Expose the exceptions info in the diagnostics page.

pkg/analysis_server/lib/src/analysis_server.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:core';
 import 'dart:io' as io;
 import 'dart:math' show max;
 
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart'
     hide AnalysisOptions;
 import 'package:analysis_server/src/analysis_logger.dart';
 import 'package:analysis_server/src/channel/channel.dart';
+import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/computer/computer_highlights.dart';
 import 'package:analysis_server/src/computer/computer_highlights2.dart';
 import 'package:analysis_server/src/computer/computer_outline.dart';
 import 'package:analysis_server/src/computer/new_notifications.dart';
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/domains/analysis/navigation.dart';
 import 'package:analysis_server/src/domains/analysis/navigation_dart.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences_dart.dart';
 import 'package:analysis_server/src/ide_options.dart';
@@ skipping 229 matching lines @@
   /**
    * Return the total time the server's been alive.
    */
   Duration get uptime {
     DateTime start = new DateTime.fromMillisecondsSinceEpoch(
         performanceDuringStartup.startTime);
     return new DateTime.now().difference(start);
   }
 
   /**
+   * A [RecentBuffer] of the most recent exceptions encountered by the analysis
+   * server.
+   */
+  final RecentBuffer<ServerException> exceptions = new RecentBuffer(10);
+
+  /**
    * The class into which performance information is currently being recorded.
    * During startup, this will be the same as [performanceDuringStartup]
    * and after startup is complete, this switches to [performanceAfterStartup].
    */
   ServerPerformance _performance;
 
   /**
    * The [Completer] that completes when analysis is complete.
    */
   Completer _onAnalysisCompleteCompleter;
@@ skipping 951 matching lines @@
   void sendResponse(Response response) {
     channel.sendResponse(response);
   }
 
   /**
    * Sends a `server.error` notification.
    */
   void sendServerErrorNotification(String message, exception, stackTrace,
       {bool fatal: false}) {
     StringBuffer buffer = new StringBuffer();
-    if (exception != null) {
-      buffer.write(exception);
-    } else {
-      buffer.write('null exception');
-    }
+    buffer.write(exception ?? 'null exception');
     if (stackTrace != null) {
       buffer.writeln();
       buffer.write(stackTrace);
     } else if (exception is! CaughtException) {
-      try {
-        throw 'ignored';
-      } catch (ignored, stackTrace) {
-        buffer.writeln();
-        buffer.write(stackTrace);
-      }
+      stackTrace = StackTrace.current;
+      buffer.writeln();
+      buffer.write(stackTrace);
     }
+
     // send the notification
     channel.sendNotification(
         new ServerErrorParams(fatal, message, buffer.toString())
             .toNotification());
+
+    // remember the last few exceptions
+    if (exception is CaughtException) {
+      stackTrace ??= exception.stackTrace;
+    }
+    exceptions.add(new ServerException(message, exception, stackTrace, fatal));
   }
 
   /**
    * Send status notification to the client. The `operation` is the operation
    * being performed or `null` if analysis is complete.
    */
   void sendStatusNotification(ServerOperation operation) {
     // Only send status when subscribed.
     if (!serverServices.contains(ServerService.STATUS)) {
       return;
@@ skipping 1111 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = new PerformanceTag('serverRequests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }
+
+/**
+ * Used to record server exceptions.
+ */
+class ServerException {
+  final String message;
+  final dynamic exception;
+  final StackTrace stackTrace;
+  final bool fatal;
+
+  ServerException(this.message, this.exception, this.stackTrace, this.fatal);
+
+  @override
+  String toString() => message;
+}