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subscriber: make boxed subscribers not useless #2023

Merged
merged 5 commits into from
Mar 25, 2022
Merged

subscriber: make boxed subscribers not useless #2023

merged 5 commits into from
Mar 25, 2022

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hawkw
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@hawkw hawkw commented Mar 25, 2022

Motivation

Currently, there is an impl<C: Collect> Subscribe for Box<dyn Subscribe<C>> intended to allow type-erasing a subscriber.
Unfortunately, however, this impl is...completely and utterly useless.

In order to be set as the default, a collector must be Send + Sync + 'static. Because the boxed trait object does not bound the subscriber
with these traits, adding a boxed subscriber to a collector will make
that collector impossible to use. This means that a Box<dyn Subscribe<C>> has no practical purpose whatsoever.

Solution

This branch adds an impl<C: Collect> for Box<dyn Subscribe<C> + Send + Sync + 'static>, and removes the useless impl.

In addition, I've improved the documentation on runtime configuration of
subscribers to include an example of using Box to type-erase a
subscriber. This is, incidentally, how I found out that using Boxed
subscribers is currently useless.

Notes

  • When this change is backported to v0.1.x, we'll have to un-delete the
    useless impl for Box<dyn Layer<S>>, as removing it is technically a
    breaking change. But, no one is actually using that impl for any
    practical purpose, since they...can't.

  • We may want to just add a Self: Send + Sync + 'static bound to the
    Subscribe trait, too; this would make it much easier to avoid this
    kind of issue in the future. But, that's a breaking change that can't
    easily be backported to v0.1.x

@hawkw
docs: reorganize "runtime configuration" section
19c15f2 
this moves the "runtime configuration with subscribers" section into a
subsection of "composing subscribers".

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
make Subscribe impl for Box not useless
a6e3574 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
add example using boxed erased subscriber
3413ef2 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw
remove useless impl
039b9b5 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw self-assigned this Mar 25, 2022
@hawkw hawkw requested review from davidbarsky and a team as code owners March 25, 2022 18:18
@hawkw hawkw mentioned this pull request Mar 25, 2022
Merged
@hawkw hawkw enabled auto-merge (squash) March 25, 2022 18:20
@hawkw
hopefully fix prelude rustdoc link
35c0fb7 
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw merged commit afdad8f into master Mar 25, 2022
@hawkw hawkw deleted the eliza/fix-box branch March 25, 2022 18:38
hawkw added a commit that referenced this pull request Mar 25, 2022
@hawkw
subscriber: fix FmtSubscriber's auto traits inheriting Cs (#2024)
c1de498 
Depends on #2023 

## Motivation

Currently, `FmtSubscriber` holds a `PhantomData<C>` with the `Collect`
type it wraps. This is unfortunate because it means that the
subscriber's auto traits such as `Send`, `Sync`, and `'static` (as well
as `UnwindSafe`, `Unpin`, etc) depend on the collector type's auto
traits...but the subscriber will never actually _store_ a value of type
`C`. While all collectors will be `Send + Sync + 'static` in practice,
the `PhantomData` means that functions returning a boxed `FmtSubscriber`
must unnecessarily bound the collector type parameter.

## Solution

This commit changes the `PhantomData` to `PhantomData<fn(C)>`, solving
the problem.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 25, 2022
@hawkw
subscriber: add Subscribe::boxed method
b0f62e0 
## Motivation

PR #2023 made the `impl Subscribe` for boxed `dyn Subscribe` trait
objects actually be useful. One minor annoyance when working with boxed
trait objects is that, in some cases, in order to use `Box::new` to
erase a subscriber's type, it's necessary to add a type annotation like
this:
```rust
let boxed_subscriber: Box<dyn Subscribe<_> + Send + Sync + 'static>
    = Box::new(some_subscriber);
```

Because the trait object includes `Send + Sync + 'static`, this is a bit
wordy to type out.

## Solution

This commit adds a `Subscribe::boxed` method that takes `Self` and boxes
it as a type-erased `dyn Subscribe` trait object. This can then be
chained after a a chain of subscriber builder methods. Because the
`boxed` method _explicitly_ returns a `dyn Subscribe + ...` trait
object, it's not necessary to use a wordy type annotation when
using this method.
@hawkw hawkw mentioned this pull request Mar 25, 2022
Merged
hawkw added a commit that referenced this pull request Mar 26, 2022
@hawkw
subscriber: add Subscribe::boxed method (#2026)
ba0b940 
## Motivation

PR #2023 made the `impl Subscribe` for boxed `dyn Subscribe` trait
objects actually be useful. One minor annoyance when working with boxed
trait objects is that, in some cases, in order to use `Box::new` to
erase a subscriber's type, it's necessary to add a type annotation like
this:
```rust
let boxed_subscriber: Box<dyn Subscribe<_> + Send + Sync + 'static>
    = Box::new(some_subscriber);
```

Because the trait object includes `Send + Sync + 'static`, this is a bit
wordy to type out.

## Solution

This commit adds a `Subscribe::boxed` method that takes `Self` and boxes
it as a type-erased `dyn Subscribe` trait object. This can then be
chained after a a chain of subscriber builder methods. Because the
`boxed` method _explicitly_ returns a `dyn Subscribe + ...` trait
object, it's not necessary to use a wordy type annotation when
using this method.
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: document boxed Layers (#2023)
7043420 
Currently, there is an `impl<S: Subscriber> Layer for Box<dyn
Layer<S> + Send + Sync>` intended to allow type-erasing a subscriber.
This change improves the documentation on runtime configuration of
layers to include an example of using `Box` to type-erase a
layer.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: fix FmtLayer's auto traits inheriting S's (#2024)
871f12a 
Depends on #2023

## Motivation

Currently, `FmtLayer` holds a `PhantomData<S>` with the `Subscriber`
type it wraps. This is unfortunate because it means that the
layer's auto traits such as `Send`, `Sync`, and `'static` (as well
as `UnwindSafe`, `Unpin`, etc) depend on the `Subscriber` type's auto
traits...but the layer will never actually _store_ a value of type
`S`. While all `Subscriber` will be `Send + Sync + 'static` in practice,
the `PhantomData` means that functions returning a boxed `FmtLayer`
must unnecessarily bound the subscriber type parameter.

