Function package_dir_within 

pub fn package_dir_within(
    from_dir: &Path,
    name: &str,
    boundary: &Path,
) -> Result<PathBuf>

package_dir, but the ascent stops at boundary (inclusive): a package installed only above it is not found. The boundary is canonicalized once; each candidate level is compared canonically, so a symlinked start directory cannot slip past it.