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 </pre><pre class="rust"><code><span class="doccomment">//! A scoped, structured logging and diagnostics system.
 //!
 //! # Overview
 //!
 //! `tracing` is a framework for instrumenting Rust programs to collect
 //! structured, event-based diagnostic information.
 //!
 //! In asynchronous systems like Tokio, interpreting traditional log messages can
 //! often be quite challenging. Since individual tasks are multiplexed on the same
 //! thread, associated events and log lines are intermixed making it difficult to
 //! trace the logic flow. `tracing` expands upon logging-style diagnostics by
 //! allowing libraries and applications to record structured events with additional
 //! information about *temporality* and *causality* — unlike a log message, a span
 //! in `tracing` has a beginning and end time, may be entered and exited by the
 //! flow of execution, and may exist within a nested tree of similar spans. In
 //! addition, `tracing` spans are *structured*, with the ability to record typed
 //! data as well as textual messages.
 //!
 //! The `tracing` crate provides the APIs necessary for instrumenting libraries
 //! and applications to emit trace data.
 //!
 //! *Compiler support: [requires `rustc` 1.49+][msrv]*
 //!
 //! [msrv]: #supported-rust-versions
 //! # Core Concepts
 //!
 //! The core of `tracing`&#39;s API is composed of _spans_, _events_ and
 //! _subscribers_. We&#39;ll cover these in turn.
 //!
 //! ## Spans
 //!
 //! To record the flow of execution through a program, `tracing` introduces the
 //! concept of [spans]. Unlike a log line that represents a _moment in
 //! time_, a span represents a _period of time_ with a beginning and an end. When a
 //! program begins executing in a context or performing a unit of work, it
 //! _enters_ that context&#39;s span, and when it stops executing in that context,
 //! it _exits_ the span. The span in which a thread is currently executing is
 //! referred to as that thread&#39;s _current_ span.
 //!
 //! For example:
 //! ```
 //! use tracing::{span, Level};
 //! # fn main() {
 //! let span = span!(Level::TRACE, &quot;my_span&quot;);
 //! // `enter` returns a RAII guard which, when dropped, exits the span. this
 //! // indicates that we are in the span for the current lexical scope.
 //! let _enter = span.enter();
 //! // perform some work in the context of `my_span`...
 //! # }
 //!```
 //!
 //! The [`span` module][span]&#39;s documentation provides further details on how to
 //! use spans.
 //!
 //! &lt;div class=&quot;example-wrap&quot; style=&quot;display:inline-block&quot;&gt;&lt;pre class=&quot;compile_fail&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 //!
 //!  **Warning**: In asynchronous code that uses async/await syntax,
 //!  `Span::enter` may produce incorrect traces if the returned drop
 //!  guard is held across an await point. See
 //!  [the method documentation][Span#in-asynchronous-code] for details.
 //!
 //! &lt;/pre&gt;&lt;/div&gt;
 //!
 //! ## Events
 //!
 //! An [`Event`] represents a _moment_ in time. It signifies something that
 //! happened while a trace was being recorded. `Event`s are comparable to the log
 //! records emitted by unstructured logging code, but unlike a typical log line,
 //! an `Event` may occur within the context of a span.
 //!
 //! For example:
 //! ```
 //! use tracing::{event, span, Level};
 //!
 //! # fn main() {
 //! // records an event outside of any span context:
 //! event!(Level::INFO, &quot;something happened&quot;);
 //!
 //! let span = span!(Level::INFO, &quot;my_span&quot;);
 //! let _guard = span.enter();
 //!
 //! // records an event within &quot;my_span&quot;.
 //! event!(Level::DEBUG, &quot;something happened inside my_span&quot;);
 //! # }
 //!```
 //!
 //! In general, events should be used to represent points in time _within_ a
 //! span — a request returned with a given status code, _n_ new items were
 //! taken from a queue, and so on.
 //!
 //! The [`Event` struct][`Event`] documentation provides further details on using
 //! events.
 //!
 //! ## Subscribers
 //!
 //! As `Span`s and `Event`s occur, they are recorded or aggregated by
 //! implementations of the [`Subscriber`] trait. `Subscriber`s are notified
 //! when an `Event` takes place and when a `Span` is entered or exited. These
 //! notifications are represented by the following `Subscriber` trait methods:
 //!
 //! + [`event`][Subscriber::event], called when an `Event` takes place,
 //! + [`enter`], called when execution enters a `Span`,
 //! + [`exit`], called when execution exits a `Span`
 //!
 //! In addition, subscribers may implement the [`enabled`] function to _filter_
 //! the notifications they receive based on [metadata] describing each `Span`
 //! or `Event`. If a call to `Subscriber::enabled` returns `false` for a given
 //! set of metadata, that `Subscriber` will *not* be notified about the
 //! corresponding `Span` or `Event`. For performance reasons, if no currently
 //! active subscribers express interest in a given set of metadata by returning
 //! `true`, then the corresponding `Span` or `Event` will never be constructed.
 //!
 //! # Usage
 //!
 //! First, add this to your `Cargo.toml`:
 //!
 //! ```toml
 //! [dependencies]
 //! tracing = &quot;0.1&quot;
 //! ```
 //!
 //! ## Recording Spans and Events
 //!
 //! Spans and events are recorded using macros.
 //!
 //! ### Spans
 //!
 //! The [`span!`] macro expands to a [`Span` struct][`Span`] which is used to
 //! record a span. The [`Span::enter`] method on that struct records that the
 //! span has been entered, and returns a [RAII] guard object, which will exit
 //! the span when dropped.
 //!
 //! For example:
 //!
 //! ```rust
 //! use tracing::{span, Level};
 //! # fn main() {
 //! // Construct a new span named &quot;my span&quot; with trace log level.
 //! let span = span!(Level::TRACE, &quot;my span&quot;);
 //!
 //! // Enter the span, returning a guard object.
 //! let _enter = span.enter();
 //!
 //! // Any trace events that occur before the guard is dropped will occur
 //! // within the span.
 //!
 //! // Dropping the guard will exit the span.
 //! # }
 //! ```
 //!
 //! The [`#[instrument]`][instrument] attribute provides an easy way to
 //! add `tracing` spans to functions. A function annotated with `#[instrument]`
 //! will create and enter a span with that function&#39;s name every time the
 //! function is called, with arguments to that function will be recorded as
 //! fields using `fmt::Debug`.
 //!
 //! For example:
 //! ```ignore
 //! # // this doctest is ignored because we don&#39;t have a way to say
 //! # // that it should only be run with cfg(feature = &quot;attributes&quot;)
 //! use tracing::{Level, event, instrument};
 //!
 //! #[instrument]
 //! pub fn my_function(my_arg: usize) {
 //!     // This event will be recorded inside a span named `my_function` with the
 //!     // field `my_arg`.
 //!     event!(Level::INFO, &quot;inside my_function!&quot;);
 //!     // ...
 //! }
 //! # fn main() {}
 //! ```
 //!
 //! For functions which don&#39;t have built-in tracing support and can&#39;t have
 //! the `#[instrument]` attribute applied (such as from an external crate),
 //! the [`Span` struct][`Span`] has a [`in_scope()` method][`in_scope`]
 //! which can be used to easily wrap synchonous code in a span.
 //!
 //! For example:
 //! ```rust
 //! use tracing::info_span;
 //!
 //! # fn doc() -&gt; Result&lt;(), ()&gt; {
 //! # mod serde_json {
 //! #    pub(crate) fn from_slice(buf: &amp;[u8]) -&gt; Result&lt;(), ()&gt; { Ok(()) }
 //! # }
 //! # let buf: [u8; 0] = [];
 //! let json = info_span!(&quot;json.parse&quot;).in_scope(|| serde_json::from_slice(&amp;buf))?;
 //! # let _ = json; // suppress unused variable warning
 //! # Ok(())
 //! # }
 //! ```
 //!
