[recipes.py] upgrade recipes.py to allow recipe_engine override

BUG=662654
TBR=nodir@chromium.org

Change-Id: Ifbce962d4968af9871ee62862b485dc1cc06cc22
Reviewed-on: https://chromium-review.googlesource.com/445044Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

recipes.py

@@ -26,6 +26,7 @@ RECIPES_CFG = os.path.join('infra', 'config', 'recipes.cfg')
 
 BOOTSTRAP_VERSION = 1
 
+import argparse
 import ast
 import logging
 import random
@@ -103,15 +104,38 @@ def _subprocess_call(argv, **kwargs):
   logging.info('Running %r', argv)
   return subprocess.call(argv, **kwargs)
 
+
 def _subprocess_check_call(argv, **kwargs):
   logging.info('Running %r', argv)
   subprocess.check_call(argv, **kwargs)
 
 
+def find_engine_override(argv):
+  """Since the bootstrap process attempts to defer all logic to the recipes-py
+  repo, we need to be aware if the user is overriding the recipe_engine
+  dependency. This looks for and returns the overridden recipe_engine path, if
+  any, or None if the user didn't override it."""
+  PREFIX = 'recipe_engine='
+
+  p = argparse.ArgumentParser()
+  p.add_argument('-O', '--project-override', action='append')
+  args, _ = p.parse_known_args(argv)
+  for override in args.project_override or ():
+    if override.startswith(PREFIX):
+      return override[len(PREFIX):]
+  return None
+
+
 def main():
   if '--verbose' in sys.argv:
     logging.getLogger().setLevel(logging.INFO)
 
+  if REPO_ROOT is None or RECIPES_CFG is None:
+    logging.error(
+      'In order to use this script, please copy it to your repo and '
+      'replace the REPO_ROOT and RECIPES_CFG values with approprite paths.')
+    sys.exit(1)
+
   if sys.platform.startswith(('win', 'cygwin')):
     git = 'git.bat'
   else:
@@ -135,31 +159,32 @@ def main():
   recipes_path = os.path.join(repo_root,
       get_unique(protobuf['recipes_path']).replace('/', os.path.sep))
   deps_path = os.path.join(recipes_path, '.recipe_deps')
-  engine_path = os.path.join(deps_path, 'recipe_engine')
-
-  # Ensure that we have the recipe engine cloned.
-  def ensure_engine():
-    if not os.path.exists(deps_path):
-      os.makedirs(deps_path)
-    if not os.path.exists(engine_path):
-      _subprocess_check_call([git, 'clone', engine_url, engine_path])
-
-    needs_fetch = _subprocess_call(
-        [git, 'rev-parse', '--verify', '%s^{commit}' % engine_revision],
-        cwd=engine_path, stdout=open(os.devnull, 'w'))
-    if needs_fetch:
-      _subprocess_check_call([git, 'fetch'], cwd=engine_path)
-    _subprocess_check_call(
-        [git, 'checkout', '--quiet', engine_revision], cwd=engine_path)
-
-  try:
-    ensure_engine()
-  except subprocess.CalledProcessError:
-    logging.exception('ensure_engine failed')
-
-    # Retry errors.
-    time.sleep(random.uniform(2,5))
-    ensure_engine()
+  engine_path = find_engine_override(sys.argv[1:])
+  if not engine_path:
+    # Ensure that we have the recipe engine cloned.
+    engine_path = os.path.join(deps_path, 'recipe_engine')
+    def ensure_engine():
+      if not os.path.exists(deps_path):
+        os.makedirs(deps_path)
+      if not os.path.exists(engine_path):
+        _subprocess_check_call([git, 'clone', engine_url, engine_path])
+
+      needs_fetch = _subprocess_call(
+          [git, 'rev-parse', '--verify', '%s^{commit}' % engine_revision],
+          cwd=engine_path, stdout=open(os.devnull, 'w'))
+      if needs_fetch:
+        _subprocess_check_call([git, 'fetch'], cwd=engine_path)
+      _subprocess_check_call(
+          [git, 'checkout', '--quiet', engine_revision], cwd=engine_path)
+
+    try:
+      ensure_engine()
+    except subprocess.CalledProcessError:
+      logging.exception('ensure_engine failed')
+
+      # Retry errors.
+      time.sleep(random.uniform(2,5))
+      ensure_engine()
 
   args = ['--package', recipes_cfg_path] + sys.argv[1:]
   return _subprocess_call([