procutil: make stream detection in make_line_buffered more correct and strict In make_line_buffered(), we don’t want to wrap the stream if we know that lines get flushed to the underlying raw stream already. Previously, the heuristic was too optimistic. It assumed that any stream which is not an instance of io.BufferedIOBase doesn’t need wrapping. However, there are buffered streams that aren’t instances of io.BufferedIOBase, like Mercurial’s own winstdout. The new logic is different in two ways: First, only for the check, if unwraps any combination of WriteAllWrapper and winstdout. Second, it skips wrapping the stream only if it is an instance of io.RawIOBase (or already wrapped). If it is an instance of io.BufferedIOBase, it gets wrapped. In any other case, the function raises an exception. This ensures that, if an unknown stream is passed or we add another wrapper in the future, we don’t wrap the stream if it’s already line buffered or not wrap the stream if it’s not line buffered. In fact, this was already helpful during development of this change. Without it, I possibly would have forgot that WriteAllWrapper needs to be ignored for the check, leading to unnecessary wrapping if stdout is unbuffered. The alternative would have been to always wrap unknown streams. However, I don’t think that anyone would benefit from being less strict. We can expect streams from the standard library to be subclassing either io.RawIOBase or io.BufferedIOBase, so running Mercurial in the standard way should not regress by this change. Py2exe might replace sys.stdout and sys.stderr, but that currently breaks Mercurial anyway and also these streams don’t claim to be interactive, so this function is not called for them.

import argparse
import zipfile

ap = argparse.ArgumentParser()
ap.add_argument("out", metavar="some.zip", type=str, nargs=1)
args = ap.parse_args()

with zipfile.ZipFile(args.out[0], "w", zipfile.ZIP_STORED) as zf:
    zf.writestr(
        "manifest_zero",
        '''\0PKG-INFO\09b3ed8f2b81095a13064402e930565f083346e9a
README\080b6e76643dcb44d4bc729e932fc464b3e36dbe3
hg\0b6444347c629cc058d478023905cfb83b7f5bb9d
mercurial/__init__.py\0b80de5d138758541c5f05265ad144ab9fa86d1db
mercurial/byterange.py\017f5a9fbd99622f31a392c33ac1e903925dc80ed
mercurial/fancyopts.py\0b6f52e23e356748c5039313d8b639cda16bf67ba
mercurial/hg.py\023cc12f225f1b42f32dc0d897a4f95a38ddc8f4a
mercurial/mdiff.py\0a05f65c44bfbeec6a42336cd2ff0b30217899ca3
mercurial/revlog.py\0217bc3fde6d82c0210cf56aeae11d05a03f35b2b
mercurial/transaction.py\09d180df101dc14ce3dd582fd998b36c98b3e39aa
notes.txt\0703afcec5edb749cf5cec67831f554d6da13f2fb
setup.py\0ccf3f6daf0f13101ca73631f7a1769e328b472c9
tkmerge\03c922edb43a9c143682f7bc7b00f98b3c756ebe7
''',
    )
    zf.writestr("badmanifest_shorthashes", "\0narf\0aa\nnarf2\0aaa\n")
    zf.writestr(
        "badmanifest_nonull",
        "\0narf\0cccccccccccccccccccccccccccccccccccccccc\n"
        "narf2aaaaaaaaaaaaaaaaaaaa\n",
    )

    zf.writestr(
        "manifest_long_nodes",
        "\1a\0ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff\n",
    )