Integrate Salsa into document tracking for server (#148)

crates/djls-server/src/session.rs

@@ -1,15 +1,43 @@
 use djls_conf::Settings;
 use djls_project::DjangoProject;
+use salsa::StorageHandle;
 use tower_lsp_server::lsp_types::ClientCapabilities;
 
+use crate::db::ServerDatabase;
 use crate::documents::Store;
 
-#[derive(Debug, Default)]
+#[derive(Default)]
 pub struct Session {
     client_capabilities: Option<ClientCapabilities>,
     project: Option<DjangoProject>,
     documents: Store,
     settings: Settings,
+
+    /// A thread-safe Salsa database handle that can be shared between threads.
+    ///
+    /// This implements the insight from [this Salsa Zulip discussion](https://salsa.zulipchat.com/#narrow/channel/145099-Using-Salsa/topic/.E2.9C.94.20Advice.20on.20using.20salsa.20from.20Sync.20.2B.20Send.20context/with/495497515)
+    /// where we're using the `StorageHandle` to create a thread-safe handle that can be
+    /// shared between threads. When we need to use it, we clone the handle to get a new reference.
+    ///
+    /// Usage:
+    /// ```rust,ignore
+    /// // Use the StorageHandle in Session
+    /// let db_handle = StorageHandle::new(None);
+    ///
+    /// // Clone it to pass to different threads
+    /// let db_handle_clone = db_handle.clone();
+    ///
+    /// // Use it in an async context
+    /// async_fn(move || {
+    ///     // Get a database from the handle
+    ///     let storage = db_handle_clone.into_storage();
+    ///     let db = ServerDatabase::new(storage);
+    ///
+    ///     // Use the database
+    ///     db.some_query(args)
+    /// });
+    /// ```
+    db_handle: StorageHandle<ServerDatabase>,
 }
 
 impl Session {
@@ -19,11 +47,12 @@ impl Session {
             project: None,
             documents: Store::new(),
             settings: Settings::default(),
+            db_handle: StorageHandle::new(None),
         }
     }
 
-    pub fn client_capabilities(&self) -> &Option<ClientCapabilities> {
-        &self.client_capabilities
+    pub fn client_capabilities(&self) -> Option<&ClientCapabilities> {
+        self.client_capabilities.as_ref()
     }
 
     pub fn client_capabilities_mut(&mut self) -> &mut Option<ClientCapabilities> {
@@ -53,4 +82,21 @@ impl Session {
     pub fn settings_mut(&mut self) -> &mut Settings {
         &mut self.settings
     }
+
+    /// Get the raw database handle from the session
+    ///
+    /// Note: In most cases, you'll want to use `db()` instead to get a usable
+    /// database instance directly.
+    pub fn db_handle(&self) -> &StorageHandle<ServerDatabase> {
+        &self.db_handle
+    }
+
+    /// Get a database instance directly from the session
+    ///
+    /// This creates a usable database from the handle, which can be used
+    /// to query and update data in the database.
+    pub fn db(&self) -> ServerDatabase {
+        let storage = self.db_handle.clone().into_storage();
+        ServerDatabase::new(storage)
+    }
 }