generate_osl.bzl

def _generate_osl_impl(ctx):
    """Implements `_generate_osl`.

    # Gather all licenses and write information to OSL.
    """
    # Declare the output OSL file.
    osl_file = ctx.actions.declare_file("osl.txt")

    target = ctx.attr.src
    if not TransitiveLicensesInfo in target:
        return [OutputGroupInfo(licenses = depset())]
    target_trans_license_info = target[TransitiveLicensesInfo]

    # If the result doesn't contain licenses, we simply return the provider
    if not hasattr(target_trans_license_info, "target_under_license"):
        return [OutputGroupInfo(licenses = depset())]

    # Write the output file for the target
    lic_info, lic_files = licenses_info_to_json(target_trans_license_info)
    content = "[\n%s\n]\n" % ",\n".join(lic_info)
    
    licenseinfo_json = ctx.actions.declare_file("_%s_licenses_info.json" % ctx.label.name)
    ctx.actions.write(
        output = licenseinfo_json,
        content = content,
    )
    
    # generate osl file
    args = ctx.actions.args()
    args.add_all([
        licenseinfo_json,
        osl_file,
    ])
    ctx.actions.run(
        outputs = [osl_file],
        executable = ctx.executable._osl_generator,
        inputs = [licenseinfo_json] + lic_files,
        arguments = [args],
        progress_message = "Generating OSL file {} by parsing the json \
        containing license information".format(ctx.label),
    )