Print the span info on span exit and entry

[oli-obk]

I may have went a bit overboard with this one. I wanted to somehow render the fact that we're just re-emitting the current span info

[davidbarsky]

This rules! Thanks for opening this PR.

How do you feel introducing a similar implementation that you have in on_exit to on_close but also emitting the duration of the span? Since spans can be entered and existed multiple times having something to delineate that a span has just closed/exited for the last time can be really handy.

[oli-obk]

Do you mean just the current duration from the start, or the duration the span was open? In the latter case we have to store the opening somewhere, any tips?

[davidbarsky]

I'm sorry my message wasn't more clear, let me try to rephrase. I think that there are a few distinct requests that I didn't properly separate.

• I'd like to be able to visually distinguish between a span that has exited and a span that has closed. That could be done with durations, but that's not the only approach.
  • As I'm writing this comment, I remembered that tracing-tree isn't really used with asynchronous or non-blocking code. Therefore, I'm not sure how useful this feature is in the first place.
• One idea I had was to use durations from the start of the span. However, after thinking about it a bit more, I realized that this opens a larger design space that's best discussed in a separate issue. I'd prefer to not block merging this PR on that point.

In the latter case we have to store the opening somewhere, any tips?

Sure! Here's the approach I was thinking of:

• new_span creates a DateTime<Local>. Nothing needs to change here.
• In an on_exit or on_close method, copy this approach to calculate the elapsed time of the span.

Again, the above approach can be done in a followup, but I'd like to hash out an approach first in an issue. I really love this PR as is and I'd be happy to merge it as-is, as I don't want to let perfect be the enemy of good 😄.

[oli-obk]

We have a few subtle ways to signal that something is different. One would be to use some of the bold or double box drawing chars from https://en.wikipedia.org/wiki/Box-drawing_character This could look like

│┌┘
╞╛

(without the space between the lines, that's just github)

Also we can use bold lines instead of double lines.

I'll open an issue for the timings

[davidbarsky]

We have a few subtle ways to signal that something is different. One would be to use some of the bold or double box drawing chars from https://en.wikipedia.org/wiki/Box-drawing_character. This could look like [redacted]

That's a reasonable approach. For what it's worth, I think this PR is fine as-is. We can add some specific formatting for a span closing, if there's a need for it. I think that printing:

• The time the span was most recently active on exit, and
• The time the span was most recently active and it's total age (busy + idle)

will allow us to distinguish between an exited span and a closed span, respectively.

[oli-obk]

For what it's worth, I think this PR is fine as-is.

ok :D then let's merge it for now and figure out the details about other improvements in the issue.