use `git status` to check if it's a repo

not just checking if `.git` exists.

`.git` may be broken, or git may be unavailable.

IPython/utils/submodule.py

@@ -1,96 +1,105 b''
 """utilities for checking submodule status"""
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2013  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import subprocess
 import sys
 
 #-----------------------------------------------------------------------------
 # Globals
 #-----------------------------------------------------------------------------
 
 pjoin = os.path.join
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 def ipython_parent():
     """return IPython's parent (i.e. root if run from git)"""
     from IPython.utils.path import get_ipython_package_dir
     return os.path.abspath(os.path.dirname(get_ipython_package_dir()))
 
 def ipython_submodules(root):
     """return IPython submodules relative to root"""
     return [
         pjoin(root, 'IPython', 'html', 'static', 'components'),
     ]
 
 def is_repo(d):
     """is d a git repo?"""
-    return os.path.exists(pjoin(d, '.git'))
+    if not os.path.exists(pjoin(d, '.git')):
+        return False
+    proc = subprocess.Popen('git status',
+                            stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE,
+                            shell=True,
+                            cwd=d,
+    )
+    status, _ = proc.communicate()
+    return status == 0
 
 def check_submodule_status(root=None):
     """check submodule status
 
     Has three return values:
 
     'missing' - submodules are absent
     'unclean' - submodules have unstaged changes
     'clean' - all submodules are up to date
     """
 
     if hasattr(sys, "frozen"):
         # frozen via py2exe or similar, don't bother
         return 'clean'
 
     if not root:
         root = ipython_parent()
     
     if not is_repo(root):
         # not in git, assume clean
         return 'clean'
 
     submodules = ipython_submodules(root)
 
     for submodule in submodules:
         if not os.path.exists(submodule):
             return 'missing'
     
     # Popen can't handle unicode cwd on Windows Python 2
     if sys.platform == 'win32' and sys.version_info[0] < 3 \
         and not isinstance(root, bytes):
         root = root.encode(sys.getfilesystemencoding() or 'ascii')
     # check with git submodule status
     proc = subprocess.Popen('git submodule status',
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE,
                             shell=True,
                             cwd=root,
     )
     status, _ = proc.communicate()
     status = status.decode("ascii", "replace")
 
     for line in status.splitlines():
         if line.startswith('-'):
             return 'missing'
         elif line.startswith('+'):
             return 'unclean'
 
     return 'clean'
 
 def update_submodules(repo_dir):
     """update submodules in a repo"""
     subprocess.check_call("git submodule init", cwd=repo_dir, shell=True)
     subprocess.check_call("git submodule update --recursive", cwd=repo_dir, shell=True)