feat: Use info log level for crates named zksync_* by default

core/lib/vlog/src/lib.rs

@@ -254,15 +254,32 @@ impl ObservabilityBuilder {
         subscriber.with(layer)
     }
 
+    /// Builds a filter for the logs.
+    ///
+    /// Uses `zksync=info` as a default which is then merged with user-defined directives.
+    /// Provided directives can extend/override the default value.
+    ///
+    /// The provided default convers all the crates with a name starting with `zksync` (per `tracing`
+    /// [documentation][1]), which is a good enough default for any project.
+    ///
+    /// If `log_directives` are provided via `with_log_directives`, they will be used.
+    /// Otherwise, the value will be parsed from the environment variable `RUST_LOG`.
+    ///
+    /// [1]: https://docs.rs/tracing-subscriber/0.3.18/tracing_subscriber/filter/targets/struct.Targets.html#filtering-with-targets
+    fn build_filter(&self) -> EnvFilter {
+        let mut directives = "zksync=info,".to_string();
+        if let Some(log_directives) = &self.log_directives {
+            directives.push_str(log_directives);
+        } else if let Ok(env_directives) = std::env::var(EnvFilter::DEFAULT_ENV) {
+            directives.push_str(&env_directives);
+        };
+        EnvFilter::new(directives)
+    }
+
     /// Initializes the observability subsystem.
     pub fn build(self) -> ObservabilityGuard {
         // Initialize logs.
-
-        let env_filter = if let Some(log_directives) = self.log_directives {
-            tracing_subscriber::EnvFilter::new(log_directives)
-        } else {
-            tracing_subscriber::EnvFilter::from_default_env()
-        };
+        let env_filter = self.build_filter();
 
         match self.log_format {
             LogFormat::Plain => {