 //! You can find more examples showing how to use this crate [here][examples].
 //!
 //! [RAII]: https://github.com/rust-unofficial/patterns/blob/master/patterns/behavioural/RAII.md
 //! [examples]: https://github.com/tokio-rs/tracing/tree/master/examples
 //!
 //! ### Events
 //!
 //! [`Event`]s are recorded using the [`event!`] macro:
 //!
 //! ```rust
 //! # fn main() {
 //! use tracing::{event, Level};
 //! event!(Level::INFO, &quot;something has happened!&quot;);
 //! # }
 //! ```
 //!
 //! ## Using the Macros
 //!
 //! The [`span!`] and [`event!`] macros as well as the `#[instrument]` attribute
 //! use fairly similar syntax, with some exceptions.
 //!
 //! ### Configuring Attributes
 //!
 //! Both macros require a [`Level`] specifying the verbosity of the span or
 //! event. Optionally, the [target] and [parent span] may be overridden. If the
 //! target and parent span are not overridden, they will default to the
 //! module path where the macro was invoked and the current span (as determined
 //! by the subscriber), respectively.
 //!
 //! For example:
 //!
 //! ```
 //! # use tracing::{span, event, Level};
 //! # fn main() {
 //! span!(target: &quot;app_spans&quot;, Level::TRACE, &quot;my span&quot;);
 //! event!(target: &quot;app_events&quot;, Level::INFO, &quot;something has happened!&quot;);
 //! # }
 //! ```
 //! ```
 //! # use tracing::{span, event, Level};
 //! # fn main() {
 //! let span = span!(Level::TRACE, &quot;my span&quot;);
 //! event!(parent: &amp;span, Level::INFO, &quot;something has happened!&quot;);
 //! # }
 //! ```
 //!
 //! The span macros also take a string literal after the level, to set the name
 //! of the span.
 //!
 //! ### Recording Fields
 //!
 //! Structured fields on spans and events are specified using the syntax
 //! `field_name = field_value`. Fields are separated by commas.
 //!
 //! ```
 //! # use tracing::{event, Level};
 //! # fn main() {
 //! // records an event with two fields:
 //! //  - &quot;answer&quot;, with the value 42
 //! //  - &quot;question&quot;, with the value &quot;life, the universe and everything&quot;
 //! event!(Level::INFO, answer = 42, question = &quot;life, the universe, and everything&quot;);
 //! # }
 //! ```
 //!
 //! As shorthand, local variables may be used as field values without an
 //! assignment, similar to [struct initializers]. For example:
 //!
 //! ```
 //! # use tracing::{span, Level};
 //! # fn main() {
 //! let user = &quot;ferris&quot;;
 //!
 //! span!(Level::TRACE, &quot;login&quot;, user);
 //! // is equivalent to:
 //! span!(Level::TRACE, &quot;login&quot;, user = user);
 //! # }
 //!```
 //!
 //! Field names can include dots, but should not be terminated by them:
 //! ```
 //! # use tracing::{span, Level};
 //! # fn main() {
 //! let user = &quot;ferris&quot;;
 //! let email = &quot;ferris@rust-lang.org&quot;;
 //! span!(Level::TRACE, &quot;login&quot;, user, user.email = email);
 //! # }
 //!```
 //!
 //! Since field names can include dots, fields on local structs can be used
 //! using the local variable shorthand:
 //! ```
 //! # use tracing::{span, Level};
 //! # fn main() {
 //! # struct User {
 //! #    name: &amp;&#39;static str,
 //! #    email: &amp;&#39;static str,
 //! # }
 //! let user = User {
 //!     name: &quot;ferris&quot;,
 //!     email: &quot;ferris@rust-lang.org&quot;,
 //! };
 //! // the span will have the fields `user.name = &quot;ferris&quot;` and
 //! // `user.email = &quot;ferris@rust-lang.org&quot;`.
 //! span!(Level::TRACE, &quot;login&quot;, user.name, user.email);
 //! # }
 //!```
 //!
 //! Fields with names that are not Rust identifiers, or with names that are Rust reserved words,
 //! may be created using quoted string literals. However, this may not be used with the local
 //! variable shorthand.
 //! ```
 //! # use tracing::{span, Level};
 //! # fn main() {
 //! // records an event with fields whose names are not Rust identifiers
 //! //  - &quot;guid:x-request-id&quot;, containing a `:`, with the value &quot;abcdef&quot;
 //! //  - &quot;type&quot;, which is a reserved word, with the value &quot;request&quot;
 //! span!(Level::TRACE, &quot;api&quot;, &quot;guid:x-request-id&quot; = &quot;abcdef&quot;, &quot;type&quot; = &quot;request&quot;);
 //! # }
 //!```
 //!
 //! The `?` sigil is shorthand that specifies a field should be recorded using
 //! its [`fmt::Debug`] implementation:
 //! ```
 //! # use tracing::{event, Level};
 //! # fn main() {
 //! #[derive(Debug)]
 //! struct MyStruct {
 //!     field: &amp;&#39;static str,
 //! }
 //!
 //! let my_struct = MyStruct {
 //!     field: &quot;Hello world!&quot;
 //! };
 //!
 //! // `my_struct` will be recorded using its `fmt::Debug` implementation.
 //! event!(Level::TRACE, greeting = ?my_struct);
 //! // is equivalent to:
 //! event!(Level::TRACE, greeting = tracing::field::debug(&amp;my_struct));
 //! # }
 //! ```
 //!
 //! The `%` sigil operates similarly, but indicates that the value should be
 //! recorded using its [`fmt::Display`] implementation:
 //! ```
 //! # use tracing::{event, Level};
 //! # fn main() {
 //! # #[derive(Debug)]
 //! # struct MyStruct {
 //! #     field: &amp;&#39;static str,
 //! # }
 //! #
 //! # let my_struct = MyStruct {
 //! #     field: &quot;Hello world!&quot;
 //! # };
 //! // `my_struct.field` will be recorded using its `fmt::Display` implementation.
 //! event!(Level::TRACE, greeting = %my_struct.field);
 //! // is equivalent to:
 //! event!(Level::TRACE, greeting = tracing::field::display(&amp;my_struct.field));
 //! # }
 //! ```
 //!
 //! The `%` and `?` sigils may also be used with local variable shorthand:
 //!
 //! ```
 //! # use tracing::{event, Level};
 //! # fn main() {
 //! # #[derive(Debug)]
 //! # struct MyStruct {
 //! #     field: &amp;&#39;static str,
 //! # }
 //! #
 //! # let my_struct = MyStruct {
 //! #     field: &quot;Hello world!&quot;
 //! # };
 //! // `my_struct.field` will be recorded using its `fmt::Display` implementation.
 //! event!(Level::TRACE, %my_struct.field);
 //! # }
 //! ```
 //!
 //! Additionally, a span may declare fields with the special value [`Empty`],
 //! which indicates that that the value for that field does not currently exist
 //! but may be recorded later. For example:
 //!
 //! ```
 //! use tracing::{trace_span, field};
 //!
 //! // Create a span with two fields: `greeting`, with the value &quot;hello world&quot;, and
 //! // `parting`, without a value.
 //! let span = trace_span!(&quot;my_span&quot;, greeting = &quot;hello world&quot;, parting = field::Empty);
 //!
 //! // ...
 //!
 //! // Now, record a value for parting as well.
 //! span.record(&quot;parting&quot;, &amp;&quot;goodbye world!&quot;);
 //! ```
 //!
 //! Note that a span may have up to 32 fields. The following will not compile:
 //!
 //! ```rust,compile_fail
 //! # use tracing::Level;
 //! # fn main() {
 //! let bad_span = span!(
 //!     Level::TRACE,
 //!     &quot;too many fields!&quot;,
 //!     a = 1, b = 2, c = 3, d = 4, e = 5, f = 6, g = 7, h = 8, i = 9,
 //!     j = 10, k = 11, l = 12, m = 13, n = 14, o = 15, p = 16, q = 17,
 //!     r = 18, s = 19, t = 20, u = 21, v = 22, w = 23, x = 24, y = 25,
 //!     z = 26, aa = 27, bb = 28, cc = 29, dd = 30, ee = 31, ff = 32, gg = 33
 //! );
 //! # }
 //! ```
 //!
 //! Finally, events may also include human-readable messages, in the form of a
 //! [format string][fmt] and (optional) arguments, **after** the event&#39;s
 //! key-value fields. If a format string and arguments are provided,
 //! they will implicitly create a new field named `message` whose value is the
 //! provided set of format arguments.
 //!
 //! For example:
 //!
 //! ```
 //! # use tracing::{event, Level};
 //! # fn main() {
 //! let question = &quot;the ultimate question of life, the universe, and everything&quot;;
 //! let answer = 42;
