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+//! Extension traits and other utilities to make working with subscribers more
+//! ergonomic.
+use core::fmt;
+#[cfg(feature = "std")]
+use std::error::Error;
+use tracing_core::dispatcher::{self, Dispatch};
+#[cfg(feature = "tracing-log")]
+use tracing_log::AsLog;
+
+/// Extension trait adding utility methods for subscriber initialization.
+///
+/// This trait provides extension methods to make configuring and setting a
+/// [default subscriber] more ergonomic. It is automatically implemented for all
+/// types that can be converted into a [trace dispatcher]. Since `Dispatch`
+/// implements `From<T>` for all `T: Subscriber`, all `Subscriber`
+/// implementations will implement this extension trait as well. Types which
+/// can be converted into `Subscriber`s, such as builders that construct a
+/// `Subscriber`, may implement `Into<Dispatch>`, and will also receive an
+/// implementation of this trait.
+///
+/// [default subscriber]: https://docs.rs/tracing/0.1.21/tracing/dispatcher/index.html#setting-the-default-subscriber
+/// [trace dispatcher]: https://docs.rs/tracing/0.1.21/tracing/dispatcher/index.html
+pub trait SubscriberInitExt
+where
+ Self: Into<Dispatch>,
+{
+ /// Sets `self` as the [default subscriber] in the current scope, returning a
+ /// guard that will unset it when dropped.
+ ///
+ /// If the "tracing-log" feature flag is enabled, this will also initialize
+ /// a [`log`] compatibility layer. This allows the subscriber to consume
+ /// `log::Record`s as though they were `tracing` `Event`s.
+ ///
+ /// [default subscriber]: https://docs.rs/tracing/0.1.21/tracing/dispatcher/index.html#setting-the-default-subscriber
+ /// [`log`]: https://crates.io/log
+ #[cfg(feature = "std")]
+ #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+ fn set_default(self) -> dispatcher::DefaultGuard {
+ #[cfg(feature = "tracing-log")]
+ let _ = tracing_log::LogTracer::init();
+
+ dispatcher::set_default(&self.into())
+ }
+
+ /// Attempts to set `self` as the [global default subscriber] in the current
+ /// scope, returning an error if one is already set.
+ ///
+ /// If the "tracing-log" feature flag is enabled, this will also attempt to
+ /// initialize a [`log`] compatibility layer. This allows the subscriber to
+ /// consume `log::Record`s as though they were `tracing` `Event`s.
+ ///
+ /// This method returns an error if a global default subscriber has already
+ /// been set, or if a `log` logger has already been set (when the
+ /// "tracing-log" feature is enabled).
+ ///
+ /// [global default subscriber]: https://docs.rs/tracing/0.1.21/tracing/dispatcher/index.html#setting-the-default-subscriber
+ /// [`log`]: https://crates.io/log
+ fn try_init(self) -> Result<(), TryInitError> {
+ dispatcher::set_global_default(self.into()).map_err(TryInitError::new)?;
+
+ // Since we are setting the global default subscriber, we can
+ // opportunistically go ahead and set its global max level hint as
+ // the max level for the `log` crate as well. This should make
+ // skipping `log` diagnostics much faster.
+ #[cfg(feature = "tracing-log")]
+ tracing_log::LogTracer::builder()
+ // Note that we must call this *after* setting the global default
+ // subscriber, so that we get its max level hint.
+ .with_max_level(tracing_core::LevelFilter::current().as_log())
+ .init()
+ .map_err(TryInitError::new)?;
+
+ Ok(())
+ }
+
+ /// Attempts to set `self` as the [global default subscriber] in the current
+ /// scope, panicking if this fails.
+ ///
+ /// If the "tracing-log" feature flag is enabled, this will also attempt to
+ /// initialize a [`log`] compatibility layer. This allows the subscriber to
+ /// consume `log::Record`s as though they were `tracing` `Event`s.
+ ///
+ /// This method panics if a global default subscriber has already been set,
+ /// or if a `log` logger has already been set (when the "tracing-log"
+ /// feature is enabled).
+ ///
+ /// [global default subscriber]: https://docs.rs/tracing/0.1.21/tracing/dispatcher/index.html#setting-the-default-subscriber
+ /// [`log`]: https://crates.io/log
+ fn init(self) {
+ self.try_init()
+ .expect("failed to set global default subscriber")
+ }
+}
+
+impl<T> SubscriberInitExt for T where T: Into<Dispatch> {}
+
+/// Error returned by [`try_init`](SubscriberInitExt::try_init) if a global default subscriber could not be initialized.
+pub struct TryInitError {
+ #[cfg(feature = "std")]
+ inner: Box<dyn Error + Send + Sync + 'static>,
+
+ #[cfg(not(feature = "std"))]
+ _p: (),
+}
+
+// ==== impl TryInitError ====
+
+impl TryInitError {
+ #[cfg(feature = "std")]
+ fn new(e: impl Into<Box<dyn Error + Send + Sync + 'static>>) -> Self {
+ Self { inner: e.into() }
+ }
+
+ #[cfg(not(feature = "std"))]
+ fn new<T>(_: T) -> Self {
+ Self { _p: () }
+ }
+}
+
+impl fmt::Debug for TryInitError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ #[cfg(feature = "std")]
+ {
+ fmt::Debug::fmt(&self.inner, f)
+ }
+
+ #[cfg(not(feature = "std"))]
+ {
+ f.write_str("TryInitError(())")
+ }
+ }
+}
+
+impl fmt::Display for TryInitError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ #[cfg(feature = "std")]
+ {
+ fmt::Display::fmt(&self.inner, f)
+ }
+
+ #[cfg(not(feature = "std"))]
+ {
+ f.write_str("failed to set global default subscriber")
+ }
+ }
+}
+
+#[cfg(feature = "std")]
+impl Error for TryInitError {
+ fn source(&self) -> Option<&(dyn Error + 'static)> {
+ self.inner.source()
+ }
+}