Add unified file and LSP logging using tracing to server (#178)

crates/djls-server/Cargo.toml

@@ -21,6 +21,8 @@ serde_json = { workspace = true }
 tokio = { workspace = true }
 tower-lsp-server = { workspace = true }
 tracing = { workspace = true }
+tracing-appender = { workspace = true }
+tracing-subscriber = { workspace = true }
 
 [build-dependencies]
 djls-dev = { workspace = true }

crates/djls-server/src/lib.rs

@@ -48,7 +48,12 @@ pub fn run() -> Result<()> {
 
         let (service, socket) = LspService::build(|client| {
             client::init_client(client);
-            DjangoLanguageServer::new()
+
+            let log_guard = logging::init_tracing(|message_type, message| {
+                client::log_message(message_type, message);
+            });
+
+            DjangoLanguageServer::new(log_guard)
         })
         .finish();
 

crates/djls-server/src/logging.rs

@@ -1,4 +1,16 @@
-//! Temporary logging macros for dual-dispatch to both LSP client and tracing.
+//! Logging infrastructure bridging tracing events to LSP client messages.
+//!
+//! This module provides both temporary dual-dispatch macros and the permanent
+//! `LspLayer` implementation for forwarding tracing events to the LSP client.
+//!
+//! ## `LspLayer`
+//!
+//! The `LspLayer` is a tracing `Layer` that intercepts tracing events and
+//! forwards appropriate ones to the LSP client. It filters events by level:
+//! - ERROR, WARN, INFO, DEBUG → forwarded to LSP client
+//! - TRACE → kept server-side only (for performance)
+//!
+//! ## Temporary Macros
 //!
 //! These macros bridge the gap during our migration from `client::log_message`
 //! to the tracing infrastructure. They ensure messages are sent to both systems
@@ -27,6 +39,130 @@
 //! - For format strings, we format once for the client but pass the original
 //!   format string and args to tracing to preserve structured data
 
+use std::sync::Arc;
+
+use tower_lsp_server::lsp_types::MessageType;
+use tracing::field::Visit;
+use tracing::Level;
+use tracing_appender::non_blocking::WorkerGuard;
+use tracing_subscriber::fmt;
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+use tracing_subscriber::EnvFilter;
+use tracing_subscriber::Layer;
+use tracing_subscriber::Registry;
+
+/// A tracing Layer that forwards events to the LSP client.
+///
+/// This layer intercepts tracing events and converts them to LSP log messages
+/// that are sent to the client. It filters events by level to avoid overwhelming
+/// the client with verbose trace logs.
+pub struct LspLayer {
+    send_message: Arc<dyn Fn(MessageType, String) + Send + Sync>,
+}
+
+impl LspLayer {
+    pub fn new<F>(send_message: F) -> Self
+    where
+        F: Fn(MessageType, String) + Send + Sync + 'static,
+    {
+        Self {
+            send_message: Arc::new(send_message),
+        }
+    }
+}
+
+/// Visitor that extracts the message field from tracing events.
+struct MessageVisitor {
+    message: Option<String>,
+}
+
+impl MessageVisitor {
+    fn new() -> Self {
+        Self { message: None }
+    }
+}
+
+impl Visit for MessageVisitor {
+    fn record_debug(&mut self, field: &tracing::field::Field, value: &dyn std::fmt::Debug) {
+        if field.name() == "message" {
+            self.message = Some(format!("{value:?}"));
+        }
+    }
+
+    fn record_str(&mut self, field: &tracing::field::Field, value: &str) {
+        if field.name() == "message" {
+            self.message = Some(value.to_string());
+        }
+    }
+}
+
+impl<S> Layer<S> for LspLayer
+where
+    S: tracing::Subscriber,
+{
+    fn on_event(
+        &self,
+        event: &tracing::Event<'_>,
+        _ctx: tracing_subscriber::layer::Context<'_, S>,
+    ) {
+        let metadata = event.metadata();
+
+        let message_type = match *metadata.level() {
+            Level::ERROR => MessageType::ERROR,
+            Level::WARN => MessageType::WARNING,
+            Level::INFO => MessageType::INFO,
+            Level::DEBUG => MessageType::LOG,
+            Level::TRACE => {
+                // Skip TRACE level - too verbose for LSP client
+                // TODO: Add MessageType::Debug in LSP 3.18.0
+                return;
+            }
+        };
+
+        let mut visitor = MessageVisitor::new();
+        event.record(&mut visitor);
+
+        if let Some(message) = visitor.message {
+            (self.send_message)(message_type, message);
+        }
+    }
+}
+
+/// Initialize the dual-layer tracing subscriber.
+///
+/// Sets up:
+/// - File layer: writes to /tmp/djls.log with daily rotation
+/// - LSP layer: forwards INFO+ messages to the client
+/// - `EnvFilter`: respects `RUST_LOG` env var, defaults to "info"
+///
+/// Returns a `WorkerGuard` that must be kept alive for the file logging to work.
+pub fn init_tracing<F>(send_message: F) -> WorkerGuard
+where
+    F: Fn(MessageType, String) + Send + Sync + 'static,
+{
+    let file_appender = tracing_appender::rolling::daily("/tmp", "djls.log");
+    let (non_blocking, guard) = tracing_appender::non_blocking(file_appender);
+
+    let env_filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info"));
+    let file_layer = fmt::layer()
+        .with_writer(non_blocking)
+        .with_ansi(false)
+        .with_thread_ids(true)
+        .with_thread_names(true)
+        .with_target(true)
+        .with_file(true)
+        .with_line_number(true)
+        .with_filter(env_filter);
+
+    let lsp_layer =
+        LspLayer::new(send_message).with_filter(tracing_subscriber::filter::LevelFilter::INFO);
+
+    Registry::default().with(file_layer).with(lsp_layer).init();
+
+    guard
+}
+
 #[macro_export]
 macro_rules! log_info {
     ($msg:literal) => {

crates/djls-server/src/server.rs

@@ -23,6 +23,7 @@ use tower_lsp_server::lsp_types::TextDocumentSyncOptions;
 use tower_lsp_server::lsp_types::WorkspaceFoldersServerCapabilities;
 use tower_lsp_server::lsp_types::WorkspaceServerCapabilities;
 use tower_lsp_server::LanguageServer;
+use tracing_appender::non_blocking::WorkerGuard;
 
 use crate::log_error;
 use crate::log_info;
@@ -35,14 +36,16 @@ const SERVER_VERSION: &str = "0.1.0";
 pub struct DjangoLanguageServer {
     session: Arc<RwLock<Option<Session>>>,
     queue: Queue,
+    _log_guard: WorkerGuard,
 }
 
 impl DjangoLanguageServer {
     #[must_use]
-    pub fn new() -> Self {
+    pub fn new(log_guard: WorkerGuard) -> Self {
         Self {
             session: Arc::new(RwLock::new(None)),
             queue: Queue::new(),
+            _log_guard: log_guard,
         }
     }