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subscriber: add Subscribe impl for Vec<S: Subscribe> #2027

Merged
merged 16 commits into from
Mar 29, 2022
Merged

subscriber: add Subscribe impl for Vec<S: Subscribe> #2027

merged 16 commits into from
Mar 29, 2022

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hawkw
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@hawkw hawkw commented Mar 25, 2022 •
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Depends on #2028

Motivation

In many cases, it is desirable to have a variable number of subscribers
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing Subscribe are
composed at the type level into Layered subscribers, doesn't work well
when the number of subscribers varies at runtime.

Solution

To solve this, this branch adds a Subscribe implementation for
Vec<S> where S: Subscribe. This allows variable-length lists of
subscribers to be added to a collector. Although the impl for Vec<S>
requires all the subscribers to be the same type, it can also be used in
conjunction with Box<dyn Subscribe<C> + ...> trait objects to
implement a variable-length list of subscribers of multiple types.

I also wrote a bunch of docs examples.

Notes

Alternatively, we could have a separate type defined in
tracing-subscriber for a variable-length list of type-erased
subscribers. This would have one primary usability benefit, which is
that we could have a push operation that takes an impl Subscribe
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as Vec and Box, rather than adding a whole new API.
Additionally, it allows avoiding the additional Boxing in the case
where the list consists of subscribers that are all the same type.

Closes #1708

@hawkw hawkw requested review from davidbarsky and a team as code owners March 25, 2022 23:26
Base automatically changed from eliza/boxed-combinator to master March 26, 2022 02:07
@hawkw
subscriber: fix boxed subscriber not forwarding max_level_hint
83f853d 
Currently, the implementation of `Subscribe` for
`Box<dyn Subscribe<C> + ...>` does not implement the `max_level_hint`
method. This means that if the boxed subscriber has a max level hint, it
will be lost when boxing the subscriber.

This commit adds the missing method implementation.
@hawkw hawkw mentioned this pull request Mar 28, 2022
Merged
hawkw added 12 commits March 28, 2022 11:02
@hawkw
wip
521cad9
@hawkw
docs
8ad14f7 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
add test for vec with per-layer filters
f59fe48 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
ensure vecs evaluate all per-layer filters
28e55d2 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
add docs
c81151f 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
fix downcasting
45d99b1 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
mention reload
d6884cc 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
use combinator to make tests look nicer
b4f328a 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
use .all()
012da66 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
add test for Vec<S> per-layer filter caching
e8b950e 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
add tests for level hints
2709f97 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
fix interest combining for mixed PSF/non-PSF vecs
82ed40a 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 28, 2022
@hawkw
subscriber: fix boxed subscriber not forwarding max_level_hint (#2030)
baaab24 
## Motivation

Currently, the implementation of `Subscribe` for
`Box<dyn Subscribe<C> + ...>` does not implement the `max_level_hint`
method. This means that if the boxed subscriber has a max level hint, it
will be lost when boxing a subscriber.

Found this while working on tests for #2027.

## Solution

This commit adds the missing method implementation.
davidbarsky
davidbarsky reviewed Mar 29, 2022
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@hawkw hawkw requested a review from davidbarsky March 29, 2022 23:07
@hawkw @davidbarsky
Apply suggestions from code review
069f39c 
Co-authored-by: David Barsky <me@davidbarsky.com>
@hawkw hawkw enabled auto-merge (squash) March 29, 2022 23:37
@hawkw hawkw merged commit a3e7944 into master Mar 29, 2022
@hawkw hawkw deleted the eliza/dyn-layer-list branch March 29, 2022 23:54
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: add Layer impl for Vec<L: Layer> (#2027)
9cc9c49 
Depends on #2028

## Motivation

In many cases, it is desirable to have a variable number of `Layer`s
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing `Layer` are
composed at the type level into `Layered` layers, doesn't work well
when the number of layers varies at runtime.

