feat(global): set default propagator to noop (open-telemetry#329)

Author: morigs

opentelemetry/src/global/propagation.rs

@@ -1,14 +1,12 @@
 use crate::propagation::TextMapPropagator;
-use crate::sdk::propagation::{
-    BaggagePropagator, TextMapCompositePropagator, TraceContextPropagator,
-};
+use crate::sdk::propagation::TextMapCompositePropagator;
 use std::sync::RwLock;
 
 lazy_static::lazy_static! {
     /// The current global `TextMapPropagator` propagator.
-    static ref GLOBAL_TEXT_MAP_PROPAGATOR: RwLock<Box<dyn TextMapPropagator + Send + Sync>> = RwLock::new(Box::new(TextMapCompositePropagator::new(vec![Box::new(TraceContextPropagator::new()), Box::new(BaggagePropagator::new())])));
+    static ref GLOBAL_TEXT_MAP_PROPAGATOR: RwLock<Box<dyn TextMapPropagator + Send + Sync>> = RwLock::new(Box::new(TextMapCompositePropagator::new(vec![])));
     /// The global default `TextMapPropagator` propagator.
-    static ref DEFAULT_TEXT_MAP_PROPAGATOR: TextMapCompositePropagator = TextMapCompositePropagator::new(vec![Box::new(TraceContextPropagator::new()), Box::new(BaggagePropagator::new())]);
+    static ref DEFAULT_TEXT_MAP_PROPAGATOR: TextMapCompositePropagator = TextMapCompositePropagator::new(vec![]);
 }
 
 /// Sets the given [`TextMapPropagator`] propagator as the current global propagator.

opentelemetry/src/sdk/propagation/composite.rs

@@ -186,6 +186,34 @@ mod tests {
         ]
     }
 
+    #[test]
+    fn zero_propogators_are_noop() {
+        let composite_propagator = TextMapCompositePropagator::new(vec![]);
+
+        let cx = Context::default().with_span(TestSpan(SpanContext::new(
+            TraceId::from_u128(1),
+            SpanId::from_u64(1),
+            0,
+            false,
+            TraceState::default(),
+        )));
+        let mut injector = HashMap::new();
+        composite_propagator.inject_context(&cx, &mut injector);
+
+        assert_eq!(injector.len(), 0);
+
+        for (header_name, header_value) in test_data() {
+            let mut extractor = HashMap::new();
+            extractor.insert(header_name.to_string(), header_value.to_string());
+            assert_eq!(
+                composite_propagator
+                    .extract(&extractor)
+                    .remote_span_context(),
+                None
+            );
+        }
+    }
+
     #[test]
     fn inject_multiple_propagators() {
         let test_propagator = TestPropagator::new();