Update top_dir with git repo root just when cwd locate in a git repo.

gclient_utils.py

 # Copyright (c) 2012 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.
 
 """Generic utils."""
 
 import codecs
 import cStringIO
 import datetime
 import logging
@@ skipping 644 matching lines @@
   """Returns 'mac', 'win', or 'linux', matching the current platform."""
   if sys.platform.startswith(('cygwin', 'win')):
     return 'win'
   elif sys.platform.startswith('linux'):
     return 'linux'
   elif sys.platform == 'darwin':
     return 'mac'
   raise Error('Unknown platform: ' + sys.platform)
 
 
 def GetPrimarySolutionPath():

[agable, 2016/08/03 16:39:50]

The only things which call this function are GetBuildtoolsPath and
dart_format.py
The only things which call GetBuildtoolsPath are GetBuildtoolsPlatformBinaryPath
and clang_format.py
The only things which call GetBuildtoolsPlatformBinaryPath are clang_format.py
and gn.py

This logic should not exist in gclient; it is very specific to the fact that
chromium/src.git contains a directory named 'buildtools'. Those tools
(dart_format, clang_format, and gn) should determine that they are being invoked
from chromium/src.git and locate buildtools themselves, not rely on heuristics
built in to a generic repository synchronization tool.

   """Returns the full path to the primary solution. (gclient_root + src)"""
 
   gclient_root = FindGclientRoot(os.getcwd())
   if not gclient_root:

[agable, 2016/08/03 16:39:50]

Under what circumstances do we actually enter this branch? Why are you calling
gclient without a .gclient file at all?

[hanpfei, 2016/08/04 01:35:57]

I didn't call gclient. I just called gn.
I want to use net module of chromium and gn + ninja flow in our projects. So I
create an environment that just include net module and the components it depends
on. Then I found this issue.

     # Some projects might not use .gclient. Try to see whether we're in a git
     # checkout.
     top_dir = [os.getcwd()]
     def filter_fn(line):
-      top_dir[0] = os.path.normpath(line.rstrip('\n'))
+      repo_root_path = os.path.normpath(line.rstrip('\n'))
+      if os.path.exists(repo_root_path):
+        top_dir[0] = repo_root_path
     try:
       CheckCallAndFilter(["git", "rev-parse", "--show-toplevel"],
                          print_stdout=False, filter_fn=filter_fn)
     except Exception:
       pass
     top_dir = top_dir[0]
     if os.path.exists(os.path.join(top_dir, 'buildtools')):
       return top_dir
     return None
 
@@ skipping 538 matching lines @@
     # Just incase we have some ~/blah paths.
     target = os.path.abspath(os.path.expanduser(target))
     if os.path.isfile(target) and os.access(target, os.X_OK):
       return target
     if sys.platform.startswith('win'):
       for suffix in ('.bat', '.cmd', '.exe'):
         alt_target = target + suffix
         if os.path.isfile(alt_target) and os.access(alt_target, os.X_OK):
           return alt_target
   return None