This PR adds documentation on `valuable` support in `tracing-serde` and
`tracing-subscriber`.

This branch fixes some broken documentation links and other docs issues
in `tracing-subscriber`.

## Motivation

As discussed on discord, this API + `Targets` being `: Clone` makes it
easier to solve the original problem I had tried to solve in
#1889.

My plan on how to use this is in
https://github.com/MaterializeInc/materialize/issues/10441 if you are
interested!

## Solution

I considered doing some macro magic to create a `Metadata` with a
callsite and empty fields and everything, to be able to called
`DirectiveSet::enabled`, but it felt cleaner and easier to reason about
the special-case-ness (`Targets` never having field filters) using a new
set of methods that do a similar thing.

For testing I opted for just a doc-test, let me know if thats fine!

# 0.1.3 (February 4, 2022)

This release adds *experimental* support for recording structured field
values using the [`valuable`] crate. See [this blog post][post] for
details on `valuable`.

Note that `valuable` support currently requires `--cfg
tracing_unstable`. See the documentation for details.

### Added

- **valuable**: Experimental support for serializing user-defined types
  using [`valuable`] and [`valuable-serde`] ([#1862])
- Support for serializing `f64` values ([#1507])

### Fixed

- Fixed incorrect size hint in `SerializeFieldSet` ([#1333])
- A number of documentation fixes

Thanks to @akinnane and @maxburke for contributing to this release!

[`valuable`]: https://crates.io/crates/valuable
[`valuable-serde`]: https://crates.io/crates/valuable-serde
[post]: https://tokio.rs/blog/2021-05-valuable
[#1862]: #1862
[#1507]: #1507
[#1333]: #1333

(I also noticed there was a missing changelog entry for v0.1.2, so I
fixed that while I was here)

# 0.3.8 (Feb 4, 2022)

This release adds *experimental* support for recording structured field
values using the [`valuable`] crate to the `format::Json` formatter. In
particular, user-defined types which are recorded using their
[`valuable::Valuable`] implementations will be serialized as JSON
objects, rather than using their `fmt::Debug` representation. See [this
blog post][post] for details on `valuable`.

Note that `valuable` support currently requires `--cfg
tracing_unstable`. See the documentation for details.

Additionally, this release includes a number of other smaller API
improvements.

### Added

- **json**: Experimental support for recording [`valuable`] values as
  structured JSON ([#1862], [#1901])
- **filter**: `Targets::would_enable` method for testing if a `Targets`
  filter would enable a given target ([#1903])
- **fmt**: `map_event_format`, `map_fmt_fields`, and `map_writer`
  methods to `fmt::Layer` and `fmt::SubscriberBuilder` ([#1871])

### Changed

- `tracing-core`: updated to [0.1.22][core-0.1.22]

### Fixed

- Set `smallvec` minimal version to 1.2.0, to fix compilation errors
  with `-Z minimal-versions` ([#1890])
- Minor documentation fixes ([#1902], [#1893])

Thanks to @guswynn, @glts, and @lilyball for contributing to this
release!

[`valuable`]: https://crates.io/crates/valuable
[`valuable::Valuable`]: https://docs.rs/valuable/latest/valuable/trait.Valuable.html
[post]: https://tokio.rs/blog/2021-05-valuable
[core-0.1.22]: https://github.com/tokio-rs/tracing/releases/tag/tracing-core-0.1.22
[#1862]: #1862
[#1901]: #1901
[#1903]: #1903
[#1871]: #1871
[#1890]: #1890
[#1902]: #1902
[#1893]: #1893

This updates all crates' MSRVs to 1.49 if they were not already greater
than that (`tracing-appender` is at 1.53). Rust 1.49+ is required to
update `parking_lot` to v0.12 (see #1878). Also, `futures-task` (which I
believe is only needed as a transitive dep) now needs 1.45+, so this
also fixes our CI build.

Because `tracing-opentelemetry` previously required 1.46.0, it had a
separate CI MSRV job. Since 1.49.0 is greater than 1.46.0, the separate
check for `tracing-opentelemetry` is no longer needed.

In the process, I removed deprecated uses of
`core::atomic::spin_loop_hint`, which is replaced with
`core::hint::spin_loop` in 1.49.

Fixes #1879

## Motivation

`journald-tracing>=0.2.1` doesn't build with old glibc.

