1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/rust/tracing/src/subscriber.rs b/third_party/rust/tracing/src/subscriber.rs
new file mode 100644
index 0000000000..f55698d13f
--- /dev/null
+++ b/third_party/rust/tracing/src/subscriber.rs
@@ -0,0 +1,65 @@
+//! Collects and records trace data.
+pub use tracing_core::subscriber::*;
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub use tracing_core::dispatcher::DefaultGuard;
+
+/// Sets this [`Subscriber`] as the default for the current thread for the
+/// duration of a closure.
+///
+/// The default subscriber is used when creating a new [`Span`] or
+/// [`Event`].
+///
+///
+/// [`Span`]: super::span::Span
+/// [`Subscriber`]: super::subscriber::Subscriber
+/// [`Event`]: super::event::Event
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub fn with_default<T, S>(subscriber: S, f: impl FnOnce() -> T) -> T
+where
+    S: Subscriber + Send + Sync + 'static,
+{
+    crate::dispatcher::with_default(&crate::Dispatch::new(subscriber), f)
+}
+
+/// Sets this subscriber as the global default for the duration of the entire program.
+/// Will be used as a fallback if no thread-local subscriber has been set in a thread (using `with_default`.)
+///
+/// Can only be set once; subsequent attempts to set the global default will fail.
+/// Returns whether the initialization was successful.
+///
+/// Note: Libraries should *NOT* call `set_global_default()`! That will cause conflicts when
+/// executables try to set them later.
+///
+/// [span]: super::span
+/// [`Subscriber`]: super::subscriber::Subscriber
+/// [`Event`]: super::event::Event
+pub fn set_global_default<S>(subscriber: S) -> Result<(), SetGlobalDefaultError>
+where
+    S: Subscriber + Send + Sync + 'static,
+{
+    crate::dispatcher::set_global_default(crate::Dispatch::new(subscriber))
+}
+
+/// Sets the [`Subscriber`] as the default for the current thread for the
+/// duration of the lifetime of the returned [`DefaultGuard`].
+///
+/// The default subscriber is used when creating a new [`Span`] or [`Event`].
+///
+/// [`Span`]: super::span::Span
+/// [`Subscriber`]: super::subscriber::Subscriber
+/// [`Event`]: super::event::Event
+/// [`DefaultGuard`]: super::dispatcher::DefaultGuard
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+#[must_use = "Dropping the guard unregisters the subscriber."]
+pub fn set_default<S>(subscriber: S) -> DefaultGuard
+where
+    S: Subscriber + Send + Sync + 'static,
+{
+    crate::dispatcher::set_default(&crate::Dispatch::new(subscriber))
+}
+
+pub use tracing_core::dispatcher::SetGlobalDefaultError;