feat(divan): export benchmark tracing spans over OTLP behind an otel feature

crates/codspeed/Cargo.toml

@@ -28,6 +28,36 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 statrs = { version = "0.18.0", default-features = false }
 
+opentelemetry = { version = "0.33", default-features = false, features = ["trace"], optional = true }
+opentelemetry_sdk = { version = "0.33", default-features = false, features = ["trace"], optional = true }
+futures-executor = { version = "0.3", default-features = false, features = ["std"], optional = true }
+opentelemetry-otlp = { version = "0.33", default-features = false, features = [
+    "trace",
+    "http-proto",
+    "reqwest-blocking-client",
+], optional = true }
+tracing = { version = "0.1", default-features = false, features = ["std"], optional = true }
+tracing-opentelemetry = { version = "0.34", default-features = false, optional = true }
+tracing-subscriber = { version = "0.3", default-features = false, features = [
+    "std",
+    "registry",
+    "env-filter",
+], optional = true }
+# Unused directly: raises the floor of `sharded-slab`'s `lazy_static = "1"`, which fails to build below 1.1
+lazy_static = { version = "1.1", optional = true }
+
+[features]
+otel = [
+    "dep:futures-executor",
+    "dep:opentelemetry",
+    "dep:opentelemetry_sdk",
+    "dep:opentelemetry-otlp",
+    "dep:tracing",
+    "dep:tracing-opentelemetry",
+    "dep:tracing-subscriber",
+    "dep:lazy_static",
+]
+
 [[bench]]
 name = "native"
 harness = false

crates/codspeed/src/benchmark_scope.rs

@@ -0,0 +1,21 @@
+//! The benchmark being run, which the exported telemetry is attributed to.
+//!
+//! Without the `otel` feature, entering and exiting a scope does nothing.
+
+/// Marks the start of the benchmark `uri`. Spans started until [`exit`] carry its URI.
+///
+/// Call it outside the measured section.
+pub fn enter(uri: &str) {
+    #[cfg(feature = "otel")]
+    crate::otel::enter_benchmark(uri);
+    #[cfg(not(feature = "otel"))]
+    let _ = uri;
+}
+
+/// Marks the end of the current benchmark and exports the spans held so far.
+///
+/// Call it outside the measured section, before the benchmark is reported as executed.
+pub fn exit() {
+    #[cfg(feature = "otel")]
+    crate::otel::exit_benchmark();
+}

crates/codspeed/src/codspeed.rs

@@ -81,6 +81,7 @@ impl CodSpeed {
     #[inline(always)]
     pub fn start_benchmark(&mut self, name: &str) {
         self.current_benchmark = CString::new(name).expect("CString::new failed");
+        crate::benchmark_scope::enter(name);
 
         if let InstrumentationStatus::InstrumentHooks(hooks_instance) = &self.instrumentation_status
         {
@@ -99,9 +100,15 @@ impl CodSpeed {
         // The overhead in case we are not running valgrind is extremely low, and we do not want to
         // add a conditionnal branch to valgrind measurements.
         measurement::stop(&self.current_benchmark);
-        if let InstrumentationStatus::InstrumentHooks(hooks_instance) = &self.instrumentation_status
-        {
+        let hooks_instance = match &self.instrumentation_status {
+            InstrumentationStatus::InstrumentHooks(hooks_instance) => Some(*hooks_instance),
+            _ => None,
+        };
+        if let Some(hooks_instance) = hooks_instance {
             let _ = hooks_instance.stop_benchmark();
+        }
+        crate::benchmark_scope::exit();
+        if let Some(hooks_instance) = hooks_instance {
             let _ =
                 hooks_instance.set_executed_benchmark(&self.current_benchmark.to_string_lossy());
         }

crates/codspeed/src/lib.rs

@@ -1,9 +1,12 @@
+pub mod benchmark_scope;
 pub mod codspeed;
 
 pub mod instrument_hooks;
 
 mod macros;
 mod measurement;
+#[cfg(feature = "otel")]
+pub mod otel;
 mod request;
 pub mod utils;
 pub mod walltime_results;