fix: avoid SetGlobalDefaultError panic when rolldown devtools is enabled

Skip installing a global tracing subscriber during NAPI module init when
VITE_LOG is not set. Previously, init_tracing() always installed a no-op
subscriber (empty Targets filter) that occupied the global default slot.
When rolldown devtools was later enabled via build.rolldownOptions.devtools,
DebugTracer::init() would panic trying to claim the already-occupied slot.

Now the global default slot stays free for other components unless VITE_LOG
is explicitly set, and even then try_init() is used for graceful fallback.

Closes #1356

Author: fengmk2

crates/vite_shared/src/tracing.rs

@@ -1,6 +1,6 @@
 //! Tracing initialization for vite-plus
 
-use std::sync::OnceLock;
+use std::{str::FromStr, sync::OnceLock};
 
 use tracing_subscriber::{
     filter::{LevelFilter, Targets},
@@ -14,25 +14,30 @@ use crate::env_vars;
 /// Uses `OnceLock` to ensure tracing is only initialized once,
 /// even if called multiple times.
 ///
+/// Only sets the global default subscriber when `VITE_LOG` is set.
+/// When unset, the global default slot is left free so that other
+/// subscribers (e.g., rolldown devtools) can claim it without panicking.
+///
 /// # Environment Variables
 /// - `VITE_LOG`: Controls log filtering (e.g., "debug", "vite_task=trace")
 pub fn init_tracing() {
     static TRACING: OnceLock<()> = OnceLock::new();
     TRACING.get_or_init(|| {
+        let Ok(env_var) = std::env::var(env_vars::VITE_LOG) else {
+            // No VITE_LOG set — skip subscriber installation so the global
+            // default slot stays available for other components.
+            return;
+        };
+
         tracing_subscriber::registry()
             .with(
-                std::env::var(env_vars::VITE_LOG)
-                    .map_or_else(
-                        |_| Targets::new(),
-                        |env_var| {
-                            use std::str::FromStr;
-                            Targets::from_str(&env_var).unwrap_or_default()
-                        },
-                    )
+                Targets::from_str(&env_var)
+                    .unwrap_or_default()
                     // disable brush-parser tracing
                     .with_targets([("tokenize", LevelFilter::OFF), ("parse", LevelFilter::OFF)]),
             )
             .with(tracing_subscriber::fmt::layer())
-            .init();
+            .try_init()
+            .ok();
     });
 }