[ty] Add documentation for server traits

Author: dhruvmanila

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

@@ -3,7 +3,7 @@ use std::borrow::Cow;
 use lsp_types::request::DocumentDiagnosticRequest;
 use lsp_types::{
     DocumentDiagnosticParams, DocumentDiagnosticReport, DocumentDiagnosticReportResult,
-    FullDocumentDiagnosticReport, RelatedFullDocumentDiagnosticReport,
+    FullDocumentDiagnosticReport, RelatedFullDocumentDiagnosticReport, Url,
 };
 
 use crate::server::Result;
@@ -22,7 +22,7 @@ impl RequestHandler for DocumentDiagnosticRequestHandler {
 }
 
 impl BackgroundDocumentRequestHandler for DocumentDiagnosticRequestHandler {
-    fn document_url(params: &DocumentDiagnosticParams) -> Cow<lsp_types::Url> {
+    fn document_url(params: &DocumentDiagnosticParams) -> Cow<Url> {
         Cow::Borrowed(&params.text_document.uri)
     }
 

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

@@ -1,22 +1,59 @@
-//! A stateful LSP implementation that calls into the ty API.
+//! Traits for handling requests and notifications from the LSP client.
+//!
+//! This module defines the trait abstractions used by the language server to handle incoming
+//! requests and notifications from clients. It provides a type-safe way to implement LSP handlers
+//! with different execution models (synchronous or asynchronous) and automatic retry capabilities.
+//!
+//! All request and notification handlers must implement the base traits [`RequestHandler`] and
+//! [`NotificationHandler`], respectively, which associate them with specific LSP request or
+//! notification types. These base traits are then extended by more specific traits that define
+//! the execution model of the handler.
+//!
+//! The [`SyncRequestHandler`] and [`SyncNotificationHandler`] traits are for handlers that
+//! executes synchronously on the main loop, providing mutable access to the [`Session`] that
+//! contains the current state of the server. This is useful for handlers that need to modify
+//! the server state such as when the content of a file changes.
+//!
+//! The [`BackgroundDocumentRequestHandler`] and [`BackgroundDocumentNotificationHandler`] traits
+//! are for handlers that operate on a single document and can be executed on a background thread.
+//! These handlers will have access to a snapshot of the document at the time of the request or
+//! notification, allowing them to perform operations without blocking the main loop. There is also
+//! the [`BackgroundRequestHandler`] trait for handlers that operate on the entire workspace
+//! instead of a single document and can also be executed on a background thread like fetching the
+//! workspace diagnostics.
+//!
+//! The [`RetriableRequestHandler`] trait is a marker trait for handlers that can be retried if the
+//! Salsa database is modified during execution.
+//!
+//! The [`SyncNotificationHandler`] is the most common trait that would be used because most
+//! notifications are specific to a single document and require updating the server state.
+//! Similarly, the [`BackgroundDocumentRequestHandler`] is the most common request handler that
+//! would be used as most requests are document-specific and can be executed in the background.
+//!
+//! See the `./requests` and `./notifications` directories for concrete implementations of these
+//! traits in action.
+
+use std::borrow::Cow;
 
 use crate::session::client::Client;
 use crate::session::{DocumentSnapshot, Session, WorkspaceSnapshot};
 
-use lsp_types::notification::Notification as LSPNotification;
+use lsp_types::Url;
+use lsp_types::notification::Notification;
 use lsp_types::request::Request;
 use ty_project::ProjectDatabase;
 
 /// A supertrait for any server request handler.
 pub(super) trait RequestHandler {
     type RequestType: Request;
-    const METHOD: &'static str = <<Self as RequestHandler>::RequestType as Request>::METHOD;
+    const METHOD: &'static str = <<Self as RequestHandler>::RequestType>::METHOD;
 }
 
 /// A request handler that needs mutable access to the session.
-/// This will block the main message receiver loop, meaning that no
-/// incoming requests or notifications will be handled while `run` is
-/// executing. Try to avoid doing any I/O or long-running computations.
+///
+/// This will block the main message receiver loop, meaning that no incoming requests or
+/// notifications will be handled while `run` is executing. Try to avoid doing any I/O or
+/// long-running computations.
 pub(super) trait SyncRequestHandler: RequestHandler {
     fn run(
         session: &mut Session,
@@ -29,7 +66,13 @@ pub(super) trait RetriableRequestHandler: RequestHandler {
     /// Whether this request can be cancelled if the Salsa database is modified.
     const RETRY_ON_CANCELLATION: bool = false;
 
