withContext calls are not reflected in coroutine debug dumps

[vsalavatov]

Reproducer:

@Test
fun testProbes() = runBlocking {
    val b1 = CompletableDeferred<Unit>()
    val b2 = CompletableDeferred<Unit>()
    println("runBlocking context: ${currentCoroutineContext()}")
    launch { // in the context of runBlocking
        withContext(Dispatchers.IO + CoroutineName("A")) {
            println("launched job context: ${currentCoroutineContext()}")
            b1.complete(Unit)
            b2.await()
        }
    }
    b1.await()
    println("debug probes")
    println(DebugProbes.dumpCoroutinesInfo())
}

Outputs:

runBlocking context: [CoroutineId(1), "coroutine#1":BlockingCoroutine{Active}@b665f0a, BlockingEventLoop@3c0fe39d]
launched job context: [CoroutineId(2), CoroutineName(A), "A#2":DispatchedCoroutine{Active}@2cd23013, Dispatchers.IO]
debug probes
[CoroutineInfo(state=RUNNING,context=[CoroutineId(1), "coroutine#1":BlockingCoroutine{Active}@b665f0a, BlockingEventLoop@3c0fe39d]), CoroutineInfo(state=SUSPENDED,context=[CoroutineId(2), "coroutine#2":StandaloneCoroutine{Active}@7ed255c1, BlockingEventLoop@3c0fe39d])]

Note that the debug info for the second coroutine does not show the effect of withContext switch.

This is likely because kotlinx.coroutines.debug.internal.DebugCoroutineInfoImpl has immutable context and it is not updated from the frame in updateState.

The issue occasionally shows up in problem investigations, wrong context in the debug probes causes confusion.