Add Subscribe::event_enabled to conditionally dis/enable events based on fields

tracing-core/src/collect.rs

@@ -701,6 +701,11 @@ impl Collect for alloc::boxed::Box<dyn Collect + Send + Sync + 'static> {
         self.as_ref().record_follows_from(span, follows)
     }
 
+    #[inline]
+    fn event_enabled(&self, event: &Event<'_>) -> bool {
+        self.as_ref().event_enabled(event)
+    }
+
     #[inline]
     fn event(&self, event: &Event<'_>) {
         self.as_ref().event(event)
@@ -772,6 +777,11 @@ impl Collect for alloc::sync::Arc<dyn Collect + Send + Sync + 'static> {
         self.as_ref().record_follows_from(span, follows)
     }
 
+    #[inline]
+    fn event_enabled(&self, event: &Event<'_>) -> bool {
+        self.as_ref().event_enabled(event)
+    }
+
     #[inline]
     fn event(&self, event: &Event<'_>) {
         self.as_ref().event(event)

tracing-core/src/dispatch.rs

@@ -682,7 +682,10 @@ impl Dispatch {
     /// [`event`]: super::collect::Collect::event
     #[inline]
     pub fn event(&self, event: &Event<'_>) {
-        self.collector().event(event)
+        let collector = self.collector();
+        if collector.event_enabled(event) {
+            collector.event(event);
+        }
     }
 
     /// Records that a span has been can_enter.

tracing-subscriber/src/fmt/mod.rs

@@ -393,6 +393,11 @@ where
         self.inner.record_follows_from(span, follows)
     }
 
+    #[inline]
+    fn event_enabled(&self, event: &Event<'_>) -> bool {
+        self.inner.event_enabled(event)
+    }
+
     #[inline]
     fn event(&self, event: &Event<'_>) {
         self.inner.event(event);