[red-knot] Support files outside of any workspace (#13041)

## Summary

This PR adds basic support for files outside of any workspace in the red
knot server.

This also limits the red knot server to only work in a single workspace.
The server will not start if there are multiple workspaces.

## Test Plan

https://github.com/user-attachments/assets/de601387-0ad5-433c-9d2c-7b6ae5137654

crates/red_knot_server/src/server.rs

@@ -99,6 +99,11 @@ impl Server {
                 anyhow::anyhow!("Failed to get the current working directory while creating a default workspace.")
             })?;
 
+        if workspaces.len() > 1 {
+            // TODO(dhruvmanila): Support multi-root workspaces
+            anyhow::bail!("Multi-root workspaces are not supported yet");
+        }
+
         Ok(Self {
             connection,
             worker_threads,

crates/red_knot_server/src/server/api.rs

@@ -7,7 +7,6 @@ mod requests;
 mod traits;
 
 use notifications as notification;
-use red_knot_workspace::db::RootDatabase;
 use requests as request;
 
 use self::traits::{NotificationHandler, RequestHandler};
@@ -85,9 +84,10 @@ fn background_request_task<'a, R: traits::BackgroundDocumentRequestHandler>(
         let Ok(path) = url_to_system_path(&url) else {
             return Box::new(|_, _| {});
         };
-        let db = session
-            .workspace_db_for_path(path.as_std_path())
-            .map(RootDatabase::snapshot);
+        let db = match session.workspace_db_for_path(path.as_std_path()) {
+            Some(db) => db.snapshot(),
+            None => session.default_workspace_db().snapshot(),
+        };
 
         let Some(snapshot) = session.take_snapshot(url) else {
             return Box::new(|_, _| {});

crates/red_knot_server/src/server/api/notifications/did_close.rs

@@ -2,8 +2,6 @@ use lsp_server::ErrorCode;
 use lsp_types::notification::DidCloseTextDocument;
 use lsp_types::DidCloseTextDocumentParams;
 
-use ruff_db::files::File;
-
 use crate::server::api::diagnostics::clear_diagnostics;
 use crate::server::api::traits::{NotificationHandler, SyncNotificationHandler};
 use crate::server::api::LSPResult;
@@ -25,7 +23,7 @@ impl SyncNotificationHandler for DidCloseTextDocumentHandler {
         _requester: &mut Requester,
         params: DidCloseTextDocumentParams,
     ) -> Result<()> {
-        let Ok(path) = url_to_system_path(&params.text_document.uri) else {
+        let Ok(_path) = url_to_system_path(&params.text_document.uri) else {
             return Ok(());
         };
 
@@ -34,10 +32,6 @@ impl SyncNotificationHandler for DidCloseTextDocumentHandler {
             .close_document(&key)
             .with_failure_code(ErrorCode::InternalError)?;
 
-        if let Some(db) = session.workspace_db_for_path_mut(path.as_std_path()) {
-            File::sync_path(db, &path);
-        }
-
         clear_diagnostics(key.url(), &notifier)?;
 
         Ok(())

crates/red_knot_server/src/server/api/notifications/did_close_notebook.rs

@@ -1,8 +1,6 @@
 use lsp_types::notification::DidCloseNotebookDocument;
 use lsp_types::DidCloseNotebookDocumentParams;
 
-use ruff_db::files::File;
-
 use crate::server::api::traits::{NotificationHandler, SyncNotificationHandler};
 use crate::server::api::LSPResult;
 use crate::server::client::{Notifier, Requester};
@@ -23,7 +21,7 @@ impl SyncNotificationHandler for DidCloseNotebookHandler {
         _requester: &mut Requester,
         params: DidCloseNotebookDocumentParams,
     ) -> Result<()> {
-        let Ok(path) = url_to_system_path(&params.notebook_document.uri) else {
+        let Ok(_path) = url_to_system_path(&params.notebook_document.uri) else {
             return Ok(());
         };
 
@@ -32,10 +30,6 @@ impl SyncNotificationHandler for DidCloseNotebookHandler {
             .close_document(&key)
             .with_failure_code(lsp_server::ErrorCode::InternalError)?;
 
