Merging upstream version 1.66.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1275 insertions, 0 deletions

diff --git a/vendor/tracing-subscriber-0.3.3/src/fmt/mod.rs b/vendor/tracing-subscriber-0.3.3/src/fmt/mod.rs
new file mode 100644
index 000000000..d5deb8f0c
--- /dev/null
+++ b/vendor/tracing-subscriber-0.3.3/src/fmt/mod.rs
@@ -0,0 +1,1275 @@
+//! A `Subscriber` for formatting and logging `tracing` data.
+//!
+//! # Overview
+//!
+//! [`tracing`] is a framework for instrumenting Rust programs with context-aware,
+//! structured, event-based diagnostic information. This crate provides an
+//! implementation of the [`Subscriber`] trait that records `tracing`'s `Event`s
+//! and `Span`s by formatting them as text and logging them to stdout.
+//!
+//! # Usage
+//!
+//! First, add this to your `Cargo.toml` file:
+//!
+//! ```toml
+//! [dependencies]
+//! tracing-subscriber = "0.2"
+//! ```
+//!
+//! *Compiler support: requires rustc 1.39+*
+//!
+//! Add the following to your executable to initialize the default subscriber:
+//! ```rust
+//! use tracing_subscriber;
+//!
+//! tracing_subscriber::fmt::init();
+//! ```
+//!
+//! ## Filtering Events with Environment Variables
+//!
+//! The default subscriber installed by `init` enables you to filter events
+//! at runtime using environment variables (using the [`EnvFilter`]).
+//!
+//! The filter syntax is a superset of the [`env_logger`] syntax.
+//!
+//! For example:
+//! - Setting `RUST_LOG=debug` enables all `Span`s and `Event`s
+//!     set to the log level `DEBUG` or higher
+//! - Setting `RUST_LOG=my_crate=trace` enables `Span`s and `Event`s
+//!     in `my_crate` at all log levels
+//!
+//! **Note**: This should **not** be called by libraries. Libraries should use
+//! [`tracing`] to publish `tracing` `Event`s.
+//!
+//! # Configuration
+//!
+//! You can configure a subscriber instead of using the defaults with
+//! the following functions:
+//!
+//! ### Subscriber
+//!
+//! The [`FmtSubscriber`] formats and records `tracing` events as line-oriented logs.
+//! You can create one by calling:
+//!
+//! ```rust
+//! let subscriber = tracing_subscriber::fmt()
+//!     // ... add configuration
+//!     .finish();
+//! ```
+//!
+//! You can find the configuration methods for [`FmtSubscriber`] in
+//! [`SubscriberBuilder`].
+//!
+//! ## Formatters
+//!
+//! The output format used by the layer and subscriber in this module is
+//! represented by implementing the [`FormatEvent`] trait, and can be
+//! customized. This module provides a number of formatter implementations:
+//!
+//! * [`format::Full`]: The default formatter. This emits human-readable,
+//!   single-line logs for each event that occurs, with the current span context
+//!   displayed before the formatted representation of the event.
+//!
+//!   For example:
+//!   <pre><font color="#4E9A06"><b>    Finished</b></font> dev [unoptimized + debuginfo] target(s) in 1.59s
+//!   <font color="#4E9A06"><b>     Running</b></font> `target/debug/examples/fmt`
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#4E9A06"> INFO</font> fmt: preparing to shave yaks number_of_yaks=3
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#4E9A06"> INFO</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: fmt::yak_shave: shaving yaks
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=1<b>}</b>: fmt::yak_shave: hello! I&apos;m gonna shave a yak excitement=&quot;yay!&quot;
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=1<b>}</b>: fmt::yak_shave: yak shaved successfully
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#3465A4">DEBUG</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: yak_events: yak=1 shaved=true
+//!   <font color="#AAAAAA">Oct 24 12:55:47.814 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: fmt::yak_shave: yaks_shaved=1
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=2<b>}</b>: fmt::yak_shave: hello! I&apos;m gonna shave a yak excitement=&quot;yay!&quot;
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=2<b>}</b>: fmt::yak_shave: yak shaved successfully
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#3465A4">DEBUG</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: yak_events: yak=2 shaved=true
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: fmt::yak_shave: yaks_shaved=2
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=3<b>}</b>: fmt::yak_shave: hello! I&apos;m gonna shave a yak excitement=&quot;yay!&quot;
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#C4A000"> WARN</font> <b>shaving_yaks{</b>yaks=3<b>}</b>:<b>shave{</b>yak=3<b>}</b>: fmt::yak_shave: could not locate yak
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#3465A4">DEBUG</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: yak_events: yak=3 shaved=false
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#CC0000">ERROR</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: fmt::yak_shave: failed to shave yak yak=3 error=missing yak
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#75507B">TRACE</font> <b>shaving_yaks{</b>yaks=3<b>}</b>: fmt::yak_shave: yaks_shaved=2
+//!   <font color="#AAAAAA">Oct 24 12:55:47.815 </font><font color="#4E9A06"> INFO</font> fmt: yak shaving completed all_yaks_shaved=false
+//!   </pre>
+//!
+//! * [`format::Pretty`]: Emits excessively pretty, multi-line logs, optimized
+//!   for human readability. This is primarily intended to be used in local
+//!   development and debugging, or for command-line applications, where
+//!   automated analysis and compact storage of logs is less of a priority than
+//!   readability and visual appeal.
+//!
+//!   For example:
+//!   <pre><font color="#4E9A06"><b>    Finished</b></font> dev [unoptimized + debuginfo] target(s) in 1.61s
+//!   <font color="#4E9A06"><b>     Running</b></font> `target/debug/examples/fmt-pretty`
+//!   Oct 24 12:57:29.386 <font color="#4E9A06"><b>fmt_pretty</b></font><font color="#4E9A06">: preparing to shave yaks, </font><font color="#4E9A06"><b>number_of_yaks</b></font><font color="#4E9A06">: 3</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt-pretty.rs:16<font color="#AAAAAA"><i> on</i></font> main
+//!
