sentry: Implement basic traces_sampler function

Author: Turbo87

Diff for: src/sentry/mod.rs

@@ -2,7 +2,8 @@ mod middleware;
 
 use crate::env_optional;
 pub use middleware::CustomSentryMiddleware as SentryMiddleware;
-use sentry::{ClientInitGuard, ClientOptions, IntoDsn};
+use sentry::{ClientInitGuard, ClientOptions, IntoDsn, TransactionContext};
+use std::sync::Arc;
 
 /// Initializes the Sentry SDK from the environment variables.
 ///
@@ -28,13 +29,15 @@ pub fn init() -> ClientInitGuard {
 
     let traces_sample_rate = env_optional("SENTRY_TRACES_SAMPLE_RATE").unwrap_or(0.0);
 
+    let traces_sampler = move |_ctx: &TransactionContext| -> f32 { traces_sample_rate };
+
     let opts = ClientOptions {
         auto_session_tracking: true,
         dsn,
         environment,
         release,
         session_mode: sentry::SessionMode::Request,
-        traces_sample_rate,
+        traces_sampler: Some(Arc::new(traces_sampler)),
         ..Default::default()
     };