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subscriber: add minimal #![no_std] support #1648

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merged 14 commits into from
Oct 19, 2021
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@hawkw hawkw commented Oct 19, 2021

Depends on #1649

Motivation

Presently, the tracing-subscriber crate requires the Rust standard
library and doesn't build with #![no_std] targets. For the most part,
this is fine, as much of tracing-subscriber inherently depends on
std APIs.

However, tracing-subscriber also contains some key abstractions that
are necessary for interoperability: the Subscriber and LookupSpan
traits. Since these traits are in tracing-subscriber, no-std users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for #![no_std] projects.

Solution

This branch adds "std" and "alloc" feature flags to
tracing-subscriber, for conditionally enabling libstd and
liballoc, respectively. The registry, fmt, EnvFilter, and
reload APIs all require libstd, and cannot be implemented without it,
but the core Subscribe and LookupSpan traits are now available with
#![no_std].

Fixes #999

@hawkw hawkw requested a review from a team as a code owner October 19, 2021 17:09
Implementing `Subscribe` for `Arc`s, which are immutable, breaks the
ability to implement `Subscribe::on_layer` with a mutable reference.
This is necessary for per-layer filtering. See
#1576 (comment) for
details. Therefore, the `Layer` impls for `Arc`s should not be used.

In 0.3, we have the opportunity to remove these APIs. Therefore, this PR
removes them.
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw changed the base branch from master to eliza/rm-arc-impls October 19, 2021 17:22
Base automatically changed from eliza/rm-arc-impls to master October 19, 2021 17:26
tracing-subscriber/Cargo.toml Outdated Show resolved Hide resolved
apparently this behaves differently on 1.42.0, so we can't use the macro
here...

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw requested a review from jtescher as a code owner October 19, 2021 21:19
@hawkw hawkw merged commit 226f605 into master Oct 19, 2021
@hawkw hawkw deleted the eliza/subscriber-no-std branch October 19, 2021 21:55
hawkw added a commit that referenced this pull request Oct 21, 2021
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Oct 21, 2021
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Oct 22, 2021
# 0.3.0 (Oct 22, 2021)

This is a breaking release of `tracing-subscriber`. The primary breaking
change in this release is the removal of the dependency on the [`chrono`
crate], due to [RUSTSEC-2020-0159]. To replace `chrono`, support is
added for formatting timestamps using the [`time` crate] instead.

In addition, this release includes a number of other breaking API
changes, such as adding (limited) support for `#![no_std]` targets,
removing previously deprecated APIs, and more.

### Breaking Changes

- Removed APIs deprecated in the v0.2.x release series.
- Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn Layer<S> +
  ...>` ([#1649])
- Replaced the [`chrono` crate] with the [`time` crate] for timestamp
  formatting, to resolve [RUSTSEC-2020-0159] ([#1646])
- Removed `json` and `env-filter` from default features. They must now
  be enabled explictly ([#1647])
- Changed `FormatEvent::format_event` and `FormatFields::format_fields`
  trait methods to take a `Writer` type, rather than a `&mut dyn
  fmt::Write` trait object ([#1661])
- Changed the signature of the `MakeWriter` trait by adding a lifetime
  parameter ([#781])
  ### Changed

- **layer**: Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- **fmt**: Changed `FormatEvent::format_event` and
  `FormatFields::format_fields` trait methods to take a `Writer` type,
  rather than a `&mut dyn fmt::Write` trait object ([#1661])
- **json**, **env-filter**: `json` and `env-filter` feature flags are no
  longer enabled by default ([#1647])
  ### Removed

- Removed deprecated `CurrentSpan` type ([#1320])
- **registry**: Removed deprecated `SpanRef::parents` iterator, replaced
  by `SpanRef::scope` in [#1431] ([#1648)])
- **layer**: Removed deprecated `Context::scope` iterator, replaced by
  `Context::span_scope` and `Context::event_scope` in [#1431] and
  [#1434] ([#1648)])
- **layer**: Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn
  Layer<S> + ...>`. These interfere with per-layer filtering. ([#1649])
- **fmt**: Removed deprecated `LayerBuilder` type ([#1673])
- **fmt**: Removed `fmt::Layer::on_event` (renamed to
  `fmt::Layer::fmt_event`) ([#1673])
- **fmt**, **chrono**: Removed the `chrono` feature flag and APIs for
  using the [`chrono` crate] for timestamp formatting ([#1646])
  ### Added

- **fmt**, **time**: `LocalTime` and `UtcTime` types for formatting
  timestamps using the [`time` crate] ([#1646])
- **fmt**: Added a lifetime parameter to the `MakeWriter` trait,
  allowing it to return a borrowed writer. This enables implementations
  of `MakeWriter` for types such as `Mutex<T: io::Write>` and
  `std::fs::File`. ([#781])
- **env-filter**: Documentation improvements ([#1637])
- Support for some APIs on `#![no_std]` targets, by disabling the `std`
  feature flag ([#1660])

Thanks to @Folyd and @nmathewson for contributing to this release!

