Dispatchers.Main.isMissing throws when dispatcher is missing (since 1.10.0)

[consp1racy]

Describe the bug

Expected behavior: Dispatchers.Main.isMissing() returns true in JVM tests where Dispatchers.setMain() wasn't called.

Actual behavior:

java.lang.IllegalStateException: Dispatchers.Main was accessed when the platform dispatcher was absent and the test dispatcher was unset. Please make sure that Dispatchers.setMain() is called before accessing Dispatchers.Main and that Dispatchers.Main is not accessed after Dispatchers.resetMain().
	at kotlinx.coroutines.test.internal.TestMainDispatcherJvmKt.reportMissingMainCoroutineDispatcher(TestMainDispatcherJvm.kt:45)
	at kotlinx.coroutines.test.internal.TestMainDispatcherJvmKt.access$reportMissingMainCoroutineDispatcher(TestMainDispatcherJvm.kt:1)
	at kotlinx.coroutines.test.internal.TestMainDispatcherFactory.createDispatcher$lambda$4(TestMainDispatcherJvm.kt:20)
	at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:83)
	at kotlinx.coroutines.test.internal.TestMainDispatcher.getMainDispatcher(TestMainDispatcher.kt:18)
	at kotlinx.coroutines.test.internal.TestMainDispatcher.getDispatcher(TestMainDispatcher.kt:22)
	at kotlinx.coroutines.test.internal.TestMainDispatcher.getImmediate(TestMainDispatcher.kt:28)
	at kotlinx.coroutines.internal.MainDispatchersKt.isMissing(MainDispatchers.kt:62)
	...

Probably introduced here.

Provide a Reproducer

The following method didn't crash before when called in JVM tests where Dispatchers.setMain() wasn't called:

/**
 * @throws AssertionError when called from the main thread and assertions are enabled
 */
@WorkerThread
fun <T> runBlockingOrThrow(
    context: CoroutineContext = EmptyCoroutineContext,
    block: suspend CoroutineScope.() -> T,
): T {
    contract {
        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
    }

    val mainDispatcher = Dispatchers.Main.immediate
    if (!mainDispatcher.isMissing()) {
        assert(mainDispatcher.isDispatchNeeded(context)) {
            "runBlockingOrThrow MUST NOT be called from the main thread"
        }
    }

    return runBlocking(context, block)
}

[dkhalanskyjb]

Hi! fun MainCoroutineDispatcher.isMissing() is marked with @InternalCoroutinesApi, which means it's not intended for usage in client code (see https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-internal-coroutines-api/). Catching IllegalStateException is a more reliable indicator of Dispatchers.Main being absent. If you think isMissing() is worth introducing publicly, please open a separate issue.

[consp1racy]

Missed the annotation. Works for my case, thanks!