Add a BuildSystemDelegate which supports notifications for build settings changes

Introduce a `BuildSystemDelegate` to handle notifications from the build system

* `SourceKitServer` is the main delegate to process these notifications
* Currently limited to changes in `FileBuildSettings`
* Delegate informs the `BuildSystem` of files to watch via `registerChangeWatching(for: URL)` and `unregisterChangeWatching(for: URL)`
* In the future we could have more integration for handling changes in dependencies

Handling changes in `FileBuildSettings`

* `SourceKitServer` sends notifications to the internal LSPs informing them of any opened documents that have changes in their compiler flags
    * For clangd, we send a notification to update the compilation database
    * For SourceKit/sourcekitd we must close and reopen the file to force a new AST with the new compiler flags

Author: DavidGoldman

Sources/LanguageServerProtocol/WorkspaceSettings.swift

@@ -16,6 +16,7 @@
 public enum WorkspaceSettingsChange: Codable, Hashable {
 
   case clangd(ClangWorkspaceSettings)
+  case documentUpdated(DocumentUpdatedBuildSettings)
   case unknown
 
   public init(from decoder: Decoder) throws {
@@ -24,6 +25,8 @@ public enum WorkspaceSettingsChange: Codable, Hashable {
     // it will rectify this issue.
     if let settings = try? ClangWorkspaceSettings(from: decoder) {
       self = .clangd(settings)
+    } else if let settings = try? DocumentUpdatedBuildSettings(from: decoder) {
+      self = .documentUpdated(settings)
     } else {
       self = .unknown
     }
@@ -33,6 +36,8 @@ public enum WorkspaceSettingsChange: Codable, Hashable {
     switch self {
     case .clangd(let settings):
       try settings.encode(to: encoder)
+    case .documentUpdated(let settings):
+      try settings.encode(to: encoder)
     case .unknown:
       break // Nothing to do.
     }
@@ -74,3 +79,17 @@ public struct ClangCompileCommand: Codable, Hashable {
     self.workingDirectory = workingDirectory
   }
 }
+
+/// Workspace settings for a document that has updated build settings.
+public struct DocumentUpdatedBuildSettings: Codable, Hashable {
+  /// The url of the document that has updated.
+  public var url: URL
+
+   /// The language of the document that has updated.
+  public var language: Language
+
+   public init(url: URL, language: Language) {
+    self.url = url
+    self.language = language
+  }
+}

Sources/SKCore/BuildServerBuildSystem.swift

@@ -30,6 +30,9 @@ public final class BuildServerBuildSystem {
   var buildServer: Connection?
   public private(set) var indexStorePath: AbsolutePath?
 
+  /// Delegate to handle any build system events.
+  public weak var delegate: BuildSystemDelegate? = nil
+
   public init(projectRoot: AbsolutePath, buildFolder: AbsolutePath?, fileSystem: FileSystem = localFileSystem) throws {
     let configPath = projectRoot.appending(component: "buildServer.json")
     let config = try loadBuildServerConfig(path: configPath, fileSystem: fileSystem)
@@ -116,6 +119,19 @@ final class BuildServerHandler: LanguageServerEndpoint {
 
 extension BuildServerBuildSystem: BuildSystem {
 
+  /// Register the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func registerForChangeNotifications(for url: LanguageServerProtocol.URL) {
+    // TODO: Implement via BSP extensions.
+  }
+
+  /// Unregister the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func unregisterForChangeNotifications(for url: LanguageServerProtocol.URL) {
+    // TODO: Implement via BSP extensions.
+  }
+
+
   public var indexDatabasePath: AbsolutePath? {
     return buildFolder?.appending(components: "index", "db")
   }

