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core: impl Value for dyn Error + Send/Sync
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`Value` was already implemented for `dyn Error + 'static`, but rust
doesn't silently coerce trait objects. This means that passing an error
of type `dyn Error + Send + Sync + 'static` would not work. These extra
impls just delegate to the existing `dyn Error + 'static` impl.

Also update one of the examples to use `dyn Error + Send + Sync` to
demonstrate that this works.

Refs: tokio-rs#1308
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lilyball committed Mar 8, 2022
1 parent 4f714f0 commit c9cfe7e
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Showing 2 changed files with 34 additions and 1 deletion.
2 changes: 1 addition & 1 deletion examples/examples/fmt/yak_shave.rs
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use tracing::{debug, error, info, span, trace, warn, Level};
// every time the instrumented function is called. The span is named after the
// the function or method. Paramaters passed to the function are recorded as fields.
#[tracing::instrument]
pub fn shave(yak: usize) -> Result<(), Box<dyn Error + 'static>> {
pub fn shave(yak: usize) -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
// this creates an event at the TRACE log level with two fields:
// - `excitement`, with the key "excitement" and the value "yay!"
// - `message`, with the key "message" and the value "hello! I'm gonna shave a yak."
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33 changes: 33 additions & 0 deletions tracing-core/src/field.rs
Original file line number Diff line number Diff line change
Expand Up @@ -523,6 +523,39 @@ impl Value for dyn std::error::Error + 'static {
}
}

#[cfg(feature = "std")]
impl crate::sealed::Sealed for dyn std::error::Error + Send + 'static {}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl Value for dyn std::error::Error + Send + 'static {
fn record(&self, key: &Field, visitor: &mut dyn Visit) {
(self as &dyn std::error::Error).record(key, visitor)
}
}

#[cfg(feature = "std")]
impl crate::sealed::Sealed for dyn std::error::Error + Sync + 'static {}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl Value for dyn std::error::Error + Sync + 'static {
fn record(&self, key: &Field, visitor: &mut dyn Visit) {
(self as &dyn std::error::Error).record(key, visitor)
}
}

#[cfg(feature = "std")]
impl crate::sealed::Sealed for dyn std::error::Error + Send + Sync + 'static {}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl Value for dyn std::error::Error + Send + Sync + 'static {
fn record(&self, key: &Field, visitor: &mut dyn Visit) {
(self as &dyn std::error::Error).record(key, visitor)
}
}

impl<'a, T: ?Sized> crate::sealed::Sealed for &'a T where T: Value + crate::sealed::Sealed + 'a {}

impl<'a, T: ?Sized> Value for &'a T
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