def available_licenses(d):
    """
    Return the available licenses by searching the directories specified by
    COMMON_LICENSE_DIR and LICENSE_PATH.
    """
    lic_dirs = ((d.getVar('COMMON_LICENSE_DIR') or '') + ' ' +
                (d.getVar('LICENSE_PATH') or '')).split()

    licenses = set()
    for lic_dir in lic_dirs:
        licenses.update(os.listdir(lic_dir))

    return licenses

COMPATIBLE_LICENSES ??= ""

# Mark all licenses that are not in COMPATIBLE_LICENSES as incompatible.
INCOMPATIBLE_LICENSE ?= "${@' '.join(sorted(available_licenses(d) - set(d.getVar('COMPATIBLE_LICENSES').split())))}"