Add `pybind11_protobuf::check_unknown_fields::ExtensionsWithUnknownFi…

…eldsPolicy`.

BEGIN_PUBLIC

Add `pybind11_protobuf::check_unknown_fields::ExtensionsWithUnknownFieldsPolicy`.

END_PUBLIC

This feature is primarily to support rolling out PyCLIF-pybind11 (go/pyclif_pybind11_fusion) without first having to resolve the ~11.7k test failures shown under b/304628404.

In the presumably very rare cases that the serialize/parse runtime overhead is noticeable, `//third_party/pybind11_protobuf:disallow_extensions_with_unknown_fields` can be added to the `deps` of the affected `py_binary` (or `py_test`) targets, to thereby enforce that the required `cc_proto_library` dependencies are added.

PiperOrigin-RevId: 595557800

clif/pybind11/generator.py

@@ -197,6 +197,9 @@ def generate_from(self, ast: ast_pb2.AST):
     if self._codegen_info.requires_status:
       yield I + I + ('pybind11::module_::import('
                      '"util.task.python.error");')
+    yield I + I + 'pybind11_protobuf::check_unknown_fields::'
+    yield I + I + '    ExtensionsWithUnknownFieldsPolicy::'
+    yield I + I + '        WeakEnableFallbackToSerializeParse();'
     yield I + I + 'pybind11_protobuf::ImportNativeProtoCasters();'
 
     for decl in ast.decls: