feat(tracing): Add method for accessing span data

sentry-core/src/performance.rs

@@ -1,5 +1,6 @@
-use std::sync::Arc;
-use std::sync::Mutex;
+use std::collections::BTreeMap;
+use std::ops::{Deref, DerefMut};
+use std::sync::{Arc, Mutex, MutexGuard};
 
 #[cfg(all(feature = "profiling", target_family = "unix"))]
 use crate::profiling;
@@ -601,6 +602,23 @@ impl Transaction {
     }
 }
 
+/// A smart pointer to a span's [`data` field](protocol::Span::data).
+pub struct Data<'a>(MutexGuard<'a, protocol::Span>);
+
+impl<'a> Deref for Data<'a> {
+    type Target = BTreeMap<String, protocol::Value>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0.data
+    }
+}
+
+impl<'a> DerefMut for Data<'a> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0.data
+    }
+}
+
 /// A running Performance Monitoring Span.
 ///
 /// The span needs to be explicitly finished via [`Span::finish`], otherwise it
@@ -621,6 +639,14 @@ impl Span {
         span.data.insert(key.into(), value);
     }
 
+    /// Returns a smart pointer to the span's [`data` field](protocol::Span::data).
+    ///
+    /// Since [`Data`] implements `Deref` and `DerefMut`, this can be used to read and mutate
+    /// the span data.
+    pub fn data(&self) -> Data {
+        Data(self.span.lock().unwrap())
+    }
+
     /// Get the TransactionContext of the Span.
     ///
     /// Note that this clones the underlying value.