Make tracing optional

Author: taiki-e

Cargo.toml

@@ -20,7 +20,7 @@ async-io = "2.1.0"
 cfg-if = "1.0"
 event-listener = "5.1.0"
 futures-lite = "2.0.0"
-tracing = { version = "0.1.40", default-features = false }
+tracing = { version = "0.1.40", default-features = false, optional = true }
 
 [target.'cfg(unix)'.dependencies]
 async-signal = "0.2.3"

src/reaper/wait.rs

@@ -113,8 +113,9 @@ impl ChildGuard {
 
                 // Wait on this child forever.
                 let result = future::poll_fn(|cx| inner.poll_wait(cx)).await;
-                if let Err(e) = result {
-                    tracing::error!("error while polling zombie process: {}", e);
+                if let Err(_e) = result {
+                    #[cfg(feature = "tracing")]
+                    tracing::error!("error while polling zombie process: {}", _e);
                 }
             }
         };