How to cancel a publisher when using withTaskCancellationHandler

Using Swift
, ,
4

Also, if I comment out the call to cancel():

public func query(parameters: QueryParameters) async throws -> FeatureQueryResult {
        var sub: AnyCancellable?
        return try await withTaskCancellationHandler {
            //sub?.cancel()
        } operation: {
            try await withCheckedThrowingContinuation { continuation in
                ...
                sub = myPublisher.sink { completion in
                    ...
                    continuation.resume(with: myResult)
                } receiveValue: { _ in }
            }
        }
    }

Then it compiles but I get a warning:

Variable 'sub' was written to, but never read

Then of course if I don't hold onto the cancellable at all:

public func query(parameters: QueryParameters) async throws -> FeatureQueryResult {
        return try await withTaskCancellationHandler {
        } operation: {
            try await withCheckedThrowingContinuation { continuation in
                ...
                let _ = myPublisher.sink { completion in
                    ...
                    continuation.resume(with: myResult)
                } receiveValue: { _ in }
            }
        }
    }

Then I end up with a runtime error:

SWIFT TASK CONTINUATION MISUSE: queryFeatures(parameters:) leaked its continuation!