## Solution

This commit changes the `PhantomData` to `PhantomData<fn(S)>`, solving
the problem.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: add Layer::boxed method (#2026)
6380c71 
## Motivation

PR #2023 made the `impl Layer` for boxed `dyn Layer` trait
objects actually be useful. One minor annoyance when working with boxed
trait objects is that, in some cases, in order to use `Box::new` to
erase a `Layer`'s type, it's necessary to add a type annotation like
this:
```rust
let boxed_layer: Box<dyn Layer<_> + Send + Sync + 'static>
    = Box::new(some_layer);
```

Because the trait object includes `Send + Sync + 'static`, this is a bit
wordy to type out.

## Solution

This commit adds a `Layer::boxed` method that takes `Self` and boxes
it as a type-erased `dyn Layer` trait object. This can then be
chained after a a chain of layer builder methods. Because the
`boxed` method _explicitly_ returns a `dyn Layer<_> + ...` trait
object, it's not necessary to use a wordy type annotation when
using this method.
@hawkw hawkw mentioned this pull request Mar 29, 2022
Merged
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: document boxed Layers (#2023)
2decb45 
Currently, there is an `impl<S: Subscriber> Layer for Box<dyn
Layer<S> + Send + Sync>` intended to allow type-erasing a subscriber.
This change improves the documentation on runtime configuration of
layers to include an example of using `Box` to type-erase a
layer.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: fix FmtLayer's auto traits inheriting S's (#2024)
b21d236 
Depends on #2023

## Motivation

Currently, `FmtLayer` holds a `PhantomData<S>` with the `Subscriber`
type it wraps. This is unfortunate because it means that the
layer's auto traits such as `Send`, `Sync`, and `'static` (as well
as `UnwindSafe`, `Unpin`, etc) depend on the `Subscriber` type's auto
traits...but the layer will never actually _store_ a value of type
`S`. While all `Subscriber` will be `Send + Sync + 'static` in practice,
the `PhantomData` means that functions returning a boxed `FmtLayer`
must unnecessarily bound the subscriber type parameter.

## Solution

This commit changes the `PhantomData` to `PhantomData<fn(S)>`, solving
the problem.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 29, 2022
@hawkw
subscriber: add Layer::boxed method (#2026)
7921a3b 
## Motivation

PR #2023 made the `impl Layer` for boxed `dyn Layer` trait
objects actually be useful. One minor annoyance when working with boxed
trait objects is that, in some cases, in order to use `Box::new` to
erase a `Layer`'s type, it's necessary to add a type annotation like
this:
```rust
let boxed_layer: Box<dyn Layer<_> + Send + Sync + 'static>
    = Box::new(some_layer);
```

Because the trait object includes `Send + Sync + 'static`, this is a bit
wordy to type out.

## Solution

This commit adds a `Layer::boxed` method that takes `Self` and boxes
it as a type-erased `dyn Layer` trait object. This can then be
chained after a a chain of layer builder methods. Because the
`boxed` method _explicitly_ returns a `dyn Layer<_> + ...` trait
object, it's not necessary to use a wordy type annotation when
using this method.
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
@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: document boxed Layers (tokio-rs#2023)
47378c7 
Currently, there is an `impl<S: Subscriber> Layer for Box<dyn
Layer<S> + Send + Sync>` intended to allow type-erasing a subscriber.
This change improves the documentation on runtime configuration of
layers to include an example of using `Box` to type-erase a
layer.

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: fix FmtLayer's auto traits inheriting S's (tokio-rs#2024
8cbe3c5 
)

Depends on tokio-rs#2023

## Motivation

Currently, `FmtLayer` holds a `PhantomData<S>` with the `Subscriber`
type it wraps. This is unfortunate because it means that the
layer's auto traits such as `Send`, `Sync`, and `'static` (as well
as `UnwindSafe`, `Unpin`, etc) depend on the `Subscriber` type's auto
traits...but the layer will never actually _store_ a value of type
`S`. While all `Subscriber` will be `Send + Sync + 'static` in practice,
the `PhantomData` means that functions returning a boxed `FmtLayer`
must unnecessarily bound the subscriber type parameter.

## Solution

This commit changes the `PhantomData` to `PhantomData<fn(S)>`, solving
the problem.

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: add Layer::boxed method (tokio-rs#2026)
beb4e56 
## Motivation

PR tokio-rs#2023 made the `impl Layer` for boxed `dyn Layer` trait
objects actually be useful. One minor annoyance when working with boxed
trait objects is that, in some cases, in order to use `Box::new` to
erase a `Layer`'s type, it's necessary to add a type annotation like
this:
```rust
let boxed_layer: Box<dyn Layer<_> + Send + Sync + 'static>
    = Box::new(some_layer);
```

Because the trait object includes `Send + Sync + 'static`, this is a bit
wordy to type out.

## Solution

This commit adds a `Layer::boxed` method that takes `Self` and boxes
it as a type-erased `dyn Layer` trait object. This can then be
chained after a a chain of layer builder methods. Because the
`boxed` method _explicitly_ returns a `dyn Layer<_> + ...` trait
object, it's not necessary to use a wordy type annotation when
using this method.
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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