nix/doc/manual/rl-next/self-submodules-attr.md

synopsis	prs
`inputs.self.submodules` flake attribute	12421

Flakes in Git repositories can now declare that they need Git submodules to be enabled:

{
  inputs.self.submodules = true;
}

Thus, it's no longer needed for the caller of the flake to pass submodules = true.