chore: change the set_parent method to return a Result

Author: bantonsson

examples/opentelemetry-remote-context.rs

@@ -37,7 +37,7 @@ fn main() {
         let app_root = span!(tracing::Level::INFO, "app_start");
 
         // Assign parent trace from external context
-        app_root.set_parent(parent_context);
+        let _ = app_root.set_parent(parent_context);
 
         // To include tracing context in client requests from _this_ app,
         // use `context` to extract the current OpenTelemetry context.

src/layer.rs

@@ -2254,13 +2254,13 @@ mod tests {
 
             let child1 = trace_span!("child-1");
             let root_context = root.context(); // SpanData (None)
-            child1.set_parent(root_context); // Clone context, but SpanData(None)
+            let _ = child1.set_parent(root_context); // Clone context, but SpanData(None)
 
             let _enter_root = root.enter();
             drop(_enter_root);
 
             let child2 = trace_span!("child-2");
-            child2.set_parent(root.context());
+            let _ = child2.set_parent(root.context());
         });
 
         // Let's check the spans
@@ -2333,10 +2333,10 @@ mod tests {
             _ = root.enter();
 
             let child1 = trace_span!("child-1");
-            child1.set_parent(root.context());
+            let _ = child1.set_parent(root.context());
 
             trace_span!(parent: &child1, "child-2");
-            child1.set_parent(root.context()); // <-- this is what causes the issue
+            let _ = child1.set_parent(root.context()); // <-- this is what causes the issue
 
             trace_span!(parent: &child1, "child-3");
         });

src/span_ext.rs

@@ -17,6 +17,10 @@ pub trait OpenTelemetrySpanExt {
     /// Associates `self` with a given OpenTelemetry trace, using the provided
     /// parent [`Context`].
     ///
+    /// This method provides error handling for cases where the span context
+    /// cannot be set, such as when the OpenTelemetry layer is not present
+    /// or when the span has already been started.
+    ///
     /// [`Context`]: opentelemetry::Context
     ///
     /// # Examples
@@ -41,12 +45,12 @@ pub trait OpenTelemetrySpanExt {
     /// let app_root = tracing::span!(tracing::Level::INFO, "app_start");
     ///
     /// // Assign parent trace from external context
-    /// app_root.set_parent(parent_context.clone());
+    /// let _ = app_root.set_parent(parent_context.clone());
     ///
     /// // Or if the current span has been created elsewhere:
-    /// Span::current().set_parent(parent_context);
+    /// let _ = Span::current().set_parent(parent_context);
     /// ```
-    fn set_parent(&self, cx: Context);
+    fn set_parent(&self, cx: Context) -> Result<(), &'static str>;
 
     /// Associates `self` with a given OpenTelemetry trace, using the provided
     /// followed span [`SpanContext`].
@@ -224,10 +228,14 @@ impl OpenTelemetrySpanExt for tracing::Span {
     /// Additionally, once a span has been fully built - and the SpanBuilder has been consumed -
     /// the parent _cannot_ be mutated.
     ///
-    fn set_parent(&self, cx: Context) {
+    fn set_parent(&self, cx: Context) -> Result<(), &'static str> {
         let mut cx = Some(cx);
+        let mut result = Ok(());
+        let result_ref = &mut result;
+
         self.with_subscriber(move |(id, subscriber)| {
             let Some(get_context) = subscriber.downcast_ref::<WithContext>() else {
+                *result_ref = Err("OpenTelemetry layer not found");
                 return;
             };
             // Set the parent OTel for the current span
@@ -245,10 +253,14 @@ impl OpenTelemetrySpanExt for tracing::Span {
                         // new parent context when it's eventually built
                         *parent_cx = new_cx;
                     }
-                    OtelDataState::Context { .. } => (),
+                    OtelDataState::Context { .. } => {
+                        *result_ref = Err("Span has already been started, cannot set parent");
+                    }
                 }
             });
         });
+
+        result
     }
 
     fn add_link(&self, cx: SpanContext) {

tests/trace_state_propagation.rs

@@ -37,7 +37,7 @@ fn trace_with_assigned_otel_context() {
 
     tracing::subscriber::with_default(subscriber, || {
         let child = tracing::debug_span!("child");
-        child.set_parent(cx);
+        let _ = child.set_parent(cx);
     });
 
     drop(provider); // flush all spans
@@ -70,7 +70,7 @@ fn propagate_invalid_context() {
 
     tracing::subscriber::with_default(subscriber, || {
         let root = tracing::debug_span!("root");
-        root.set_parent(invalid_cx);
+        let _ = root.set_parent(invalid_cx);
         root.in_scope(|| tracing::debug_span!("child"));
     });
 
@@ -90,7 +90,7 @@ fn inject_context_into_outgoing_requests() {
 
     tracing::subscriber::with_default(subscriber, || {
         let root = tracing::debug_span!("root");
-        root.set_parent(cx);
+        let _ = root.set_parent(cx);
         let _g = root.enter();
         let child = tracing::debug_span!("child");
         propagator.inject_context(&child.context(), &mut outgoing_req_carrier);
@@ -125,7 +125,7 @@ fn sampling_decision_respects_new_parent() {
         // Observation: if you force the _child_ to materialize before the parent, e.g.,
         // if you swap these two lines - bad things will happen, and we shouldn't support
         // this.
-        child.set_parent(Context::current_with_span(root_span));
+        let _ = child.set_parent(Context::current_with_span(root_span));
         child.context(); // force a sampling decision
     });