What's the recommend way to indicate debug is also implicated sampled in tracing context

[TommyCpp]

Hi, so we are have some discussion around how should the tracing context handle the situation where the debug is also a implicated sampled decision.

We have a bitmask to represent the sampling state in tracing context where sampled and debug are represent in different bit. And the tracing context has isSampled() method to tell user whether or not to record current span.

In order to make sure isSampled() method returns true when the sampling state is either debug or sampled. We have the following two choices.

1. Set debug bit and sampled bit when decision is debug. And isSampled() method will simplely return whether the sampled bit is set.

2. Set debug bit only when decision is debug. But isSampled() method will have to return true if debug bit or sampled bit is set.

We are wonder if there is a preferred way from the spec standpoint. Thanks in advance!

[codefromthecrypt]

in brave, we ensure the sampling bits are assigned when debug is, even if they weren't propagated. This means that outgoing would have both sampled and debug even if sampled wasn't passed on the way it. This is better in practice as some tools don't understand debug.

  static int debug(boolean debug, int flags) {
    if (debug) {
      flags |= FLAG_DEBUG | FLAG_SAMPLED_SET | FLAG_SAMPLED;
    } else {
      flags &= ~FLAG_DEBUG;
    }
    return flags;
  }

https://github.com/openzipkin/brave/blob/master/brave/src/main/java/brave/propagation/SamplingFlags.java#L178-L185