Sources/SKCore/BuildSystem.swift

@@ -15,13 +15,13 @@ import TSCBasic
 
 /// Provider of FileBuildSettings and other build-related information.
 ///
-/// The primary role of the build system is to answer queries for FileBuildSettings and (TODO) to
-/// notify clients when they change. The BuildSystem is also the source of related informatino,
-/// such as where the index datastore is located.
+/// The primary role of the build system is to answer queries for FileBuildSettings and to notify
+/// its delegate when they change. The BuildSystem is also the source of related information, such
+/// as where the index datastore is located.
 ///
 /// For example, a SwiftPMWorkspace provides compiler arguments for the files contained in a
 /// SwiftPM package root directory.
-public protocol BuildSystem {
+public protocol BuildSystem: AnyObject {
 
   /// The path to the raw index store data, if any.
   var indexStorePath: AbsolutePath? { get }
@@ -35,5 +35,14 @@ public protocol BuildSystem {
   /// Returns the toolchain to use to compile this file
   func toolchain(for: URL, _ language: Language) -> Toolchain?
 
-  // TODO: notifications when settings change.
+  /// Delegate to handle any build system events such as file build settings changing.
+  var delegate: BuildSystemDelegate? { get set }
+
+  /// Register the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  func registerForChangeNotifications(for: URL)
+
+  /// Unregister the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  func unregisterForChangeNotifications(for: URL)
 }

Sources/SKCore/BuildSystemDelegate.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 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
+import TSCBasic
+
+/// Handles  build system events, such as file build settings changes.
+public protocol BuildSystemDelegate: AnyObject {
+
+  /// Notify the delegate that the given files' build settings have changed.
+  ///
+  /// The callee should request new build settings for any of the given files that they are interested in.
+  func fileBuildSettingsChanged(_ changedFiles: Set<URL>)
+}

Sources/SKCore/BuildSystemList.swift

@@ -16,6 +16,12 @@ import LanguageServerProtocol
 /// Provides build settings from a list of build systems in priority order.
 public final class BuildSystemList {
 
+  /// Delegate to handle any build system events.
+  public var delegate: BuildSystemDelegate? {
+    get { return providers.first?.delegate }
+    set { providers.first?.delegate = newValue }
+  }
+
   /// The build systems to try (in order).
   public var providers: [BuildSystem] = [
     FallbackBuildSystem()
@@ -25,7 +31,6 @@ public final class BuildSystemList {
 }
 
 extension BuildSystemList: BuildSystem {
-
   public var indexStorePath: AbsolutePath? { return providers.first?.indexStorePath }
 
   public var indexDatabasePath: AbsolutePath? { return providers.first?.indexDatabasePath }
@@ -39,6 +44,20 @@ extension BuildSystemList: BuildSystem {
     return nil
   }
 
+  /// Register the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func registerForChangeNotifications(for url: URL) {
+    // Only register with the primary build system, since we only use its delegate.
+    providers.first?.registerForChangeNotifications(for: url)
+  }
+
+  /// Unregister the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func unregisterForChangeNotifications(for url: URL) {
+    // Only unregister with the primary build system, since we only use its delegate.
+    providers.first?.unregisterForChangeNotifications(for: url)
+  }
+
   public func toolchain(for url: URL, _ language: Language) -> Toolchain? {
     return providers.first?.toolchain(for: url, language)
   }

Sources/SKCore/CompilationDatabaseBuildSystem.swift

@@ -23,6 +23,9 @@ public final class CompilationDatabaseBuildSystem {
   /// The compilation database.
   var compdb: CompilationDatabase? = nil
 
+  /// Delegate to handle any build system events.
+  public weak var delegate: BuildSystemDelegate? = nil
+
   let fileSystem: FileSystem
 
   public init(projectRoot: AbsolutePath? = nil, fileSystem: FileSystem = localFileSystem) {
@@ -50,6 +53,12 @@ extension CompilationDatabaseBuildSystem: BuildSystem {
 
   public func toolchain(for: URL, _ language: Language) -> Toolchain? { return nil }
 
+  /// We don't support change watching.
+  public func registerForChangeNotifications(for: URL) {}
+
+  /// We don't support change watching.
+  public func unregisterForChangeNotifications(for: URL) {}
+
   func database(for url: URL) -> CompilationDatabase? {
     if let path = try? AbsolutePath(validating: url.path) {
       return database(for: path)

