Make the action actually work. PR still pending a bunch of stuff.

borgmatic/actions/diff.py

@@ -1,13 +1,12 @@
 import logging
 
 import borgmatic.actions.pattern
-import borgmatic.borg.pattern
 import borgmatic.borg.diff
+import borgmatic.borg.pattern
 
 logger = logging.getLogger(__name__)
 
 
-
 def run_diff(
     repository,
     config,
@@ -23,9 +22,7 @@ def run_diff(
 
     # Collect and process patterns.
     processed_patterns = borgmatic.actions.pattern.process_patterns(
-        (
-            *borgmatic.actions.pattern.collect_patterns(config),
-        ),
+        (*borgmatic.actions.pattern.collect_patterns(config),),
         config,
         borgmatic.config.paths.get_working_directory(config),
     )

borgmatic/borg/diff.py

@@ -76,6 +76,7 @@ def diff(
                 else flags.make_repository_flags(repository, local_borg_version)
             )
         )
+        + (diff_arguments.second_archive, )
     )
 
     borgmatic.execute.execute_command(

borgmatic/commands/arguments.py

@@ -1976,7 +1976,6 @@ def make_parsers(schema, unparsed_arguments):  # noqa: PLR0915
         aliases=ACTION_ALIASES['diff'],
         help='This command finds differences (file contents, user/group/mode) between archives',
         description='This command finds differences (file contents, user/group/mode) between archives',
-        add_help=False,
     )
     diff_group = diff_parser.add_argument_group('diff arguments')
     diff_group.add_argument(
@@ -1987,6 +1986,10 @@ def make_parsers(schema, unparsed_arguments):  # noqa: PLR0915
         '--archive',
         help='Archive name, hash, or series to diff, defaults to all archives in the repository (if specified)',
     )
+    diff_group.add_argument(
+        '--second-archive',
+        help='Second archive name, hash, or series to diff',
+    )
 
     borg_parser = action_parsers.add_parser(
         'borg',