fix(tvix/tracing): Enable tracing in tvix-build.

Change-Id: Ica9734d7774da4d5e2a5cacab6b9feb27becc3e2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12720
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/build/src/bin/tvix-build.rs

@@ -50,7 +50,9 @@ enum Commands {
 async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
     let cli = Cli::parse();
 
-    let _ = tvix_tracing::TracingBuilder::default().enable_progressbar();
+    tvix_tracing::TracingBuilder::default()
+        .enable_progressbar()
+        .build()?;
 
     match cli.command {
         Commands::Daemon {

tvix/cli/src/main.rs

@@ -57,7 +57,7 @@ fn lint(code: &str, path: Option<PathBuf>, args: &Args) -> bool {
 fn main() {
     let args = Args::parse();
 
-    let _ = tvix_tracing::TracingBuilder::default()
+    tvix_tracing::TracingBuilder::default()
         .enable_progressbar()
         .build()
         .expect("unable to set up tracing subscriber");

tvix/tracing/src/lib.rs

@@ -145,6 +145,7 @@ impl TracingHandle {
     }
 }
 
+#[must_use = "Don't forget to call build() to enable tracing."]
 #[derive(Default)]
 pub struct TracingBuilder {
     progess_bar: bool,