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def generated_file_staleness_test(name, outs, generated_pattern):
    """Tests that checked-in file(s) match the contents of generated file(s).

    The resulting test will verify that all output files exist and have the
    correct contents.  If the test fails, it can be invoked with --fix to
    bring the checked-in files up to date.

    Args:
      name: Name of the rule.
      outs: the checked-in files that are copied from generated files.
      generated_pattern: the pattern for transforming each "out" file into a
        generated file.  For example, if generated_pattern="generated/%s" then
        a file foo.txt will look for generated file generated/foo.txt.
    """

    script_name = name + ".py"
    script_src = ":staleness_test.py"

    # Filter out non-existing rules so Blaze doesn't error out before we even
    # run the test.
    existing_outs = native.glob(include = outs)

    # The file list contains a few extra bits of information at the end.
    # These get unpacked by the Config class in staleness_test_lib.py.
    file_list = outs + [generated_pattern, native.package_name() or ".", name]

    native.genrule(
        name = name + "_makescript",
        outs = [script_name],
        srcs = [script_src],
        testonly = 1,
        cmd = "cat $(location " + script_src + ") > $@; " +
              "sed -i.bak -e 's|INSERT_FILE_LIST_HERE|" + "\\\n  ".join(file_list) + "|' $@",
    )

    native.py_test(
        name = name,
        srcs = [script_name],
        data = existing_outs + [generated_pattern % file for file in outs],
        deps = [
            ":staleness_test_lib",
        ],
    )