`EnvFilter` could implement `Clone`

[jamesmunns]

Feature Request

Crates

tracing-subscriber

Motivation

As of clap v4, there is now a Clone requirement on some part of the parse machinery. This means that trying to take/parse an EnvFilter does not work, as it does not fulfill the Clone bound

Proposal

Add the Clone bound to EnvFilter, or provide a type that does, which can be used with Clap.

Alternatives

Provide some other documented way of taking tracing Filter directives from Clap and other similar tools

[jamesmunns]

If it's useful, I could provide a minimal repro of a small project that takes trace level directives from a CLI.

I have a version written by Eliza that works with clap v3 in my melpomene project, though there have been some changes to the derive proc macro format in v4.

[jamesmunns]

Also, if this is as simple as "okay add Clone to the derive list", I can open a PR that does this! I just wasn't sure if this was intentional or there would be some compelling or complicated reason not to do this.

[davidbarsky]

I'm trying to remember if we can add Clone to the derive list, but I recall that adding Layer implementations for Arc<dyn Layer> broke per-layer filtering. I don't recall if this would also apply to EnvFilter—it might, it's kinda a hairy implementation—but I'd try adding Clone to it and using in per-layer Filters and seeing if things go screwy.

[Benjamin-L]

Clone would also be useful in cases where you're using layer.with_filter(env_filter) on multiple layers. In my case, I'm trying to combine tokio-console (which needs an unfiltered layer) with several logging-related layers that need the same filter.

It looks like there was a PR for this open a while ago (#2398), but it was closed by the author. I'm good to pick it up again, if it's likely to be accepted.