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():
+  # Change current directory to the repo root: the rest of this script
+  # assumes it is running from the repo root.
+  os.chdir(utils.DART_DIR)

[ricow1, 2014/09/16 08:11:29]

to be nice and change back you could do:
with utils.ChangedWorkingDirectory(utils.DART_DIR):
  utils.ConfigureJava()
  ....


When you exit the with block (either finish or error) the actual running cwd
will be restored

[Nathan Collins, 2014/09/16 17:38:57]

This couldn't hurt, but the cd was happening in the beginning of 'Main', so I
expect the script would exit right before cd-ing back anway.  However, I
realized it's not so simple to fix this bug: the command line options may
include relative paths!

+
   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())