Sources/SKCore/FallbackBuildSystem.swift

@@ -31,6 +31,9 @@ public final class FallbackBuildSystem: BuildSystem {
     return nil
   }()
 
+  /// Delegate to handle any build system events.
+  public weak var delegate: BuildSystemDelegate? = nil
+
   public var indexStorePath: AbsolutePath? { return nil }
 
   public var indexDatabasePath: AbsolutePath? { return nil }
@@ -50,6 +53,12 @@ public final class FallbackBuildSystem: BuildSystem {
     }
   }
 
+  /// We don't support change watching.
+  public func registerForChangeNotifications(for: URL) {}
+
+  /// We don't support change watching.
+  public func unregisterForChangeNotifications(for: URL) {}
+
   public func toolchain(for: URL, _ language: Language) -> Toolchain? { return nil }
 
   func settingsSwift(_ path: AbsolutePath) -> FileBuildSettings {

Sources/SKCore/FileBuildSettings.swift

@@ -14,7 +14,7 @@
 ///
 /// Encapsulates all the settings needed to compile a single file, including the compiler arguments
 /// and working directory. FileBuildSettings are typically the result of a BuildSystem query.
-public struct FileBuildSettings {
+public struct FileBuildSettings: Equatable {
 
   /// The compiler arguments to use for this file.
   public var compilerArguments: [String]

Sources/SKSwiftPMWorkspace/SwiftPMWorkspace.swift

@@ -37,6 +37,9 @@ public final class SwiftPMWorkspace {
     case cannotDetermineHostToolchain
   }
 
+  /// Delegate to handle any build system events.
+  public weak var delegate: BuildSystemDelegate? = nil
+
   let workspacePath: AbsolutePath
   let packageRoot: AbsolutePath
   var packageGraph: PackageGraph
@@ -218,6 +221,18 @@ extension SwiftPMWorkspace: BuildSystem {
     return nil
   }
 
+  /// Register the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func registerForChangeNotifications(for url: LanguageServerProtocol.URL) {
+    // TODO: Support for change detection (via file watching)
+  }
+
+  /// Unregister the given file for build-system level change notifications, such as command
+  /// line flag changes, dependency changes, etc.
+  public func unregisterForChangeNotifications(for url: LanguageServerProtocol.URL) {
+    // TODO: Support for change detection (via file watching)
+  }
+
   /// Returns the resolved target description for the given file, if one is known.
   func targetDescription(for file: AbsolutePath) -> TargetBuildDescription? {
     if let td = fileToTarget[file] {

Sources/SourceKit/DocumentManager.swift

@@ -61,6 +61,13 @@ public final class DocumentManager {
 
   var documents: [URL: Document] = [:]
 
+  /// All currently opened documents.
+  public var openDocuments: Set<URL> {
+    return queue.sync {
+      return Set(documents.keys)
+    }
+  }
+
   /// Opens a new document with the given content and metadata.
   ///
   /// - returns: The initial contents of the file.

Sources/SourceKit/SourceKitServer.swift

@@ -216,6 +216,32 @@ public final class SourceKitServer: LanguageServer {
   }
 }
 
+// MARK: - Build System Delegate
+
+extension SourceKitServer: BuildSystemDelegate {
+  public func fileBuildSettingsChanged(_ changedFiles: Set<URL>) {
+    guard let workspace = self.workspace else {
+      return
+    }
+    let documentManager = workspace.documentManager
+    let openDocuments = documentManager.openDocuments
+    for url in changedFiles {
+      guard openDocuments.contains(url) else {
+        continue
+      }
+
+      log("Build settings changed for opened file \(url)")
+      if let snapshot = documentManager.latestSnapshot(url),
+         let service = languageService(for: url, snapshot.document.language, in: workspace) {
+        service.send(
+          DidChangeConfiguration(settings:
+            .documentUpdated(
+              DocumentUpdatedBuildSettings(url: url, language: snapshot.document.language))))
+      }
+    }
+  }
+}
+
 // MARK: - Request and notification handling
 
 extension SourceKitServer {
@@ -259,6 +285,9 @@ extension SourceKitServer {
       )
     }
 