+//!   Oct 24 12:57:29.386 <font color="#4E9A06"><b>fmt_pretty::yak_shave</b></font><font color="#4E9A06">: shaving yaks</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:38<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: hello! I&apos;m gonna shave a yak, </font><font color="#75507B"><b>excitement</b></font><font color="#75507B">: &quot;yay!&quot;</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:14<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 1
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: yak shaved successfully</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:22<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 1
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#3465A4"><b>yak_events</b></font><font color="#3465A4">: </font><font color="#3465A4"><b>yak</b></font><font color="#3465A4">: 1, </font><font color="#3465A4"><b>shaved</b></font><font color="#3465A4">: true</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:43<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: </font><font color="#75507B"><b>yaks_shaved</b></font><font color="#75507B">: 1</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:52<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: hello! I&apos;m gonna shave a yak, </font><font color="#75507B"><b>excitement</b></font><font color="#75507B">: &quot;yay!&quot;</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:14<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 2
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: yak shaved successfully</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:22<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 2
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#3465A4"><b>yak_events</b></font><font color="#3465A4">: </font><font color="#3465A4"><b>yak</b></font><font color="#3465A4">: 2, </font><font color="#3465A4"><b>shaved</b></font><font color="#3465A4">: true</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:43<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: </font><font color="#75507B"><b>yaks_shaved</b></font><font color="#75507B">: 2</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:52<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: hello! I&apos;m gonna shave a yak, </font><font color="#75507B"><b>excitement</b></font><font color="#75507B">: &quot;yay!&quot;</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:14<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 3
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#C4A000"><b>fmt_pretty::yak_shave</b></font><font color="#C4A000">: could not locate yak</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:16<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shave</b> <font color="#AAAAAA"><i>with</i></font> <b>yak</b>: 3
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#3465A4"><b>yak_events</b></font><font color="#3465A4">: </font><font color="#3465A4"><b>yak</b></font><font color="#3465A4">: 3, </font><font color="#3465A4"><b>shaved</b></font><font color="#3465A4">: false</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:43<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#CC0000"><b>fmt_pretty::yak_shave</b></font><font color="#CC0000">: failed to shave yak, </font><font color="#CC0000"><b>yak</b></font><font color="#CC0000">: 3, </font><font color="#CC0000"><b>error</b></font><font color="#CC0000">: missing yak</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:48<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#75507B"><b>fmt_pretty::yak_shave</b></font><font color="#75507B">: </font><font color="#75507B"><b>yaks_shaved</b></font><font color="#75507B">: 2</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt/yak_shave.rs:52<font color="#AAAAAA"><i> on</i></font> main
+//!     <font color="#AAAAAA"><i>in</i></font> fmt_pretty::yak_shave::<b>shaving_yaks</b> <font color="#AAAAAA"><i>with</i></font> <b>yaks</b>: 3
+//!
+//!   Oct 24 12:57:29.387 <font color="#4E9A06"><b>fmt_pretty</b></font><font color="#4E9A06">: yak shaving completed, </font><font color="#4E9A06"><b>all_yaks_shaved</b></font><font color="#4E9A06">: false</font>
+//!     <font color="#AAAAAA"><i>at</i></font> examples/examples/fmt-pretty.rs:19<font color="#AAAAAA"><i> on</i></font> main
+//!   </pre>
+//!
+//! * [`format::Json`]: Outputs newline-delimited JSON logs. This is intended
+//!   for production use with systems where structured logs are consumed as JSON
+//!   by analysis and viewing tools. The JSON output, as seen below, is *not*
+//!   optimized for human readability.
+//!
+//!   For example:
+//!   <pre><font color="#4E9A06"><b>    Finished</b></font> dev [unoptimized + debuginfo] target(s) in 1.58s
+//!   <font color="#4E9A06"><b>     Running</b></font> `target/debug/examples/fmt-json`
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.873&quot;,&quot;level&quot;:&quot;INFO&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;preparing to shave yaks&quot;,&quot;number_of_yaks&quot;:3},&quot;target&quot;:&quot;fmt_json&quot;}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;INFO&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;shaving yaks&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;hello! I&apos;m gonna shave a yak&quot;,&quot;excitement&quot;:&quot;yay!&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;1&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;yak shaved successfully&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;1&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;DEBUG&quot;,&quot;fields&quot;:{&quot;yak&quot;:1,&quot;shaved&quot;:true},&quot;target&quot;:&quot;yak_events&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;yaks_shaved&quot;:1},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;hello! I&apos;m gonna shave a yak&quot;,&quot;excitement&quot;:&quot;yay!&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;2&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;yak shaved successfully&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;2&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;DEBUG&quot;,&quot;fields&quot;:{&quot;yak&quot;:2,&quot;shaved&quot;:true},&quot;target&quot;:&quot;yak_events&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;yaks_shaved&quot;:2},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.874&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;hello! I&apos;m gonna shave a yak&quot;,&quot;excitement&quot;:&quot;yay!&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;3&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.875&quot;,&quot;level&quot;:&quot;WARN&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;could not locate yak&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;},{&quot;yak&quot;:&quot;3&quot;,&quot;name&quot;:&quot;shave&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.875&quot;,&quot;level&quot;:&quot;DEBUG&quot;,&quot;fields&quot;:{&quot;yak&quot;:3,&quot;shaved&quot;:false},&quot;target&quot;:&quot;yak_events&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.875&quot;,&quot;level&quot;:&quot;ERROR&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;failed to shave yak&quot;,&quot;yak&quot;:3,&quot;error&quot;:&quot;missing yak&quot;},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.875&quot;,&quot;level&quot;:&quot;TRACE&quot;,&quot;fields&quot;:{&quot;yaks_shaved&quot;:2},&quot;target&quot;:&quot;fmt_json::yak_shave&quot;,&quot;spans&quot;:[{&quot;yaks&quot;:3,&quot;name&quot;:&quot;shaving_yaks&quot;}]}
+//!   {&quot;timestamp&quot;:&quot;Oct 24 13:00:00.875&quot;,&quot;level&quot;:&quot;INFO&quot;,&quot;fields&quot;:{&quot;message&quot;:&quot;yak shaving completed&quot;,&quot;all_yaks_shaved&quot;:false},&quot;target&quot;:&quot;fmt_json&quot;}
+//!   </pre>
+//!
+//! ### Customizing Formatters
+//!