 //! // records an event with the following fields:
 //! // - `question.answer` with the value 42,
 //! // - `question.tricky` with the value `true`,
 //! // - &quot;message&quot;, with the value &quot;the answer to the ultimate question of life, the
 //! //    universe, and everything is 42.&quot;
 //! event!(
 //!     Level::DEBUG,
 //!     question.answer = answer,
 //!     question.tricky = true,
 //!     &quot;the answer to {} is {}.&quot;, question, answer
 //! );
 //! # }
 //! ```
 //!
 //! Specifying a formatted message in this manner does not allocate by default.
 //!
 //! [struct initializers]: https://doc.rust-lang.org/book/ch05-01-defining-structs.html#using-the-field-init-shorthand-when-variables-and-fields-have-the-same-name
 //! [target]: Metadata::target
 //! [parent span]: span::Attributes::parent
 //! [determined contextually]: span::Attributes::is_contextual
 //! [`fmt::Debug`]: std::fmt::Debug
 //! [`fmt::Display`]: std::fmt::Display
 //! [fmt]: std::fmt#usage
 //! [`Empty`]: field::Empty
 //!
 //! ### Shorthand Macros
 //!
 //! `tracing` also offers a number of macros with preset verbosity levels.
 //! The [`trace!`], [`debug!`], [`info!`], [`warn!`], and [`error!`] behave
 //! similarly to the [`event!`] macro, but with the [`Level`] argument already
 //! specified, while the corresponding [`trace_span!`], [`debug_span!`],
 //! [`info_span!`], [`warn_span!`], and [`error_span!`] macros are the same,
 //! but for the [`span!`] macro.
 //!
 //! These are intended both as a shorthand, and for compatibility with the [`log`]
 //! crate (see the next section).
 //!
 //! [`span!`]: span!
 //! [`event!`]: event!
 //! [`trace!`]: trace!
 //! [`debug!`]: debug!
 //! [`info!`]: info!
 //! [`warn!`]: warn!
 //! [`error!`]: error!
 //! [`trace_span!`]: trace_span!
 //! [`debug_span!`]: debug_span!
 //! [`info_span!`]: info_span!
 //! [`warn_span!`]: warn_span!
 //! [`error_span!`]: error_span!
 //!
 //! ### For `log` Users
 //!
 //! Users of the [`log`] crate should note that `tracing` exposes a set of
 //! macros for creating `Event`s (`trace!`, `debug!`, `info!`, `warn!`, and
 //! `error!`) which may be invoked with the same syntax as the similarly-named
 //! macros from the `log` crate. Often, the process of converting a project to
 //! use `tracing` can begin with a simple drop-in replacement.
 //!
 //! Let&#39;s consider the `log` crate&#39;s yak-shaving example:
 //!
 //! ```rust,ignore
 //! use std::{error::Error, io};
 //! use tracing::{debug, error, info, span, warn, Level};
 //!
 //! // the `#[tracing::instrument]` attribute creates and enters a span
 //! // every time the instrumented function is called. The span is named after the
 //! // the function or method. Parameters passed to the function are recorded as fields.
 //! #[tracing::instrument]
 //! pub fn shave(yak: usize) -&gt; Result&lt;(), Box&lt;dyn Error + &#39;static&gt;&gt; {
 //!     // this creates an event at the DEBUG level with two fields:
 //!     // - `excitement`, with the key &quot;excitement&quot; and the value &quot;yay!&quot;
 //!     // - `message`, with the key &quot;message&quot; and the value &quot;hello! I&#39;m gonna shave a yak.&quot;
 //!     //
 //!     // unlike other fields, `message`&#39;s shorthand initialization is just the string itself.
 //!     debug!(excitement = &quot;yay!&quot;, &quot;hello! I&#39;m gonna shave a yak.&quot;);
 //!     if yak == 3 {
 //!         warn!(&quot;could not locate yak!&quot;);
 //!         // note that this is intended to demonstrate `tracing`&#39;s features, not idiomatic
 //!         // error handling! in a library or application, you should consider returning
 //!         // a dedicated `YakError`. libraries like snafu or thiserror make this easy.
 //!         return Err(io::Error::new(io::ErrorKind::Other, &quot;shaving yak failed!&quot;).into());
 //!     } else {
 //!         debug!(&quot;yak shaved successfully&quot;);
 //!     }
 //!     Ok(())
 //! }
 //!
 //! pub fn shave_all(yaks: usize) -&gt; usize {
 //!     // Constructs a new span named &quot;shaving_yaks&quot; at the TRACE level,
 //!     // and a field whose key is &quot;yaks&quot;. This is equivalent to writing:
 //!     //
 //!     // let span = span!(Level::TRACE, &quot;shaving_yaks&quot;, yaks = yaks);
 //!     //
 //!     // local variables (`yaks`) can be used as field values
 //!     // without an assignment, similar to struct initializers.
 //!     let _span = span!(Level::TRACE, &quot;shaving_yaks&quot;, yaks).entered();
 //!
 //!     info!(&quot;shaving yaks&quot;);
 //!
 //!     let mut yaks_shaved = 0;
 //!     for yak in 1..=yaks {
 //!         let res = shave(yak);
 //!         debug!(yak, shaved = res.is_ok());
 //!
 //!         if let Err(ref error) = res {
 //!             // Like spans, events can also use the field initialization shorthand.
 //!             // In this instance, `yak` is the field being initalized.
 //!             error!(yak, error = error.as_ref(), &quot;failed to shave yak!&quot;);
 //!         } else {
 //!             yaks_shaved += 1;
 //!         }
 //!         debug!(yaks_shaved);
 //!     }
 //!
 //!     yaks_shaved
 //! }
 //! ```
 //!
 //! ## In libraries
 //!
 //! Libraries should link only to the `tracing` crate, and use the provided
 //! macros to record whatever information will be useful to downstream
 //! consumers.
 //!
 //! ## In executables
 //!
 //! In order to record trace events, executables have to use a `Subscriber`
 //! implementation compatible with `tracing`. A `Subscriber` implements a
 //! way of collecting trace data, such as by logging it to standard output.
 //!
 //! This library does not contain any `Subscriber` implementations; these are
 //! provided by [other crates](#related-crates).
 //!
 //! The simplest way to use a subscriber is to call the [`set_global_default`]
 //! function:
 //!
 //! ```
 //! extern crate tracing;
 //! # pub struct FooSubscriber;
 //! # use tracing::{span::{Id, Attributes, Record}, Metadata};
 //! # impl tracing::Subscriber for FooSubscriber {
 //! #   fn new_span(&amp;self, _: &amp;Attributes) -&gt; Id { Id::from_u64(0) }
 //! #   fn record(&amp;self, _: &amp;Id, _: &amp;Record) {}
 //! #   fn event(&amp;self, _: &amp;tracing::Event) {}
 //! #   fn record_follows_from(&amp;self, _: &amp;Id, _: &amp;Id) {}
 //! #   fn enabled(&amp;self, _: &amp;Metadata) -&gt; bool { false }
 //! #   fn enter(&amp;self, _: &amp;Id) {}
 //! #   fn exit(&amp;self, _: &amp;Id) {}
 //! # }
 //! # impl FooSubscriber {
 //! #   fn new() -&gt; Self { FooSubscriber }
 //! # }
 //! # fn main() {
 //!
 //! let my_subscriber = FooSubscriber::new();
 //! tracing::subscriber::set_global_default(my_subscriber)
 //!     .expect(&quot;setting tracing default failed&quot;);
 //! # }
 //! ```
 //!
 //! &lt;pre class=&quot;compile_fail&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 //!     &lt;strong&gt;Warning&lt;/strong&gt;: In general, libraries should &lt;em&gt;not&lt;/em&gt; call
 //!     &lt;code&gt;set_global_default()&lt;/code&gt;! Doing so will cause conflicts when
 //!     executables that depend on the library try to set the default later.
 //! &lt;/pre&gt;
 //!
 //! This subscriber will be used as the default in all threads for the
 //! remainder of the duration of the program, similar to setting the logger
 //! in the `log` crate.
 //!
 //! In addition, the default subscriber can be set through using the
 //! [`with_default`] function. This follows the `tokio` pattern of using
 //! closures to represent executing code in a context that is exited at the end
 //! of the closure. For example:
 //!
 //! ```rust
 //! # pub struct FooSubscriber;
 //! # use tracing::{span::{Id, Attributes, Record}, Metadata};
 //! # impl tracing::Subscriber for FooSubscriber {
 //! #   fn new_span(&amp;self, _: &amp;Attributes) -&gt; Id { Id::from_u64(0) }
