Make 'tools/build.py -h' warn the user to run it from the repo root.

tools/build.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 
 import optparse
 import os
 import re
@@ skipping 493 matching lines @@
   if toolchainprefix == None:
     print "Couldn't figure out the cross-toolchain"
     return 1
   strip = toolchainprefix + '-strip'
   subprocess.call([strip, os.path.join(bin, 'dart')])
 
   return 0
 
 
 def Main():
+  # This script assumes it is running from the repo root and can
+  # silently fail when that's not true. A more user friendly option
+  # would be to make it run from anywhere. For now we just fail early
+  # and loudly.
+  if os.path.abspath(utils.DART_DIR) != os.path.abspath(os.getcwd()):

[Ivan Posva, 2014/09/17 03:48:55]

This is not entirely correct. Sometimes you need to run the build.py script from
within a subdirectory of the dart repo.

+    print 'This script must be run from the repo root!'
+    print 'Please cd into'
+    print ''
+    print '  %s' % utils.DART_DIR
+    print ''
+    print 'before running.'
+    return 1
+
   utils.ConfigureJava()
   # Parse the options.
   parser = BuildOptions()
   (options, args) = parser.parse_args()
   if not ProcessOptions(options, args):
     parser.print_help()
     return 1
   # Determine which targets to build. By default we build the "all" target.
   if len(args) == 0:
     if HOST_OS == 'macos':
@@ skipping 15 matching lines @@
           else:
             if BuildOneConfig(options, target, target_os,
                               mode, arch, cross_build) != 0:
               return 1
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(Main())