Vendor things

third-party/vendor/tracing-core/README.md

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+![Tracing — Structured, application-level diagnostics][splash]
+
+[splash]: https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/splash.svg
+
+# tracing-core
+
+Core primitives for application-level tracing.
+
+[![Crates.io][crates-badge]][crates-url]
+[![Documentation][docs-badge]][docs-url]
+[![Documentation (master)][docs-master-badge]][docs-master-url]
+[![MIT licensed][mit-badge]][mit-url]
+[![Build Status][actions-badge]][actions-url]
+[![Discord chat][discord-badge]][discord-url]
+
+[Documentation][docs-url] | [Chat][discord-url]
+
+[crates-badge]: https://img.shields.io/crates/v/tracing-core.svg
+[crates-url]: https://crates.io/crates/tracing-core/0.1.31
+[docs-badge]: https://docs.rs/tracing-core/badge.svg
+[docs-url]: https://docs.rs/tracing-core/0.1.31
+[docs-master-badge]: https://img.shields.io/badge/docs-master-blue
+[docs-master-url]: https://tracing-rs.netlify.com/tracing_core
+[mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg
+[mit-url]: LICENSE
+[actions-badge]: https://github.com/tokio-rs/tracing/workflows/CI/badge.svg
+[actions-url]:https://github.com/tokio-rs/tracing/actions?query=workflow%3ACI
+[discord-badge]: https://img.shields.io/discord/500028886025895936?logo=discord&label=discord&logoColor=white
+[discord-url]: https://discord.gg/EeF3cQw
+
+## Overview
+
+[`tracing`] is a framework for instrumenting Rust programs to collect
+structured, event-based diagnostic information. This crate defines the core
+primitives of `tracing`.
+
+The crate provides:
+
+* [`span::Id`] identifies a span within the execution of a program.
+
+* [`Event`] represents a single event within a trace.
+
+* [`Subscriber`], the trait implemented to collect trace data.
+
+* [`Metadata`] and [`Callsite`] provide information describing spans and
+  events.
+
+* [`Field`], [`FieldSet`], [`Value`], and [`ValueSet`] represent the
+  structured data attached to spans and events.
+
+* [`Dispatch`] allows spans and events to be dispatched to `Subscriber`s.
+
+In addition, it defines the global callsite registry and per-thread current
+dispatcher which other components of the tracing system rely on.
+
+*Compiler support: [requires `rustc` 1.56+][msrv]*
+
+[msrv]: #supported-rust-versions
+
+## Usage
+  
+Application authors will typically not use this crate directly. Instead, they
+will use the [`tracing`] crate, which provides a much more fully-featured
+API. However, this crate's API will change very infrequently, so it may be used
+when dependencies must be very stable.
+
+`Subscriber` implementations may depend on `tracing-core` rather than `tracing`,
+as the additional APIs provided by `tracing` are primarily useful for
+instrumenting libraries and applications, and are generally not necessary for
+`Subscriber` implementations.
+
+###  Crate Feature Flags
+
+The following crate feature flags are available:
+
+* `std`: Depend on the Rust standard library (enabled by default).
+
+  `no_std` users may disable this feature with `default-features = false`:
+
+  ```toml
+  [dependencies]
+  tracing-core = { version = "0.1.31", default-features = false }
+  ```
+
+  **Note**:`tracing-core`'s `no_std` support requires `liballoc`.
+
+[`tracing`]: ../tracing
+[`span::Id`]: https://docs.rs/tracing-core/0.1.31/tracing_core/span/struct.Id.html
+[`Event`]: https://docs.rs/tracing-core/0.1.31/tracing_core/event/struct.Event.html
+[`Subscriber`]: https://docs.rs/tracing-core/0.1.31/tracing_core/subscriber/trait.Subscriber.html
+[`Metadata`]: https://docs.rs/tracing-core/0.1.31/tracing_core/metadata/struct.Metadata.html
+[`Callsite`]: https://docs.rs/tracing-core/0.1.31/tracing_core/callsite/trait.Callsite.html
+[`Field`]: https://docs.rs/tracing-core/0.1.31/tracing_core/field/struct.Field.html
+[`FieldSet`]: https://docs.rs/tracing-core/0.1.31/tracing_core/field/struct.FieldSet.html
+[`Value`]: https://docs.rs/tracing-core/0.1.31/tracing_core/field/trait.Value.html
+[`ValueSet`]: https://docs.rs/tracing-core/0.1.31/tracing_core/field/struct.ValueSet.html
+[`Dispatch`]: https://docs.rs/tracing-core/0.1.31/tracing_core/dispatcher/struct.Dispatch.html
+
+## Supported Rust Versions
+
+Tracing is built against the latest stable release. The minimum supported
+version is 1.56. 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 1.69, the minimum supported version will not be increased
+past 1.69, 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](LICENSE).
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in Tokio by you, shall be licensed as MIT, without any additional
+terms or conditions.