Add --dot option to gyp-explain

tools/gyp-explain.py

 #!/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#
+  tools/gyp-explain.py [--dot] 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()
@@ skipping 14 matching lines @@
   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 EscapeForDot(string):
+  suffix = '#target'
+  if string.endswith(suffix):
+    string = string[:-len(suffix)]
+  string = string.replace('\\', '\\\\')
+  return '"' + string + '"'
+
+
+def GenerateDot(fro, to, paths):
+  """Generates an input file for graphviz's dot program."""
+  prefixes = [os.path.commonprefix(path) for path in paths]
+  prefix = os.path.commonprefix(prefixes)
+  print '// Build with "dot -Tpng -ooutput.png this_file.dot"'
+  # "strict" collapses common paths.
+  print 'strict digraph {'
+  for path in paths:
+    print (' -> '.join(EscapeForDot(item[len(prefix):]) for item in path)), ';'
+  print '}'
+
+
 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:
+  if len(argv) not in (3, 4):
     usage()
     sys.exit(1)
 
+  generate_dot = argv[1] == '--dot'
+  if generate_dot:
+    argv.pop(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)
+    if generate_dot:
+      GenerateDot(fro, to, paths)
+    else:
+      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)