Alert on zero online devices when last devices file is missing or empty.

build/android/device_status_check.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2012 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.
 
 """A class to keep track of devices across builds and report state."""
 import logging
 import optparse
 import os
@@ skipping 89 matching lines @@
     if not os.path.exists(out_dir):
       os.makedirs(out_dir)
     with open(path, 'w') as f:
       # Write devices currently visible plus devices previously seen.
       f.write('\n'.join(set(device_list)))
 
   last_devices_path = os.path.join(out_dir, '.last_devices')
   last_devices = ReadDeviceList('.last_devices')
   missing_devs = list(set(last_devices) - set(adb_online_devs))
 
-  WriteDeviceList('.last_devices', (adb_online_devs + last_devices))
+  all_known_devices = list(set(adb_online_devs) | set(last_devices))
+  WriteDeviceList('.last_devices', all_known_devices)
   WriteDeviceList('.last_missing', missing_devs)
 
+  if not all_known_devices:
+    # This can happen if for some reason the .last_devices file is not
+    # present or if it was empty.
+    return ['No online devices. Have any devices been plugged in?']
   if missing_devs:
     devices_missing_msg = '%d devices not detected.' % len(missing_devs)
     buildbot_report.PrintSummaryText(devices_missing_msg)
 
     # TODO(navabi): Debug by printing both output from GetCmdOutput and
     # GetAttachedDevices to compare results.
     return ['Current online devices: %s' % adb_online_devs,
             '%s are no longer visible. Were they removed?\n' % missing_devs,
             'SHERIFF: See go/chrome_device_monitor',
             'Cache file: %s\n\n' % last_devices_path,
@@ skipping 60 matching lines @@
     msg = '\n'.join(err_msg)
     print msg
     SendDeviceStatusAlert(msg)
 
   if not devices:
     return 1
 
 
 if __name__ == '__main__':
   sys.exit(main())