new_contents: #!/usr/bin/python
  
  # Copyright (c) 2011 Google Inc. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  """Using the JSON dumped by the dump-dependency-json generator,
  generate input suitable for graphviz to render a dependency graph of
  targets."""
  
  import collections
  import json
  import sys
  
  
  def ParseTarget(target):
    target, _, suffix = target.partition('#')
    filename, _, target = target.partition(':')
    return filename, target, suffix
  
  
  def LoadEdges(filename, targets):
    """Load the edges map from the dump file, and filter it to only
    show targets in |targets| and their depedendents."""
  
    file = open('dump.json')
    edges = json.load(file)
    file.close()
  
    # Copy out only the edges we're interested in from the full edge list.
    target_edges = {}
    to_visit = targets[:]
    while to_visit:
      src = to_visit.pop()
      if src in target_edges:
        continue
      target_edges[src] = edges[src]
      to_visit.extend(edges[src])
  
    return target_edges
  
  
  def WriteGraph(edges):
    """Print a graphviz graph to stdout.
    |edges| is a map of target to a list of other targets it depends on."""
  
    # Bucket targets by file.
    files = collections.defaultdict(list)
    for src, dst in edges.items():
      build_file, target_name, toolset = ParseTarget(src)
      files[build_file].append(src)
  
    print 'digraph D {'
    print '  fontsize=8'  # Used by subgraphs.
    print '  node [fontsize=8]'
  
    # Output nodes by file.  We must first write out each node within
    # its file grouping before writing out any edges that may refer
    # to those nodes.
    for filename, targets in files.items():
      if len(targets) == 1:
        # If there's only one node for this file, simplify
        # the display by making it a box without an internal node.
        target = targets[0]
        build_file, target_name, toolset = ParseTarget(target)
        print '  "%s" [shape=box, label="%s\\n%s"]' % (target, filename,
                                                       target_name)
      else:
        # Group multiple nodes together in a subgraph.
        print '  subgraph "cluster_%s" {' % filename
        print '    label = "%s"' % filename
        for target in targets:
          build_file, target_name, toolset = ParseTarget(target)
          print '    "%s" [label="%s"]' % (target, target_name)
        print '  }'
  
    # Now that we've placed all the nodes within subgraphs, output all
    # the edges between nodes.
    for src, dsts in edges.items():
      for dst in dsts:
        print '  "%s" -> "%s"' % (src, dst)
  
    print '}'
  
  
  if __name__ == '__main__':
    if len(sys.argv) < 2:
      print >>sys.stderr, __doc__
      print >>sys.stderr
      print >>sys.stderr, 'usage: %s target1 target2...' % (sys.argv[0])
      sys.exit(1)
  
    edges = LoadEdges('dump.json', sys.argv[1:])
  
    WriteGraph(edges)
  
subject: Check in a tool that dumps graphviz output.