 //! #   fn record(&amp;self, _: &amp;Id, _: &amp;Record) {}
 //! #   fn event(&amp;self, _: &amp;tracing::Event) {}
 //! #   fn record_follows_from(&amp;self, _: &amp;Id, _: &amp;Id) {}
 //! #   fn enabled(&amp;self, _: &amp;Metadata) -&gt; bool { false }
 //! #   fn enter(&amp;self, _: &amp;Id) {}
 //! #   fn exit(&amp;self, _: &amp;Id) {}
 //! # }
 //! # impl FooSubscriber {
 //! #   fn new() -&gt; Self { FooSubscriber }
 //! # }
 //! # fn main() {
 //!
 //! let my_subscriber = FooSubscriber::new();
 //! # #[cfg(feature = &quot;std&quot;)]
 //! tracing::subscriber::with_default(my_subscriber, || {
 //!     // Any trace events generated in this closure or by functions it calls
 //!     // will be collected by `my_subscriber`.
 //! })
 //! # }
 //! ```
 //!
 //! This approach allows trace data to be collected by multiple subscribers
 //! within different contexts in the program. Note that the override only applies to the
 //! currently executing thread; other threads will not see the change from with_default.
 //!
 //! Any trace events generated outside the context of a subscriber will not be collected.
 //!
 //! Once a subscriber has been set, instrumentation points may be added to the
 //! executable using the `tracing` crate&#39;s macros.
 //!
 //! ## `log` Compatibility
 //!
 //! The [`log`] crate provides a simple, lightweight logging facade for Rust.
 //! While `tracing` builds upon `log`&#39;s foundation with richer structured
 //! diagnostic data, `log`&#39;s simplicity and ubiquity make it the &quot;lowest common
 //! denominator&quot; for text-based logging in Rust — a vast majority of Rust
 //! libraries and applications either emit or consume `log` records. Therefore,
 //! `tracing` provides multiple forms of interoperability with `log`: `tracing`
 //! instrumentation can emit `log` records, and a compatibility layer enables
 //! `tracing` [`Subscriber`]s to consume `log` records as `tracing` [`Event`]s.
 //!
 //! ### Emitting `log` Records
 //!
 //! This crate provides two feature flags, &quot;log&quot; and &quot;log-always&quot;, which will
 //! cause [spans] and [events] to emit `log` records. When the &quot;log&quot; feature is
 //! enabled, if no `tracing` `Subscriber` is active, invoking an event macro or
 //! creating a span with fields will emit a `log` record. This is intended
 //! primarily for use in libraries which wish to emit diagnostics that can be
 //! consumed by applications using `tracing` *or* `log`, without paying the
 //! additional overhead of emitting both forms of diagnostics when `tracing` is
 //! in use.
 //!
 //! Enabling the &quot;log-always&quot; feature will cause `log` records to be emitted
 //! even if a `tracing` `Subscriber` _is_ set. This is intended to be used in
 //! applications where a `log` `Logger` is being used to record a textual log,
 //! and `tracing` is used only to record other forms of diagnostics (such as
 //! metrics, profiling, or distributed tracing data). Unlike the &quot;log&quot; feature,
 //! libraries generally should **not** enable the &quot;log-always&quot; feature, as doing
 //! so will prevent applications from being able to opt out of the `log` records.
 //!
 //! See [here][flags] for more details on this crate&#39;s feature flags.
 //!
 //! The generated `log` records&#39; messages will be a string representation of the
 //! span or event&#39;s fields, and all additional information recorded by `log`
 //! (target, verbosity level, module path, file, and line number) will also be
 //! populated. Additionally, `log` records are also generated when spans are
 //! entered, exited, and closed. Since these additional span lifecycle logs have
 //! the potential to be very verbose, and don&#39;t include additional fields, they
 //! will always be emitted at the `Trace` level, rather than inheriting the
 //! level of the span that generated them. Furthermore, they are are categorized
 //! under a separate `log` target, &quot;tracing::span&quot; (and its sub-target,
 //! &quot;tracing::span::active&quot;, for the logs on entering and exiting a span), which
 //! may be enabled or disabled separately from other `log` records emitted by
 //! `tracing`.
 //!
 //! ### Consuming `log` Records
 //!
 //! The [`tracing-log`] crate provides a compatibility layer which
 //! allows a `tracing` [`Subscriber`] to consume `log` records as though they
 //! were `tracing` [events]. This allows applications using `tracing` to record
 //! the logs emitted by dependencies using `log` as events within the context of
 //! the application&#39;s trace tree. See [that crate&#39;s documentation][log-tracer]
 //! for details.
 //!
 //! [log-tracer]: https://docs.rs/tracing-log/latest/tracing_log/#convert-log-records-to-tracing-events
 //!
 //! ## Related Crates
 //!
 //! In addition to `tracing` and `tracing-core`, the [`tokio-rs/tracing`] repository
 //! contains several additional crates designed to be used with the `tracing` ecosystem.
 //! This includes a collection of `Subscriber` implementations, as well as utility
 //! and adapter crates to assist in writing `Subscriber`s and instrumenting
 //! applications.
 //!
 //! In particular, the following crates are likely to be of interest:
 //!
 //!  - [`tracing-futures`] provides a compatibility layer with the `futures`
 //!    crate, allowing spans to be attached to `Future`s, `Stream`s, and `Executor`s.
 //!  - [`tracing-subscriber`] provides `Subscriber` implementations and
 //!    utilities for working with `Subscriber`s. This includes a [`FmtSubscriber`]
 //!    `FmtSubscriber` for logging formatted trace data to stdout, with similar
 //!    filtering and formatting to the [`env_logger`] crate.
 //!  - [`tracing-log`] provides a compatibility layer with the [`log`] crate,
 //!    allowing log messages to be recorded as `tracing` `Event`s within the
 //!    trace tree. This is useful when a project using `tracing` have
 //!    dependencies which use `log`. Note that if you&#39;re using
 //!    `tracing-subscriber`&#39;s `FmtSubscriber`, you don&#39;t need to depend on
 //!    `tracing-log` directly.
 //!  - [`tracing-appender`] provides utilities for outputting tracing data,
 //!     including a file appender and non blocking writer.
 //!
 //! Additionally, there are also several third-party crates which are not
 //! maintained by the `tokio` project. These include:
 //!
 //!  - [`tracing-timing`] implements inter-event timing metrics on top of `tracing`.
 //!    It provides a subscriber that records the time elapsed between pairs of
 //!    `tracing` events and generates histograms.
 //!  - [`tracing-opentelemetry`] provides a subscriber for emitting traces to
 //!    [OpenTelemetry]-compatible distributed tracing systems.
 //!  - [`tracing-honeycomb`] Provides a layer that reports traces spanning multiple machines to [honeycomb.io]. Backed by [`tracing-distributed`].
 //!  - [`tracing-distributed`] Provides a generic implementation of a layer that reports traces spanning multiple machines to some backend.
 //!  - [`tracing-actix-web`] provides `tracing` integration for the `actix-web` web framework.
 //!  - [`tracing-actix`] provides `tracing` integration for the `actix` actor
 //!    framework.
 //!  - [`tracing-gelf`] implements a subscriber for exporting traces in Greylog
 //!    GELF format.
 //!  - [`tracing-coz`] provides integration with the [coz] causal profiler
 //!    (Linux-only).
 //!  - [`tracing-bunyan-formatter`] provides a layer implementation that reports events and spans
 //!    in [bunyan] format, enriched with timing information.
 //!  - [`tracing-wasm`] provides a `Subscriber`/`Layer` implementation that reports
 //!    events and spans via browser `console.log` and [User Timing API (`window.performance`)].
 //!  - [`tracing-web`] provides a layer implementation of level-aware logging of events
