Automatically discover the mojoconfig file.

mojo/devtools/common/devtoolslib/paths.py

 # Copyright 2015 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.
 
 """Supports inferring locations of files in default checkout layouts.
 
 These functions allow devtools scripts to work out-of-the-box with regular Mojo
 checkouts.
 """
 
 import collections
 import os.path
 import sys
 
 
-def find_ancestor_with(relpath):
+def find_ancestor_with(relpath, start_path=None):
   """Returns the lowest ancestor of this file that contains |relpath|."""
-  cur_dir_path = os.path.abspath(os.path.dirname(__file__))
+  cur_dir_path = start_path or os.path.abspath(os.path.dirname(__file__))
   while True:
     if os.path.exists(os.path.join(cur_dir_path, relpath)):
       return cur_dir_path
 
     next_dir_path = os.path.dirname(cur_dir_path)
     if next_dir_path != cur_dir_path:
       cur_dir_path = next_dir_path
     else:
       return None
 
 
+def find_within_ancestors(target_relpath, start_path=None):
+  """Returns the absolute path to |target_relpath| in the lowest ancestor of
+  |start_path| that contains it.
+  """
+  ancestor = find_ancestor_with(target_relpath, start_path)
+  if not ancestor:
+    return None
+  return os.path.join(ancestor, target_relpath)
+
+
 def infer_paths(is_android, is_debug, target_cpu):
   """Infers the locations of select build output artifacts in a regular
   Chromium-like checkout. This should grow thinner or disappear as we introduce
   per-repo config files, see https://github.com/domokit/devtools/issues/28.
 
   Returns:
     Defaultdict with the inferred paths.
   """
   build_dir = (('android_' if is_android else '') +
                (target_cpu + '_' if target_cpu else '') +
@@ skipping 37 matching lines @@
   # Rare case, it's not even in PATH, look upward up to root.
   root_dir = os.path.dirname(os.path.abspath(__file__))
   previous_dir = os.path.abspath(__file__)
   while root_dir and root_dir != previous_dir:
     i = os.path.join(root_dir, 'depot_tools')
     if _is_real_depot_tools(i):
       return i
     previous_dir = root_dir
     root_dir = os.path.dirname(root_dir)
   return None