Adjusted compare-failures to report logdog URLs: Use a regular one!

tools/gardening/lib/src/compare_failures_impl.dart

 // Copyright (c) 2017, 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.
 
 /// Compares the test log of a build step with previous builds.
 ///
 /// Use this to detect flakiness of failures, especially timeouts.
 
 import 'dart:async';
+import 'dart:io';
 
 import 'package:gardening/src/bot.dart';
 import 'package:gardening/src/buildbot_structures.dart';
 import 'package:gardening/src/buildbot_data.dart';
 import 'package:gardening/src/util.dart';
 
 Future mainInternal(Bot bot, List<String> args, {int runCount: 10}) async {
   printBuildResultsSummary(
       await loadBuildResults(bot, args, runCount: runCount), args);
 }
 
+RegExp logdogUrlRegexp =
+    new RegExp(r'https://luci-logdog.appspot.com/.*client.dart');
+
 /// Loads [BuildResult]s for the [runCount] last builds for the build(s) in
 /// [args]. [args] can be a list of [BuildGroup] names or a list of log uris.
 Future<Map<BuildUri, List<BuildResult>>> loadBuildResults(
     Bot bot, List<String> args,
     {int runCount: 10}) async {
   List<BuildUri> buildUriList = <BuildUri>[];
+  for (String arg in args) {
+    if (logdogUrlRegexp.hasMatch(arg)) {
+      print('Encountered a logdog URI ("${arg.substring(0,40)}...").');
+      print('Please use the regular log URI, even with --logdog.');
+      exit(-1);
+    }
+  }
   for (BuildGroup buildGroup in buildGroups) {
     if (args.contains(buildGroup.groupName)) {
       buildUriList.addAll(buildGroup.createUris(bot.mostRecentBuildNumber));
     }
   }
   if (buildUriList.isEmpty) {
     for (String url in args) {
       buildUriList.add(new BuildUri.fromUrl(url));
     }
   }
@@ skipping 84 matching lines @@
 }
 
 class Summary {
   final BuildUri buildUri;
   final List<BuildResult> results;
   final Set<TestConfiguration> timeoutIds = new Set<TestConfiguration>();
   final Set<TestConfiguration> errorIds = new Set<TestConfiguration>();
 
   Summary(this.buildUri, this.results) {
     for (BuildResult result in results) {
+      if (result == null) continue;
       timeoutIds
           .addAll(result.timeouts.map((TestFailure failure) => failure.id));
       errorIds.addAll(result.errors.map((TestFailure failure) => failure.id));
     }
   }
 
   bool get isEmpty => timeoutIds.isEmpty && errorIds.isEmpty;
 
   /// Generate a summary of the timeouts and other failures in [results].
   void printOn(StringBuffer sb) {
@@ skipping 70 matching lines @@
       sb.write('No errors found for ${name}');
     }
   }
 
   String get name => results.isNotEmpty
       // Use the first result as name since it most likely has an absolute build
       // number.
       ? results.first.buildUri.toString()
       : buildUri.toString();
 }