log: Deprecate passing git options

kart/log.py

@@ -16,6 +16,10 @@
 from . import diff_estimation
 
 
+class RemovalInKart012Warning(UserWarning):
+    pass
+
+
 class PreserveDoubleDash(click.Command):
     """
     Preserves the double-dash ("--") arg from user input.
@@ -35,7 +39,7 @@ def parse_args(self, ctx, args):
                     # which ideally we'd like them to stop doing.
                     warnings.warn(
                         "Using '--' twice is no longer needed, and will behave differently or fail in Kart 0.12",
-                        UserWarning,
+                        RemovalInKart012Warning,
                     )
                 else:
                     # Insert a second `--` arg.
@@ -84,6 +88,12 @@ def parse_extra_args(
                 # So we can assume it's a CLI flag, presumably for git rather than kart.
                 # It *could* be a path, but in that case the user should add a `--` before this option
                 # to disambiguate, and they haven't done so here.
+                issue_link = "https://github.com/koordinates/kart/issues/508"
+                warnings.warn(
+                    f"{arg!r} is unknown to Kart and will be passed directly to git. "
+                    f"This will be removed in Kart 0.12! Please comment on {issue_link} if you need to use this option.",
+                    RemovalInKart012Warning,
+                )
                 other_args.append(arg)
                 continue