+//! The formatting of log lines for spans and events is controlled by two
+//! traits, [`FormatEvent`] and [`FormatFields`]. The [`FormatEvent`] trait
+//! determines the overall formatting of the log line, such as what information
+//! from the event's metadata and span context is included and in what order.
+//! The [`FormatFields`] trait determines how fields &mdash; both the event's
+//! fields and fields on spans &mdash; are formatted.
+//!
+//! The [`fmt::format`] module provides several types which implement these traits,
+//! many of which expose additional configuration options to customize their
+//! output. The [`format::Format`] type implements common configuration used by
+//! all the formatters provided in this crate, and can be used as a builder to
+//! set specific formatting settings. For example:
+//!
+//! ```
+//! use tracing_subscriber::fmt;
+//!
+//! // Configure a custom event formatter
+//! let format = fmt::format()
+//!    .with_level(false) // don't include levels in formatted output
+//!    .with_target(false) // don't include targets
+//!    .with_thread_ids(true) // include the thread ID of the current thread
+//!    .with_thread_names(true) // include the name of the current thread
+//!    .compact(); // use the `Compact` formatting style.
+//!
+//! // Create a `fmt` collector that uses our custom event format, and set it
+//! // as the default.
+//! tracing_subscriber::fmt()
+//!     .event_format(format)
+//!     .init();
+//! ```
+//!
+//! However, if a specific output format is needed, other crates can
+//! also implement [`FormatEvent`] and [`FormatFields`]. See those traits'
+//! documentation for details on how to implement them.
+//!
+//! ## Filters
+//!
+//! If you want to filter the `tracing` `Events` based on environment
+//! variables, you can use the [`EnvFilter`] as follows:
+//!
+//! ```rust
+//! use tracing_subscriber::EnvFilter;
+//!
+//! let filter = EnvFilter::from_default_env();
+//! ```
+//!
+//! As mentioned above, the [`EnvFilter`] allows `Span`s and `Event`s to
+//! be filtered at runtime by setting the `RUST_LOG` environment variable.
+//!
+//! You can find the other available [`filter`]s in the documentation.
+//!
+//! ### Using Your Subscriber
+//!
+//! Finally, once you have configured your `Subscriber`, you need to
+//! configure your executable to use it.
+//!
+//! A subscriber can be installed globally using:
+//! ```rust
+//! use tracing;
+//! use tracing_subscriber::FmtSubscriber;
+//!
+//! let subscriber = FmtSubscriber::new();
+//!
+//! tracing::subscriber::set_global_default(subscriber)
+//!     .map_err(|_err| eprintln!("Unable to set global default subscriber"));
+//! // Note this will only fail if you try to set the global default
+//! // subscriber multiple times
+//! ```
+//!
+//! ### Composing Layers
+//!
+//! Composing an [`EnvFilter`] `Layer` and a [format `Layer`](../fmt/struct.Layer.html):
+//!
+//! ```rust
+//! use tracing_subscriber::{fmt, EnvFilter};
+//! use tracing_subscriber::prelude::*;
+//!
+//! let fmt_layer = fmt::layer()
+//!     .with_target(false);
+//! let filter_layer = EnvFilter::try_from_default_env()
+//!     .or_else(|_| EnvFilter::try_new("info"))
+//!     .unwrap();
+//!
+//! tracing_subscriber::registry()
+//!     .with(filter_layer)
+//!     .with(fmt_layer)
+//!     .init();
+//! ```
+//!
+//! [`EnvFilter`]: ../filter/struct.EnvFilter.html
+//! [`env_logger`]: https://docs.rs/env_logger/
+//! [`filter`]: ../filter/index.html
+//! [`SubscriberBuilder`]: ./struct.SubscriberBuilder.html
+//! [`FmtSubscriber`]: ./struct.Subscriber.html
+//! [`Subscriber`]:
+//!     https://docs.rs/tracing/latest/tracing/trait.Subscriber.html
+//! [`tracing`]: https://crates.io/crates/tracing
+//! [`fmt::format`]: mod@crate::fmt::format
+use std::{any::TypeId, error::Error, io};
+use tracing_core::{span, subscriber::Interest, Event, Metadata};
+
+mod fmt_layer;
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub mod format;
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub mod time;
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub mod writer;
+
+pub use fmt_layer::{FmtContext, FormattedFields, Layer};
+
+use crate::layer::Layer as _;
+use crate::{
+    filter::LevelFilter,
+    layer,
+    registry::{LookupSpan, Registry},
+};
+
+#[doc(inline)]
+pub use self::{
+    format::{format, FormatEvent, FormatFields},
+    time::time,
+    writer::{MakeWriter, TestWriter},
+};
+
+/// A `Subscriber` that logs formatted representations of `tracing` events.
+///
+/// This consists of an inner `Formatter` wrapped in a layer that performs filtering.
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+#[derive(Debug)]
+pub struct Subscriber<
+    N = format::DefaultFields,
+    E = format::Format<format::Full>,
+    F = LevelFilter,
+    W = fn() -> io::Stdout,
+> {
+    inner: layer::Layered<F, Formatter<N, E, W>>,
+}
+
+/// A `Subscriber` that logs formatted representations of `tracing` events.
+/// This type only logs formatted events; it does not perform any filtering.
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub type Formatter<
+    N = format::DefaultFields,
+    E = format::Format<format::Full>,
+    W = fn() -> io::Stdout,
+> = layer::Layered<fmt_layer::Layer<Registry, N, E, W>, Registry>;
+
+/// Configures and constructs `Subscriber`s.
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+#[derive(Debug)]
+pub struct SubscriberBuilder<
+    N = format::DefaultFields,
+    E = format::Format<format::Full>,
+    F = LevelFilter,
+    W = fn() -> io::Stdout,
+> {
+    filter: F,
+    inner: Layer<Registry, N, E, W>,
+}
+
+/// Returns a new [`SubscriberBuilder`] for configuring a [formatting subscriber].
+///
+/// This is essentially shorthand for [`SubscriberBuilder::default()]`.
+///
+/// # Examples
+///
+/// Using [`init`] to set the default subscriber:
+///
+/// ```rust
+/// tracing_subscriber::fmt().init();
+/// ```
+///
+/// Configuring the output format:
+///
+/// ```rust
+///
+/// tracing_subscriber::fmt()
+///     // Configure formatting settings.
