subscriber: Rename `Layer::new_span` method for consistency

[yaahc]

Right now the four event handling fns spans in the Layer trait are called

on_exit, on_enter, on_close, and new_span

new_span breaks the pattern set by the other methods and can be a little surprising / confusing, I spent more than a few seconds trying to find a method called on_open.

Next time we are making breaking changes we should consider renaming new_span to on_new_span or on_open.

[hawkw]

👍 we could also start this in a non-breaking change by adding a separate on_new_span/on_open method and deprecating new_span (and having on_open call new_span by default, to avoid breaking existing implementations). However, the default changes would take a little thinking about to make sure we don't introduce weird behavior by accident...

BTW: I edited the issue title a little to make it clearer that this is about changing the Layer::new_span method, not Subscriber::new_span in tracing-core.

[bnjjj]

Hi @hawkw I would like to make a PR for this. Is it possible ?

For the naming I prefer on_new_span but let me know what is your preference. And my plan is to update the trait making as you said the new_span method deprecated and create on_new_span method and call the previous one inside. I also plan to update all the implementation of layer to use the new method. What do you think ? Let me know if I forget something.

[hawkw]

@bnjjj so, we would definitely welcome a PR. However, I should let you know that there is one issue with this ticket in particular. This would require a breaking change, and, in order to limit the frequency of breaking releases, we try to wait until we have a large number of breaking changes to make before publishing a breaking change release (in this case, tracing-subscriber 0.3.0).

So, while we'd welcome a PR, it may not be able to merge until we're ready to publish 0.3.0. This may take some time, since we would need to prepare other potential breaking changes. This means that if code that your PR changes is changed in other PRs as well, you'd have to update it when we're ready to merge. Just thought you should be aware of that complication. Thanks for your interest in contributing!

[bnjjj]

Seems good for me. I will take the point and update PR further if needed.