tests: add test for tracing-error deadlock

This deadlock can happen when extensions of a span are locked while we
visit either an event or attributes of a span. A `Debug` implementation
can also try to access the extensions which results in a deadlock.

See #59 and #95 for additional information.

Author: mladedav

Cargo.toml

@@ -51,6 +51,7 @@ futures-util = { version = "0.3", default-features = false }
 tokio = { version = "1", features = ["full"] }
 tokio-stream = "0.1"
 tracing = { version = "0.1.35", default-features = false, features = ["std", "attributes"] }
+tracing-error = "0.2.0"
 tracing-subscriber = { version = "0.3.0", default-features = false, features = ["registry", "std", "fmt"] }
 
 [target.'cfg(not(target_os = "windows"))'.dev-dependencies]

src/layer.rs

@@ -1746,4 +1746,29 @@ mod tests {
             )
         );
     }
+
+    #[test]
+    fn tracing_error_compatibility() {
+        let tracer = TestTracer(Arc::new(Mutex::new(None)));
+        let subscriber = tracing_subscriber::registry()
+            .with(
+                layer()
+                    .with_error_fields_to_exceptions(false)
+                    .with_tracer(tracer.clone()),
+            )
+            .with(tracing_error::ErrorLayer::default());
+
+        tracing::subscriber::with_default(subscriber, || {
+            let span = tracing::info_span!("Blows up!", exception = tracing::field::Empty);
+            let _entered = span.enter();
+            let context = tracing_error::SpanTrace::capture();
+
+            // This can cause a deadlock if `on_record` locks extensions while attributes are visited
+            span.record("exception", &tracing::field::debug(&context));
+            // This can cause a deadlock if `on_event` locks extensions while the event is visited
+            tracing::info!(exception = &tracing::field::debug(&context), "hello");
+        });
+
+        // No need to assert anything, as long as this finished (and did not panic), everything is ok.
+    }
 }