Add a small tool to answer questions like "Why does target A depend on target B".

tools/gyp-explain.py

Index: tools/gyp-explain.py
diff --git a/tools/gyp-explain.py b/tools/gyp-explain.py
new file mode 100755
index 0000000000000000000000000000000000000000..4def5a17f3e57a566d8362520ecc199dc417674a
--- /dev/null
+++ b/tools/gyp-explain.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python
+

[M-A Ruel, 2011/11/23 20:06:30]

Copyright

[Nico, 2011/11/23 20:12:07]

Done.

+"""Prints paths between gyp targets.
+"""
+
+import json
+import os
+import sys
+import time
+
+from collections import deque
+
+def usage():
+  print """\
+Usage:
+  tools/gyp-explain.sh chrome_dll gtest#

[viettrungluu, 2011/11/23 20:19:51]

Drive-by: ".sh"?

It might be more helpful to put:

Usage:
  ... <from_target> <to_target>

Example:
  ... chrome_dll gtest

[Nico, 2011/11/23 20:22:58]

Done.
Not done.

+"""
+
+def GetPath(graph, fro, to, get_all=False):

[viettrungluu, 2011/11/23 20:19:51]

Is get_all even necessary, given that you're returning a generator? 

[Nico, 2011/11/23 20:22:58]

Oh, good point. Removed.

+  """Given a graph in (node -> list of successor nodes) dictionary format,
+  yields either the shortest path from |fro| to |to|, or if |get_all| is True,
+  all paths from |fro| to |to|."""
+  # Storing full paths in the queue is a bit wasteful, but good enough for this.
+  q = deque([(fro, [])])
+  while len(q) > 0:
+    t, path = q.popleft()
+    if t == to:
+      yield path + [t]
+      if not get_all:
+        break
+    for d in g[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 g:
+    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]
+
+
+if __name__ == '__main__':

[M-A Ruel, 2011/11/23 20:06:30]

Use a main()

[Nico, 2011/11/23 20:12:07]

Done.

+  # 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 IOError:
+    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(sys.argv) != 3:
+    usage()
+    sys.exit(1)
+
+  fro = MatchNode(g, sys.argv[1])
+  to = MatchNode(g, sys.argv[2])
+
+  paths = list(GetPath(g, fro, to, get_all=True))
+  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)