Expected Behavior

When a switchOnFirst function returns a single item that contains the input flux but is not derived through operators, the input flux should remain available without restriction.

Actual Behavior

The input flux is cancelled when the outer flux is cancelled (e.g. by Mono.from), making it unusable.

Steps to Reproduce

    public static void main(String[] args) {
        Flux<String> input = Flux.just("foo", "bar");
        Mono<Flux<String>> nested = Mono.from(input.switchOnFirst((first, all) -> Mono.just(all)));
        Flux<String> item = nested.block();
        System.out.println(item); // prints SwitchOnFirstMain as expected
        System.out.println(item.collectList().block()); // never terminates as the item has been cancelled
    }

Possible Solution

In the above example, Mono.from sees the onNext immediately, and cancels the FluxSwitchOnFirst. Cancelling FluxSwitchOnFirst however also cancels the SwitchOnFirstMain, which it should not. Cancellation should only be sent to the publisher returned by the switchOnFirst lambda (in this case the Mono.just)

Your Environment

• Reactor version(s) used: 3.6.9
• Other relevant libraries versions (eg. netty, ...): N/A