CoroutineDispatcher isActive after cancel() since 1.7.0

[Doctoror]

Describe the bug
Since 1.7.0, CoroutineDispatcher isActive is still true after cancel()

Provide a Reproducer

@Test
fun dispatcherIsNotActiveAfterCancellation() = runTest {
    val dispatcher = Dispatchers.Default // same for UnconfinedTestDispatcher or any other
    dispatcher.cancel()
    assertFalse(dispatcher.isActive)
}

org.jetbrains.kotlinx:kotlinx-coroutines-test:1.6.4 - test passes
org.jetbrains.kotlinx:kotlinx-coroutines-test:1.7.0 - AssertionError (same for v1.7.3, which is currently the latest stable)

[psteiger]

CoroutineDispather.cancel() is a call that does not make sense here: it resolves to CoroutineContext.cancel() (because every CoroutineContext.Element is a CoroutineContext itself).

The call checks for a Job in the context and cancels it if it's present. A dispatcher never has a Job (at least not the dispatchers shipped with the library, not sure if they even can have a Job).

The behavior change stems from #3300: isActive now returns true when a job is not present in context.

[dkhalanskyjb]

Yep, not a bug, just some very weird code.

[Doctoror]

Thank you, @psteiger. Your comment and the linked change explains everything.