Only add 'args' argument once to command parser.

If a custom management LabelCommand or AppCommand uses 'args' then only
the last positional argument provided is passed to the command, because
argparse's behaviour when two calls to add_argument with the same name
is undefined (it appears to put all the arguments bar one in the first
'*' argument, then the last one in the '+' argument).

This shows this with a test, and fixes it by not making the first call
to parser.add_argument('args') if it's a LabelCommand or AppCommand.

django/core/management/base.py

@@ -349,7 +349,7 @@ def store_as_int(option, opt_str, value, parser):
                 help='Raise on CommandError exceptions')
             parser.add_argument('--no-color', action='store_true', dest='no_color', default=False,
                 help="Don't colorize the command output.")
-            if self.args:
+            if self.args and not isinstance(self, LabelCommand) and not isinstance(self, AppCommand):
                 # Keep compatibility and always accept positional arguments, like optparse when args is set
                 parser.add_argument('args', nargs='*')
             self.add_arguments(parser)

tests/admin_scripts/tests.py

@@ -1683,6 +1683,14 @@ def test_label_command_multiple_label(self):
         self.assertOutput(out, "EXECUTE:LabelCommand label=testlabel, options=[('no_color', False), ('pythonpath', None), ('settings', None), ('traceback', False), ('verbosity', 1)]")
         self.assertOutput(out, "EXECUTE:LabelCommand label=anotherlabel, options=[('no_color', False), ('pythonpath', None), ('settings', None), ('traceback', False), ('verbosity', 1)]")
 
+    def test_label_command_with_args_multiple_label(self):
+        "User LabelCommands using 'args' are executed multiple times if multiple labels are provided"
+        args = ['label_command_with_args', 'testlabel', 'anotherlabel']
+        out, err = self.run_manage(args)
+        self.assertNoOutput(err)
+        self.assertOutput(out, "EXECUTE:LabelCommand label=testlabel, options=[('no_color', False), ('pythonpath', None), ('settings', None), ('traceback', False), ('verbosity', 1)]")
+        self.assertOutput(out, "EXECUTE:LabelCommand label=anotherlabel, options=[('no_color', False), ('pythonpath', None), ('settings', None), ('traceback', False), ('verbosity', 1)]")
+
     @ignore_warnings(category=RemovedInDjango19Warning)
     def test_requires_model_validation_and_requires_system_checks_both_defined(self):
         from .management.commands.validation_command import InvalidCommand