Ensure that cli options specified with action=Highlander can only be set once, even if the set value is a default value. Add tests for action=Highlander. See #7500 #6269

src/borg/archiver/_common.py

@@ -249,9 +249,14 @@ def with_archive(method):
 class Highlander(argparse.Action):
     """make sure some option is only given once"""
 
+    def __init__(self, *args, **kwargs):
+        self.__called = False
+        super().__init__(*args, **kwargs)
+
     def __call__(self, parser, namespace, values, option_string=None):
-        if getattr(namespace, self.dest, None) != self.default:
+        if self.__called:
             raise argparse.ArgumentError(self, "There can be only one.")
+        self.__called = True
         setattr(namespace, self.dest, values)
 
 

src/borg/testsuite/archiver/argparsing.py

@@ -11,6 +11,23 @@ class ArchiverTestCase(ArchiverTestCaseBase):
         self.cmd(f"--repo={self.repository_location}", "create", "test", "input")
         self.cmd(f"--repo={self.repository_location}", "delete", "--first", "1", "--last", "1", fork=True, exit_code=2)
 
+    def test_highlander(self):
+        self.cmd(f"--repo={self.repository_location}", "rcreate", RK_ENCRYPTION)
+        self.cmd(f"--repo={self.repository_location}", "create", "--comment", "comment 1", "test-1", __file__)
+        error_msg = "There can be only one"
+        # Default umask value is 0077
+        # Test that it works with a one time specified default or custom value
+        output_default = self.cmd(f"--repo={self.repository_location}", "--umask", "0077", "rlist")
+        assert error_msg not in output_default
+        output_custom = self.cmd(f"--repo={self.repository_location}", "--umask", "0007", "rlist")
+        assert error_msg not in output_custom
+        # Test that all combinations of custom and default values fail
+        for first, second in [("0007", "0007"), ("0007", "0077"), ("0077", "0007"), ("0077", "0077")]:
+            output_custom = self.cmd(
+                f"--repo={self.repository_location}", "--umask", first, "--umask", second, "rlist", exit_code=2
+            )
+            assert error_msg in output_custom
+
 
 def test_get_args():
     archiver = Archiver()