Use timeout to read most recent build from http

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';
 
@@ skipping 46 matching lines @@
     } else {
       nonEmptySummaries.add(summary);
     }
   });
   StringBuffer sb = new StringBuffer();
   if (nonEmptySummaries.isEmpty) {
     if (emptySummaries.isNotEmpty) {
       if (LOG || emptySummaries.length < 3) {
         if (emptySummaries.length == 1) {
           sb.writeln('No errors found for build bot:');
-          sb.write(emptySummaries.single.buildUri);
+          sb.write(emptySummaries.single.name);
         } else {
           sb.writeln('No errors found for any of these build bots:');
           for (Summary summary in emptySummaries) {
-            sb.writeln('${summary.buildUri}');
+            sb.writeln('${summary.name}');
           }
         }
       } else {
         sb.write('No errors found for any of the '
             '${emptySummaries.length} bots.');
       }
     } else {
       sb.write('No build bot results found for args: ${args}');
     }
   } else {
     for (Summary summary in nonEmptySummaries) {
       summary.printOn(sb);
     }
     if (emptySummaries.isNotEmpty) {
       if (LOG || emptySummaries.length < 3) {
         sb.writeln('No errors found for the remaining build bots:');
         for (Summary summary in emptySummaries) {
-          sb.writeln('${summary.buildUri}');
+          sb.writeln('${summary.name}');
         }
       } else {
         sb.write(
             'No errors found for the ${emptySummaries.length} remaining bots.');
       }
     }
   }
   print(sb);
 }
 
 /// Creates a [BuildResult] for [buildUri] and, if it contains failures, the
 /// [BuildResult]s for the previous [runCount] builds.
 Future<List<BuildResult>> readBuildResults(
     BuildbotClient client, BuildUri buildUri, int runCount) async {
   List<BuildResult> summaries = <BuildResult>[];
   BuildResult summary = await client.readResult(buildUri);
+  if (summary == null) {
+    print('No result found for $buildUri');
+    return summaries;
+  }
   summaries.add(summary);
   if (summary.hasFailures) {
     for (int i = 0; i < runCount; i++) {
       buildUri = summary.buildUri.prev();
       summary = await client.readResult(buildUri);
       summaries.add(summary);
     }
   }
   return summaries;
 }
@@ skipping 22 matching lines @@
       Set<String> stepNames = new Set<String>();
       for (BuildResult result in results) {
         for (Timing timing in result.timings) {
           Map<int, Map<String, Timing>> builds = map.putIfAbsent(
               timing.step.id, () => <int, Map<String, Timing>>{});
           stepNames.add(timing.step.stepName);
           builds.putIfAbsent(timing.uri.buildNumber, () => <String, Timing>{})[
               timing.step.stepName] = timing;
         }
       }
-      sb.write('Timeouts for ${buildUri} :\n');
+      sb.write('Timeouts for ${name} :\n');
       map.forEach(
           (TestConfiguration id, Map<int, Map<String, Timing>> timings) {
         if (!timeoutIds.contains(id)) return;
         sb.write('$id\n');
         sb.write(
             '${' ' * 8} ${stepNames.map((t) => padRight(t, 14)).join(' ')}\n');
         for (BuildResult result in results) {
           int buildNumber = result.buildUri.buildNumber;
           Map<String, Timing> steps = timings[buildNumber] ?? const {};
           sb.write(padRight(' ${buildNumber}: ', 8));
@@ skipping 12 matching lines @@
     }
     if (errorIds.isNotEmpty) {
       Map<TestConfiguration, Map<int, TestFailure>> map =
           <TestConfiguration, Map<int, TestFailure>>{};
       for (BuildResult result in results) {
         for (TestFailure failure in result.errors) {
           map.putIfAbsent(failure.id, () => <int, TestFailure>{})[
               failure.uri.buildNumber] = failure;
         }
       }
-      sb.write('Errors for ${buildUri} :\n');
+      sb.write('Errors for ${name} :\n');
       // TODO(johnniwinther): Improve comparison of non-timeouts.
       map.forEach((TestConfiguration id, Map<int, TestFailure> failures) {
         if (!errorIds.contains(id)) return;
         sb.write('$id\n');
         for (BuildResult result in results) {
           int buildNumber = result.buildUri.buildNumber;
           TestFailure failure = failures[buildNumber];
           sb.write(padRight(' ${buildNumber}: ', 8));
           if (failure != null) {
             sb.write(padRight(failure.expected, 10));
             sb.write(' / ');
             sb.write(padRight(failure.actual, 10));
           } else {
             sb.write(' ' * 10);
             sb.write(' / ');
             sb.write(padRight('-- OK --', 10));
           }
           sb.write('\n');
         }
         sb.write('\n');
       });
     }
     if (timeoutIds.isEmpty && errorIds.isEmpty) {
-      sb.write('No errors found for ${buildUri}');
+      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();
 }