no_submodules

Flag the presence of .gitmodules at the repo root — always, regardless of paths. For general “file X must not exist” checks, use file_absent.

- id: no-submods
  kind: no_submodules
  level: warning
  fix:
    file_remove: {}

Note the fix only deletes .gitmodules; git submodule deinit and cleaning .git/modules/ are still on the user.