-        if let Some(db) = session.workspace_db_for_path_mut(path.as_std_path()) {
-            File::sync_path(db, &path);
-        }
-
         Ok(())
     }
 }

crates/red_knot_server/src/server/api/notifications/did_open.rs

@@ -1,7 +1,7 @@
 use lsp_types::notification::DidOpenTextDocument;
 use lsp_types::DidOpenTextDocumentParams;
 
-use ruff_db::files::system_path_to_file;
+use red_knot_workspace::watch::ChangeEvent;
 
 use crate::server::api::traits::{NotificationHandler, SyncNotificationHandler};
 use crate::server::client::{Notifier, Requester};
@@ -30,11 +30,11 @@ impl SyncNotificationHandler for DidOpenTextDocumentHandler {
         let document = TextDocument::new(params.text_document.text, params.text_document.version);
         session.open_text_document(params.text_document.uri, document);
 
-        if let Some(db) = session.workspace_db_for_path_mut(path.as_std_path()) {
-            // TODO(dhruvmanila): Store the `file` in `DocumentController`
-            let file = system_path_to_file(db, &path).unwrap();
-            file.sync(db);
-        }
+        let db = match session.workspace_db_for_path_mut(path.as_std_path()) {
+            Some(db) => db,
+            None => session.default_workspace_db_mut(),
+        };
+        db.apply_changes(vec![ChangeEvent::Opened(path)], None);
 
         // TODO(dhruvmanila): Publish diagnostics if the client doesn't support pull diagnostics
 

crates/red_knot_server/src/server/api/notifications/did_open_notebook.rs

@@ -2,7 +2,7 @@ use lsp_server::ErrorCode;
 use lsp_types::notification::DidOpenNotebookDocument;
 use lsp_types::DidOpenNotebookDocumentParams;
 
-use ruff_db::files::system_path_to_file;
+use red_knot_workspace::watch::ChangeEvent;
 
 use crate::edit::NotebookDocument;
 use crate::server::api::traits::{NotificationHandler, SyncNotificationHandler};
@@ -38,11 +38,11 @@ impl SyncNotificationHandler for DidOpenNotebookHandler {
         .with_failure_code(ErrorCode::InternalError)?;
         session.open_notebook_document(params.notebook_document.uri.clone(), notebook);
 
-        if let Some(db) = session.workspace_db_for_path_mut(path.as_std_path()) {
-            // TODO(dhruvmanila): Store the `file` in `DocumentController`
-            let file = system_path_to_file(db, &path).unwrap();
-            file.sync(db);
-        }
+        let db = match session.workspace_db_for_path_mut(path.as_std_path()) {
+            Some(db) => db,
+            None => session.default_workspace_db_mut(),
+        };
+        db.apply_changes(vec![ChangeEvent::Opened(path)], None);
 
         // TODO(dhruvmanila): Publish diagnostics if the client doesn't support pull diagnostics
 

crates/red_knot_server/src/server/api/requests/diagnostic.rs

@@ -26,13 +26,11 @@ impl BackgroundDocumentRequestHandler for DocumentDiagnosticRequestHandler {
 
     fn run_with_snapshot(
         snapshot: DocumentSnapshot,
-        db: Option<RootDatabase>,
+        db: RootDatabase,
         _notifier: Notifier,
         _params: DocumentDiagnosticParams,
     ) -> Result<DocumentDiagnosticReportResult> {
-        let diagnostics = db
-            .map(|db| compute_diagnostics(&snapshot, &db))
-            .unwrap_or_default();
+        let diagnostics = compute_diagnostics(&snapshot, &db);
 
