Explicitly set settings for the tracing subscriber.

src/main.rs

@@ -1,12 +1,23 @@
 use crate::parser::document;
+use tracing::trace;
+use tracing::Level;
 
 mod parser;
 
 const TEST_DOC: &'static str = include_str!("../toy_language.txt");
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let subscriber = tracing_subscriber::FmtSubscriber::new();
+    let format = tracing_subscriber::fmt::format()
+        .with_file(true)
+        .with_line_number(true)
+        .with_thread_ids(false)
+        .with_target(false);
+    let subscriber = tracing_subscriber::fmt()
+        .event_format(format)
+        .with_max_level(Level::TRACE)
+        .finish();
     tracing::subscriber::set_global_default(subscriber)?;
+    trace!("TESTING");
     println!("{}\n\n\n", TEST_DOC);
     println!("{:#?}", document(TEST_DOC));
     Ok(())