Add code to handle errors in .gclient configuration files

gclient.py

 #!/usr/bin/python
 #
 # Copyright 2008 Google Inc.  All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
@@ skipping 922 matching lines @@
   def __init__(self, root_dir, options):
     self._root_dir = root_dir
     self._options = options
     self._config_content = None
     self._config_dict = {}
     self._deps_hooks = []
 
   def SetConfig(self, content):
     self._config_dict = {}
     self._config_content = content
-    exec(content, self._config_dict)
+    try:
+      exec(content, self._config_dict)
+    except SyntaxError, e:
+      try:
+        # Try to construct a human readable error message
+        error_message = [
+            'There is a syntax error in your configuration file.',
+            'Line #%s, character %s:' % (e.lineno, e.offset),
+            '"%s"' % re.sub(r'[\r\n]*$', '', e.text) ]
+      except:
+        # Something went wrong, re-raise the original exception
+        raise e
+      else:
+        # Raise a new exception with the human readable message:
+        raise Error('\n'.join(error_message))
 
   def SaveConfig(self):
     FileWrite(os.path.join(self._root_dir, self._options.config_filename),
               self._config_content)
 
   def _LoadConfig(self):
     client_source = FileRead(os.path.join(self._root_dir,
                                           self._options.config_filename))
     self.SetConfig(client_source)
 
@@ skipping 768 matching lines @@
 
 if "__main__" == __name__:
   try:
     result = Main(sys.argv)
   except Error, e:
     print >> sys.stderr, "Error: %s" % str(e)
     result = 1
   sys.exit(result)
 
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