+///     .with_target(false)
+///     .with_timer(tracing_subscriber::fmt::time::uptime())
+///     .with_level(true)
+///     // Set the subscriber as the default.
+///     .init();
+/// ```
+///
+/// [`try_init`] returns an error if the default subscriber could not be set:
+///
+/// ```rust
+/// use std::error::Error;
+///
+/// fn init_subscriber() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+///     tracing_subscriber::fmt()
+///         // Configure the subscriber to emit logs in JSON format.
+///         .json()
+///         // Configure the subscriber to flatten event fields in the output JSON objects.
+///         .flatten_event(true)
+///         // Set the subscriber as the default, returning an error if this fails.
+///         .try_init()?;
+///
+///     Ok(())
+/// }
+/// ```
+///
+/// Rather than setting the subscriber as the default, [`finish`] _returns_ the
+/// constructed subscriber, which may then be passed to other functions:
+///
+/// ```rust
+/// let subscriber = tracing_subscriber::fmt()
+///     .with_max_level(tracing::Level::DEBUG)
+///     .compact()
+///     .finish();
+///
+/// tracing::subscriber::with_default(subscriber, || {
+///     // the subscriber will only be set as the default
+///     // inside this closure...
+/// })
+/// ```
+///
+/// [formatting subscriber]: Subscriber
+/// [`SubscriberBuilder::default()`]: SubscriberBuilder::default()
+/// [`init`]: SubscriberBuilder::init()
+/// [`try_init`]: SubscriberBuilder::try_init()
+/// [`finish`]: SubscriberBuilder::finish()
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub fn fmt() -> SubscriberBuilder {
+    SubscriberBuilder::default()
+}
+
+/// Returns a new [formatting layer] that can be [composed] with other layers to
+/// construct a [`Subscriber`].
+///
+/// This is a shorthand for the equivalent [`Layer::default`] function.
+///
+/// [formatting layer]: Layer
+/// [composed]: crate::layer
+#[cfg_attr(docsrs, doc(cfg(all(feature = "fmt", feature = "std"))))]
+pub fn layer<S>() -> Layer<S> {
+    Layer::default()
+}
+
+impl Subscriber {
+    /// The maximum [verbosity level] that is enabled by a `Subscriber` by
+    /// default.
+    ///
+    /// This can be overridden with the [`SubscriberBuilder::with_max_level`] method.
+    ///
+    /// [verbosity level]: https://docs.rs/tracing-core/0.1.5/tracing_core/struct.Level.html
+    /// [`SubscriberBuilder::with_max_level`]: struct.SubscriberBuilder.html#method.with_max_level
+    pub const DEFAULT_MAX_LEVEL: LevelFilter = LevelFilter::INFO;
+
+    /// Returns a new `SubscriberBuilder` for configuring a format subscriber.
+    pub fn builder() -> SubscriberBuilder {
+        SubscriberBuilder::default()
+    }
+
+    /// Returns a new format subscriber with the default configuration.
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+impl Default for Subscriber {
+    fn default() -> Self {
+        SubscriberBuilder::default().finish()
+    }
+}
+
+// === impl Subscriber ===
+
+impl<N, E, F, W> tracing_core::Subscriber for Subscriber<N, E, F, W>
+where
+    N: for<'writer> FormatFields<'writer> + 'static,
+    E: FormatEvent<Registry, N> + 'static,
+    F: layer::Layer<Formatter<N, E, W>> + 'static,
+    W: for<'writer> MakeWriter<'writer> + 'static,
+    layer::Layered<F, Formatter<N, E, W>>: tracing_core::Subscriber,
+    fmt_layer::Layer<Registry, N, E, W>: layer::Layer<Registry>,
+{
+    #[inline]
+    fn register_callsite(&self, meta: &'static Metadata<'static>) -> Interest {
+        self.inner.register_callsite(meta)
+    }
+
+    #[inline]
+    fn enabled(&self, meta: &Metadata<'_>) -> bool {
+        self.inner.enabled(meta)
+    }
+
+    #[inline]
+    fn new_span(&self, attrs: &span::Attributes<'_>) -> span::Id {
+        self.inner.new_span(attrs)
+    }
+
+    #[inline]
+    fn record(&self, span: &span::Id, values: &span::Record<'_>) {
+        self.inner.record(span, values)
+    }
+
+    #[inline]
+    fn record_follows_from(&self, span: &span::Id, follows: &span::Id) {
+        self.inner.record_follows_from(span, follows)
+    }
+
+    #[inline]
+    fn event(&self, event: &Event<'_>) {
+        self.inner.event(event);
+    }
+
+    #[inline]
+    fn enter(&self, id: &span::Id) {
+        // TODO: add on_enter hook
+        self.inner.enter(id);
+    }
+
+    #[inline]
+    fn exit(&self, id: &span::Id) {
+        self.inner.exit(id);
+    }
+
+    #[inline]
+    fn current_span(&self) -> span::Current {
+        self.inner.current_span()
+    }
+
+    #[inline]
+    fn clone_span(&self, id: &span::Id) -> span::Id {
+        self.inner.clone_span(id)
+    }
+
+    #[inline]
+    fn try_close(&self, id: span::Id) -> bool {
+        self.inner.try_close(id)
+    }
+
+    #[inline]
+    fn max_level_hint(&self) -> Option<tracing_core::LevelFilter> {
+        self.inner.max_level_hint()
+    }
+
+    unsafe fn downcast_raw(&self, id: TypeId) -> Option<*const ()> {
+        if id == TypeId::of::<Self>() {
+            Some(self as *const Self as *const ())
+        } else {
+            self.inner.downcast_raw(id)
+        }
+    }
+}
+
+impl<'a, N, E, F, W> LookupSpan<'a> for Subscriber<N, E, F, W>
+where
+    layer::Layered<F, Formatter<N, E, W>>: LookupSpan<'a>,
+{
+    type Data = <layer::Layered<F, Formatter<N, E, W>> as LookupSpan<'a>>::Data;
+
+    fn span_data(&'a self, id: &span::Id) -> Option<Self::Data> {
+        self.inner.span_data(id)
+    }
+}
+
+// ===== impl SubscriberBuilder =====
+
+impl Default for SubscriberBuilder {
+    fn default() -> Self {
+        SubscriberBuilder {
+            filter: Subscriber::DEFAULT_MAX_LEVEL,
+            inner: Default::default(),
+        }
+    }
+}
+
+impl<N, E, F, W> SubscriberBuilder<N, E, F, W>
+where
+    N: for<'writer> FormatFields<'writer> + 'static,
+    E: FormatEvent<Registry, N> + 'static,
+    W: for<'writer> MakeWriter<'writer> + 'static,
+    F: layer::Layer<Formatter<N, E, W>> + Send + Sync + 'static,
+    fmt_layer::Layer<Registry, N, E, W>: layer::Layer<Registry> + Send + Sync + 'static,
+{
+    /// Finish the builder, returning a new `FmtSubscriber`.
