enable placeholder usage in --comment, fixes #4559

src/borg/archiver.py

@@ -50,7 +50,7 @@ try:
     from .helpers import EXIT_SUCCESS, EXIT_WARNING, EXIT_ERROR
     from .helpers import Error, NoManifestError, set_ec
     from .helpers import positive_int_validator, location_validator, archivename_validator, ChunkerParams, Location
-    from .helpers import PrefixSpec, GlobSpec, SortBySpec, HUMAN_SORT_KEYS, FilesCacheMode
+    from .helpers import PrefixSpec, GlobSpec, CommentSpec, SortBySpec, HUMAN_SORT_KEYS, FilesCacheMode
     from .helpers import BaseFormatter, ItemFormatter, ArchiveFormatter
     from .helpers import format_timedelta, format_file_size, parse_file_size, format_archive
     from .helpers import safe_encode, remove_surrogates, bin_to_hex, prepare_dump_dict
@@ -2336,8 +2336,8 @@ class Archiver:
                 # don't backup the other home directories
                 - /home/*\n\n''')
     helptext['placeholders'] = textwrap.dedent('''
-        Repository (or Archive) URLs, ``--prefix``, ``--glob-archives`` and ``--remote-path``
-        values support these placeholders:
+        Repository (or Archive) URLs, ``--prefix``, ``--glob-archives``, ``--comment``
+        and ``--remote-path`` values support these placeholders:
 
         {hostname}
             The (short) hostname of the machine.
@@ -3357,7 +3357,7 @@ class Archiver:
                                    'regular files. Also follows symlinks pointing to these kinds of files.')
 
         archive_group = subparser.add_argument_group('Archive options')
-        archive_group.add_argument('--comment', dest='comment', metavar='COMMENT', default='',
+        archive_group.add_argument('--comment', dest='comment', metavar='COMMENT', type=CommentSpec, default='',
                                    help='add a comment text to the archive')
         archive_group.add_argument('--timestamp', metavar='TIMESTAMP', dest='timestamp',
                                    type=timestamp, default=None,
@@ -3942,7 +3942,7 @@ class Archiver:
         archive_group.add_argument('-c', '--checkpoint-interval', dest='checkpoint_interval',
                                    type=int, default=1800, metavar='SECONDS',
                                    help='write checkpoint every SECONDS seconds (Default: 1800)')
-        archive_group.add_argument('--comment', dest='comment', metavar='COMMENT', default=None,
+        archive_group.add_argument('--comment', dest='comment', metavar='COMMENT', type=CommentSpec, default=None,
                                    help='add a comment text to the archive')
         archive_group.add_argument('--timestamp', metavar='TIMESTAMP', dest='timestamp',
                                    type=timestamp, default=None,

src/borg/helpers.py

@@ -687,6 +687,8 @@ PrefixSpec = replace_placeholders
 
 GlobSpec = replace_placeholders
 
+CommentSpec = replace_placeholders
+
 HUMAN_SORT_KEYS = ['timestamp'] + list(ArchiveInfo._fields)
 HUMAN_SORT_KEYS.remove('ts')