use_inherit_from.py

import json
import posixpath
import os

checkout = '/home/nodir/chromium/src'

with open('/home/nodir/tmp/dirmd/computed.json') as f:
  computed = json.load(f)

with open('/home/nodir/tmp/dirmd/reduced.json') as f:
  reduced = json.load(f)

# Simplify dicts
for md in (computed, reduced):
  for d in md['dirs'].itervalues():
    if 'monorail' in d and 'component' in d['monorail']:
      d['component'] = d['monorail']['component']

for root, dirs, files in os.walk(checkout):
  rel = os.path.relpath(root, checkout)
  if 'DIR_METADATA' not in files or 'OWNERS' not in files or (rel.startswith('third_party/blink') or rel.startswith('third_party/')):
    continue

  inherit_from = ''
  with open(os.path.join(root, 'OWNERS')) as f:
    for line in f:
      line = line.strip()
      if line.startswith('file://') and line.endswith('/OWNERS') and line != 'file://OWNERS':
        inherit_from = line[5:-7]
        break
  if not inherit_from or inherit_from == posixpath.dirname(rel):
    continue

  current = computed['dirs'].get(rel, {})
  own = reduced['dirs'].get(rel, {})
  inheritable = computed['dirs'].get(inherit_from[2:], {})

  gain = []
  loss = []
  change = []
  for key in ('component', 'teamEmail', 'os'):
    if key in current and key not in own and key not in inheritable:
      loss.append(key)
    elif key in current and key in inheritable and inheritable[key] != current[key]:
      change.append(key)
    elif key in inheritable and key not in current:
      gain.append(key)
  if loss or change or not gain:
    continue

  meta_file = os.path.join(root, 'DIR_METADATA')
  with open(meta_file, 'r+') as f:
    lines = list(f)
    f.seek(0)

    while lines and (lines[0].startswith('#') or lines[0] == '\n'):
      f.write(lines[0])
      lines.pop(0)

    f.write('inherit_from: "%s"\n' % inherit_from)

    for line in lines:
      f.write(line)

  print 'updated inheritance'
  print '  parent: %s' % inherit_from
  print '  child:  //%s' % rel
  for key in gain:
    print '  gain:   %s: %r -> %r' % (key, current.get(key), inheritable[key])