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

…-labs#2296)

## What ❔

Makes `zksync=info` default log entry, which later can be
overridden/extended.

## Why ❔

Provides a good enough default for any env, simplifies configuration of
the system.

## Checklist

<!-- Check your PR fulfills the following items. -->
<!-- For draft PRs check the boxes as you complete them. -->

- [ ] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zk fmt` and `zk lint`.

core/bin/block_reverter/src/main.rs

@@ -92,7 +92,9 @@ async fn main() -> anyhow::Result<()> {
         .parse()
         .context("Invalid log format")?;
 
-    let mut builder = vlog::ObservabilityBuilder::new().with_log_format(log_format);
+    let mut builder = vlog::ObservabilityBuilder::new()
+        .with_log_format(log_format)
+        .disable_default_logs(); // It's a CLI application, so we only need to show logs that were actually requested.
     if let Some(sentry_url) = observability_config.sentry_url {
         builder = builder
             .with_sentry_url(&sentry_url)

core/lib/vlog/src/lib.rs

@@ -139,6 +139,7 @@ pub struct OpenTelemetryOptions {
 /// Currently capable of configuring logging output and sentry integration.
 #[derive(Debug, Default)]
 pub struct ObservabilityBuilder {
+    disable_default_logs: bool,
     log_format: LogFormat,
     log_directives: Option<String>,
     sentry_url: Option<Dsn>,
@@ -176,6 +177,14 @@ impl ObservabilityBuilder {
         self
     }
 
+    /// Disables logs enabled by default.
+    /// May be used, for example, in interactive CLI applications, where the user may want to fully control
+    /// the verbosity.
+    pub fn disable_default_logs(mut self) -> Self {
+        self.disable_default_logs = true;
+        self
+    }
+
     /// Enables Sentry integration.
     /// Returns an error if the provided Sentry URL is invalid.
     pub fn with_sentry_url(
@@ -254,15 +263,36 @@ impl ObservabilityBuilder {
         subscriber.with(layer)
     }
 
+    /// Builds a filter for the logs.
+    ///
+    /// Unless `disable_default_logs` was set, 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 = if self.disable_default_logs {
+            "".to_string()
+        } else {
+            "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 => {