Don't warn about missing dirs in autorefresh mode

This fixes the slightly annoying behaviur in #191 but also makes
conceptual sense: in autorefresh mode files and directories can not
exist when the application starts and be added later, so it doesn't make
sense to complain about their absence on startup.

tests/test_whitenoise.py

@@ -234,6 +234,12 @@ def test_no_error_on_very_long_filename(self):
         response = self.server.get('/blah' * 1000)
         self.assertNotEqual(response.status_code, 500)
 
+    def test_warn_about_missing_directories(self):
+        # This is the one minor behavioural difference when autorefresh is
+        # enabled: we don't warn about missing directories as these can be
+        # created after the application is started
+        pass
+
     @classmethod
     def tearDownClass(cls):
         super(WhiteNoiseTest, cls).tearDownClass()

whitenoise/base.py

@@ -92,16 +92,16 @@ def add_files(self, root, prefix=None):
         root = root.rstrip(os.path.sep) + os.path.sep
         prefix = decode_if_byte_string(prefix)
         prefix = ensure_leading_trailing_slash(prefix)
-        is_directory = os.path.isdir(root)
-        if not is_directory:
-            warnings.warn(u'No directory at: {}'.format(root))
         if self.autorefresh:
             # Later calls to `add_files` overwrite earlier ones, hence we need
             # to store the list of directories in reverse order so later ones
             # match first when they're checked in "autorefresh" mode
             self.directories.insert(0, (root, prefix))
-        elif is_directory:
-            self.update_files_dictionary(root, prefix)
+        else:
+            if os.path.isdir(root):
+                self.update_files_dictionary(root, prefix)
+            else:
+                warnings.warn(u'No directory at: {}'.format(root))
 
     def update_files_dictionary(self, root, prefix):
         # Build a mapping from paths to the results of `os.stat` calls