 //!    to web browsers&#39; `console.*` and span events to the [User Timing API (`window.performance`)].
 //!  - [`tide-tracing`] provides a [tide] middleware to trace all incoming requests and responses.
 //!  - [`test-log`] takes care of initializing `tracing` for tests, based on
 //!    environment variables with an `env_logger` compatible syntax.
 //!  - [`tracing-unwrap`] provides convenience methods to report failed unwraps
 //!    on `Result` or `Option` types to a `Subscriber`.
 //!  - [`diesel-tracing`] provides integration with [`diesel`] database connections.
 //!  - [`tracing-tracy`] provides a way to collect [Tracy] profiles in instrumented
 //!    applications.
 //!  - [`tracing-elastic-apm`] provides a layer for reporting traces to [Elastic APM].
 //!  - [`tracing-etw`] provides a layer for emitting Windows [ETW] events.
 //!  - [`tracing-fluent-assertions`] provides a fluent assertions-style testing
 //!    framework for validating the behavior of `tracing` spans.
 //!  - [`sentry-tracing`] provides a layer for reporting events and traces to [Sentry].
 //!  - [`tracing-forest`] provides a subscriber that preserves contextual coherence by
 //!    grouping together logs from the same spans during writing.
 //!  - [`tracing-loki`] provides a layer for shipping logs to [Grafana Loki].
 //!  - [`tracing-logfmt`] provides a layer that formats events and spans into the logfmt format.
 //!  - [`reqwest-tracing`] provides a middleware to trace [`reqwest`] HTTP requests.
 //!
 //! If you&#39;re the maintainer of a `tracing` ecosystem crate not listed above,
 //! please let us know! We&#39;d love to add your project to the list!
 //!
 //! [`tracing-opentelemetry`]: https://crates.io/crates/tracing-opentelemetry
 //! [OpenTelemetry]: https://opentelemetry.io/
 //! [`tracing-honeycomb`]: https://crates.io/crates/tracing-honeycomb
 //! [`tracing-distributed`]: https://crates.io/crates/tracing-distributed
 //! [honeycomb.io]: https://www.honeycomb.io/
 //! [`tracing-actix-web`]: https://crates.io/crates/tracing-actix-web
 //! [`tracing-actix`]: https://crates.io/crates/tracing-actix
 //! [`tracing-gelf`]: https://crates.io/crates/tracing-gelf
 //! [`tracing-coz`]: https://crates.io/crates/tracing-coz
 //! [coz]: https://github.com/plasma-umass/coz
 //! [`tracing-bunyan-formatter`]: https://crates.io/crates/tracing-bunyan-formatter
 //! [bunyan]: https://github.com/trentm/node-bunyan
 //! [`tracing-wasm`]: https://docs.rs/tracing-wasm
 //! [`tracing-web`]: https://docs.rs/tracing-web
 //! [User Timing API (`window.performance`)]: https://developer.mozilla.org/en-US/docs/Web/API/User_Timing_API
 //! [`tide-tracing`]: https://crates.io/crates/tide-tracing
 //! [tide]: https://crates.io/crates/tide
 //! [`test-log`]: https://crates.io/crates/test-log
 //! [`tracing-unwrap`]: https://docs.rs/tracing-unwrap
 //! [`diesel`]: https://crates.io/crates/diesel
 //! [`diesel-tracing`]: https://crates.io/crates/diesel-tracing
 //! [`tracing-tracy`]: https://crates.io/crates/tracing-tracy
 //! [Tracy]: https://github.com/wolfpld/tracy
 //! [`tracing-elastic-apm`]: https://crates.io/crates/tracing-elastic-apm
 //! [Elastic APM]: https://www.elastic.co/apm
 //! [`tracing-etw`]: https://github.com/microsoft/tracing-etw
 //! [ETW]: https://docs.microsoft.com/en-us/windows/win32/etw/about-event-tracing
 //! [`tracing-fluent-assertions`]: https://crates.io/crates/tracing-fluent-assertions
 //! [`sentry-tracing`]: https://crates.io/crates/sentry-tracing
 //! [Sentry]: https://sentry.io/welcome/
 //! [`tracing-forest`]: https://crates.io/crates/tracing-forest
 //! [`tracing-loki`]: https://crates.io/crates/tracing-loki
 //! [Grafana Loki]: https://grafana.com/oss/loki/
 //! [`tracing-logfmt`]: https://crates.io/crates/tracing-logfmt
 //! [`reqwest-tracing`]: https://crates.io/crates/reqwest-tracing
 //! [`reqwest`]: https://crates.io/crates/reqwest
 //!
 //! &lt;pre class=&quot;ignore&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 //!     &lt;strong&gt;Note&lt;/strong&gt;: Some of these ecosystem crates are currently
 //!     unreleased and/or in earlier stages of development. They may be less stable
 //!     than &lt;code&gt;tracing&lt;/code&gt; and &lt;code&gt;tracing-core&lt;/code&gt;.
 //! &lt;/pre&gt;
 //!
 //! ## Crate Feature Flags
 //!
 //! The following crate [feature flags] are available:
 //!
 //! * A set of features controlling the [static verbosity level].
 //! * `log`: causes trace instrumentation points to emit [`log`] records as well
 //!   as trace events, if a default `tracing` subscriber has not been set. This
 //!   is intended for use in libraries whose users may be using either `tracing`
 //!   or `log`.
 //! * `log-always`: Emit `log` records from all `tracing` spans and events, even
 //!   if a `tracing` subscriber has been set. This should be set only by
 //!   applications which intend to collect traces and logs separately; if an
 //!   adapter is used to convert `log` records into `tracing` events, this will
 //!   cause duplicate events to occur.
 //! * `attributes`: Includes support for the `#[instrument]` attribute.
 //!   This is on by default, but does bring in the `syn` crate as a dependency,
 //!   which may add to the compile time of crates that do not already use it.
 //! * `std`: Depend on the Rust standard library (enabled by default).
 //!
 //!   `no_std` users may disable this feature with `default-features = false`:
 //!
 //!   ```toml
 //!   [dependencies]
 //!   tracing = { version = &quot;0.1.37&quot;, default-features = false }
 //!   ```
 //!
 //! &lt;pre class=&quot;ignore&quot; style=&quot;white-space:normal;font:inherit;&quot;&gt;
 //!     &lt;strong&gt;Note&lt;/strong&gt;: &lt;code&gt;tracing&lt;/code&gt;&#39;s &lt;code&gt;no_std&lt;/code&gt; support
 //!     requires &lt;code&gt;liballoc&lt;/code&gt;.
 //! &lt;/pre&gt;
 //!
 //! ### 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 1.49. 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.
 //!
 //! [`log`]: https://docs.rs/log/0.4.6/log/
 //! [span]: mod@span
 //! [spans]: mod@span
 //! [`Span`]: span::Span
 //! [`in_scope`]: span::Span::in_scope
 //! [event]: Event
 //! [events]: Event
 //! [`Subscriber`]: subscriber::Subscriber
 //! [Subscriber::event]: subscriber::Subscriber::event
 //! [`enter`]: subscriber::Subscriber::enter
 //! [`exit`]: subscriber::Subscriber::exit
 //! [`enabled`]: subscriber::Subscriber::enabled
 //! [metadata]: Metadata
 //! [`field::display`]: field::display
 //! [`field::debug`]: field::debug
 //! [`set_global_default`]: subscriber::set_global_default
 //! [`with_default`]: subscriber::with_default
 //! [`tokio-rs/tracing`]: https://github.com/tokio-rs/tracing
 //! [`tracing-futures`]: https://crates.io/crates/tracing-futures
 //! [`tracing-subscriber`]: https://crates.io/crates/tracing-subscriber
 //! [`tracing-log`]: https://crates.io/crates/tracing-log
 //! [`tracing-timing`]: https://crates.io/crates/tracing-timing
 //! [`tracing-appender`]: https://crates.io/crates/tracing-appender
 //! [`env_logger`]: https://crates.io/crates/env_logger
 //! [`FmtSubscriber`]: https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/struct.Subscriber.html
 //! [static verbosity level]: level_filters#compile-time-filters
 //! [instrument]: https://docs.rs/tracing-attributes/latest/tracing_attributes/attr.instrument.html
 //! [flags]: #crate-feature-flags
 </span><span class="attribute">#![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))]
 #![doc(html_root_url = <span class="string">&quot;https://docs.rs/tracing/0.1.37&quot;</span>)]
 #![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>)]
 #![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 = <span class="string">&quot;std&quot;</span>))]
 </span><span class="kw">extern crate </span>alloc;

