Improve error handling for log filter

[LucDrenth]

Objective

This PR aims to improve error handling for log filters.

Closes #13850

Solution

I changed the parsing of LogPlugin its filter to lossy, so that it prints the directives with an error but does not skip them. I decided on letting it gracefully handle the error instead of panicking to be consistent with the parsing from an environment variable that it tries to do before parsing it from the LogPlugin filter.

If the user decides to specify the filter by an environment variable, it would silently fail and default to the LogPlugin filter value. It now prints an error before defaulting to the LogPlugin filter value.

Unfortunately, I could not try and loosely set the filter from the environment variable because the tracing-subscriber module does not expose the function it uses to get the environment variable, and I would rather not copy its code. We may want to check if the maintainers are open to exposing the method.

Testing

Consider the following bevy app, where the second of the 3 filters is invalid:

use bevy::{log::LogPlugin, prelude::*};

fn main() {
    App::new().add_plugins(DefaultPlugins
        .set(LogPlugin {
            filter: "wgpu=error,my_package=invalid_log_level,naga=warn".into(),
            ..default()
        })
    ).run();
}

In the previous situation, it would panic with a non-descriptive error: "called Result::unwrap() on an Err value: ParseError { kind: Other(None) }", while only 1 of the 3 filters is invalid. When running cargo run, it will now use the two valid filters and print an error on the invalid filter.

ignoring my_package=invalid_log_level: invalid filter directive

This error comes from tracing-subscriber and cannot be altered as far as I can see.

To test setting the log filter through an environment variable, you can use RUST_LOG="wgpu=error,my_package=invalid_log_level,naga=warn" cargo run to run your app. In the previous situation it would silently fail and use the LogPlugin filter. It will now print an error before using the LogPlugin filter.

LogPlugin failed to parse filter from env: invalid filter directive

Changelog

• Added warning when using invalid filter in the RUST_LOG environment variable
• Prevent the app from panicking when setting an invalid LogPlugin filter

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[alice-i-cecile]

We may want to check if the maintainers are open to exposing the method.

Agreed, can you open an issue on their repo linking this PR?

[LucDrenth]

We may want to check if the maintainers are open to exposing the method.

Agreed, can you open an issue on their repo linking this PR?

Here is the issue tokio-rs/tracing#3009. Shall I open an issue in this repo to follow on this once this PR is merged?

[alice-i-cecile]

Yes please.