tracing/tracing-core
Eliza Weisman 3f8280ae69
docs: consistent MSRV docs & policy explanation (#941)
## Motivation

PR #934 fixed a bug in the CI configuration where MSRV checks were not
being run correctly. After this was fixed, it was necessary to bump the
MSRV to 1.40.0, as the tests were no longer actually passing on 1.39,
because some dependencies no longer support it.

While updating the documentation to indicate that the new MSRV is 1.40,
I noticed that the note on the MSRV was located inconsistently in the
READMEs and `lib.rs` documentation of various crates, and missing
entirely in some cases. Additionally, there have been some questions on
what our MSRV _policies_ are, and whether MSRV bumps are considered
breaking changes (see e.g. #936). 

## Solution

I've updated all the MSRV notes in the documentation and READMEs to
indicate that the MSRV is 1.40. I've also ensured that the MSRV note is
in the same place for every crate (at the end of the "Overview" section
in the docs), and that it's formatted consistently.

Furthermore, I added a new section to the READMEs and `lib.rs` docs
explaining the current MSRV policy in some detail. Hopefully, this
should answer questions like #936 in the future. The MSRV note in the
overview section includes a link to the section with further details.

Finally, while doing this, I noticed a couple of crates
(`tracing-journald` and `tracing-serde`) were missing top-level `lib.rs`
docs. Rather than just adding an MSRV note and nothing else, I went
ahead and fixed this using documentation from those crate's READMEs.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
2020-08-18 12:11:16 -07:00
..

Tracing — Structured, application-level diagnostics

tracing-core

Core primitives for application-level tracing.

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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 Subscribers.

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 1.40+

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:

    [dependencies]
    tracing-core = { version = "0.1.14", default-features = false }
    

    Note:tracing-core's no_std support requires liballoc.

Supported Rust Versions

Tracing is built against the latest stable release. The minimum supported version is 1.40. 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 Tokio by you, shall be licensed as MIT, without any additional terms or conditions.