130c499b7c
## Motivation Currently, when using the `Layer` impl for `Option<S: Layer<...>>`, the `Layer::max_level_hint` returns `Some(LevelFilter::OFF)`. This was intended to allow totally disabling output in the case where a `Subscriber` is composed entirely of `None` `Layer`s. However, when other `Layer`s *do* exist but return `None` from their `max_level_hint` implementations to indicate that they don't care what the max level is, the presence of a single `None` layer will globally disable everything, which is not the wanted behavior. Fixes #2265 ## Solution This branch introduces a special downcast marker that can be used to detect when a `Layer` in a `Layered` is `None`. This allows the `pick_level_hint` method to short-circuit when a `Layer` implementation which is `None` returns `Some(LevelFilter::OFF)` from its `max_level_hint` if the other half of the `Layered` is not `None`. The tests I added should be pretty thorough! Additionally, the downcast marker is special-cased in the `reload` `Layer`. Normally, this `Layer` doesn't support downcasting, but it can in the case of the special marker value. Co-authored-by: Eliza Weisman <eliza@buoyant.io>
tracing-subscriber
Utilities for implementing and composing tracing subscribers.
Compiler support: requires rustc 1.49+
Supported Rust Versions
Tracing is built against the latest stable release. The minimum supported version is 1.49. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.
Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.45, the minimum supported version will not be increased past 1.42, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tracing by you, shall be licensed as MIT, without any additional terms or conditions.