Fix index bug in readResults

R=floitsch@google.com

Review-Url: https://codereview.chromium.org/2996013002 .

tools/gardening/lib/src/bot.dart

@@ -40,14 +40,16 @@ class Bot {
     return _client.readResult(buildUri);
   }
 
+  /// Maximum number of [BuildResult]s read concurrently by [readResults].
+  static const maxParallel = 20;
+
   /// Reads the build results of all given uris.
   ///
   /// Returns a list of the results. If a uri couldn't be read, then the entry
   /// in the list is `null`.
   Future<List<BuildResult>> readResults(List<BuildUri> buildUris) async {
     var result = <BuildResult>[];
     int i = 0;
-    const maxParallel = 20;
     while (i < buildUris.length) {
       var end = i + maxParallel;
       if (end > buildUris.length) end = buildUris.length;
@@ -60,7 +62,7 @@ class Bot {
         }
         return result;
       })));
-      i = end + 1;
+      i = end;
     }
     return result;
   }

tools/gardening/lib/src/compare_failures_impl.dart

@@ -37,7 +37,11 @@ Future<Map<BuildUri, List<BuildResult>>> loadBuildResults(
   Map<BuildUri, List<BuildResult>> pastResultsMap =
       <BuildUri, List<BuildResult>>{};
   List<BuildResult> buildResults = await bot.readResults(buildUriList);
-  for (int index = 0; index < buildUriList.length; index++) {
+  if (buildResults.length != buildUriList.length) {
+    print('Result mismatch: Pulled ${buildUriList.length} uris, '
+        'received ${buildResults.length} results.');
+  }
+  for (int index = 0; index < buildResults.length; index++) {
     BuildUri buildUri = buildUriList[index];
     BuildResult buildResult = buildResults[index];
     List<BuildResult> results =

tools/gardening/test/bot_test.dart

@@ -0,0 +1,20 @@
+// 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.
+
+import 'package:expect/expect.dart';
+import 'package:gardening/src/bot.dart';
+import 'package:gardening/src/buildbot_data.dart';
+import 'package:gardening/src/buildbot_structures.dart';
+import 'test_client.dart';
+
+main() async {
+  Bot bot = new Bot.internal(new DummyClient());
+  List<BuildUri> buildUriList = buildGroups
+      .firstWhere((g) => g.groupName == 'dart2js-linux')
+      .createUris(bot.mostRecentBuildNumber);
+  Expect.isTrue(buildUriList.length > Bot.maxParallel);
+  List<BuildResult> buildResults = await bot.readResults(buildUriList);
+  Expect.equals(buildUriList.length, buildResults.length);
+  bot.close();
+}

tools/gardening/test/test_client.dart

@@ -63,3 +63,17 @@ class TestClient implements BuildbotClient {
   @override
   int get mostRecentBuildNumber => -1;
 }
+
+class DummyClient implements BuildbotClient {
+  @override
+  Future<BuildResult> readResult(BuildUri buildUri) {
+    return new Future.value(
+        new BuildResult(buildUri, 1, const [], const [], const []));
+  }
+
+  @override
+  void close() {}
+
+  @override
+  int get mostRecentBuildNumber => -1;
+}