Add ToolchainLanguageServerCrashHandler to handle crashes

Sources/Csourcekitd/include/sourcekitd_functions.h

@@ -69,6 +69,8 @@ typedef const char *(^sourcekitd_str_from_uid_handler_t)(sourcekitd_uid_t uid);
 typedef struct {
   void (*initialize)(void);
   void (*shutdown)(void);
+  void (*set_interrupted_connection_handler)(
+      sourcekitd_interrupted_connection_handler_t handler);
 
   sourcekitd_uid_t (*uid_get_from_cstr)(const char *string);
   sourcekitd_uid_t (*uid_get_from_buf)(const char *buf, size_t length);

Sources/SourceKit/SourceKitServer.swift

@@ -191,7 +191,7 @@ public final class SourceKitServer: LanguageServer {
 
     // Start a new service.
     return orLog("failed to start language service", level: .error) {
-      guard let service = try SourceKit.languageService(for: toolchain, language, options: options, client: self) else {
+      guard let service = try SourceKit.languageService(for: toolchain, language, options: options, client: self, crashHandler: self) else {
         return nil
       }
 
@@ -258,6 +258,15 @@ extension SourceKitServer: BuildSystemDelegate {
   }
 }
 
+// MARK: - Crash Handling
+
+extension SourceKitServer: ToolchainLanguageServerCrashHandler {
+  public func handleCrash(_ languageService: ToolchainLanguageServer, _ debugInfo: String) {
+    // TODO: Chose to re-initialize the given languageService or not, log the crash, and
+    // possibly notify the user.
+  }
+}
+
 // MARK: - Request and notification handling
 
 extension SourceKitServer {
@@ -702,17 +711,22 @@ public func languageService(
   for toolchain: Toolchain,
   _ language: Language,
   options: SourceKitServer.Options,
-  client: MessageHandler) throws -> ToolchainLanguageServer?
+  client: MessageHandler,
+  crashHandler: ToolchainLanguageServerCrashHandler) throws -> ToolchainLanguageServer?
 {
   switch language {
 
   case .c, .cpp, .objective_c, .objective_cpp:
     guard toolchain.clangd != nil else { return nil }
-    return try makeJSONRPCClangServer(client: client, toolchain: toolchain, buildSettings: (client as? SourceKitServer)?.workspace?.buildSettings, clangdOptions: options.clangdOptions)
+    let service = try makeJSONRPCClangServer(client: client, toolchain: toolchain, buildSettings: (client as? SourceKitServer)?.workspace?.buildSettings, clangdOptions: options.clangdOptions)
+    service.crashHandler = crashHandler
+    return service
 
   case .swift:
     guard let sourcekitd = toolchain.sourcekitd else { return nil }
-    return try makeLocalSwiftServer(client: client, sourcekitd: sourcekitd, buildSettings: (client as? SourceKitServer)?.workspace?.buildSettings, clientCapabilities: (client as? SourceKitServer)?.workspace?.clientCapabilities)
+    let service = try makeLocalSwiftServer(client: client, sourcekitd: sourcekitd, buildSettings: (client as? SourceKitServer)?.workspace?.buildSettings, clientCapabilities: (client as? SourceKitServer)?.workspace?.clientCapabilities)
+    service.crashHandler = crashHandler
+    return service
 
   default:
     return nil

Sources/SourceKit/ToolchainLanguageServer.swift

@@ -18,6 +18,8 @@ public protocol ToolchainLanguageServer: AnyObject {
 
   // MARK: Lifetime
 
+  var crashHandler: ToolchainLanguageServerCrashHandler? {get set}
+
   func initializeSync(_ initialize: InitializeRequest) throws -> InitializeResult
   func clientInitialized(_ initialized: InitializedNotification)
 

Sources/SourceKit/ToolchainLanguageServerCrashHandler.swift

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 Foundation
+
+public protocol ToolchainLanguageServerCrashHandler: AnyObject {
+  /// Called when the given `ToolchainLanguageServer` has crashed and needs to be reinitialized with information
+  /// such as the list of open documents.
+  ///
+  /// The handler may or may not chose to re-open previously open documents and/or
+  /// stop sending any further requests to the given `ToolchainLanguageServer`.
+  func handleCrash(_ languageService: ToolchainLanguageServer, _ debugInfo: String)
+}

Sources/SourceKit/clangd/ClangLanguageServer.swift

@@ -19,10 +19,11 @@ import Foundation
 
 /// A thin wrapper over a connection to a clangd server providing build setting handling.
 final class ClangLanguageServerShim: ToolchainLanguageServer {
-
   /// The server's request queue, used to serialize requests and responses to `clangd`.
   public let queue: DispatchQueue = DispatchQueue(label: "clangd-language-server-queue", qos: .userInitiated)
 
+  public weak var crashHandler: ToolchainLanguageServerCrashHandler? = nil
+
   let clangd: Connection
 
   var capabilities: ServerCapabilities? = nil
@@ -215,6 +216,7 @@ func makeJSONRPCClangServer(
   process.standardOutput = serverToClient
   process.standardInput = clientToServer
   process.terminationHandler = { process in
+    // TODO: Inform the crash handler and provide a way to restart clangd.
     log("clangd exited: \(process.terminationReason) \(process.terminationStatus)")
     connection.close()
   }

Sources/SourceKit/sourcekitd/SwiftLanguageServer.swift

@@ -23,6 +23,8 @@ public final class SwiftLanguageServer: ToolchainLanguageServer {
   /// The server's request queue, used to serialize requests and responses to `sourcekitd`.
   public let queue: DispatchQueue = DispatchQueue(label: "swift-language-server-queue", qos: .userInitiated)
 
+  public weak var crashHandler: ToolchainLanguageServerCrashHandler? = nil
+
   let client: Connection
 
   let sourcekitd: SwiftSourceKitFramework
@@ -129,6 +131,11 @@ extension SwiftLanguageServer {
       }
     }
 
+    api.set_interrupted_connection_handler { [weak self] in
+      guard let self = self else { return }
+      self.crashHandler?.handleCrash(self, "sourcekitd connection interrupted")
+    }
+
     return InitializeResult(capabilities: ServerCapabilities(
       textDocumentSync: TextDocumentSyncOptions(
         openClose: true,
@@ -162,6 +169,7 @@ extension SwiftLanguageServer {
 
   func shutdown(_ request: Request<Shutdown>) {
     api.set_notification_handler(nil)
+    api.set_interrupted_connection_handler(nil)
   }
 
   func exit(_ notification: Notification<Exit>) {

Sources/SourceKit/sourcekitd/SwiftSourceKitFramework.swift

@@ -69,6 +69,7 @@ final class SwiftSourceKitFramework {
 
     api.initialize = try dlsym_required(dylib, symbol: "sourcekitd_initialize")
     api.shutdown = try dlsym_required(dylib, symbol: "sourcekitd_shutdown")
+    api.set_interrupted_connection_handler = try dlsym_required(dylib, symbol: "sourcekitd_set_interrupted_connection_handler")
     api.uid_get_from_cstr = try dlsym_required(dylib, symbol: "sourcekitd_uid_get_from_cstr")
     api.uid_get_from_buf = try dlsym_required(dylib, symbol: "sourcekitd_uid_get_from_buf")
     api.uid_get_length = try dlsym_required(dylib, symbol: "sourcekitd_uid_get_length")