Report all swarming and isolate fatal errors in a consistent way.

utils/tools.py

 # Copyright 2013 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.
 
 """Various utility functions and classes not specific to any single area."""
 
 import logging
 import logging.handlers
 import optparse
 import os
 import sys
 import time
+import traceback
 
 
 class OptionParserWithLogging(optparse.OptionParser):
   """Adds --verbose option."""
 
   # Set to True to enable --log-file options.
   enable_log_file = True
 
   def __init__(self, verbose=0, log_file=None, **kwargs):
     kwargs.setdefault('description', sys.modules['__main__'].__doc__)
@@ skipping 82 matching lines @@
 
 
 def fix_python_path(cmd):
   """Returns the fixed command line to call the right python executable."""
   out = cmd[:]
   if out[0] == 'python':
     out[0] = sys.executable
   elif out[0].endswith('.py'):
     out.insert(0, sys.executable)
   return out
+
+
+def report_error(error):
+  """Prints a error to stderr, wrapping it into header and footer.
+
+  That way errors can be reliably extracted from logs. It's indented to be used
+  only for non recoverable unexpected errors. Is should NOT be used for input
+  validation, command line argument errors, etc.
+
+  Arguments:
+    error: error message string (possibly multiple lines) or an instance of
+           Exception subclass. In the later case a traceback will also be
+           reported. It's assumed that |report_error| is called in an except
+           block where |error| was caught.
+  """
+  print >> sys.stderr, '[------ Swarming Error ------]'
+  print >> sys.stderr, str(error)
+  if isinstance(error, Exception):
+    print >> sys.stderr, traceback.format_exc(),
+  print >> sys.stderr, '[----------------------------]'