 <span class="comment">// Somehow this `use` statement is necessary for us to re-export the `core`
 // macros on Rust 1.26.0. I&#39;m not sure how this makes it work, but it does.
 </span><span class="attribute">#[allow(unused_imports)]
 #[doc(hidden)]
 </span><span class="kw">use </span>tracing_core::<span class="kw-2">*</span>;

 <span class="attribute">#[doc(inline)]
 </span><span class="kw">pub use </span><span class="self">self</span>::instrument::Instrument;
 <span class="kw">pub use </span><span class="self">self</span>::{dispatcher::Dispatch, event::Event, field::Value, subscriber::Subscriber};

 <span class="attribute">#[doc(hidden)]
 </span><span class="kw">pub use </span><span class="self">self</span>::span::Id;

 <span class="attribute">#[doc(hidden)]
 </span><span class="kw">pub use </span>tracing_core::{
     callsite::{<span class="self">self</span>, Callsite},
     metadata,
 };
 <span class="kw">pub use </span>tracing_core::{event, Level, Metadata};

 <span class="attribute">#[doc(inline)]
 </span><span class="kw">pub use </span><span class="self">self</span>::span::Span;
 <span class="attribute">#[cfg(feature = <span class="string">&quot;attributes&quot;</span>)]
 #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">&quot;attributes&quot;</span>)))]
 #[doc(inline)]
 </span><span class="kw">pub use </span>tracing_attributes::instrument;