## Solution

To solve this, this branch adds a `Layer` implementation for
`Vec<L> where L: Layer`. This allows variable-length lists of
layers to be added to a subscriber. Although the impl for `Vec<L>`
requires all the layers to be the same type, it can also be used in
 onjunction with `Box<dyn Layer<S> + ...>` trait objects to
implement a variable-length list of layers of multiple types.

I also wrote a bunch of docs examples.

## Notes

Alternatively, we could have a separate type defined in
`tracing-subscriber` for a variable-length list of type-erased
`Layer`s. This would have one primary usability benefit, which is
that we could have a `push` operation that takes an `impl Layer`
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as `Vec` and `Box`, rather than adding a whole new API.
Additionally, it allows avoiding the additional `Box`ing in the case
where the list consists of layers that are all the same type.

Closes #1708

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: add Layer impl for Vec<L: Layer> (#2027)
0852ab3 
Depends on #2028

## Motivation

In many cases, it is desirable to have a variable number of `Layer`s
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing `Layer` are
composed at the type level into `Layered` layers, doesn't work well
when the number of layers varies at runtime.

## Solution

To solve this, this branch adds a `Layer` implementation for
`Vec<L> where L: Layer`. This allows variable-length lists of
layers to be added to a subscriber. Although the impl for `Vec<L>`
requires all the layers to be the same type, it can also be used in
 onjunction with `Box<dyn Layer<S> + ...>` trait objects to
implement a variable-length list of layers of multiple types.

I also wrote a bunch of docs examples.

## Notes

Alternatively, we could have a separate type defined in
`tracing-subscriber` for a variable-length list of type-erased
`Layer`s. This would have one primary usability benefit, which is
that we could have a `push` operation that takes an `impl Layer`
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as `Vec` and `Box`, rather than adding a whole new API.
Additionally, it allows avoiding the additional `Box`ing in the case
where the list consists of layers that are all the same type.

Closes #1708

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: add Layer impl for Vec<L: Layer> (#2027)
dcf1e0c 
Depends on #2028

## Motivation

In many cases, it is desirable to have a variable number of `Layer`s
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing `Layer` are
composed at the type level into `Layered` layers, doesn't work well
when the number of layers varies at runtime.

## Solution

To solve this, this branch adds a `Layer` implementation for
`Vec<L> where L: Layer`. This allows variable-length lists of
layers to be added to a subscriber. Although the impl for `Vec<L>`
requires all the layers to be the same type, it can also be used in
 onjunction with `Box<dyn Layer<S> + ...>` trait objects to
implement a variable-length list of layers of multiple types.

I also wrote a bunch of docs examples.

## Notes

Alternatively, we could have a separate type defined in
`tracing-subscriber` for a variable-length list of type-erased
`Layer`s. This would have one primary usability benefit, which is
that we could have a `push` operation that takes an `impl Layer`
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as `Vec` and `Box`, rather than adding a whole new API.
Additionally, it allows avoiding the additional `Box`ing in the case
where the list consists of layers that are all the same type.

Closes #1708

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: add Layer impl for Vec<L: Layer> (#2027)
5cd4b57 
Depends on #2028

## Motivation

In many cases, it is desirable to have a variable number of `Layer`s
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing `Layer` are
composed at the type level into `Layered` layers, doesn't work well
when the number of layers varies at runtime.

## Solution

To solve this, this branch adds a `Layer` implementation for
`Vec<L> where L: Layer`. This allows variable-length lists of
layers to be added to a subscriber. Although the impl for `Vec<L>`
requires all the layers to be the same type, it can also be used in
 onjunction with `Box<dyn Layer<S> + ...>` trait objects to
implement a variable-length list of layers of multiple types.

I also wrote a bunch of docs examples.

## Notes

Alternatively, we could have a separate type defined in
`tracing-subscriber` for a variable-length list of type-erased
`Layer`s. This would have one primary usability benefit, which is
that we could have a `push` operation that takes an `impl Layer`
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as `Vec` and `Box`, rather than adding a whole new API.
Additionally, it allows avoiding the additional `Box`ing in the case
where the list consists of layers that are all the same type.

