Add a -vv log level and make -v more readable

[konstin]

Behind error messages, the debug log is the second most important resource to finding out what and why went wrong when there was a problem with uv. It is important to see which paths it has found and how the decisions in the resolver were made. I'm trying to improve the experience interacting with the debug log.

The hierarchical layer is verbose and hard to follow, so it's moved to the -vv extra verbose setting, while -v works like RUST_LOG=uv=debug.

For installing jupyter with a warm cache:

• Default: https://gist.github.com/konstin/4de6e466127311c5a5fc2f99c56a8e11
• -v: https://gist.github.com/konstin/e7bafe0ec7d07e47ba98a3865ae2ef3e
• -vv: https://gist.github.com/konstin/3ee1aaff37f91cceb6275dd5525f180e
  Ideally, we would have -v, -vv and -vvv, but we're lacking the the info! layer for -v, so there's only two layers for now.

The tracing_subcriber formatter always print the current span, so i replaced it with a custom formatter.

Best read commit-by-commit.

[zanieb]

Without reading through everything here.. my initial thoughts about logging are:

• -v should include some additional tracing messages. It should not be for debugging. It should be for users who want to understand what uv is doing. We definitely need to show less messages than our current verbose output. A flat format makes a lot of sense.
• -vv should include debug level messages. It should be used for debugging. I think using a flat format is fine here too. This should be our recommended level when reporting bugs.
• -vvv should include trace level messages. It should be used for advanced debugging. Using the nested format makes sense here.

[konstin]

My thought was to not have too many flags but have users quickly switch to RUST_LOG=debug or RUST_LOG=<module>=trace, the filtering feature is something a counted cli flag can't compete with.

[zanieb]

I don't think RUST_LOG levels are a reasonable thing to expect from users. It seems like a power-user feature. I agree filtering seems nice but it's not like a counted flag will prevent power users from using it? We don't have to override RUST_LOG if it is set.

[konstin]

We definitely need to show less messages than our current verbose output

Where would you source those messages, from what we currently show as reporter spinner status message?

[zanieb]

We definitely need to show less messages than our current verbose output

Where would you source those messages, from what we currently show as reporter spinner status message?

I'm not sure! I'm not super familiar with our logging setup. I presume we'd use info! level logs for things that should be shown with -v

[konstin]

I agree, but we're currently lacking an info! layer, we effectively don't use it at all but only debug! and trace!. I don't want to extend the scope here even more to recategorizing all our debug! into info! and debug!. Instead, i'd like to go ahead with the -v/-vv split now, we can split them into three levels later.