Adjust Once to not violate feature additivity principle #760
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When the following dependencies and their features were specified:
```toml
tracing-core = { version = "0.1", default-features = false, features = ["std"] }
tracing = { version = "0.1", default-features = false }
```
The build would fail with the following error:
```
error[E0412]: cannot find type `Once` in crate `tracing_core`
--> tracing/src/lib.rs:840:35
|
840 | pub type Once = tracing_core::Once<()>;
| ^^^^ not found in `tracing_core`
|
```
This happened because `tracing-core` exports `Once` only if its `std`
feature is disabled. And the depending `tracing` crate assumed that if
its `std` feature was disabled, so would be the `std` feature in
`tracing-core`.
This is a violation of the [undocumented "features must be additive"
guideline][ag]. In this commit tracing-core is adjusted to export `Once`
regardless of whether `std` is disabled or not.
[ag]: rust-lang/cargo#4328
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hawkw
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Jun 21, 2020
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Jul 8, 2020
Changed - Replaced use of `inner_local_macros` with `$crate::` (#729) Added - `must_use` warning to guards returned by `dispatcher::set_default` (#686) - `fmt::Debug` impl to `dyn Value`s (#696) - Functions to convert between `span::Id` and `NonZeroU64` (#770) - More obvious warnings in documentation (#769) Fixed - Compiler error when `tracing-core/std` feature is enabled but `tracing/std` is not (#760) - Clippy warning on vtable address comparison in `callsite::Identifier` (#749) - Documentation formatting issues (#715, #771) Thanks to @bkchr, @majecty, @taiki-e, @nagisa, and @nqvz for contributing to this release!
hawkw
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### Changed - Replaced use of `inner_local_macros` with `$crate::` (#729) ### Added - `must_use` warning to guards returned by `dispatcher::set_default` (#686) - `fmt::Debug` impl to `dyn Value`s (#696) - Functions to convert between `span::Id` and `NonZeroU64` (#770) - More obvious warnings in documentation (#769) ### Fixed - Compiler error when `tracing-core/std` feature is enabled but `tracing/std` is not (#760) - Clippy warning on vtable address comparison in `callsite::Identifier` (#749) - Documentation formatting issues (#715, #771) Thanks to @bkchr, @majecty, @taiki-e, @nagisa, and @nvzqz for contributing to this release!
hawkw
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Jul 8, 2020
Added - **attributes**: Support for arbitrary expressions as fields in `#[instrument]` (#672) - **attributes**: `#[instrument]` now emits a compiler warning when ignoring unrecognized input (#672, #786) - Improved documentation on using `tracing` in async code (#769) Changed - Updated `tracing-core` dependency to 0.1.11 Fixed - **macros**: Excessive monomorphization in macros, which could lead to longer compilation times (#787) - **log**: Compiler warnings in macros when `log` or `log-always` features are enabled (#753) - Compiler error when `tracing-core/std` feature is enabled but `tracing/std` is not (#760) Thanks to @nagisa for contributing to this release!
hawkw
added a commit
that referenced
this pull request
Jul 8, 2020
### Added - **attributes**: Support for arbitrary expressions as fields in `#[instrument]` (#672) - **attributes**: `#[instrument]` now emits a compiler warning when ignoring unrecognized input (#672, #786) - Improved documentation on using `tracing` in async code (#769) ### Changed - Updated `tracing-core` dependency to 0.1.11 ### Fixed - **macros**: Excessive monomorphization in macros, which could lead to longer compilation times (#787) - **log**: Compiler warnings in macros when `log` or `log-always` features are enabled (#753) - Compiler error when `tracing-core/std` feature is enabled but `tracing/std` is not (#760) Thanks to @nagisa, and everyone who contributed to the new `tracing-core` and `tracing-attributes` versions, for contributing to this release!
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When the following dependencies and their features were specified:
The build would fail with the following error:
This happened because
tracing-coreexportsOnceonly if itsstdfeature is disabled. And the depending
tracingcrate assumed that ifits
stdfeature was disabled, so would be thestdfeature intracing-core.This is a violation of the undocumented "features must be additive"
guideline. In this commit tracing-core is adjusted to export
Onceregardless of whether
stdis disabled or not.