+    pub fn finish(self) -> Subscriber<N, E, F, W> {
+        let subscriber = self.inner.with_subscriber(Registry::default());
+        Subscriber {
+            inner: self.filter.with_subscriber(subscriber),
+        }
+    }
+
+    /// Install this Subscriber as the global default if one is
+    /// not already set.
+    ///
+    /// If the `tracing-log` feature is enabled, this will also install
+    /// the LogTracer to convert `Log` records into `tracing` `Event`s.
+    ///
+    /// # Errors
+    /// Returns an Error if the initialization was unsuccessful, likely
+    /// because a global subscriber was already installed by another
+    /// call to `try_init`.
+    pub fn try_init(self) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+        use crate::util::SubscriberInitExt;
+        self.finish().try_init()?;
+
+        Ok(())
+    }
+
+    /// Install this Subscriber as the global default.
+    ///
+    /// If the `tracing-log` feature is enabled, this will also install
+    /// the LogTracer to convert `Log` records into `tracing` `Event`s.
+    ///
+    /// # Panics
+    /// Panics if the initialization was unsuccessful, likely because a
+    /// global subscriber was already installed by another call to `try_init`.
+    pub fn init(self) {
+        self.try_init()
+            .expect("Unable to install global subscriber")
+    }
+}
+
+impl<N, E, F, W> From<SubscriberBuilder<N, E, F, W>> for tracing_core::Dispatch
+where
+    N: for<'writer> FormatFields<'writer> + 'static,
+    E: FormatEvent<Registry, N> + 'static,
+    W: for<'writer> MakeWriter<'writer> + 'static,
+    F: layer::Layer<Formatter<N, E, W>> + Send + Sync + 'static,
+    fmt_layer::Layer<Registry, N, E, W>: layer::Layer<Registry> + Send + Sync + 'static,
+{
+    fn from(builder: SubscriberBuilder<N, E, F, W>) -> tracing_core::Dispatch {
+        tracing_core::Dispatch::new(builder.finish())
+    }
+}
+
+impl<N, L, T, F, W> SubscriberBuilder<N, format::Format<L, T>, F, W>
+where
+    N: for<'writer> FormatFields<'writer> + 'static,
+{
+    /// Use the given [`timer`] for log message timestamps.
+    ///
+    /// See the [`time` module] for the provided timer implementations.
+    ///
+    /// Note that using the `"time`"" feature flag enables the
+    /// additional time formatters [`UtcTime`] and [`LocalTime`], which use the
+    /// [`time` crate] to provide more sophisticated timestamp formatting
+    /// options.
+    ///
+    /// [`timer`]: time::FormatTime
+    /// [`time` module]: mod@time
+    /// [`UtcTime`]: time::UtcTime
+    /// [`LocalTime`]: time::LocalTime
+    /// [`time` crate]: https://docs.rs/time/0.3
+    pub fn with_timer<T2>(self, timer: T2) -> SubscriberBuilder<N, format::Format<L, T2>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.with_timer(timer),
+        }
+    }
+
+    /// Do not emit timestamps with log messages.
+    pub fn without_time(self) -> SubscriberBuilder<N, format::Format<L, ()>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.without_time(),
+        }
+    }
+
+    /// Configures how synthesized events are emitted at points in the [span
+    /// lifecycle][lifecycle].
+    ///
+    /// The following options are available:
+    ///
+    /// - `FmtSpan::NONE`: No events will be synthesized when spans are
+    ///    created, entered, exited, or closed. Data from spans will still be
+    ///    included as the context for formatted events. This is the default.
+    /// - `FmtSpan::NEW`: An event will be synthesized when spans are created.
+    /// - `FmtSpan::ENTER`: An event will be synthesized when spans are entered.
+    /// - `FmtSpan::EXIT`: An event will be synthesized when spans are exited.
+    /// - `FmtSpan::CLOSE`: An event will be synthesized when a span closes. If
+    ///    [timestamps are enabled][time] for this formatter, the generated
+    ///    event will contain fields with the span's _busy time_ (the total
+    ///    time for which it was entered) and _idle time_ (the total time that
+    ///    the span existed but was not entered).
+    /// - `FmtSpan::ACTIVE`: An event will be synthesized when spans are entered
+    ///    or exited.
+    /// - `FmtSpan::FULL`: Events will be synthesized whenever a span is
+    ///    created, entered, exited, or closed. If timestamps are enabled, the
+    ///    close event will contain the span's busy and idle time, as
+    ///    described above.
+    ///
+    /// The options can be enabled in any combination. For instance, the following
+    /// will synthesize events whenever spans are created and closed:
+    ///
+    /// ```rust
+    /// use tracing_subscriber::fmt::format::FmtSpan;
+    /// use tracing_subscriber::fmt;
+    ///
+    /// let subscriber = fmt()
+    ///     .with_span_events(FmtSpan::NEW | FmtSpan::CLOSE)
+    ///     .finish();
+    /// ```
+    ///
+    /// Note that the generated events will only be part of the log output by
+    /// this formatter; they will not be recorded by other `Subscriber`s or by
+    /// `Layer`s added to this subscriber.
+    ///
+    /// [lifecycle]: https://docs.rs/tracing/latest/tracing/span/index.html#the-span-lifecycle
+    /// [time]: #method.without_time
+    pub fn with_span_events(self, kind: format::FmtSpan) -> Self {
+        SubscriberBuilder {
+            inner: self.inner.with_span_events(kind),
+            ..self
+        }
+    }
+
+    /// Enable ANSI encoding for formatted events.
