Function repo_view_name_at 

pub fn repo_view_name_at(
    view: &str,
    store: &BufferStoreHandle,
    scopes: &RepoScopes,
    active: BufferId,
    at: Option<&Path>,
) -> String

PC.3: repo_view_name for an explicitly-named repository.

at is resolved to a repository the same way every other path is — through workdir_for_file, so naming a file INSIDE a checkout works as well as naming its root. A path that is not in a repository falls back to the ordinary resolution rather than composing a name for a repo that is not there: the view then says “Not a git repository.” exactly as it does when you trigger it from a non-repo buffer, which is one behaviour instead of two.