         Ok(DocumentDiagnosticReportResult::Report(
             DocumentDiagnosticReport::Full(RelatedFullDocumentDiagnosticReport {
@@ -66,11 +64,11 @@ fn to_lsp_diagnostic(message: &str) -> Diagnostic {
 
     let (range, message) = match words.as_slice() {
         [_filename, line, column, message] => {
-            let line = line.parse::<u32>().unwrap_or_default();
+            let line = line.parse::<u32>().unwrap_or_default().saturating_sub(1);
             let column = column.parse::<u32>().unwrap_or_default();
             (
                 Range::new(
-                    Position::new(line.saturating_sub(1), column.saturating_sub(1)),
+                    Position::new(line, column.saturating_sub(1)),
                     Position::new(line, column),
                 ),
                 message.trim(),

crates/red_knot_server/src/server/api/traits.rs

@@ -34,7 +34,7 @@ pub(super) trait BackgroundDocumentRequestHandler: RequestHandler {
 
     fn run_with_snapshot(
         snapshot: DocumentSnapshot,
-        db: Option<RootDatabase>,
+        db: RootDatabase,
         notifier: Notifier,
         params: <<Self as RequestHandler>::RequestType as Request>::Params,
     ) -> super::Result<<<Self as RequestHandler>::RequestType as Request>::Result>;

crates/red_knot_server/src/session.rs

@@ -82,6 +82,12 @@ impl Session {
         })
     }
 
+    // TODO(dhruvmanila): Ideally, we should have a single method for `workspace_db_for_path_mut`
+    // and `default_workspace_db_mut` but the borrow checker doesn't allow that.
+    // https://github.com/astral-sh/ruff/pull/13041#discussion_r1726725437
+
+    /// Returns a reference to the workspace [`RootDatabase`] corresponding to the given path, if
+    /// any.
     pub(crate) fn workspace_db_for_path(&self, path: impl AsRef<Path>) -> Option<&RootDatabase> {
         self.workspaces
             .range(..=path.as_ref().to_path_buf())
@@ -89,6 +95,8 @@ impl Session {
             .map(|(_, db)| db)
     }
 
+    /// Returns a mutable reference to the workspace [`RootDatabase`] corresponding to the given
+    /// path, if any.
     pub(crate) fn workspace_db_for_path_mut(
         &mut self,
         path: impl AsRef<Path>,
@@ -99,6 +107,19 @@ impl Session {
             .map(|(_, db)| db)
     }
 
+    /// Returns a reference to the default workspace [`RootDatabase`]. The default workspace is the
+    /// minimum root path in the workspace map.
+    pub(crate) fn default_workspace_db(&self) -> &RootDatabase {
+        // SAFETY: Currently, red knot only support a single workspace.
+        self.workspaces.values().next().unwrap()
+    }
+
+    /// Returns a mutable reference to the default workspace [`RootDatabase`].
+    pub(crate) fn default_workspace_db_mut(&mut self) -> &mut RootDatabase {
+        // SAFETY: Currently, red knot only support a single workspace.
+        self.workspaces.values_mut().next().unwrap()
+    }
+
     pub fn key_from_url(&self, url: Url) -> DocumentKey {
         self.index().key_from_url(url)
     }

crates/red_knot_workspace/src/db/changes.rs

@@ -72,7 +72,8 @@ impl RootDatabase {
             }
 
             match change {
-                watch::ChangeEvent::Changed { path, kind: _ } => sync_path(self, &path),
+                watch::ChangeEvent::Changed { path, kind: _ }
+                | watch::ChangeEvent::Opened(path) => sync_path(self, &path),
 
                 watch::ChangeEvent::Created { kind, path } => {
                     match kind {

crates/red_knot_workspace/src/watch.rs

@@ -20,6 +20,9 @@ mod workspace_watcher;
 /// event instead of emitting an event for each file or subdirectory in that path.
 #[derive(Debug, PartialEq, Eq)]
 pub enum ChangeEvent {
+    /// The file corresponding to the given path was opened in an editor.
+    Opened(SystemPathBuf),
+
     /// A new path was created
     Created {
         path: SystemPathBuf,
@@ -52,7 +55,8 @@ impl ChangeEvent {
 
     pub fn path(&self) -> Option<&SystemPath> {
         match self {
-            ChangeEvent::Created { path, .. }
+            ChangeEvent::Opened(path)
+            | ChangeEvent::Created { path, .. }
             | ChangeEvent::Changed { path, .. }
             | ChangeEvent::Deleted { path, .. } => Some(path),
             ChangeEvent::Rescan => None,