Add feature flag for log support.

[samscott89]

Just a quick potential fix to #306 (if desired).

[LucioFranco]

@samscott89 would this still provide tracing support?

[samscott89]

I believe so. AFAICT, the idea seems to be move everything to tracing, and then use the tracing/log feature to provide compatibility with log. (I'm going off of ~ this convo #298 (comment)). Which is on by default since people using log would other see their logs disappear.

The problem is for people using tracing first, and redirecting log outputs to tracing, we now get double the logs. And also a ton of noise since tracing/log logs a bunch of extra stuff, like when spans are entered. Although that is a separate thing.

[hawkw]

The problem is for people using tracing first, and redirecting log outputs to tracing, we now get double the logs. And also a ton of noise since tracing/log logs a bunch of extra stuff, like when spans are entered. Although that is a separate thing.

@samscott89 I think there's potentially some strategies we could use to work around the problem of duplicate logs when both tracing-log's LogTracer and the log feature flag are in use, though they might need some design --- there's a tracing ticket in there for sure.

[samscott89]

The problem is for people using tracing first, and redirecting log outputs to tracing, we now get double the logs. And also a ton of noise since tracing/log logs a bunch of extra stuff, like when spans are entered. Although that is a separate thing.

@samscott89 I think there's potentially some strategies we could use to work around the problem of duplicate logs when both tracing-log's LogTracer and the log feature flag are in use, though they might need some design --- there's a tracing ticket in there for sure.

Hmm, yeah the idea that everyone would expose a log feature does seem a bit unwieldy.

I submitted tokio-rs/tracing#204 as a starting point

[samscott89]

Okay, I'll close this PR then in favour of solving it in tracing.