## Solution

Make the `memfd_create` syscall ourselves.

cc @lunaryorn @Ralith

)

Updates the requirements on [parking_lot](https://github.com/Amanieu/parking_lot) to permit the latest version.
- [Release notes](https://github.com/Amanieu/parking_lot/releases)
- [Changelog](https://github.com/Amanieu/parking_lot/blob/master/CHANGELOG.md)
- [Commits](Amanieu/parking_lot@0.11.2...0.12.0)

---
updated-dependencies:
- dependency-name: parking_lot
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Eliza Weisman <eliza@buoyant.io>

# 0.2.3 (February 7, 2022)

### Fixed

- Fixed missing `memfd_create` with `glibc` versions < 2.25 ([#1912])

### Changed

- Updated minimum supported Rust version to 1.49.0 ([#1913])

Thanks to @9999years for contributing to this release!

[#1912]: #1912
[#1913]: #1913

Re-application of changes made in #1842 which were lost in f1cf1f1

Integration tests added for regression.

---

## Motivation

In my library I define a `macro_rules! concat` macro, i.e.
[`callbag::concat`](https://docs.rs/callbag/latest/callbag/macro.concat.html).

When I try to call `tracing::info!(...)`, I get error output such as
this:

<details>
<summary>error output</summary>

<!-- leave a blank line above -->
```
> RUSTFLAGS='-Z macro-backtrace' cargo +nightly clippy --features trace
    Checking callbag v0.14.0 (/home/teohhanhui/projects/teohhanhui/callbag-rs)
error[E0308]: mismatched types
  --> src/concat.rs:89:9
   |
89 |         info!("from sink: {message:?}");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&str`, found `u32`

error[E0277]: the trait bound `std::sync::Arc<core::Callbag<never::Never, _>>: std::convert::From<&str>` is not satisfied
    --> src/concat.rs:58:9
     |
56   | / macro_rules! concat {
57   | |     ($($s:expr),* $(,)?) => {
58   | |         $crate::concat(::std::vec![$($s),*].into_boxed_slice())
     | |         ^^^^^^^^^^^^^^ the trait `std::convert::From<&str>` is not implemented for `std::sync::Arc<core::Callbag<never::Never, _>>`
59   | |     };
60   | | }
     | |_- in this expansion of `concat!` (#5)
...
89   |           info!("from sink: {message:?}");
     |           ------------------------------- in this macro invocation (#1)
     |
    ::: src/utils/tracing.rs:47:1
     |
47   | / macro_rules! info {
48   | |     ($($arg:tt)+) => {
49   | |         ::cfg_if::cfg_if! {
50   | |             if #[cfg(feature = "trace")] {
51   | |                 ::tracing::info!($($arg)+)
     | |                 -------------------------- in this macro invocation (#2)
...    |
54   | |     };
55   | | }
     | |_- in this expansion of `info!` (#1)
     |
    ::: /home/teohhanhui/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-0.1.29/src/macros.rs:586:1
     |
586  |   macro_rules! event {
     |  _-
     | |_|
     | |
587  | |     (target: $target:expr, parent: $parent:expr, $lvl:expr, { $($fields:tt)* } )=> (
588  | |         $crate::__tracing_log!(
589  | |             target: $target,
...    |
644  |                   name: concat!(
     |  _______________________-
645  |                       "event ",
646  |                       file!(),
647  |                       ":",
648  |                       line!()
649  | |                 ),
     | |_________________- in this macro invocation (#5)
...
667  | /         $crate::event!(
668  |               target: $target,
669  |               $lvl,
670  |               { message = format_args!($($arg)+), $($fields)* }
671  | |         )
     | |_________- in this macro invocation (#4)
...
791  | |     );
792  | | }
     | | -
     | |_|
     | |_in this expansion of `$crate::event!` (#3)
     |   in this expansion of `$crate::event!` (#4)
...
1229 | / macro_rules! info {
1230 |        (target: $target:expr, parent: $parent:expr, { $($field:tt)* }, $($arg:tt)* ) => (
1231 |           $crate::event!(target: $target, parent: $parent, $crate::Level::INFO, { $($field)* }, $($arg)*)
1232 |       );
...
1398 | /         $crate::event!(
1399 | |             target: module_path!(),
1400 | |             $crate::Level::INFO,
1401 | |             {},
1402 | |             $($arg)+
1403 | |         )
     | |_________- in this macro invocation (#3)
1404 |       );
1405 | | }