+    #[cfg(feature = "ansi")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))]
+    pub fn with_ansi(self, ansi: bool) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
+        SubscriberBuilder {
+            inner: self.inner.with_ansi(ansi),
+            ..self
+        }
+    }
+
+    /// Sets whether or not an event's target is displayed.
+    pub fn with_target(
+        self,
+        display_target: bool,
+    ) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
+        SubscriberBuilder {
+            inner: self.inner.with_target(display_target),
+            ..self
+        }
+    }
+
+    /// Sets whether or not an event's level is displayed.
+    pub fn with_level(
+        self,
+        display_level: bool,
+    ) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
+        SubscriberBuilder {
+            inner: self.inner.with_level(display_level),
+            ..self
+        }
+    }
+
+    /// Sets whether or not the [name] of the current thread is displayed
+    /// when formatting events
+    ///
+    /// [name]: https://doc.rust-lang.org/stable/std/thread/index.html#naming-threads
+    pub fn with_thread_names(
+        self,
+        display_thread_names: bool,
+    ) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
+        SubscriberBuilder {
+            inner: self.inner.with_thread_names(display_thread_names),
+            ..self
+        }
+    }
+
+    /// Sets whether or not the [thread ID] of the current thread is displayed
+    /// when formatting events
+    ///
+    /// [thread ID]: https://doc.rust-lang.org/stable/std/thread/struct.ThreadId.html
+    pub fn with_thread_ids(
+        self,
+        display_thread_ids: bool,
+    ) -> SubscriberBuilder<N, format::Format<L, T>, F, W> {
+        SubscriberBuilder {
+            inner: self.inner.with_thread_ids(display_thread_ids),
+            ..self
+        }
+    }
+
+    /// Sets the subscriber being built to use a less verbose formatter.
+    ///
+    /// See [`format::Compact`].
+    pub fn compact(self) -> SubscriberBuilder<N, format::Format<format::Compact, T>, F, W>
+    where
+        N: for<'writer> FormatFields<'writer> + 'static,
+    {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.compact(),
+        }
+    }
+
+    /// Sets the subscriber being built to use an [excessively pretty, human-readable formatter](crate::fmt::format::Pretty).
+    #[cfg(feature = "ansi")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))]
+    pub fn pretty(
+        self,
+    ) -> SubscriberBuilder<format::Pretty, format::Format<format::Pretty, T>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.pretty(),
+        }
+    }
+
+    /// Sets the subscriber being built to use a JSON formatter.
+    ///
+    /// See [`format::Json`](../fmt/format/struct.Json.html)
+    #[cfg(feature = "json")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
+    pub fn json(
+        self,
+    ) -> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W>
+    where
+        N: for<'writer> FormatFields<'writer> + 'static,
+    {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.json(),
+        }
+    }
+}
+
+#[cfg(feature = "json")]
+#[cfg_attr(docsrs, doc(cfg(feature = "json")))]
+impl<T, F, W> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W> {
+    /// Sets the json subscriber being built to flatten event metadata.
+    ///
+    /// See [`format::Json`](../fmt/format/struct.Json.html)
+    pub fn flatten_event(
+        self,
+        flatten_event: bool,
+    ) -> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.flatten_event(flatten_event),
+        }
+    }
+
+    /// Sets whether or not the JSON subscriber being built will include the current span
+    /// in formatted events.
+    ///
+    /// See [`format::Json`](../fmt/format/struct.Json.html)
+    pub fn with_current_span(
+        self,
+        display_current_span: bool,
+    ) -> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.with_current_span(display_current_span),
+        }
+    }
+
+    /// Sets whether or not the JSON subscriber being built will include a list (from
+    /// root to leaf) of all currently entered spans in formatted events.
+    ///
+    /// See [`format::Json`](../fmt/format/struct.Json.html)
+    pub fn with_span_list(
+        self,
+        display_span_list: bool,
+    ) -> SubscriberBuilder<format::JsonFields, format::Format<format::Json, T>, F, W> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.with_span_list(display_span_list),
+        }
+    }
+}
+
+#[cfg(feature = "env-filter")]
+#[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))]
+impl<N, E, W> SubscriberBuilder<N, E, crate::EnvFilter, W>
+where
+    Formatter<N, E, W>: tracing_core::Subscriber + 'static,
+{
+    /// Configures the subscriber being built to allow filter reloading at
+    /// runtime.
+    pub fn with_filter_reloading(
+        self,
+    ) -> SubscriberBuilder<N, E, crate::reload::Layer<crate::EnvFilter, Formatter<N, E, W>>, W>
+    {
+        let (filter, _) = crate::reload::Layer::new(self.filter);
+        SubscriberBuilder {
+            filter,
+            inner: self.inner,
+        }
+    }
+}
+
+#[cfg(feature = "env-filter")]
+#[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))]
+impl<N, E, W> SubscriberBuilder<N, E, crate::reload::Layer<crate::EnvFilter, Formatter<N, E, W>>, W>
+where
+    Formatter<N, E, W>: tracing_core::Subscriber + 'static,
+{
+    /// Returns a `Handle` that may be used to reload the constructed subscriber's
+    /// filter.
+    pub fn reload_handle(&self) -> crate::reload::Handle<crate::EnvFilter, Formatter<N, E, W>> {
+        self.filter.handle()
+    }
+}
+
+impl<N, E, F, W> SubscriberBuilder<N, E, F, W> {
+    /// Sets the Visitor that the subscriber being built will use to record
+    /// fields.
+    ///
+    /// For example:
+    /// ```rust
+    /// use tracing_subscriber::fmt::format;
+    /// use tracing_subscriber::prelude::*;
+    ///
+    /// let formatter =
+    ///     // Construct a custom formatter for `Debug` fields
+    ///     format::debug_fn(|writer, field, value| write!(writer, "{}: {:?}", field, value))
+    ///         // Use the `tracing_subscriber::MakeFmtExt` trait to wrap the
+    ///         // formatter so that a delimiter is added between fields.
