Add default tar file name for source tarball

tools/create_debian_packages.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2014, 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.
 #
 
 # Script to build a Debian packages from a Dart tarball. The script
 # will build a source package and a 32-bit (i386) and 64-bit (amd64)
 # binary packages.
 
 import optparse
+import platform
 import sys
 import tarfile
 import subprocess
 import utils
-
+import os
 from os.path import join, exists, abspath
 from shutil import copyfile
 
 HOST_OS = utils.GuessOS()
 HOST_CPUS = utils.GuessCpus()
 DART_DIR = abspath(join(__file__, '..', '..'))
 
 def BuildOptions():
   result = optparse.OptionParser()
   result.add_option("--tar_filename",
                     default=None,
                     help="The tar file to build from.")
   result.add_option("--out_dir",
                     default=None,
                     help="Where to put the packages.")
- 
+
   return result
 
 def RunBuildPackage(opt, cwd):
   cmd = ['dpkg-buildpackage', '-j%d' % HOST_CPUS]
   cmd.extend(opt)
   process = subprocess.Popen(cmd,
                              stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                              cwd=cwd)
   (stdout, stderr) = process.communicate()
   if process.returncode != 0:
@@ skipping 34 matching lines @@
       '%s-1.dsc' % debbase,
       '%s.orig.tar.gz' % debbase,
       '%s-1.debian.tar.gz' % debbase
     ]
     i386_package = [
       '%s-1_i386.deb' % debbase
     ]
     amd64_package = [
       '%s-1_amd64.deb' % debbase
     ]
+
     for name in source_package:
       copyfile(join(temp_dir, name), join(out_dir, name))
     for name in i386_package:
       copyfile(join(temp_dir, name), join(out_dir, name))
     for name in amd64_package:
       copyfile(join(temp_dir, name), join(out_dir, name))
 
 def Main():
   if HOST_OS != 'linux':
     print 'Debian build only supported on linux'
     return -1
 
   options, args = BuildOptions().parse_args()
   out_dir = options.out_dir
   tar_filename = options.tar_filename
   if not options.out_dir:
     out_dir = join(DART_DIR, utils.GetBuildDir(HOST_OS, HOST_OS))
-  if not options.tar_filename:
-    raise Exception('Please specify the input filename.')
-  BuildDebianPackage(options.tar_filename, options.out_dir)
+
+  if not tar_filename:
+    tar_filename = join(DART_DIR,
+                        utils.GetBuildDir(HOST_OS, HOST_OS),
+                        'dart-%s.tar.gz' % utils.GetVersion())
+
+  BuildDebianPackage(tar_filename, out_dir)
 
 if __name__ == '__main__':
   sys.exit(Main())