-    /// The error to return if the request was cancelled due to a modification to the Salsa database.
+    /// The error to return if the request was cancelled due to a modification to the Salsa
+    /// database.
+    ///
+    /// By default, this returns a [`ContentModified`] error to indicate that the content of a
+    /// document has changed since the request was made.
+    ///
+    /// [`ContentModified`]: lsp_server::ErrorCode::ContentModified
     fn salsa_cancellation_error() -> lsp_server::ResponseError {
         lsp_server::ResponseError {
             code: lsp_server::ErrorCode::ContentModified as i32,
@@ -43,9 +86,10 @@ pub(super) trait RetriableRequestHandler: RequestHandler {
 ///
 /// This handler is specific to requests that operate on a single document.
 pub(super) trait BackgroundDocumentRequestHandler: RetriableRequestHandler {
+    /// Returns the URL of the document that this request handler operates on.
     fn document_url(
         params: &<<Self as RequestHandler>::RequestType as Request>::Params,
-    ) -> std::borrow::Cow<lsp_types::Url>;
+    ) -> Cow<Url>;
 
     fn run_with_snapshot(
         db: &ProjectDatabase,
@@ -56,6 +100,10 @@ pub(super) trait BackgroundDocumentRequestHandler: RetriableRequestHandler {
 }
 
 /// A request handler that can be run on a background thread.
+///
+/// Unlike [`BackgroundDocumentRequestHandler`], this handler operates on the entire workspace
+/// without being tied to a specific document. It is useful for operations that require access to
+/// the entire workspace state, such as fetching workspace diagnostics.
 pub(super) trait BackgroundRequestHandler: RetriableRequestHandler {
     fn run(
         snapshot: WorkspaceSnapshot,
@@ -66,35 +114,33 @@ pub(super) trait BackgroundRequestHandler: RetriableRequestHandler {
 
 /// A supertrait for any server notification handler.
 pub(super) trait NotificationHandler {
-    type NotificationType: LSPNotification;
-    const METHOD: &'static str =
-        <<Self as NotificationHandler>::NotificationType as LSPNotification>::METHOD;
+    type NotificationType: Notification;
+    const METHOD: &'static str = <<Self as NotificationHandler>::NotificationType>::METHOD;
 }
 
 /// A notification handler that needs mutable access to the session.
-/// This will block the main message receiver loop, meaning that no
-/// incoming requests or notifications will be handled while `run` is
-/// executing. Try to avoid doing any I/O or long-running computations.
+///
+/// This will block the main message receiver loop, meaning that no incoming requests or
+/// notifications will be handled while `run` is executing. Try to avoid doing any I/O or
+/// long-running computations.
 pub(super) trait SyncNotificationHandler: NotificationHandler {
     fn run(
         session: &mut Session,
         client: &Client,
-        params: <<Self as NotificationHandler>::NotificationType as LSPNotification>::Params,
+        params: <<Self as NotificationHandler>::NotificationType as Notification>::Params,
     ) -> super::Result<()>;
 }
 
 /// A notification handler that can be run on a background thread.
 pub(super) trait BackgroundDocumentNotificationHandler: NotificationHandler {
-    /// `document_url` can be implemented automatically with
-    /// `define_document_url!(params: &<YourParameterType>)` in the trait
-    /// implementation.
+    /// Returns the URL of the document that this notification handler operates on.
     fn document_url(
-        params: &<<Self as NotificationHandler>::NotificationType as LSPNotification>::Params,
-    ) -> std::borrow::Cow<lsp_types::Url>;
+        params: &<<Self as NotificationHandler>::NotificationType as Notification>::Params,
+    ) -> Cow<Url>;
 
     fn run_with_snapshot(
         snapshot: DocumentSnapshot,
         client: &Client,
-        params: <<Self as NotificationHandler>::NotificationType as LSPNotification>::Params,
+        params: <<Self as NotificationHandler>::NotificationType as Notification>::Params,
     ) -> super::Result<()>;
 }