upgrade: auto-use ignore_invalid_archive_tam

src/borg/archiver.py

@@ -76,6 +76,7 @@ try:
     from .helpers import sig_int, ignore_sigint
     from .helpers import iter_separated
     from .helpers import get_tar_filter
+    from .helpers import ignore_invalid_archive_tam
     from .helpers.parseformat import BorgJsonEncoder, safe_decode
     from .nanorst import rst_to_terminal
     from .patterns import ArgparsePatternAction, ArgparseExcludeFileAction, ArgparsePatternFileAction, parse_exclude_pattern
@@ -1613,6 +1614,7 @@ class Archiver:
     def do_upgrade(self, args, repository, manifest=None, key=None):
         """upgrade a repository from a previous version"""
         if args.archives_tam or args.check_archives_tam:
+            with ignore_invalid_archive_tam():
                 archive_tam_issues = 0
                 read_only = args.check_archives_tam
                 manifest, key = Manifest.load(repository, (Manifest.Operation.CHECK,), force_tam_not_required=args.force)

src/borg/helpers/__init__.py

@@ -5,6 +5,7 @@ that did not fit better elsewhere.
 Code used to be in borg/helpers.py but was split into the modules in this
 package, which are imported into here for compatibility.
 """
+from contextlib import contextmanager
 
 from .checks import *  # NOQA
 from .datastruct import *  # NOQA
@@ -27,6 +28,17 @@ from . import msgpack
 workarounds = tuple(os.environ.get('BORG_WORKAROUNDS', '').split(','))
 
 
+@contextmanager
+def ignore_invalid_archive_tam():
+    global workarounds
+    saved = workarounds
+    if 'ignore_invalid_archive_tam' not in workarounds:
+        # we really need this workaround here or borg will likely raise an exception.
+        workarounds += ('ignore_invalid_archive_tam',)
+    yield
+    workarounds = saved
+
+
 # element data type for warnings_list:
 warning_info = namedtuple("warning_info", "wc,msg,args,wt")