Fix multistring flags default handling (#890489)

With its 'append' action, optparse appends values to the supplied
default value. This leaves the user with no way of overriding the
default value. If you want to support overriding, you need to manually
handle setting the default value after parsing.

gflags supports overriding the default value so we must do the same.

Change-Id: I5810e16806e74876c7a310edbb6f8f27f0a3313b

nova/flags.py

@@ -71,8 +71,20 @@ class FlagValues(object):
         self._parser = optparse.OptionParser()
         self._parser.disable_interspersed_args()
         self._extra_context = extra_context
+        self._multistring_defaults = {}
         self.Reset()
 
+    def _apply_multistring_defaults(self, values):
+        #
+        # This horrendous hack is to stop optparse appending
+        # values to the default value. See:
+        #   http://bugs.python.org/issue5088
+        #
+        for flag, default in self._multistring_defaults.items():
+            if not getattr(values, flag):
+                setattr(values, flag, default)
+        return values
+
     def _parse(self):
         if not self._values is None:
             return
@@ -101,6 +113,8 @@ class FlagValues(object):
         finally:
             self._parser.error = error_catcher.orig_error
 
+        values = self._apply_multistring_defaults(values)
+
         (self._values, self._extra) = (values, extra)
 
     def __call__(self, argv):
@@ -190,7 +204,8 @@ class FlagValues(object):
                          action='callback', callback=parse_list)
 
     def define_multistring(self, name, default, help):
-        self._add_option(name, default, help, action='append')
+        self._add_option(name, [], help, action='append')
+        self._multistring_defaults[name] = default
 
 FLAGS = FlagValues()
 

nova/tests/test_flags.py

@@ -74,7 +74,11 @@ class FlagsTestCase(test.TestCase):
         self.assertEqual(self.FLAGS.float, 6.66)
 
     def test_define_multistring(self):
-        flags.DEFINE_multistring('multi', [], 'desc', flag_values=self.FLAGS)
+        flags.DEFINE_multistring('multi', ['blaa'], 'desc',
+                                 flag_values=self.FLAGS)
+
+        self.assert_(self.FLAGS['multi'])
+        self.assertEqual(self.FLAGS.multi, ['blaa'])
 
         argv = ['flags_test', '--multi', 'foo', '--multi', 'bar']
         self.FLAGS(argv)