     | |_- in this expansion of `::tracing::info!` (#2)
     |
     = help: the following implementations were found:
               <std::sync::Arc<B> as std::convert::From<std::borrow::Cow<'a, B>>>
               <std::sync::Arc<T> as std::convert::From<T>>
               <std::sync::Arc<T> as std::convert::From<std::boxed::Box<T>>>
               <std::sync::Arc<[T]> as std::convert::From<&[T]>>
             and 9 others
     = note: required because of the requirements on the impl of `std::convert::Into<std::sync::Arc<core::Callbag<never::Never, _>>>` for `&str`
note: required by a bound in `concat::concat`
    --> src/concat.rs:81:8
     |
72   | pub fn concat<
     |        ------ required by a bound in this
...
81   |     S: Into<Arc<Source<T>>> + Send + Sync,
     |        ^^^^^^^^^^^^^^^^^^^^ required by this bound in `concat::concat`

error[E0308]: mismatched types
    --> src/concat.rs:58:9
     |
56   | / macro_rules! concat {
57   | |     ($($s:expr),* $(,)?) => {
58   | |         $crate::concat(::std::vec![$($s),*].into_boxed_slice())
     | |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&str`, found struct `core::Callbag`
59   | |     };
60   | | }
     | |_- in this expansion of `concat!` (#5)
...
89   |           info!("from sink: {message:?}");
     |           ------------------------------- in this macro invocation (#1)
     |
    ::: src/utils/tracing.rs:47:1
     |
47   | / macro_rules! info {
48   | |     ($($arg:tt)+) => {
49   | |         ::cfg_if::cfg_if! {
50   | |             if #[cfg(feature = "trace")] {
51   | |                 ::tracing::info!($($arg)+)
     | |                 -------------------------- in this macro invocation (#2)
...    |
54   | |     };
55   | | }
     | |_- in this expansion of `info!` (#1)
     |
    ::: /home/teohhanhui/.cargo/registry/src/github.com-1ecc6299db9ec823/tracing-0.1.29/src/macros.rs:586:1
     |
586  |   macro_rules! event {
     |  _-
     | |_|
     | |
587  | |     (target: $target:expr, parent: $parent:expr, $lvl:expr, { $($fields:tt)* } )=> (
588  | |         $crate::__tracing_log!(
589  | |             target: $target,
...    |
644  |                   name: concat!(
     |  _______________________-
645  |                       "event ",
646  |                       file!(),
647  |                       ":",
648  |                       line!()
649  | |                 ),
     | |_________________- in this macro invocation (#5)
...
667  | /         $crate::event!(
668  |               target: $target,
669  |               $lvl,
670  |               { message = format_args!($($arg)+), $($fields)* }
671  | |         )
     | |_________- in this macro invocation (#4)
...
791  | |     );
792  | | }
     | | -
     | |_|
     | |_in this expansion of `$crate::event!` (#3)
     |   in this expansion of `$crate::event!` (#4)
...
1229 | / macro_rules! info {
1230 |        (target: $target:expr, parent: $parent:expr, { $($field:tt)* }, $($arg:tt)* ) => (
1231 |           $crate::event!(target: $target, parent: $parent, $crate::Level::INFO, { $($field)* }, $($arg)*)
1232 |       );
...
1398 | /         $crate::event!(
1399 | |             target: module_path!(),
1400 | |             $crate::Level::INFO,
1401 | |             {},
1402 | |             $($arg)+
1403 | |         )
     | |_________- in this macro invocation (#3)
1404 |       );
1405 | | }
     | |_- in this expansion of `::tracing::info!` (#2)
     |
     = note: expected reference `&'static str`
                   found struct `core::Callbag<never::Never, _>`

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.
error: could not compile `callbag` due to 3 previous errors
```
</details>

This is because of my `concat` macro being in scope.

## Solution

Change all the `tracing` macros to use the re-export of `core::concat!`
in the `__macro_support` module, rather than using an un-namespaced
`concat!`. The re-export ensures that everything still works even in a
crate that redefines the `core` name to something else.

This branch adds the source code file, module path, and line number to
OpenTelemetry events as the OpenTelemetry `code.filepath`,
`code.namespace`, and `code.lineno` fields, respectively, if they are
set in the `tracing` event's metadata.

