restore My Documents fallback for get_home_dir on Windows

IPython/utils/path.py

@@ -201,10 +201,25 b' def get_home_dir(require_writable=False):'
         return py3compat.cast_unicode(root, fs_encoding)
     
     homedir = os.path.expanduser('~')
+    
+    if not _writable_dir(homedir) and os.name == 'nt':
+        # expanduser failed, use the registry to get the 'My Documents' folder.
+        try:
+            import _winreg as wreg
+            key = wreg.OpenKey(
+                wreg.HKEY_CURRENT_USER,
+                "Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders"
+            )
+            homedir = wreg.QueryValueEx(key,'Personal')[0]
+            key.Close()
+        except:
+            pass
+    
     if (not require_writable) or _writable_dir(homedir):
         return py3compat.cast_unicode(homedir, fs_encoding)
     else:
-        raise HomeDirError('%s is not a writable dir, set $HOME env to override' % homedir)
+        raise HomeDirError('%s is not a writable dir, '
+                'set $HOME environment variable to override' % homedir)
 
 def get_xdg_dir():
     """Return the XDG_CONFIG_HOME, if it is defined and exists, else None.

IPython/utils/tests/test_path.py

@@ -166,8 +166,40 b' def test_get_home_dir_4():'
 def test_get_home_dir_5():
     """raise HomeDirError if $HOME is specified, but not a writable dir"""
     env['HOME'] = abspath(HOME_TEST_DIR+'garbage')
+    # set os.name = posix, to prevent My Documents fallback on Windows
+    os.name = 'posix'
     nt.assert_raises(path.HomeDirError, path.get_home_dir, True)
 
+
+# Should we stub wreg fully so we can run the test on all platforms?
+@skip_if_not_win32
+@with_environment
+def test_get_home_dir_8():
+    """Using registry hack for 'My Documents', os=='nt'
+
+    HOMESHARE, HOMEDRIVE, HOMEPATH, USERPROFILE and others are missing.
+    """
+    os.name = 'nt'
+    # Remove from stub environment all keys that may be set
+    for key in ['HOME', 'HOMESHARE', 'HOMEDRIVE', 'HOMEPATH', 'USERPROFILE']:
+        env.pop(key, None)
+
+    #Stub windows registry functions
+    def OpenKey(x, y):
+        class key:
+            def Close(self):
+                pass
+        return key()
+    def QueryValueEx(x, y):
+        return [abspath(HOME_TEST_DIR)]
+
+    wreg.OpenKey = OpenKey
+    wreg.QueryValueEx = QueryValueEx
+
+    home_dir = path.get_home_dir()
+    nt.assert_equal(home_dir, abspath(HOME_TEST_DIR))
+
+
 @with_environment
 def test_get_ipython_dir_1():
     """test_get_ipython_dir_1, Testcase to see if we can call get_ipython_dir without Exceptions."""