work around omni-us/jsonargparse#852

Author: ThomasWaldmann

src/borg/archiver/__init__.py

@@ -271,7 +271,12 @@ def add_argument(*args, **kwargs):
                         # Note: We control all inputs.
                         kwargs["help"] = kwargs["help"] % kwargs
                         if not is_append:
-                            kwargs["default"] = argparse.SUPPRESS
+                            # Workaround for jsonargparse bug #852: empty subcommands that have the exact same name
+                            # as a boolean option flag will cause a crash (NSKeyError) if the option's default
+                            # is set to argparse.SUPPRESS. We bypass this by providing a sentinel value. However,
+                            # we must still use argparse.SUPPRESS if the option has a 'type' validator, as
+                            # jsonargparse will throw a ValidationError for our custom sentinel object.
+                            kwargs["default"] = argparse.SUPPRESS if "type" in kwargs else self.default_sentinel
 
                 common_group.add_argument(*args, **kwargs)