Add mechanism for dynamically adding new arguments

This will allow checks to dynamically add arguments based on the
values of other arguments. This will be needed when we add an API
to verify-copyright for projects to inject their own configuration
modules which specify a different branching strategy and optionally
have their own arguments.

src/rapids_pre_commit_hooks/lint.py

@@ -246,8 +246,9 @@ def _calculate_lines(self):
 
 
 class ExecutionContext(contextlib.AbstractContextManager):
-    def __init__(self, args):
+    def __init__(self, args, extra_args):
         self.args = args
+        self.extra_args = extra_args
         self.checks = []
 
     def add_check(self, check):
@@ -291,6 +292,10 @@ def __exit__(self, exc_type, exc_value, traceback):
 class LintMain:
     context_class = ExecutionContext
 
+    @classmethod
+    def get_extra_argparser(cls, namespace):
+        return argparse.ArgumentParser()
+
     def __init__(self):
         self.argparser = argparse.ArgumentParser()
         self.argparser.add_argument(
@@ -299,4 +304,7 @@ def __init__(self):
         self.argparser.add_argument("files", nargs="+", metavar="file")
 
     def execute(self):
-        return self.context_class(self.argparser.parse_args())
+        namespace, extra_args = self.argparser.parse_known_args()
+        extra_argparser = self.get_extra_argparser(namespace)
+        extra_namespace = extra_argparser.parse_args(extra_args)
+        return self.context_class(namespace, extra_namespace)

test/rapids_pre_commit_hooks/test_lint.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
 import contextlib
 import os.path
 import tempfile
@@ -524,3 +525,23 @@ def test_bracket_file(self, bracket_file):
             call().print("[bold]note:[/bold] suggested fix applied"),
             call().print(),
         ]
+
+    def test_extra_args(self, hello_file):
+        class ExtraArgsMain(LintMain):
+            @classmethod
+            def get_extra_argparser(cls, args):
+                parser = argparse.ArgumentParser()
+                parser.add_argument("--extra-dynamic-arg", action="store")
+                return parser
+
+        with patch(
+            "sys.argv",
+            [
+                "check-test",
+                "--extra-dynamic-arg=Hello",
+                hello_file.name,
+            ],
+        ):
+            m = ExtraArgsMain()
+            with m.execute() as ctx:
+                assert ctx.extra_args.extra_dynamic_arg == "Hello"