old_contents: #!/usr/bin/env python
  # Copyright (c) 2012 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.
  
  """Prints paths between gyp targets.
  """
  
  import json
  import os
  import sys
  import time
  
  from collections import deque
  
  def usage():
    print """\
  Usage:
    tools/gyp-explain.py chrome_dll gtest#
  """
  
  
  def GetPath(graph, fro, to):
    """Given a graph in (node -> list of successor nodes) dictionary format,
    yields all paths from |fro| to |to|, starting with the shortest."""
    # Storing full paths in the queue is a bit wasteful, but good enough for this.
    q = deque([(fro, [])])
    while q:
      t, path = q.popleft()
      if t == to:
        yield path + [t]
      for d in graph[t]:
        q.append((d, path + [t]))
  
  
  def MatchNode(graph, substring):
    """Given a dictionary, returns the key that matches |substring| best. Exits
    if there's not one single best match."""
    candidates = []
    for target in graph:
      if substring in target:
        candidates.append(target)
  
    if not candidates:
      print 'No targets match "%s"' % substring
      sys.exit(1)
    if len(candidates) > 1:
      print 'More than one target matches "%s": %s' % (
          substring, ' '.join(candidates))
      sys.exit(1)
    return candidates[0]
  
  
  def Main(argv):
    if sys.platform in ['win32', 'cygwin']:
      print 'The dump_dependency_json gyp generator required for gyp-explain.py'
      print 'does not support Windows.'
      sys.exit(1)
  
    # Check that dump.json exists and that it's not too old.
    dump_json_dirty = False
    try:
      st = os.stat('dump.json')
      file_age_s = time.time() - st.st_mtime
      if file_age_s > 2 * 60 * 60:
        print 'dump.json is more than 2 hours old.'
        dump_json_dirty = True
    except OSError:
      print 'dump.json not found.'
      dump_json_dirty = True
  
    if dump_json_dirty:
      print 'Run'
      print '    GYP_GENERATORS=dump_dependency_json build/gyp_chromium'
      print 'first, then try again.'
      sys.exit(1)
  
    g = json.load(open('dump.json'))
  
    if len(argv) != 3:
      usage()
      sys.exit(1)
  
    fro = MatchNode(g, argv[1])
    to = MatchNode(g, argv[2])
  
    paths = list(GetPath(g, fro, to))
    if len(paths) > 0:
      print 'These paths lead from %s to %s:' % (fro, to)
      for path in paths:
        print ' -> '.join(path)
    else:
      print 'No paths found from %s to %s.' % (fro, to)
  
  
  if __name__ == '__main__':
    Main(sys.argv)
  
new_contents: #!/usr/bin/env python
  # Copyright (c) 2012 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.
  
  """Prints paths between gyp targets.
  """
  
  import json
  import os
  import sys
  import time
  
  from collections import deque
  
  def usage():
    print """\
  Usage:
    tools/gyp-explain.py chrome_dll# gtest#
  """
  
  
  def GetPath(graph, fro, to):
    """Given a graph in (node -> list of successor nodes) dictionary format,
    yields all paths from |fro| to |to|, starting with the shortest."""
    # Storing full paths in the queue is a bit wasteful, but good enough for this.
    q = deque([(fro, [])])
    while q:
      t, path = q.popleft()
      if t == to:
        yield path + [t]
      for d in graph[t]:
        q.append((d, path + [t]))
  
  
  def MatchNode(graph, substring):
    """Given a dictionary, returns the key that matches |substring| best. Exits
    if there's not one single best match."""
    candidates = []
    for target in graph:
      if substring in target:
        candidates.append(target)
  
    if not candidates:
      print 'No targets match "%s"' % substring
      sys.exit(1)
    if len(candidates) > 1:
      print 'More than one target matches "%s": %s' % (
          substring, ' '.join(candidates))
      sys.exit(1)
    return candidates[0]
  
  
  def Main(argv):
    # Check that dump.json exists and that it's not too old.
    dump_json_dirty = False
    try:
      st = os.stat('dump.json')
      file_age_s = time.time() - st.st_mtime
      if file_age_s > 2 * 60 * 60:
        print 'dump.json is more than 2 hours old.'
        dump_json_dirty = True
    except OSError:
      print 'dump.json not found.'
      dump_json_dirty = True
  
    if dump_json_dirty:
      print 'Run'
      print '    GYP_GENERATORS=dump_dependency_json build/gyp_chromium'
      print 'first, then try again.'
      sys.exit(1)
  
    g = json.load(open('dump.json'))
  
    if len(argv) != 3:
      usage()
      sys.exit(1)
  
    fro = MatchNode(g, argv[1])
    to = MatchNode(g, argv[2])
  
    paths = list(GetPath(g, fro, to))
    if len(paths) > 0:
      print 'These paths lead from %s to %s:' % (fro, to)
      for path in paths:
        print ' -> '.join(path)
    else:
      print 'No paths found from %s to %s.' % (fro, to)
  
  
  if __name__ == '__main__':
    Main(sys.argv)
  
subject: allow gyp-explain on Windows, and change help to work with current chrome gyp files