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//! Core primitives for `tracing`.
//!
//! [`tracing`] is a framework for instrumenting Rust programs to collect
//! structured, event-based diagnostic information. This crate defines the core
//! primitives of `tracing`.
//!
//! This 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
//! `Event`s.
//!
//! * [`Field`], [`FieldSet`], [`Value`], and [`ValueSet`] represent the
//! structured data attached to a span.
//!
//! * [`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` 1.49+][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.
//!
//! The [`tokio-rs/tracing`] repository contains less stable crates designed to
//! be used with the `tracing` ecosystem. It includes a collection of
//! `Subscriber` implementations, as well as utility and adapter crates.
//!
//! ## 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 = "0.1.22", default-features = false }
//! ```
//!
//! **Note**:`tracing-core`'s `no_std` support requires `liballoc`.
//!
//! ### Unstable Features
//!
//! These feature flags enable **unstable** features. The public API may break in 0.1.x
//! releases. To enable these features, the `--cfg tracing_unstable` must be passed to
//! `rustc` when compiling.
//!
//! The following unstable feature flags are currently available:
//!
//! * `valuable`: Enables support for recording [field values] using the
//! [`valuable`] crate.
//!
//! #### Enabling Unstable Features
//!
//! The easiest way to set the `tracing_unstable` cfg is to use the `RUSTFLAGS`
//! env variable when running `cargo` commands:
//!
//! ```shell
//! RUSTFLAGS="--cfg tracing_unstable" cargo build
//! ```
//! Alternatively, the following can be added to the `.cargo/config` file in a
//! project to automatically enable the cfg flag for that project:
//!
//! ```toml
//! [build]
//! rustflags = ["--cfg", "tracing_unstable"]
//! ```
//!
//! [field values]: crate::field
//!
//! ## 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.
//!
//!
//! [`span::Id`]: span::Id
//! [`Event`]: event::Event
//! [`Subscriber`]: subscriber::Subscriber
//! [`Metadata`]: metadata::Metadata
//! [`Callsite`]: callsite::Callsite
//! [`Field`]: field::Field
//! [`FieldSet`]: field::FieldSet
//! [`Value`]: field::Value
//! [`ValueSet`]: field::ValueSet
//! [`Dispatch`]: dispatcher::Dispatch
#
)]
#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(docsrs, feature(doc_cfg), deny(rustdoc::broken_intra_doc_links))]
#![warn(
missing_debug_implementations,
missing_docs,
rust_2018_idioms,
unreachable_pub,
bad_style,
const_err,
dead_code,
improper_ctypes,
non_shorthand_field_patterns,
no_mangle_generic_items,
overflowing_literals,
path_statements,
patterns_in_fns_without_body,
private_in_public,
unconditional_recursion,
unused,
unused_allocation,
unused_comparisons,
unused_parens,
while_true
)]
#[cfg(not(feature = "std"))]
extern crate alloc;
/// Statically constructs an [`Identifier`] for the provided [`Callsite`].
///
/// This may be used in contexts such as static initializers.
///
/// For example:
/// ```rust
/// use tracing_core::{callsite, identify_callsite};
/// # use tracing_core::{Metadata, subscriber::Interest};
/// # fn main() {
/// pub struct MyCallsite {
/// // ...
/// }
/// impl callsite::Callsite for MyCallsite {
/// # fn set_interest(&self, _: Interest) { unimplemented!() }
/// # fn metadata(&self) -> &Metadata { unimplemented!() }
/// // ...
/// }
///
/// static CALLSITE: MyCallsite = MyCallsite {
/// // ...
/// };
///
/// static CALLSITE_ID: callsite::Identifier = identify_callsite!(&CALLSITE);
/// # }
/// ```
///
/// [`Identifier`]: callsite::Identifier
/// [`Callsite`]: callsite::Callsite
#[macro_export]
macro_rules! identify_callsite {
($callsite:expr) => {
$crate::callsite::Identifier($callsite)
};
}
/// Statically constructs new span [metadata].
///
/// /// For example:
/// ```rust
/// # use tracing_core::{callsite::Callsite, subscriber::Interest};
/// use tracing_core::metadata;
/// use tracing_core::metadata::{Kind, Level, Metadata};
/// # fn main() {
/// # pub struct MyCallsite { }
/// # impl Callsite for MyCallsite {
/// # fn set_interest(&self, _: Interest) { unimplemented!() }
/// # fn metadata(&self) -> &Metadata { unimplemented!() }
/// # }
/// #
/// static FOO_CALLSITE: MyCallsite = MyCallsite {
/// // ...
/// };
///
/// static FOO_METADATA: Metadata = metadata!{
/// name: "foo",
/// target: module_path!(),
/// level: Level::DEBUG,
/// fields: &["bar", "baz"],
/// callsite: &FOO_CALLSITE,
/// kind: Kind::SPAN,
/// };
/// # }
/// ```
///
/// [metadata]: metadata::Metadata
/// [`Metadata::new`]: metadata::Metadata::new
#[macro_export]
macro_rules! metadata {
(
name: $name:expr,
target: $target:expr,
level: $level:expr,
fields: $fields:expr,
callsite: $callsite:expr,
kind: $kind:expr
) => {
$crate::metadata! {
name: $name,
target: $target,
level: $level,
fields: $fields,
callsite: $callsite,
kind: $kind,
}
};
(
name: $name:expr,
target: $target:expr,
level: $level:expr,
fields: $fields:expr,
callsite: $callsite:expr,
kind: $kind:expr,
) => {
$crate::metadata::Metadata::new(
$name,
$target,
$level,
Some(file!()),
Some(line!()),
Some(module_path!()),
$crate::field::FieldSet::new($fields, $crate::identify_callsite!($callsite)),
$kind,
)
};
}
pub(crate) mod lazy;
// Trimmed-down vendored version of spin 0.5.2 (0387621)
// Dependency of no_std lazy_static, not required in a std build
#[cfg(not(feature = "std"))]
pub(crate) mod spin;
#[cfg(not(feature = "std"))]
#[doc(hidden)]
pub type Once = self::spin::Once<()>;
#[cfg(feature = "std")]
pub use stdlib::sync::Once;
pub mod callsite;
pub mod dispatcher;
pub mod event;
pub mod field;
pub mod metadata;
mod parent;
pub mod span;
pub(crate) mod stdlib;
pub mod subscriber;
#[doc(inline)]
pub use self::{
callsite::Callsite,
dispatcher::Dispatch,
event::Event,
field::Field,
metadata::{Level, LevelFilter, Metadata},
subscriber::Subscriber,
};
pub use self::{metadata::Kind, subscriber::Interest};
mod sealed {
pub trait Sealed {}
}