examples: add renamed field to static/dynamic example

Author: mladedav

examples/custom-static-and-dynamic-fields.rs

@@ -5,14 +5,18 @@ use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 fn main() {
     let mut json_layer = fmt::layer()
         .with_level(true)
-        .with_thread_ids(true)
+        // .with_thread_ids(true)
         .with_file(true)
         .with_line_number(true)
         .with_target(false)
         .flatten_event(true);
 
     let inner_layer = json_layer.inner_layer_mut();
+    // Setting it inside the inner layer allows us to rename the field.
+    inner_layer.with_thread_ids("thread_id");
+    // This field will not change during the lifetime of the application.
     inner_layer.add_static_field("app", serde_json::Value::String("monitor".to_owned()));
+    // This field might change (we might fork a subprocess or something)
     inner_layer.add_dynamic_field("pid", |_, _| {
         Some(serde_json::Value::Number(Number::from(std::process::id())))
     });
@@ -27,7 +31,7 @@ fn main() {
     //     "level": "INFO",
     //     "line_number": 24,
     //     "pid": 3341821,
-    //     "threadId": "ThreadId(1)",
+    //     "thread_id": "ThreadId(1)",
     //     "timestamp": "2025-06-23T20:04:51.512451Z",
     //     "message": "Log with logger, app, and pid."
     // }