def METHOD_NAME(pip_download_output_file):
    """Find builddeps in output of pip download."""
    # Requirement is a sequence of non-whitespace, non-';' characters
    # Example: package, package==1.0, package[extra]==1.0
    requirement_re = r"[^\s;]+"
    # Leading whitespace => requirement is a build dependency
    # (because all recursive runtime dependencies were present in input files)
    builddep_re = re.compile(rf"^\s+Collecting ({requirement_re})")
    with open(pip_download_output_file) as f:
        matches = (builddep_re.match(line) for line in f)
        builddeps = set(match.group(1) for match in matches if match)
    return sorted(builddeps)