Properly handling non-ascii filenames in hashing function

Added fs_to_text() function that ensures a filename is always unicode (python
2) or str (python 3).

os.walk() gets such a unicode dirname as start point, so that it tries to do
its best on python2. The resulting filenames are converted to unicode to make
really sure that the join() doesn't fail with a decoding error.

The input to the hash function is encoded, as it gives an ascii encoding error
otherwise on python 2.

src/zc/buildout/buildout.py

@@ -44,6 +44,19 @@ import tempfile
 import zc.buildout
 import zc.buildout.download
 
+PY3 = sys.version_info[0] == 3
+if PY3:
+    text_type = str
+else:
+    text_type = unicode
+
+def fs_to_text(fs_name):
+    """Return filesystem name always as unicode(2)/str(3)."""
+    if not isinstance(fs_name, text_type):
+        fs_name = fs_name.decode(sys.getfilesystemencoding(),
+                                 'surrogateescape')
+    return fs_name
+
 def _print_options(sep=' ', end='\n', file=None):
     return sep, end, file
 
@@ -1589,21 +1602,26 @@ def _open(base, filename, seen, dl_options, override, downloaded):
     return result
 
 
-ignore_directories = '.svn', 'CVS', '__pycache__'
+ignore_directories = u'.svn', u'CVS', u'__pycache__'
 _dir_hashes = {}
 def _dir_hash(dir):
+    dir = fs_to_text(dir)
+    # ^^^ fs_to_text ensures unicode, needed for os.walk() on python2 to work
+    # well with non-ascii filenames.
     dir_hash = _dir_hashes.get(dir, None)
     if dir_hash is not None:
         return dir_hash
     hash = md5()
     for (dirpath, dirnames, filenames) in os.walk(dir):
+        dirnames = [fs_to_text(dirname) for dirname in dirnames]
+        filenames = [fs_to_text(filename) for filename in filenames]
         dirnames[:] = sorted(n for n in dirnames if n not in ignore_directories)
         filenames[:] = sorted(f for f in filenames
                               if (not (f.endswith('pyc') or f.endswith('pyo'))
                                   and os.path.exists(os.path.join(dirpath, f)))
                               )
-        hash.update(' '.join(dirnames).encode())
-        hash.update(' '.join(filenames).encode())
+        hash.update(' '.join(dirnames).encode('utf-8'))
+        hash.update(' '.join(filenames).encode('utf-8'))
         for name in filenames:
             path = os.path.join(dirpath, name)
             if name == 'entry_points.txt':