[#1320]: #1320
[#1673]: #1673
[#1674]: #1674
[#1646]: #1646
[#1647]: #1647
[#1648]: #1648
[#1649]: #1649
[#1660]: #1660
[#1661]: #1661
[#1431]: #1431
[#1434]: #1434
[#781]: #781

[`chrono` crate]: https://crates.io/crates/chrono
[`time` crate]: https://crates.io/crates/time
[RUSTSEC-2020-0159]: https://rustsec.org/advisories/RUSTSEC-2020-0159.html
hawkw added a commit that referenced this pull request Oct 22, 2021
# 0.3.0 (Oct 22, 2021)

This is a breaking release of `tracing-subscriber`. The primary breaking
change in this release is the removal of the dependency on the [`chrono`
crate], due to [RUSTSEC-2020-0159]. To replace `chrono`, support is
added for formatting timestamps using the [`time` crate] instead.

In addition, this release includes a number of other breaking API
changes, such as adding (limited) support for `#![no_std]` targets,
removing previously deprecated APIs, and more.

### Breaking Changes

- Removed APIs deprecated in the v0.2.x release series.
- Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn Layer<S> +
  ...>` ([#1649])
- Replaced the [`chrono` crate] with the [`time` crate] for timestamp
  formatting, to resolve [RUSTSEC-2020-0159] ([#1646])
- Removed `json` and `env-filter` from default features. They must now
  be enabled explictly ([#1647])
- Changed `FormatEvent::format_event` and `FormatFields::format_fields`
  trait methods to take a `Writer` type, rather than a `&mut dyn
  fmt::Write` trait object ([#1661])
- Changed the signature of the `MakeWriter` trait by adding a lifetime
  parameter ([#781])
  ### Changed

- **layer**: Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- **fmt**: Changed `FormatEvent::format_event` and
  `FormatFields::format_fields` trait methods to take a `Writer` type,
  rather than a `&mut dyn fmt::Write` trait object ([#1661])
- **json**, **env-filter**: `json` and `env-filter` feature flags are no
  longer enabled by default ([#1647])
  ### Removed

- Removed deprecated `CurrentSpan` type ([#1320])
- **registry**: Removed deprecated `SpanRef::parents` iterator, replaced
  by `SpanRef::scope` in [#1431] ([#1648)])
- **layer**: Removed deprecated `Context::scope` iterator, replaced by
  `Context::span_scope` and `Context::event_scope` in [#1431] and
  [#1434] ([#1648)])
- **layer**: Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn
  Layer<S> + ...>`. These interfere with per-layer filtering. ([#1649])
- **fmt**: Removed deprecated `LayerBuilder` type ([#1673])
- **fmt**: Removed `fmt::Layer::on_event` (renamed to
  `fmt::Layer::fmt_event`) ([#1673])
- **fmt**, **chrono**: Removed the `chrono` feature flag and APIs for
  using the [`chrono` crate] for timestamp formatting ([#1646])
  ### Added

- **fmt**, **time**: `LocalTime` and `UtcTime` types for formatting
  timestamps using the [`time` crate] ([#1646])
- **fmt**: Added a lifetime parameter to the `MakeWriter` trait,
  allowing it to return a borrowed writer. This enables implementations
  of `MakeWriter` for types such as `Mutex<T: io::Write>` and
  `std::fs::File`. ([#781])
- **env-filter**: Documentation improvements ([#1637])
- Support for some APIs on `#![no_std]` targets, by disabling the `std`
  feature flag ([#1660])

Thanks to @Folyd and @nmathewson for contributing to this release!

[#1320]: #1320
[#1673]: #1673
[#1674]: #1674
[#1646]: #1646
[#1647]: #1647
[#1648]: #1648
[#1649]: #1649
[#1660]: #1660
[#1661]: #1661
[#1431]: #1431
[#1434]: #1434
[#781]: #781

[`chrono` crate]: https://crates.io/crates/chrono
[`time` crate]: https://crates.io/crates/time
[RUSTSEC-2020-0159]: https://rustsec.org/advisories/RUSTSEC-2020-0159.html

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
hawkw added a commit that referenced this pull request Mar 23, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 23, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
hawkw added a commit that referenced this pull request Mar 24, 2022
Backports #1648 from `master`.

Depends on #1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes #999
davidbarsky pushed a commit to tokio-rs/tracing-opentelemetry that referenced this pull request Mar 21, 2023
# 0.3.0 (Oct 22, 2021)

This is a breaking release of `tracing-subscriber`. The primary breaking
change in this release is the removal of the dependency on the [`chrono`
crate], due to [RUSTSEC-2020-0159]. To replace `chrono`, support is
added for formatting timestamps using the [`time` crate] instead.

