Function extend_pathspec_list_implicit_cwd 

pub fn extend_pathspec_list_implicit_cwd(
    specs: &[String],
    cwd_from_repo_root: Option<&str>,
) -> Vec<String>

When every pathspec is an exclude and none use :(top) / :/, Git prepends an implicit positive that matches only under the process cwd (relative to the work tree), not the whole repository (PATHSPEC_PREFER_CWD in pathspec.c). cwd_from_repo_root is that prefix without a trailing slash, or empty at the work tree root.