Fixes #1910

## Motivation

Currently, the `tracing-opentelemetry` subscriber will allocate several
strings for opentelemetry key-value fields in its `on_event`
implementation. Some of these allocations are not necessary, since
`opentelemetry::Value::String` can take a `Cow`, allowing `&'static str`s
to be used without allocating a new `String`.

Since this happens for _every_ event that's recorded to opentelemetry,
this probably has a meaningful performance impact.

## Solution

This branch makes two primary changes:

+ Change the `on_event` method to subscriber to use `&'static str`s for
  event targets when possible, similarly to how we did this for source
  locations in #1911. This way, when events were not recorded via the
  `tracing-log` adapter, we will use the `&'static` tracing metadata
  string for their targets, rather than allocating a new `String`. New
  `String`s are only allocated when an event came from the `log` crate
  and its target is not valid for the `'static` lifetime.

* Use `Level::as_str` for the `Level` key-value field, instead of
  `Level::to_string`. `to_string` calls `fmt::Display` and returns a
  `String`, while `as_str` returns an `&'static str`. This way, levels
  will never allocate a `String`.

# 0.17.1 (February 11, 2022)

### Added

- `OpenTelemetryLayer` can now add detailed location information to
  forwarded events (defaults to on) ([#1911])
- `OpenTelemetryLayer::with_event_location` to control whether source
  locations are recorded ([#1911])
### Changed

- Avoid unnecessary allocations to improve performance when recording
  events ([#1917])

Thanks to @djc for contributing to this release!

[#1917]: #1917
[#1911]: #1911

Closes #1919

## Motivation

Currently, the RustDoc for the `format::Compact` formatter in
`tracing-subscriber` describes the output from the `master` (v0.2.x)
version of the formatter, not the version on the v0.1.x branch.

## Solution

This PR updates the documentation to describe the actual output format.
Also, I added an example of the formatter in the `examples` directory.

Closes #1909

## Motivation

I was scrolling through the code in `tracing/src/macros.rs` and noticed
a possibly wrong log level in the `warn!` macro:

https://github.com/tokio-rs/tracing/blob/4e65750b13721fee7a7ac05b053e1b9c3d21244f/tracing/src/macros.rs#L1698

## Solution

This branch changes the level to `Level::WARN` in the incorrect macro
 arm.

Fixes: #1929

Co-authored-by: Nicolaas Geldenhuys <nicolaas.geldenhuys@cartrack.com>

## Motivation

This PR adds [`tracing-forest`](https://crates.io/crates/tracing-forest)
to the list of related crates. `tracing-forest` provides contextual
coherence when writing logs, and is being used by projects like
[Kanidm](https://github.com/kanidm/kanidm/).

## Solution

I added it to the documentation in `lib.rs` and in the README. Am I
missing anything else?

## Motivation

Currently, the documentation for the `fmt` module shows examples of the
output for each formatter in the top-level module. This is a lot of text
that makes finding other things in the documentation more difficult.
Meanwhile, the type-level docs for the various formatters are quite
terse and don't offer much useful information.

## Solution

This branch moves the example output to the type-level docs for the
various formatters, and links to it from the list of formatters. I've
also updated and expanded some of the documentation for the formatters,
and added a similar list of formatters to the `fmt::format` module.
Hopefully, this makes things easier to navigate?

Finally, I've re-generated all example output with the latest versions
of each formatter.

## Alternatives

Alternatively, we could not move the example output. The initial
intention for putting it in the top-level `fmt` module docs was to make
it _very_ easy to find what the different formats look like. Perhaps
this is worth having a lot of text to scroll through in the
module-level docs?

# 0.1.31 (February 17th, 2022)

This release increases the minimum supported Rust version (MSRV) to
1.49.0. In addition, it fixes some relatively rare macro bugs.

### Added

- Added `tracing-forest` to the list of related crates ([#1935])

### Changed

- Updated minimum supported Rust version (MSRV) to 1.49.0 ([#1913])

### Fixed

- Fixed the `warn!` macro incorrectly generating an event with the
  `TRACE` level ([#1930])
- Fixed macro hygiene issues when used in a crate that defines its own
  `concat!` macro, for real this time ([#1918])

Thanks to @QnnOkabayashi, @nicolaasg, and @teohhanhui for contributing
to this release!

[#1935]: #1935
[#1913]: #1913
[#1930]: #1930
[#1918]: #1918