In addition, this release includes a number of other breaking API
changes, such as adding (limited) support for `#![no_std]` targets,
removing previously deprecated APIs, and more.

### Breaking Changes

- Removed APIs deprecated in the v0.2.x release series.
- Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn Layer<S> +
  ...>` ([#1649])
- Replaced the [`chrono` crate] with the [`time` crate] for timestamp
  formatting, to resolve [RUSTSEC-2020-0159] ([#1646])
- Removed `json` and `env-filter` from default features. They must now
  be enabled explictly ([#1647])
- Changed `FormatEvent::format_event` and `FormatFields::format_fields`
  trait methods to take a `Writer` type, rather than a `&mut dyn
  fmt::Write` trait object ([#1661])
- Changed the signature of the `MakeWriter` trait by adding a lifetime
  parameter ([#781])
  ### Changed

- **layer**: Renamed `Layer::new_span` to `Layer::on_new_span` ([#1674])
- **fmt**: Changed `FormatEvent::format_event` and
  `FormatFields::format_fields` trait methods to take a `Writer` type,
  rather than a `&mut dyn fmt::Write` trait object ([#1661])
- **json**, **env-filter**: `json` and `env-filter` feature flags are no
  longer enabled by default ([#1647])
  ### Removed

- Removed deprecated `CurrentSpan` type ([#1320])
- **registry**: Removed deprecated `SpanRef::parents` iterator, replaced
  by `SpanRef::scope` in [#1431] ([#1648)])
- **layer**: Removed deprecated `Context::scope` iterator, replaced by
  `Context::span_scope` and `Context::event_scope` in [#1431] and
  [#1434] ([#1648)])
- **layer**: Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn
  Layer<S> + ...>`. These interfere with per-layer filtering. ([#1649])
- **fmt**: Removed deprecated `LayerBuilder` type ([#1673])
- **fmt**: Removed `fmt::Layer::on_event` (renamed to
  `fmt::Layer::fmt_event`) ([#1673])
- **fmt**, **chrono**: Removed the `chrono` feature flag and APIs for
  using the [`chrono` crate] for timestamp formatting ([#1646])
  ### Added

- **fmt**, **time**: `LocalTime` and `UtcTime` types for formatting
  timestamps using the [`time` crate] ([#1646])
- **fmt**: Added a lifetime parameter to the `MakeWriter` trait,
  allowing it to return a borrowed writer. This enables implementations
  of `MakeWriter` for types such as `Mutex<T: io::Write>` and
  `std::fs::File`. ([#781])
- **env-filter**: Documentation improvements ([#1637])
- Support for some APIs on `#![no_std]` targets, by disabling the `std`
  feature flag ([#1660])

Thanks to @Folyd and @nmathewson for contributing to this release!

[#1320]: tokio-rs/tracing#1320
[#1673]: tokio-rs/tracing#1673
[#1674]: tokio-rs/tracing#1674
[#1646]: tokio-rs/tracing#1646
[#1647]: tokio-rs/tracing#1647
[#1648]: tokio-rs/tracing#1648
[#1649]: tokio-rs/tracing#1649
[#1660]: tokio-rs/tracing#1660
[#1661]: tokio-rs/tracing#1661
[#1431]: tokio-rs/tracing#1431
[#1434]: tokio-rs/tracing#1434
[#781]: tokio-rs/tracing#781

[`chrono` crate]: https://crates.io/crates/chrono
[`time` crate]: https://crates.io/crates/time
[RUSTSEC-2020-0159]: https://rustsec.org/advisories/RUSTSEC-2020-0159.html

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
kaffarell pushed a commit to kaffarell/tracing that referenced this pull request May 22, 2024
Backports tokio-rs#1648 from `master`.

Depends on tokio-rs#1649

## Motivation

Presently, the `tracing-subscriber` crate requires the Rust standard
library and doesn't build with `#![no_std]` targets. For the most part,
this is fine, as much of `tracing-subscriber` inherently depends on
`std` APIs.

However, `tracing-subscriber` also contains some key abstractions that
are necessary for interoperability: the `Layer` and `LookupSpan`
traits. Since these traits are in `tracing-subscriber`, `no-std` users
cannot currently access them.

Some of the other utilities in this crate, such as the field visitor
combinators, may also be useful for `#![no_std]` projects.

## Solution

This branch adds "std" and "alloc" feature flags to
`tracing-subscriber`, for conditionally enabling `libstd` and
`liballoc`, respectively. The `registry`, `fmt`, `EnvFilter`, and
`reload` APIs all require libstd, and cannot be implemented without it,
but the core `Layer` and `LookupSpan` traits are now available with
`#![no_std]`.