Closes #1708

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: prepare to release v0.3.10
2a8eab8 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([#1983])
  - **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([#1973],
  [#2017], [#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([#2035])
- Several documentation fixes and improvements ([#1972], [#1971],
  [#2023], [#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[#1983]: #1983
[#1973]: #1973
[#2017]: #2017
[#2031]: #2031
[#1959]: #1959
[#2034]: #2034
[#2027]: #2027
[#2026]: #2026
[#2035]: #2035
[#1972]: #1972
[#1971]: #1971
[#2023]: #2023
@hawkw hawkw mentioned this pull request Apr 1, 2022
Merged
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: prepare to release v0.3.10
2963995 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([#1983])
  - **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([#1973],
  [#2017], [#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([#2035])
- Several documentation fixes and improvements ([#1972], [#1971],
  [#2023], [#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[#1983]: #1983
[#1973]: #1973
[#2017]: #2017
[#2031]: #2031
[#1959]: #1959
[#2034]: #2034
[#2027]: #2027
[#2026]: #2026
[#2035]: #2035
[#1972]: #1972
[#1971]: #1971
[#2023]: #2023
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: prepare to release v0.3.10
ec96350 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([#1983])
  - **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([#1973],
  [#2017], [#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([#2035])
- Several documentation fixes and improvements ([#1972], [#1971],
  [#2023], [#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[#1983]: #1983
[#1973]: #1973
[#2017]: #2017
[#2031]: #2031
[#1959]: #1959
[#2034]: #2034
[#2027]: #2027
[#2026]: #2026
[#2035]: #2035
[#1972]: #1972
[#1971]: #1971
[#2023]: #2023
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: prepare to release v0.3.10
c14a60d 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([#1983])
  - **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([#1973],
  [#2017], [#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([#2035])
- Several documentation fixes and improvements ([#1972], [#1971],
  [#2023], [#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[#1983]: #1983
[#1973]: #1973
[#2017]: #2017
[#2031]: #2031
[#1959]: #1959
[#2034]: #2034
[#2027]: #2027
[#2026]: #2026
[#2035]: #2035
[#1972]: #1972
[#1971]: #1971
[#2023]: #2023
hawkw added a commit that referenced this pull request Apr 1, 2022
@hawkw
subscriber: prepare to release v0.3.10 (#2041)
42888dc 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([#1983])
- **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([#1973],
  [#2017], [#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([#2035])
- Several documentation fixes and improvements ([#1972], [#1971],
  [#2023], [#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([#2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[#1983]: #1983
[#1973]: #1973
[#2017]: #2017
[#2031]: #2031
[#1959]: #1959
[#2034]: #2034
[#2027]: #2027
[#2026]: #2026
[#2035]: #2035
[#1972]: #1972
[#1971]: #1971
[#2023]: #2023
[#2025]: #2025
[#2029]: #2029
@stormshield-kg stormshield-kg mentioned this pull request Jul 6, 2023
Open
@davidbarsky davidbarsky mentioned this pull request Sep 26, 2023
Merged
kaffarell pushed a commit to kaffarell/tracing that referenced this pull request May 22, 2024
@hawkw @kaffarell
subscriber: add Layer impl for Vec<L: Layer> (tokio-rs#2027)
acc1fa4 
Depends on tokio-rs#2028

## Motivation

In many cases, it is desirable to have a variable number of `Layer`s
at runtime (such as when reading a logging configuration from a config
file). The current approach, where types implementing `Layer` are
composed at the type level into `Layered` layers, doesn't work well
when the number of layers varies at runtime.

## Solution

To solve this, this branch adds a `Layer` implementation for
`Vec<L> where L: Layer`. This allows variable-length lists of
layers to be added to a subscriber. Although the impl for `Vec<L>`
requires all the layers to be the same type, it can also be used in
 onjunction with `Box<dyn Layer<S> + ...>` trait objects to
implement a variable-length list of layers of multiple types.

