Function plan_uninstall_batch 

pub fn plan_uninstall_batch(
    target_dir: &Path,
    eco: &Ecosystem,
    game: &str,
    names: Option<&[String]>,
) -> Result<UninstallBatch>

Plans an uninstall, refusing before anything is mutated.

names of None means every recorded mod. A name that is not installed, or any mod that cannot be removed exactly, is an error rather than a per-item failure: this runs before any mutation, so refusing the whole request is what keeps a batch from failing partway through.