prune --list-kept/--list-pruned, fixes #7511

use this to only list the kept (or pruned) archives.
--list-pruned and --list-kept also work in a additive way.

implied logging: support multiple prune options activating same logger

if any of --list / --list-kept / --list-pruned is used,
it should put the borg.output.list logger to INFO level,
otherwise to WARN level.

src/borg/archiver/__init__.py

@@ -441,7 +441,6 @@ class Archiver(
         """turn on INFO level logging for args that imply that they will produce output"""
         # map of option name to name of logger for that option
         option_logger = {
-            "output_list": "borg.output.list",
             "show_version": "borg.output.show-version",
             "show_rc": "borg.output.show-rc",
             "stats": "borg.output.stats",
@@ -451,6 +450,10 @@ class Archiver(
             option_set = args.get(option, False)
             logging.getLogger(logger_name).setLevel("INFO" if option_set else "WARN")
 
+        # special-case --list / --list-kept / --list-pruned as they all work on same logger
+        options = [args.get(name, False) for name in ("output_list", "list_kept", "list_pruned")]
+        logging.getLogger("borg.output.list").setLevel("INFO" if any(options) else "WARN")
+
     def _setup_topic_debugging(self, args):
         """Turn on DEBUG level logging for specified --debug-topics."""
         for topic in args.debug_topics:

src/borg/archiver/prune_cmd.py

@@ -163,7 +163,11 @@ class PruneMixIn:
                         log_message = "Keeping archive (rule: {rule} #{num}):".format(
                             rule=kept_because[archive.id][0], num=kept_because[archive.id][1]
                         )
-                if args.output_list:
+                if (
+                    args.output_list
+                    or (args.list_pruned and archive in to_delete)
+                    or (args.list_kept and archive not in to_delete)
+                ):
                     list_logger.info(f"{log_message:<40} {formatter.format_item(archive)}")
             pi.finish()
             if sig_int:
@@ -265,6 +269,12 @@ class PruneMixIn:
             "--list", dest="output_list", action="store_true", help="output verbose list of archives it keeps/prunes"
         )
         subparser.add_argument("--short", dest="short", action="store_true", help="use a less wide archive part format")
+        subparser.add_argument(
+            "--list-pruned", dest="list_pruned", action="store_true", help="output verbose list of archives it prunes"
+        )
+        subparser.add_argument(
+            "--list-kept", dest="list_kept", action="store_true", help="output verbose list of archives it keeps"
+        )
         subparser.add_argument(
             "--format",
             metavar="FORMAT",