Start migration of the communication between SourceKit-LSP and build systems to happen via the Build Server Protocol (BSP)

Package.swift

@@ -254,6 +254,7 @@ let package = Package(
       dependencies: [
         "CAtomics",
         "LanguageServerProtocol",
+        "LanguageServerProtocolJSONRPC",
         "SKLogging",
         "SwiftExtensions",
         .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),

Sources/BuildServerProtocol/BuildTargets.swift

@@ -211,44 +211,3 @@ public struct OutputsItem: Codable, Hashable, Sendable {
   /// The output paths for sources that belong to this build target.
   public var outputPaths: [URI]
 }
-
-/// The build target changed notification is sent from the server to the client
-/// to signal a change in a build target. The server communicates during the
-/// initialize handshake whether this method is supported or not.
-public struct BuildTargetsChangedNotification: NotificationType {
-  public static let method: String = "buildTarget/didChange"
-
-  public var changes: [BuildTargetEvent]
-
-  public init(changes: [BuildTargetEvent]) {
-    self.changes = changes
-  }
-}
-
-public struct BuildTargetEvent: Codable, Hashable, Sendable {
-  /// The identifier for the changed build target.
-  public var target: BuildTargetIdentifier
-
-  /// The kind of change for this build target.
-  public var kind: BuildTargetEventKind?
-
-  /// Any additional metadata about what information changed.
-  public var data: LSPAny?
-
-  public init(target: BuildTargetIdentifier, kind: BuildTargetEventKind?, data: LSPAny?) {
-    self.target = target
-    self.kind = kind
-    self.data = data
-  }
-}
-
-public enum BuildTargetEventKind: Int, Codable, Hashable, Sendable {
-  /// The build target is new.
-  case created = 1
-
-  /// The build target has changed.
-  case changed = 2
-
-  /// The build target has been deleted.
-  case deleted = 3
-}

Sources/BuildServerProtocol/CMakeLists.txt

@@ -1,7 +1,10 @@
 add_library(BuildServerProtocol STATIC
   BuildTargets.swift
+  DidChangeBuildTargetNotification.swift
+  DidChangeWatchedFilesNotification.swift
   FileOptions.swift
   InitializeBuild.swift
+  InverseSourcesRequest.swift
   Messages.swift
   RegisterForChangeNotifications.swift
   ShutdownBuild.swift)

Sources/BuildServerProtocol/DidChangeBuildTargetNotification.swift

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import LanguageServerProtocol
+
+/// The build target changed notification is sent from the server to the client
+/// to signal a change in a build target. The server communicates during the
+/// initialize handshake whether this method is supported or not.
+public struct DidChangeBuildTargetNotification: NotificationType, Equatable {
+  public static let method: String = "buildTarget/didChange"
+
+  /// **(BSP Extension)**
+  /// `changes` can be `nil` to indicate that all targets might have changed.
+  public var changes: [BuildTargetEvent]?
+
+  public init(changes: [BuildTargetEvent]?) {
+    self.changes = changes
+  }
+}
+
+public struct BuildTargetEvent: Codable, Hashable, Sendable {
+  /// The identifier for the changed build target.
+  public var target: BuildTargetIdentifier
+
+  /// The kind of change for this build target.
+  public var kind: BuildTargetEventKind?
+
+  /// Kind of data to expect in the `data` field. If this field is not set, the kind of data is not specified.
+  public var dataKind: String?
+
+  /// Any additional metadata about what information changed.
+  public var data: LSPAny?
+
+  public init(target: BuildTargetIdentifier, kind: BuildTargetEventKind?, dataKind: String?, data: LSPAny?) {
+    self.target = target
+    self.kind = kind
+    self.dataKind = dataKind
+    self.data = data
+  }
+}
+
+public enum BuildTargetEventKind: Int, Codable, Hashable, Sendable {
+  /// The build target is new.
+  case created = 1
+
+  /// The build target has changed.
+  case changed = 2
+
+  /// The build target has been deleted.
+  case deleted = 3
+}

Sources/BuildServerProtocol/DidChangeWatchedFilesNotification.swift

@@ -0,0 +1,16 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import LanguageServerProtocol
+
+/// Notification sent from SourceKit-LSP to the build system to indicate that files within the project have been modified.
+public typealias DidChangeWatchedFilesNotification = LanguageServerProtocol.DidChangeWatchedFilesNotification

Sources/BuildServerProtocol/InverseSourcesRequest.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import LanguageServerProtocol
+
+public struct TextDocumentIdentifier: Codable, Sendable, Hashable {
+  /// The text document's URI.
+  public var uri: URI
+
+  public init(uri: URI) {
+    self.uri = uri
+  }
+}
+
+/// The inverse sources request is sent from the client to the server to query for the list of build targets containing
+/// a text document. The server communicates during the initialize handshake whether this method is supported or not.
+/// This request can be viewed as the inverse of buildTarget/sources, except it only works for text documents and not
+/// directories.
+public struct InverseSourcesRequest: RequestType, Hashable {
+  public static let method: String = "buildTarget/inverseSources"
+  public typealias Response = InverseSourcesResponse
+
+  public var textDocument: TextDocumentIdentifier
+
+  public init(textDocument: TextDocumentIdentifier) {
+    self.textDocument = textDocument
+  }
+}
+
+public struct InverseSourcesResponse: ResponseType, Hashable {
+  public var targets: [BuildTargetIdentifier]
+
+  public init(targets: [BuildTargetIdentifier]) {
+    self.targets = targets
+  }
+}

