chore: checkpoint before Python removal

vendor/tracing/benches/empty_span.rs

@@ -0,0 +1,43 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+mod shared;
+
+fn bench(c: &mut Criterion) {
+    let mut group = c.benchmark_group("empty_span");
+    shared::for_all_dispatches(&mut group, |b| {
+        b.iter(|| {
+            let span = tracing::span::Span::none();
+            black_box(&span);
+        })
+    });
+    group.bench_function("baseline_struct", |b| {
+        b.iter(|| {
+            let span = FakeEmptySpan::new();
+            black_box(&span);
+        })
+    });
+}
+
+struct FakeEmptySpan {
+    inner: Option<(usize, std::sync::Arc<()>)>,
+    meta: Option<&'static ()>,
+}
+
+impl FakeEmptySpan {
+    fn new() -> Self {
+        Self {
+            inner: None,
+            meta: None,
+        }
+    }
+}
+
+impl Drop for FakeEmptySpan {
+    fn drop(&mut self) {
+        black_box(&self.inner);
+        black_box(&self.meta);
+    }
+}
+
+criterion_group!(benches, bench);
+criterion_main!(benches);