I also wrote a bunch of docs examples.

## Notes

Alternatively, we could have a separate type defined in
`tracing-subscriber` for a variable-length list of type-erased
`Layer`s. This would have one primary usability benefit, which is
that we could have a `push` operation that takes an `impl Layer`
and boxes it automatically. However, I thought the approach used
here is nicer, since it's based on composing together existing
primitives such as `Vec` and `Box`, rather than adding a whole new API.
Additionally, it allows avoiding the additional `Box`ing in the case
where the list consists of layers that are all the same type.

Closes tokio-rs#1708

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
kaffarell pushed a commit to kaffarell/tracing that referenced this pull request May 22, 2024
@hawkw @kaffarell
subscriber: prepare to release v0.3.10 (tokio-rs#2041)
cdfbda5 
# 0.3.10 (Apr 1, 2022)

This release adds several new features, including a `Filter`
implementation and new builder API for `EnvFilter`, support for using a
`Vec<L> where L: Layer` as a `Layer`, and a number of smaller API
improvements to make working with dynamic and reloadable layers easier.

### Added

- **registry**: Implement `Filter` for `EnvFilter`, allowing it to be
  used with per-layer filtering ([tokio-rs#1983])
- **registry**: `Filter::on_new_span`, `Filter::on_enter`,
  `Filter::on_exit`, `Filter::on_close` and `Filter::on_record`
  callbacks to allow `Filter`s to track span states internally ([tokio-rs#1973],
  [tokio-rs#2017], [tokio-rs#2031])
- **registry**: `Filtered::filter` and `Filtered::filter_mut` accessors
  ([tokio-rs#1959])
- **registry**: `Filtered::inner` and `Filtered::inner_mut` accessors to
  borrow the wrapped `Layer` ([tokio-rs#2034])
- **layer**: Implement `Layer` for `Vec<L: Layer>`, to allow composing
  together a dynamically sized list of `Layer`s ([tokio-rs#2027])
- **layer**: `Layer::boxed` method to make type-erasing `Layer`s easier
  ([tokio-rs#2026])
- **fmt**: `fmt::Layer::writer` and `fmt::Layer::writer_mut` accessors
  ([tokio-rs#2034])
- **fmt**: `fmt::Layer::set_ansi` method to allow changing the ANSI
  formatting configuration at runtime ([tokio-rs#2034])
- **env-filter**: `EnvFilter::builder` to configure a new `EnvFilter`
  prior to parsing it ([tokio-rs#2035])
- Several documentation fixes and improvements ([tokio-rs#1972], [tokio-rs#1971],
  [tokio-rs#2023], [tokio-rs#2023])

### Fixed

- **fmt**: `fmt::Layer`'s auto traits no longer depend on the
  `Subscriber` type parameter's auto traits ([tokio-rs#2025])
- **env-filter**: Fixed missing help text when the `ansi` feature is
  disabled ([tokio-rs#2029])

Thanks to new contributors @TimoFreiberg and @wagenet, as well as @CAD97
for contributing to this release!

[tokio-rs#1983]: tokio-rs#1983
[tokio-rs#1973]: tokio-rs#1973
[tokio-rs#2017]: tokio-rs#2017
[tokio-rs#2031]: tokio-rs#2031
[tokio-rs#1959]: tokio-rs#1959
[tokio-rs#2034]: tokio-rs#2034
[tokio-rs#2027]: tokio-rs#2027
[tokio-rs#2026]: tokio-rs#2026
[tokio-rs#2035]: tokio-rs#2035
[tokio-rs#1972]: tokio-rs#1972
[tokio-rs#1971]: tokio-rs#1971
[tokio-rs#2023]: tokio-rs#2023
[tokio-rs#2025]: tokio-rs#2025
[tokio-rs#2029]: tokio-rs#2029
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@davidbarsky davidbarsky davidbarsky approved these changes

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