gc: disallow --remote without other flags

dvc/commands/gc.py

@@ -175,7 +175,7 @@ def add_parser(subparsers, parent_parser):
         "--cloud",
         action="store_true",
         default=False,
-        help="Collect garbage in remote repository.",
+        help="Collect garbage in remote storage in addition to local cache.",
     )
     gc_parser.add_argument(
         "-r",

dvc/repo/gc.py

@@ -16,6 +16,9 @@ logger = logging.getLogger(__name__)
 def _validate_args(**kwargs):
     not_in_remote = kwargs.pop("not_in_remote", None)
     cloud = kwargs.pop("cloud", None)
+    remote = kwargs.pop("remote", None)
+    if remote and not (cloud or not_in_remote):
+        raise InvalidArgumentError("`--remote` requires `--cloud` or `--not-in-remote`")
     if not_in_remote and cloud:
         raise InvalidArgumentError(
             "`--not-in-remote` and `--cloud` are mutually exclusive"

tests/unit/command/test_gc.py

@@ -60,3 +60,13 @@ def test_(dvc, scm, mocker):
     cmd = cli_args.func(cli_args)
     with pytest.raises(InvalidArgumentError):
         cmd.run()
+
+    cli_args = parse_args(["gc", "--cloud", "--not-in-remote"])
+    cmd = cli_args.func(cli_args)
+    with pytest.raises(InvalidArgumentError):
+        cmd.run()
+
+    cli_args = parse_args(["gc", "--remote", "myremote"])
+    cmd = cli_args.func(cli_args)
+    with pytest.raises(InvalidArgumentError):
+        cmd.run()