Don’t implicitly cancel code completion requests on document edits

As the user types, we filter the code completion results. Cancelling the completion request on every keystroke means that we will never build the initial list of completion results for this code completion session if building that list takes longer than the user's typing cadence (eg. for global completions) and we will thus not show any completions.

Author: ahoppen

Sources/SourceKitLSP/SourceKitLSPServer.swift

@@ -150,8 +150,9 @@ package actor SourceKitLSPServer {
     }
   }
 
-  /// For all currently handled text document requests a mapping from the document to the corresponding request ID.
-  private var inProgressTextDocumentRequests: [DocumentURI: Set<RequestID>] = [:]
+  /// For all currently handled text document requests a mapping from the document to the corresponding request ID and
+  /// the method of the request (ie. the value of `TextDocumentRequest.method`).
+  private var inProgressTextDocumentRequests: [DocumentURI: [(id: RequestID, requestMethod: String)]] = [:]
 
   var onExit: () -> Void
 
@@ -550,18 +551,26 @@ package actor SourceKitLSPServer {
 // MARK: - MessageHandler
 
 extension SourceKitLSPServer: QueueBasedMessageHandler {
+  private enum ImplicitTextDocumentRequestCancellationReason {
+    case documentChanged
+    case documentClosed
+  }
+
   package nonisolated func didReceive(notification: some NotificationType) {
     let textDocumentUri: DocumentURI
+    let cancellationReason: ImplicitTextDocumentRequestCancellationReason
     switch notification {
     case let params as DidChangeTextDocumentNotification:
       textDocumentUri = params.textDocument.uri
+      cancellationReason = .documentChanged
     case let params as DidCloseTextDocumentNotification:
       textDocumentUri = params.textDocument.uri
+      cancellationReason = .documentClosed
     default:
       return
     }
     textDocumentTrackingQueue.async(priority: .high) {
-      await self.cancelTextDocumentRequests(for: textDocumentUri)
+      await self.cancelTextDocumentRequests(for: textDocumentUri, reason: cancellationReason)
     }
   }
 
@@ -582,11 +591,18 @@ extension SourceKitLSPServer: QueueBasedMessageHandler {
   ///
   /// - Important: Should be invoked on `textDocumentTrackingQueue` to ensure that new text document requests are
   ///   registered before a notification that triggers cancellation might come in.
-  private func cancelTextDocumentRequests(for uri: DocumentURI) {
+  private func cancelTextDocumentRequests(for uri: DocumentURI, reason: ImplicitTextDocumentRequestCancellationReason) {
     guard self.options.cancelTextDocumentRequestsOnEditAndCloseOrDefault else {
       return
     }
-    for requestID in self.inProgressTextDocumentRequests[uri, default: []] {
+    for (requestID, requestMethod) in self.inProgressTextDocumentRequests[uri, default: []] {
+      if reason == .documentChanged && requestMethod == CompletionRequest.method {
+        // As the user types, we filter the code completion results. Cancelling the completion request on every
+        // keystroke means that we will never build the initial list of completion results for this code
+        // completion session if building that list takes longer than the user's typing cadence (eg. for global
+        // completions) and we will thus not show any completions.
+        continue
+      }
       logger.info("Implicitly cancelling request \(requestID)")
       self.messageHandlingHelper.cancelRequest(id: requestID)
     }
@@ -633,8 +649,8 @@ extension SourceKitLSPServer: QueueBasedMessageHandler {
 
   /// - Important: Should be invoked on `textDocumentTrackingQueue` to ensure that new text document requests are
   ///   registered before a notification that triggers cancellation might come in.
-  private func registerInProgressTextDocumentRequest(_ request: any TextDocumentRequest, id: RequestID) {
-    self.inProgressTextDocumentRequests[request.textDocument.uri, default: []].insert(id)
+  private func registerInProgressTextDocumentRequest<T: TextDocumentRequest>(_ request: T, id: RequestID) {
+    self.inProgressTextDocumentRequests[request.textDocument.uri, default: []].append((id: id, requestMethod: T.method))
   }
 
   package func handle<Request: RequestType>(
@@ -644,7 +660,7 @@ extension SourceKitLSPServer: QueueBasedMessageHandler {
   ) async {
     defer {
       if let request = params as? any TextDocumentRequest {
-        self.inProgressTextDocumentRequests[request.textDocument.uri, default: []].remove(id)
+        self.inProgressTextDocumentRequests[request.textDocument.uri, default: []].removeAll { $0.id == id }
       }
     }
 

Sources/SwiftExtensions/AsyncQueue.swift

@@ -82,16 +82,6 @@ package final class AsyncQueue<TaskMetadata: DependencyTracker>: Sendable {
 
   package init() {}
 
-  package func cancelTasks(where filter: (TaskMetadata) -> Bool) {
-    pendingTasks.withLock { pendingTasks in
-      for task in pendingTasks {
-        if filter(task.metadata) {
-          task.task.cancel()
-        }
-      }
-    }
-  }
-
   /// Schedule a new closure to be executed on the queue.
   ///
   /// If this is a serial queue, all previously added tasks are guaranteed to