 <span class="attribute">#[macro_use]
 </span><span class="kw">mod </span>macros;

 <span class="kw">pub mod </span>dispatcher;
 <span class="kw">pub mod </span>field;
 <span class="doccomment">/// Attach a span to a `std::future::Future`.
 </span><span class="kw">pub mod </span>instrument;
 <span class="kw">pub mod </span>level_filters;
 <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(hidden)]
 </span><span class="kw">pub mod </span>__macro_support {
     <span class="kw">pub use </span><span class="kw">crate</span>::callsite::Callsite;
     <span class="kw">use crate</span>::{subscriber::Interest, Metadata};
     <span class="kw">pub use </span>core::concat;

     <span class="doccomment">/// Callsite implementation used by macro-generated code.
     ///
     /// /!\ WARNING: This is *not* a stable API! /!\
     /// This type, and all code contained in the `__macro_support` module, is
     /// a *private* API of `tracing`. It is exposed publicly because it is used
     /// by the `tracing` macros, but it is not part of the stable versioned API.
     /// Breaking changes to this module may occur in small-numbered versions
     /// without warning.
     </span><span class="kw">pub use </span>tracing_core::callsite::DefaultCallsite <span class="kw">as </span>MacroCallsite;

     <span class="doccomment">/// /!\ WARNING: This is *not* a stable API! /!\
     /// This function, and all code contained in the `__macro_support` module, is
     /// a *private* API of `tracing`. It is exposed publicly because it is used
     /// by the `tracing` macros, but it is not part of the stable versioned API.
     /// Breaking changes to this module may occur in small-numbered versions
     /// without warning.
     </span><span class="kw">pub fn </span>__is_enabled(meta: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;static</span>&gt;, interest: Interest) -&gt; bool {
         interest.is_always() || <span class="kw">crate</span>::dispatcher::get_default(|default| default.enabled(meta))
     }

     <span class="doccomment">/// /!\ WARNING: This is *not* a stable API! /!\
     /// This function, and all code contained in the `__macro_support` module, is
     /// a *private* API of `tracing`. It is exposed publicly because it is used
     /// by the `tracing` macros, but it is not part of the stable versioned API.
     /// Breaking changes to this module may occur in small-numbered versions
     /// without warning.
     </span><span class="attribute">#[inline]
     #[cfg(feature = <span class="string">&quot;log&quot;</span>)]
     </span><span class="kw">pub fn </span>__disabled_span(meta: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Metadata&lt;<span class="lifetime">&#39;static</span>&gt;) -&gt; <span class="kw">crate</span>::Span {
         <span class="kw">crate</span>::Span::new_disabled(meta)
     }