+    ///         .delimited(", ");
+    ///
+    /// let subscriber = tracing_subscriber::fmt()
+    ///     .fmt_fields(formatter)
+    ///     .finish();
+    /// # drop(subscriber)
+    /// ```
+    pub fn fmt_fields<N2>(self, fmt_fields: N2) -> SubscriberBuilder<N2, E, F, W>
+    where
+        N2: for<'writer> FormatFields<'writer> + 'static,
+    {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.fmt_fields(fmt_fields),
+        }
+    }
+
+    /// Sets the [`EnvFilter`] that the subscriber will use to determine if
+    /// a span or event is enabled.
+    ///
+    /// Note that this method requires the "env-filter" feature flag to be enabled.
+    ///
+    /// If a filter was previously set, or a maximum level was set by the
+    /// [`with_max_level`] method, that value is replaced by the new filter.
+    ///
+    /// # Examples
+    ///
+    /// Setting a filter based on the value of the `RUST_LOG` environment
+    /// variable:
+    /// ```rust
+    /// use tracing_subscriber::{fmt, EnvFilter};
+    ///
+    /// fmt()
+    ///     .with_env_filter(EnvFilter::from_default_env())
+    ///     .init();
+    /// ```
+    ///
+    /// Setting a filter based on a pre-set filter directive string:
+    /// ```rust
+    /// use tracing_subscriber::fmt;
+    ///
+    /// fmt()
+    ///     .with_env_filter("my_crate=info,my_crate::my_mod=debug,[my_span]=trace")
+    ///     .init();
+    /// ```
+    ///
+    /// Adding additional directives to a filter constructed from an env var:
+    /// ```rust
+    /// use tracing_subscriber::{fmt, filter::{EnvFilter, LevelFilter}};
+    ///
+    /// # fn filter() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+    /// let filter = EnvFilter::try_from_env("MY_CUSTOM_FILTER_ENV_VAR")?
+    ///     // Set the base level when not matched by other directives to WARN.
+    ///     .add_directive(LevelFilter::WARN.into())
+    ///     // Set the max level for `my_crate::my_mod` to DEBUG, overriding
+    ///     // any directives parsed from the env variable.
+    ///     .add_directive("my_crate::my_mod=debug".parse()?);
+    ///
+    /// fmt()
+    ///     .with_env_filter(filter)
+    ///     .try_init()?;
+    /// # Ok(())}
+    /// ```
+    /// [`EnvFilter`]: ../filter/struct.EnvFilter.html
+    /// [`with_max_level`]: #method.with_max_level
+    #[cfg(feature = "env-filter")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "env-filter")))]
+    pub fn with_env_filter(
+        self,
+        filter: impl Into<crate::EnvFilter>,
+    ) -> SubscriberBuilder<N, E, crate::EnvFilter, W>
+    where
+        Formatter<N, E, W>: tracing_core::Subscriber + 'static,
+    {
+        let filter = filter.into();
+        SubscriberBuilder {
+            filter,
+            inner: self.inner,
+        }
+    }
+
+    /// Sets the maximum [verbosity level] that will be enabled by the
+    /// subscriber.
+    ///
+    /// If the max level has already been set, or a [`EnvFilter`] was added by
+    /// [`with_filter`], this replaces that configuration with the new
+    /// maximum level.
+    ///
+    /// # Examples
+    ///
+    /// Enable up to the `DEBUG` verbosity level:
+    /// ```rust
+    /// use tracing_subscriber::fmt;
+    /// use tracing::Level;
+    ///
+    /// fmt()
+    ///     .with_max_level(Level::DEBUG)
+    ///     .init();
+    /// ```
+    /// This subscriber won't record any spans or events!
+    /// ```rust
+    /// use tracing_subscriber::{fmt, filter::LevelFilter};
+    ///
+    /// let subscriber = fmt()
+    ///     .with_max_level(LevelFilter::OFF)
+    ///     .finish();
+    /// ```
+    /// [verbosity level]: https://docs.rs/tracing-core/0.1.5/tracing_core/struct.Level.html
+    /// [`EnvFilter`]: ../filter/struct.EnvFilter.html
+    /// [`with_filter`]: #method.with_filter
+    pub fn with_max_level(
+        self,
+        filter: impl Into<LevelFilter>,
+    ) -> SubscriberBuilder<N, E, LevelFilter, W> {
+        let filter = filter.into();
+        SubscriberBuilder {
+            filter,
+            inner: self.inner,
+        }
+    }
+
+    /// Sets the function that the subscriber being built should use to format
+    /// events that occur.
+    pub fn event_format<E2>(self, fmt_event: E2) -> SubscriberBuilder<N, E2, F, W>
+    where
+        E2: FormatEvent<Registry, N> + 'static,
+        N: for<'writer> FormatFields<'writer> + 'static,
+        W: for<'writer> MakeWriter<'writer> + 'static,
+    {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.event_format(fmt_event),
+        }
+    }
+
+    /// Sets the [`MakeWriter`] that the subscriber being built will use to write events.
+    ///
+    /// # Examples
+    ///
+    /// Using `stderr` rather than `stdout`:
+    ///
+    /// ```rust
+    /// use tracing_subscriber::fmt;
+    /// use std::io;
+    ///
+    /// fmt()
+    ///     .with_writer(io::stderr)
+    ///     .init();
+    /// ```
+    ///
+    /// [`MakeWriter`]: trait.MakeWriter.html
+    pub fn with_writer<W2>(self, make_writer: W2) -> SubscriberBuilder<N, E, F, W2>
+    where
+        W2: for<'writer> MakeWriter<'writer> + 'static,
+    {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.with_writer(make_writer),
+        }
+    }
+
+    /// Configures the subscriber to support [`libtest`'s output capturing][capturing] when used in
+    /// unit tests.
+    ///
+    /// See [`TestWriter`] for additional details.
+    ///
+    /// # Examples
+    ///
+    /// Using [`TestWriter`] to let `cargo test` capture test output. Note that we do not install it
+    /// globally as it may cause conflicts.