+    assert(self.workspace != nil)
+    self.workspace?.buildSettings.delegate = self
+
     req.reply(InitializeResult(capabilities: ServerCapabilities(
       textDocumentSync: TextDocumentSyncOptions(
         openClose: true,
@@ -311,15 +340,21 @@ extension SourceKitServer {
   func openDocument(_ note: Notification<DidOpenTextDocument>, workspace: Workspace) {
     workspace.documentManager.open(note)
 
-    if let service = languageService(for: note.params.textDocument.url, note.params.textDocument.language, in: workspace) {
+    let textDocument = note.params.textDocument
+    workspace.buildSettings.registerForChangeNotifications(for: textDocument.url)
+
+    if let service = languageService(for: textDocument.url, textDocument.language, in: workspace) {
       service.send(note.params)
     }
   }
 
   func closeDocument(_ note: Notification<DidCloseTextDocument>, workspace: Workspace) {
     workspace.documentManager.close(note)
 
-    if let service = workspace.documentService[note.params.textDocument.url] {
+    let url = note.params.textDocument.url
+    workspace.buildSettings.unregisterForChangeNotifications(for: url)
+
+    if let service = workspace.documentService[url] {
       service.send(note.params)
     }
   }

Sources/SourceKit/clangd/ClangLanguageServer.swift

@@ -29,8 +29,8 @@ final class ClangLanguageServerShim: LanguageServer {
   let clang: AbsolutePath?
 
   /// Creates a language server for the given client using the sourcekitd dylib at the specified path.
-  public init(client: Connection, clangd: Connection, buildSystem: BuildSystem, clang: AbsolutePath?) throws {
-
+  public init(client: Connection, clangd: Connection, buildSystem: BuildSystem,
+              clang: AbsolutePath?) throws {
     self.clangd = clangd
     self.buildSystem = buildSystem
     self.clang = clang
@@ -39,6 +39,7 @@ final class ClangLanguageServerShim: LanguageServer {
 
   public override func _registerBuiltinHandlers() {
     _register(ClangLanguageServerShim.initialize)
+    _register(ClangLanguageServerShim.didChangeConfiguration)
     _register(ClangLanguageServerShim.openDocument)
     _register(ClangLanguageServerShim.foldingRange)
   }
@@ -97,9 +98,29 @@ extension ClangLanguageServerShim {
     }
   }
 
+  // MARK: - Workspace
+
+  func didChangeConfiguration(_ note: Notification<DidChangeConfiguration>) {
+    switch note.params.settings {
+    case .clangd:
+      break
+    case .documentUpdated(let settings):
+      updateDocumentSettings(url: settings.url, language: settings.language)
+    case .unknown:
+      break
+    }
+  }
+
+  // MARK: - Text synchronization
+
   func openDocument(_ note: Notification<DidOpenTextDocument>) {
-    let url = note.params.textDocument.url
-    let settings = buildSystem.settings(for: url, note.params.textDocument.language)
+    let textDocument = note.params.textDocument
+    updateDocumentSettings(url: textDocument.url, language: textDocument.language)
+    clangd.send(note.params)
+  }
+
+  private func updateDocumentSettings(url: URL, language: Language) {
+    let settings = buildSystem.settings(for: url, language)
 
     logAsync(level: settings == nil ? .warning : .debug) { _ in
       let settingsStr = settings == nil ? "nil" : settings!.compilerArguments.description
@@ -111,8 +132,6 @@ extension ClangLanguageServerShim {
         ClangWorkspaceSettings(
           compilationDatabaseChanges: [url.path: ClangCompileCommand(settings, clang: clang)]))))
     }
-
-    clangd.send(note.params)
   }
 
   func foldingRange(_ req: Request<FoldingRangeRequest>) {