[Findit] Report the error from the last flake swarming task that failed in master_flake_analysis.py

appengine/findit/waterfall/flake/recursive_flake_pipeline.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from datetime import timedelta
 import logging
 import random
 import textwrap
 
 from common import appengine_util
@@ skipping 384 matching lines @@
     # Get MasterFlakeAnalysis success list corresponding to parameters.
     master_flake_analysis = MasterFlakeAnalysis.GetVersion(
         master_name, builder_name, master_build_number, step_name, test_name,
         version=version_number)
 
     flake_swarming_task = FlakeSwarmingTask.Get(
         master_name, builder_name, run_build_number, step_name, test_name)
 
     # Don't call another pipeline if we fail.
     if flake_swarming_task.status == analysis_status.ERROR:
-      # TODO(lijeffrey): Implement more detailed error detection and reporting,
-      # such as timeouts, dead bots, etc.
+      # Report the last flake swarming task's error that it encountered.
       # TODO(lijeffrey): Another neighboring swarming task may be needed in this
       # one's place instead of failing altogether.
-      error = {
+      error = flake_swarming_task.error or {
           'error': 'Swarming task failed',
-          'message': 'Swarming task failed'
+          'message': 'The last swarming task did not complete as expected'
       }
+
       _UpdateAnalysisStatusUponCompletion(
           master_flake_analysis, analysis_status.ERROR, error)
       return
 
     # Figure out what build_number to trigger a swarming rerun on next, if any.
     if (flakiness_algorithm_results_dict['stabled_out'] and
         flakiness_algorithm_results_dict['flaked_out']):
       next_run = sequential_next_run(
           master_flake_analysis, flakiness_algorithm_results_dict)
     else:
@@ skipping 13 matching lines @@
         master_name, builder_name, next_run, step_name, test_name,
         version_number, master_build_number,
         flakiness_algorithm_results_dict=flakiness_algorithm_results_dict,
         manually_triggered=manually_triggered,
         use_nearby_neighbor=use_nearby_neighbor,
         step_size=(run_build_number - next_run))
     pipeline_job.target = appengine_util.GetTargetNameForModule(
         constants.WATERFALL_BACKEND)
     pipeline_job.StartOffPSTPeakHours(
         queue_name=self.queue_name or constants.DEFAULT_QUEUE)