+    ///
+    /// ```rust
+    /// use tracing_subscriber::fmt;
+    /// use tracing::subscriber;
+    ///
+    /// subscriber::set_default(
+    ///     fmt()
+    ///         .with_test_writer()
+    ///         .finish()
+    /// );
+    /// ```
+    ///
+    /// [capturing]:
+    /// https://doc.rust-lang.org/book/ch11-02-running-tests.html#showing-function-output
+    /// [`TestWriter`]: writer/struct.TestWriter.html
+    pub fn with_test_writer(self) -> SubscriberBuilder<N, E, F, TestWriter> {
+        SubscriberBuilder {
+            filter: self.filter,
+            inner: self.inner.with_writer(TestWriter::default()),
+        }
+    }
+}
+
+/// Install a global tracing subscriber that listens for events and
+/// filters based on the value of the [`RUST_LOG` environment variable],
+/// if one is not already set.
+///
+/// If the `tracing-log` feature is enabled, this will also install
+/// the [`LogTracer`] to convert `log` records into `tracing` `Event`s.
+///
+/// This is shorthand for
+///
+/// ```rust
+/// # fn doc() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+/// tracing_subscriber::fmt().try_init()
+/// # }
+/// ```
+///
+///
+/// # Errors
+///
+/// Returns an Error if the initialization was unsuccessful,
+/// likely because a global subscriber was already installed by another
+/// call to `try_init`.
+///
+/// [`LogTracer`]:
+///     https://docs.rs/tracing-log/0.1.0/tracing_log/struct.LogTracer.html
+/// [`RUST_LOG` environment variable]:
+///     ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV
+pub fn try_init() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
+    let builder = Subscriber::builder();
+
+    #[cfg(feature = "env-filter")]
+    let builder = builder.with_env_filter(crate::EnvFilter::from_default_env());
+
+    builder.try_init()
+}
+
+/// Install a global tracing subscriber that listens for events and
+/// filters based on the value of the [`RUST_LOG` environment variable].
+///
+/// If the `tracing-log` feature is enabled, this will also install
+/// the LogTracer to convert `Log` records into `tracing` `Event`s.
+///
+/// This is shorthand for
+///
+/// ```rust
+/// tracing_subscriber::fmt().init()
+/// ```
+///
+/// # Panics
+/// Panics if the initialization was unsuccessful, likely because a
+/// global subscriber was already installed by another call to `try_init`.
+///
+/// [`RUST_LOG` environment variable]:
+///     ../filter/struct.EnvFilter.html#associatedconstant.DEFAULT_ENV
+pub fn init() {
+    try_init().expect("Unable to install global subscriber")
+}
+
+#[cfg(test)]
+mod test {
+    use crate::{
+        filter::LevelFilter,
+        fmt::{
+            format::{self, Format},
+            time,
+            writer::MakeWriter,
+            Subscriber,
+        },
+    };
+    use std::{
+        io,
+        sync::{Arc, Mutex, MutexGuard, TryLockError},
+    };
+    use tracing_core::dispatcher::Dispatch;
+
+    pub(crate) struct MockWriter {
+        buf: Arc<Mutex<Vec<u8>>>,
+    }
+
+    impl MockWriter {
+        pub(crate) fn new(buf: Arc<Mutex<Vec<u8>>>) -> Self {
+            Self { buf }
+        }
+
+        pub(crate) fn map_error<Guard>(err: TryLockError<Guard>) -> io::Error {
+            match err {
+                TryLockError::WouldBlock => io::Error::from(io::ErrorKind::WouldBlock),
+                TryLockError::Poisoned(_) => io::Error::from(io::ErrorKind::Other),
+            }
+        }
+
+        pub(crate) fn buf(&self) -> io::Result<MutexGuard<'_, Vec<u8>>> {
+            self.buf.try_lock().map_err(Self::map_error)
+        }
+    }
+
+    impl io::Write for MockWriter {
+        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+            self.buf()?.write(buf)
+        }
+
+        fn flush(&mut self) -> io::Result<()> {
+            self.buf()?.flush()
+        }
+    }
+
+    #[derive(Clone, Default)]
+    pub(crate) struct MockMakeWriter {
+        buf: Arc<Mutex<Vec<u8>>>,
+    }
+
+    impl MockMakeWriter {
+        pub(crate) fn new(buf: Arc<Mutex<Vec<u8>>>) -> Self {
+            Self { buf }
+        }
+
+        #[cfg(feature = "json")]
+        pub(crate) fn buf(&self) -> MutexGuard<'_, Vec<u8>> {
+            self.buf.lock().unwrap()
+        }
+
+        pub(crate) fn get_string(&self) -> String {
+            let mut buf = self.buf.lock().expect("lock shouldn't be poisoned");
+            let string = std::str::from_utf8(&buf[..])
+                .expect("formatter should not have produced invalid utf-8")
+                .to_owned();
+            buf.clear();
+            string
+        }
+    }
+
+    impl<'a> MakeWriter<'a> for MockMakeWriter {
+        type Writer = MockWriter;
+
+        fn make_writer(&'a self) -> Self::Writer {
+            MockWriter::new(self.buf.clone())
+        }
+    }
+
+    #[test]
+    fn impls() {
+        let f = Format::default().with_timer(time::Uptime::default());
+        let subscriber = Subscriber::builder().event_format(f).finish();
+        let _dispatch = Dispatch::new(subscriber);
+
+        let f = format::Format::default();
+        let subscriber = Subscriber::builder().event_format(f).finish();
+        let _dispatch = Dispatch::new(subscriber);
+
+        let f = format::Format::default().compact();
+        let subscriber = Subscriber::builder().event_format(f).finish();
+        let _dispatch = Dispatch::new(subscriber);
+    }
+
+    #[test]
+    fn subscriber_downcasts() {
+        let subscriber = Subscriber::builder().finish();
+        let dispatch = Dispatch::new(subscriber);
+        assert!(dispatch.downcast_ref::<Subscriber>().is_some());
+    }
+
+    #[test]
+    fn subscriber_downcasts_to_parts() {
+        let subscriber = Subscriber::new();
+        let dispatch = Dispatch::new(subscriber);
+        assert!(dispatch.downcast_ref::<format::DefaultFields>().is_some());
+        assert!(dispatch.downcast_ref::<LevelFilter>().is_some());
+        assert!(dispatch.downcast_ref::<format::Format>().is_some())
+    }
+
+    #[test]
+    fn is_lookup_span() {
+        fn assert_lookup_span<T: for<'a> crate::registry::LookupSpan<'a>>(_: T) {}
+        let subscriber = Subscriber::new();
+        assert_lookup_span(subscriber)
+    }
+}