Display traceback after failing to load cfg.

tools/run-bisect-perf-regression.py

 #!/usr/bin/env python
 # Copyright (c) 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.
 
 """Run Performance Test Bisect Tool
 
 This script is used by a trybot to run the src/tools/bisect-perf-regression.py
 script with the parameters specified in run-bisect-perf-regression.cfg. It will
 check out a copy of the depot in a subdirectory 'bisect' of the working
 directory provided, and run the bisect-perf-regression.py script there.
 
 """
 
 import imp
 import optparse
 import os
 import subprocess
 import sys
+import traceback
 
 
 def LoadConfigFile(path_to_file):
   """Attempts to load the file 'run-bisect-perf-regression.cfg' as a module
   and grab the global config dict.
 
   Args:
     path_to_file: Path to the run-bisect-perf-regression.cfg file.
 
   Returns:
     The config dict which should be formatted as follows:
     {'command': string, 'good_revision': string, 'bad_revision': string
      'metric': string}.
     Returns None on failure.
   """
   try:
     local_vars = {}
     execfile(os.path.join(path_to_file, 'run-bisect-perf-regression.cfg'),
              local_vars)
 
     return local_vars['config']
   except:
+    print
+    traceback.print_exc()
+    print
     return None
 
 
 def RunBisectionScript(config, working_directory, path_to_file, path_to_goma):
   """Attempts to execute src/tools/bisect-perf-regression.py with the parameters
   passed in.
 
   Args:
     config: A dict containing the parameters to pass to the script.
     working_directory: A working directory to provide to the
@@ skipping 89 matching lines @@
   if not opts.working_directory:
     print 'Error: missing required parameter: --working_directory'
     print
     parser.print_help()
     return 1
 
   path_to_file = os.path.abspath(os.path.dirname(sys.argv[0]))
 
   config = LoadConfigFile(path_to_file)
   if not config:
-    print 'Error: Could not load config file.'
+    print 'Error: Could not load config file. Double check your changes to '\
+          'run-bisect-perf-regression.cfg for syntax errors.'
     print
     return 1
 
   return RunBisectionScript(config, opts.working_directory, path_to_file,
                             opts.path_to_goma)
 
 
 if __name__ == '__main__':
   sys.exit(main())