel of any WaitFor... waiter

[mxschmitt]

The code inside the callback still continues to run and does not follow .NET's rule of periodically checking if the cancellation was requested. This is a fundamental feature which Playwright does not offer and yield in unexpected behaviour.

We recommend Task.WhenAny() instead.

[maw136]

So more spaghetti code instead. :(
In all meaningful scenarios the 'callback' as you called it is an action that triggers the request/response dialog with backend.
A cancellation would not cause any unexpected behaviour/side effects, as the action have already run to completion either way.