Sources/BuildServerProtocol/Messages.swift

@@ -12,17 +12,18 @@
 import LanguageServerProtocol
 
 fileprivate let requestTypes: [_RequestType.Type] = [
-  BuildTargets.self,
   BuildTargetOutputPaths.self,
+  BuildTargets.self,
   BuildTargetSources.self,
   InitializeBuild.self,
+  InverseSourcesRequest.self,
   RegisterForChanges.self,
   ShutdownBuild.self,
   SourceKitOptions.self,
 ]
 
 fileprivate let notificationTypes: [NotificationType.Type] = [
-  BuildTargetsChangedNotification.self,
+  DidChangeBuildTargetNotification.self,
   ExitBuildNotification.self,
   FileOptionsChangedNotification.self,
   InitializedBuildNotification.self,

Sources/BuildSystemIntegration/BuildServerBuildSystem.swift

@@ -74,6 +74,12 @@ package actor BuildServerBuildSystem: MessageHandler {
     self.delegate = delegate
   }
 
+  package weak var messageHandler: BuiltInBuildSystemMessageHandler?
+
+  package func setMessageHandler(_ messageHandler: any BuiltInBuildSystemMessageHandler) {
+    self.messageHandler = messageHandler
+  }
+
   /// The build settings that have been received from the build server.
   private var buildSettings: [DocumentURI: FileBuildSettings] = [:]
 
@@ -194,7 +200,7 @@ package actor BuildServerBuildSystem: MessageHandler {
       """
     )
     bspMessageHandlingQueue.async {
-      if let params = params as? BuildTargetsChangedNotification {
+      if let params = params as? DidChangeBuildTargetNotification {
         await self.handleBuildTargetsChanged(params)
       } else if let params = params as? FileOptionsChangedNotification {
         await self.handleFileOptionsChanged(params)
@@ -219,10 +225,8 @@ package actor BuildServerBuildSystem: MessageHandler {
     reply(.failure(ResponseError.methodNotFound(R.method)))
   }
 
-  func handleBuildTargetsChanged(
-    _ notification: BuildTargetsChangedNotification
-  ) async {
-    await self.delegate?.buildTargetsChanged(notification.changes)
+  func handleBuildTargetsChanged(_ notification: DidChangeBuildTargetNotification) async {
+    await self.messageHandler?.sendNotificationToSourceKitLSP(notification)
   }
 
   func handleFileOptionsChanged(
@@ -254,7 +258,7 @@ private func readReponseDataKey(data: LSPAny?, key: String) -> String? {
   return nil
 }
 
-extension BuildServerBuildSystem: BuildSystem {
+extension BuildServerBuildSystem: BuiltInBuildSystem {
   package nonisolated var supportsPreparation: Bool { false }
 
   /// The build settings for the given file.
@@ -263,7 +267,7 @@ extension BuildServerBuildSystem: BuildSystem {
   /// server yet or if no build settings are available for this file.
   package func buildSettings(
     for document: DocumentURI,
-    in target: ConfiguredTarget,
+    in target: BuildTargetIdentifier,
     language: Language
   ) async -> FileBuildSettings? {
     return buildSettings[document]
@@ -277,24 +281,24 @@ extension BuildServerBuildSystem: BuildSystem {
     return nil
   }
 
-  package func configuredTargets(for document: DocumentURI) async -> [ConfiguredTarget] {
-    return [ConfiguredTarget(targetID: "dummy", runDestinationID: "dummy")]
+  package func inverseSources(_ request: InverseSourcesRequest) -> InverseSourcesResponse {
+    return InverseSourcesResponse(targets: [BuildTargetIdentifier.dummy])
   }
 
   package func scheduleBuildGraphGeneration() {}
 
   package func waitForUpToDateBuildGraph() async {}
 
-  package func topologicalSort(of targets: [ConfiguredTarget]) async -> [ConfiguredTarget]? {
+  package func topologicalSort(of targets: [BuildTargetIdentifier]) async -> [BuildTargetIdentifier]? {
     return nil
   }
 
-  package func targets(dependingOn targets: [ConfiguredTarget]) -> [ConfiguredTarget]? {
+  package func targets(dependingOn targets: [BuildTargetIdentifier]) -> [BuildTargetIdentifier]? {
     return nil
   }
 
   package func prepare(
-    targets: [ConfiguredTarget],
+    targets: [BuildTargetIdentifier],
     logMessageToIndexLog: @Sendable (_ taskID: IndexTaskID, _ message: String) -> Void
   ) async throws {
     throw PrepareNotSupportedError()
@@ -326,7 +330,7 @@ extension BuildServerBuildSystem: BuildSystem {
     }
   }
 
-  package func filesDidChange(_ events: [FileEvent]) {}
+  package func didChangeWatchedFiles(notification: BuildServerProtocol.DidChangeWatchedFilesNotification) {}
 
   package func fileHandlingCapability(for uri: DocumentURI) -> FileHandlingCapability {
     guard