     <span class="doccomment">/// /!\ WARNING: This is *not* a stable API! /!\
     /// This function, and all code contained in the `__macro_support` module, is
     /// a *private* API of `tracing`. It is exposed publicly because it is used
     /// by the `tracing` macros, but it is not part of the stable versioned API.
     /// Breaking changes to this module may occur in small-numbered versions
     /// without warning.
     </span><span class="attribute">#[inline]
     #[cfg(not(feature = <span class="string">&quot;log&quot;</span>))]
     </span><span class="kw">pub fn </span>__disabled_span(<span class="kw">_</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Metadata&lt;<span class="lifetime">&#39;static</span>&gt;) -&gt; <span class="kw">crate</span>::Span {
         <span class="kw">crate</span>::Span::none()
     }

     <span class="doccomment">/// /!\ WARNING: This is *not* a stable API! /!\
     /// This function, and all code contained in the `__macro_support` module, is
     /// a *private* API of `tracing`. It is exposed publicly because it is used
     /// by the `tracing` macros, but it is not part of the stable versioned API.
     /// Breaking changes to this module may occur in small-numbered versions
     /// without warning.
     </span><span class="attribute">#[cfg(feature = <span class="string">&quot;log&quot;</span>)]
     </span><span class="kw">pub fn </span>__tracing_log(
         meta: <span class="kw-2">&amp;</span>Metadata&lt;<span class="lifetime">&#39;static</span>&gt;,
         logger: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span><span class="kw">dyn </span>log::Log,
         log_meta: log::Metadata&lt;<span class="lifetime">&#39;_</span>&gt;,
         values: <span class="kw-2">&amp;</span>tracing_core::field::ValueSet&lt;<span class="lifetime">&#39;_</span>&gt;,
     ) {
         logger.log(
             <span class="kw-2">&amp;</span><span class="kw">crate</span>::log::Record::builder()
                 .file(meta.file())
                 .module_path(meta.module_path())
                 .line(meta.line())
                 .metadata(log_meta)
                 .args(<span class="macro">format_args!</span>(
                     <span class="string">&quot;{}&quot;</span>,
                     <span class="kw">crate</span>::log::LogValueSet {
                         values,
                         is_first: <span class="bool-val">true
                     </span>}
                 ))
                 .build(),
         );
     }
 }

 <span class="attribute">#[cfg(feature = <span class="string">&quot;log&quot;</span>)]
 #[doc(hidden)]
 </span><span class="kw">pub mod </span>log {
     <span class="kw">use </span>core::fmt;
     <span class="kw">pub use </span>log::<span class="kw-2">*</span>;
     <span class="kw">use </span>tracing_core::field::{Field, ValueSet, Visit};

     <span class="doccomment">/// Utility to format [`ValueSet`]s for logging.
     </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>LogValueSet&lt;<span class="lifetime">&#39;a</span>&gt; {
         <span class="kw">pub</span>(<span class="kw">crate</span>) values: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>ValueSet&lt;<span class="lifetime">&#39;a</span>&gt;,
         <span class="kw">pub</span>(<span class="kw">crate</span>) is_first: bool,
     }

     <span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>&gt; fmt::Display <span class="kw">for </span>LogValueSet&lt;<span class="lifetime">&#39;a</span>&gt; {
         <span class="attribute">#[inline]
         </span><span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
             <span class="kw">struct </span>LogVisitor&lt;<span class="lifetime">&#39;a</span>, <span class="lifetime">&#39;b</span>&gt; {
                 f: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span><span class="kw-2">mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;b</span>&gt;,
                 is_first: bool,
                 result: fmt::Result,
             }

             <span class="kw">impl </span>Visit <span class="kw">for </span>LogVisitor&lt;<span class="lifetime">&#39;_</span>, <span class="lifetime">&#39;_</span>&gt; {
                 <span class="kw">fn </span>record_debug(<span class="kw-2">&amp;mut </span><span class="self">self</span>, field: <span class="kw-2">&amp;</span>Field, value: <span class="kw-2">&amp;</span><span class="kw">dyn </span>fmt::Debug) {
                     <span class="kw">let </span>res = <span class="kw">if </span><span class="self">self</span>.is_first {
                         <span class="self">self</span>.is_first = <span class="bool-val">false</span>;
                         <span class="kw">if </span>field.name() == <span class="string">&quot;message&quot; </span>{
                             <span class="macro">write!</span>(<span class="self">self</span>.f, <span class="string">&quot;{:?}&quot;</span>, value)
                         } <span class="kw">else </span>{
                             <span class="macro">write!</span>(<span class="self">self</span>.f, <span class="string">&quot;{}={:?}&quot;</span>, field.name(), value)
                         }
                     } <span class="kw">else </span>{
                         <span class="macro">write!</span>(<span class="self">self</span>.f, <span class="string">&quot; {}={:?}&quot;</span>, field.name(), value)
                     };
                     <span class="kw">if let </span><span class="prelude-val">Err</span>(err) = res {
                         <span class="self">self</span>.result = <span class="self">self</span>.result.and(<span class="prelude-val">Err</span>(err));
                     }
                 }

                 <span class="kw">fn </span>record_str(<span class="kw-2">&amp;mut </span><span class="self">self</span>, field: <span class="kw-2">&amp;</span>Field, value: <span class="kw-2">&amp;</span>str) {
                     <span class="kw">if </span>field.name() == <span class="string">&quot;message&quot; </span>{
                         <span class="self">self</span>.record_debug(field, <span class="kw-2">&amp;</span><span class="macro">format_args!</span>(<span class="string">&quot;{}&quot;</span>, value))
                     } <span class="kw">else </span>{
                         <span class="self">self</span>.record_debug(field, <span class="kw-2">&amp;</span>value)
                     }
                 }
             }

             <span class="kw">let </span><span class="kw-2">mut </span>visit = LogVisitor {
                 f,
                 is_first: <span class="self">self</span>.is_first,
                 result: <span class="prelude-val">Ok</span>(()),
             };
             <span class="self">self</span>.values.record(<span class="kw-2">&amp;mut </span>visit);
             visit.result
         }
     }
 }

 <span class="kw">mod </span>sealed {
     <span class="kw">pub trait </span>Sealed {}
 }
 </code></pre></div>
 </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tracing" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>