commit 49edb8604483915ee499910d30d6ab220d76780d
author Jonathan Amsterdam <jba@google.com> Sun Apr 25 13:37:07 2021 -0400
committer Jonathan Amsterdam <jba@google.com> Mon Apr 26 12:12:15 2021 +0000
tree 2f182ae1fb323234184474b254467195bed938ef
parent e860ab8327da2f66bc233bf259deb9fb4b7895de

event: suggestion: event.Start returns end

The majority of calls to start a trace span will be followed by a deferred call to end one:

    ctx = event.To(ctx).Start(name)
    defer event.To(ctx).End()

The main problem with this is that it is easy to forget that end must
be called. It's also more verbose than necessary.

Instead, have event.Start return both a context and a function that
can be deferred:

    ctx, end := event.To(ctx).Start(name)
    defer end()

The second return value will make it hard to forget the defer, and it
follows a common Go pattern.

You can also ignore it and call event.To(ctx).End() elsewhere if that
suits you.

Lastly, remove Builder.Start. It invites misuse by end users: they
should always do tracing with event.Start to properly construct the
span tree. (If you really want to do it, you can still call Deliver.)

Change-Id: Ibe7780ce5277e9d6dac5406e879a35d727a89eff
Reviewed-on: https://go-review.googlesource.com/c/exp/+/313409
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>