Using tracing/tracing_subscriber in build scripts

[liss-h]

Hi,
I was wondering if there is a "standard" way to use tracing/tracing_subscriber in build scripts.

What I had in mind roughly, would be WARN and ERROR go to stdout with cargo::warning= prepended (so that they get forwarded to the user). The rest could go to stderr which is only visible when building with verbose output.

Is there some pre-made solution for this, or something that behaves similarly?

Thanks :)

[hawkw]

I don't know of any existing implementation of something that does this, but it definitely sounds like it would be useful! If you're interested in writing a crate for this, we'd love to add it in the list of tracing ecosystem crates in the documentation.

If I was going to write an implementation of this, I would probably consider using the MakeWriter::make_writer_for method in a tracing_subscriber::fmt::MakeWriter implementation. That method is designed to allow a MakeWriter implementation to return different I/O writers based on an event's Metadata (including its level), so it can be used for sending different levels to different outputs. If you implemented a BuildScriptWriter or something using this interface, it could be composed with any FormatEvent implementation, so you wouldn't have to reimplement the formatter, and it could be used with any existing formatter.

[liss-h]

I've created it in one of our repos for now (dice-group/tracing-build-script#1).

We can keep it there, or it might also fit next to the TestWriter in tracing-subscriber itself.

Feel free to leave a review if you are interested, or tell me if I should create a PR against this repo