Fixes tokio-rs#999

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
kaffarell pushed a commit to kaffarell/tracing that referenced this pull request May 22, 2024
# 0.3.0 (Oct 22, 2021)

This is a breaking release of `tracing-subscriber`. The primary breaking
change in this release is the removal of the dependency on the [`chrono`
crate], due to [RUSTSEC-2020-0159]. To replace `chrono`, support is
added for formatting timestamps using the [`time` crate] instead.

In addition, this release includes a number of other breaking API
changes, such as adding (limited) support for `#![no_std]` targets,
removing previously deprecated APIs, and more.

### Breaking Changes

- Removed APIs deprecated in the v0.2.x release series.
- Renamed `Layer::new_span` to `Layer::on_new_span` ([tokio-rs#1674])
- Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn Layer<S> +
  ...>` ([tokio-rs#1649])
- Replaced the [`chrono` crate] with the [`time` crate] for timestamp
  formatting, to resolve [RUSTSEC-2020-0159] ([tokio-rs#1646])
- Removed `json` and `env-filter` from default features. They must now
  be enabled explictly ([tokio-rs#1647])
- Changed `FormatEvent::format_event` and `FormatFields::format_fields`
  trait methods to take a `Writer` type, rather than a `&mut dyn
  fmt::Write` trait object ([tokio-rs#1661])
- Changed the signature of the `MakeWriter` trait by adding a lifetime
  parameter ([tokio-rs#781])
  ### Changed

- **layer**: Renamed `Layer::new_span` to `Layer::on_new_span` ([tokio-rs#1674])
- **fmt**: Changed `FormatEvent::format_event` and
  `FormatFields::format_fields` trait methods to take a `Writer` type,
  rather than a `&mut dyn fmt::Write` trait object ([tokio-rs#1661])
- **json**, **env-filter**: `json` and `env-filter` feature flags are no
  longer enabled by default ([tokio-rs#1647])
  ### Removed

- Removed deprecated `CurrentSpan` type ([tokio-rs#1320])
- **registry**: Removed deprecated `SpanRef::parents` iterator, replaced
  by `SpanRef::scope` in [tokio-rs#1431] ([tokio-rs#1648)])
- **layer**: Removed deprecated `Context::scope` iterator, replaced by
  `Context::span_scope` and `Context::event_scope` in [tokio-rs#1431] and
  [tokio-rs#1434] ([tokio-rs#1648)])
- **layer**: Removed `Layer` impl for `Arc<L: Layer<S>>` and `Arc<dyn
  Layer<S> + ...>`. These interfere with per-layer filtering. ([tokio-rs#1649])
- **fmt**: Removed deprecated `LayerBuilder` type ([tokio-rs#1673])
- **fmt**: Removed `fmt::Layer::on_event` (renamed to
  `fmt::Layer::fmt_event`) ([tokio-rs#1673])
- **fmt**, **chrono**: Removed the `chrono` feature flag and APIs for
  using the [`chrono` crate] for timestamp formatting ([tokio-rs#1646])
  ### Added

- **fmt**, **time**: `LocalTime` and `UtcTime` types for formatting
  timestamps using the [`time` crate] ([tokio-rs#1646])
- **fmt**: Added a lifetime parameter to the `MakeWriter` trait,
  allowing it to return a borrowed writer. This enables implementations
  of `MakeWriter` for types such as `Mutex<T: io::Write>` and
  `std::fs::File`. ([tokio-rs#781])
- **env-filter**: Documentation improvements ([tokio-rs#1637])
- Support for some APIs on `#![no_std]` targets, by disabling the `std`
  feature flag ([tokio-rs#1660])

Thanks to @Folyd and @nmathewson for contributing to this release!

[tokio-rs#1320]: tokio-rs#1320
[tokio-rs#1673]: tokio-rs#1673
[tokio-rs#1674]: tokio-rs#1674
[tokio-rs#1646]: tokio-rs#1646
[tokio-rs#1647]: tokio-rs#1647
[tokio-rs#1648]: tokio-rs#1648
[tokio-rs#1649]: tokio-rs#1649
[tokio-rs#1660]: tokio-rs#1660
[tokio-rs#1661]: tokio-rs#1661
[tokio-rs#1431]: tokio-rs#1431
[tokio-rs#1434]: tokio-rs#1434
[tokio-rs#781]: tokio-rs#781

[`chrono` crate]: https://crates.io/crates/chrono
[`time` crate]: https://crates.io/crates/time
[RUSTSEC-2020-0159]: https://rustsec.org/advisories/RUSTSEC-2020-0159.html

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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tracing-subscriber: (minimal) no-std support
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