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 </pre><pre class="rust"><code><span class="doccomment">//! 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` 1.56+][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&#39;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 = &quot;0.1.22&quot;, default-features = false }
 //!   ```
 //!
 //!   **Note**:`tracing-core`&#39;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=&quot;--cfg tracing_unstable&quot; 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 = [&quot;--cfg&quot;, &quot;tracing_unstable&quot;]
 //! ```
 //!
 //! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section
 //! [field values]: crate::field
 //! [`valuable`]: https://crates.io/crates/valuable
 //!
 //! ## 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 1.66, 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
 //! [`tokio-rs/tracing`]: https://github.com/tokio-rs/tracing
 //! [`tracing`]: https://crates.io/crates/tracing
 </span><span class="attribute">#![doc(
     html_logo_url = <span class="string">&quot;https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png&quot;</span>,
     issue_tracker_base_url = <span class="string">&quot;https://github.com/tokio-rs/tracing/issues/&quot;
 </span>)]
 #![cfg_attr(not(feature = <span class="string">&quot;std&quot;</span>), 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,
     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 = <span class="string">&quot;std&quot;</span>))]
 </span><span class="kw">extern crate </span>alloc;

 <span class="doccomment">/// 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(&amp;self, _: Interest) { unimplemented!() }
 /// # fn metadata(&amp;self) -&gt; &amp;Metadata { unimplemented!() }
 ///     // ...
 /// }
 ///
 /// static CALLSITE: MyCallsite = MyCallsite {
 ///     // ...
 /// };
 ///
 /// static CALLSITE_ID: callsite::Identifier = identify_callsite!(&amp;CALLSITE);
 /// # }
 /// ```
 ///
 /// [`Identifier`]: callsite::Identifier
 /// [`Callsite`]: callsite::Callsite
 </span><span class="attribute">#[macro_export]
 </span><span class="macro">macro_rules! </span>identify_callsite {
     (<span class="macro-nonterminal">$callsite</span>:expr) =&gt; {
         <span class="macro-nonterminal">$crate::callsite::Identifier</span>(<span class="macro-nonterminal">$callsite</span>)
     };
 }

 <span class="doccomment">/// 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(&amp;self, _: Interest) { unimplemented!() }
 /// # fn metadata(&amp;self) -&gt; &amp;Metadata { unimplemented!() }
 /// # }
 /// #
 /// static FOO_CALLSITE: MyCallsite = MyCallsite {
 ///     // ...
 /// };
 ///
 /// static FOO_METADATA: Metadata = metadata!{
 ///     name: &quot;foo&quot;,
 ///     target: module_path!(),
 ///     level: Level::DEBUG,
 ///     fields: &amp;[&quot;bar&quot;, &quot;baz&quot;],
 ///     callsite: &amp;FOO_CALLSITE,
 ///     kind: Kind::SPAN,
 /// };
 /// # }
 /// ```
 ///
 /// [metadata]: metadata::Metadata
 /// [`Metadata::new`]: metadata::Metadata::new
 </span><span class="attribute">#[macro_export]
 </span><span class="macro">macro_rules! </span>metadata {
     (
         name: <span class="macro-nonterminal">$name</span>:expr,
         target: <span class="macro-nonterminal">$target</span>:expr,
         level: <span class="macro-nonterminal">$level</span>:expr,
         fields: <span class="macro-nonterminal">$fields</span>:expr,
         callsite: <span class="macro-nonterminal">$callsite</span>:expr,
         kind: <span class="macro-nonterminal">$kind</span>:expr
     ) =&gt; {
         <span class="macro-nonterminal">$</span><span class="macro">crate::metadata! </span>{
             <span class="macro-nonterminal">name</span>: <span class="macro-nonterminal">$name</span>,
             target: <span class="macro-nonterminal">$target</span>,
             level: <span class="macro-nonterminal">$level</span>,
             fields: <span class="macro-nonterminal">$fields</span>,
             callsite: <span class="macro-nonterminal">$callsite</span>,
             kind: <span class="macro-nonterminal">$kind</span>,
         }
     };
     (
         name: <span class="macro-nonterminal">$name</span>:expr,
         target: <span class="macro-nonterminal">$target</span>:expr,
         level: <span class="macro-nonterminal">$level</span>:expr,
         fields: <span class="macro-nonterminal">$fields</span>:expr,
         callsite: <span class="macro-nonterminal">$callsite</span>:expr,
         kind: <span class="macro-nonterminal">$kind</span>:expr,
     ) =&gt; {
         <span class="macro-nonterminal">$crate::metadata::Metadata::new</span>(
             <span class="macro-nonterminal">$name</span>,
             <span class="macro-nonterminal">$target</span>,
             <span class="macro-nonterminal">$level</span>,
             <span class="prelude-val">Some</span>(<span class="macro">file!</span>()),
             <span class="prelude-val">Some</span>(<span class="macro">line!</span>()),
             <span class="prelude-val">Some</span>(<span class="macro">module_path!</span>()),
             <span class="macro-nonterminal">$crate::field::FieldSet::new</span>(<span class="macro-nonterminal">$fields</span>, <span class="macro-nonterminal">$</span><span class="macro">crate::identify_callsite!</span>(<span class="macro-nonterminal">$callsite</span>)),
             <span class="macro-nonterminal">$kind</span>,
         )
     };
 }

 <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>lazy;

 <span class="comment">// Trimmed-down vendored version of spin 0.5.2 (0387621)
 // Dependency of no_std lazy_static, not required in a std build
 </span><span class="attribute">#[cfg(not(feature = <span class="string">&quot;std&quot;</span>))]
 </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>spin;

 <span class="attribute">#[cfg(not(feature = <span class="string">&quot;std&quot;</span>))]
 #[doc(hidden)]
 </span><span class="kw">pub type </span>Once = <span class="self">self</span>::spin::Once&lt;()&gt;;

 <span class="attribute">#[cfg(feature = <span class="string">&quot;std&quot;</span>)]
 </span><span class="kw">pub use </span>stdlib::sync::Once;

 <span class="kw">pub mod </span>callsite;
 <span class="kw">pub mod </span>dispatcher;
 <span class="kw">pub mod </span>event;
 <span class="kw">pub mod </span>field;
 <span class="kw">pub mod </span>metadata;
 <span class="kw">mod </span>parent;
 <span class="kw">pub mod </span>span;
 <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>stdlib;
 <span class="kw">pub mod </span>subscriber;

 <span class="attribute">#[doc(inline)]
 </span><span class="kw">pub use </span><span class="self">self</span>::{
     callsite::Callsite,
     dispatcher::Dispatch,
     event::Event,
     field::Field,
     metadata::{Level, LevelFilter, Metadata},
     subscriber::Subscriber,
 };

 <span class="kw">pub use </span><span class="self">self</span>::{metadata::Kind, subscriber::Interest};

 <span class="kw">mod </span>sealed {
     <span class="kw">pub trait </span>Sealed {}
 }
 </code></pre></div>
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