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..84212f5befe6de5ce9a2939c769130bed0a49a68
--- /dev/null
+++ b/tools/gyp-explain.py
@@ -0,0 +1,95 @@
+#!/usr/bin/env python
+

[M-A Ruel, 2011/11/23 20:28:05]

Most script don't put an empty line here, in fact I removed it everywhere since
it was the minority.

[Nico, 2011/11/23 20:33:01]

Done.

[Mark Mentovai, 2011/11/23 21:01:23]

I actually prefer the empty line because it lets the boilerplate lice stand off
on its own.

Let’s bikeshed.

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

[M-A Ruel, 2011/11/23 20:28:05]

Why not run it automatically? It'd be more user friendly.

Note that when I run that, I get:
KeyError: 'Undefined variable RULE_INPUT_DIRNAME in chrome/chrome.gyp while
loading dependencies of chrome/browser/sync/tools/sync_tools.gyp while loading
dependencies of build/all.gyp while trying to load build/all.gyp'

[Nico, 2011/11/23 20:33:01]

I disagree.
Yeah, dump_dependency_json used to be broken everywhere except linux. I fixed
that yesterday, but I haven't rolled gyp to pick that up in chromium yet.

[M-A Ruel, 2011/11/23 20:35:57]

Ah, why?

[Nico, 2011/11/23 20:37:30]

No particular reason. I'll roll it now.

+    print 'first, then try again.'
+    sys.exit(1)

[M-A Ruel, 2011/11/23 20:28:05]

I highly prefer to return 1 and have
  sys.exit(Main(sys.argv))
as the last script line.

[Nico, 2011/11/23 20:33:01]

Yeah, me too, but I already sys.exit from MatchNode(). Doing It Right increases
the line count considerably, and all that check in clean up already almost
doubled its line count.

+
+  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, 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)

[M-A Ruel, 2011/11/23 20:28:05]

return 1 so this can be used as a test?

[Nico, 2011/11/23 20:33:01]

Can be added once something needs it :-)

+
+
+if __name__ == '__main__':
+  Main(sys.argv)