GzipFile not allowed for tarfile.open(fileobj=...)

[asottile]

minimal reproduction:

import gzip
import tarfile


open('t', 'w').close()
with gzip.GzipFile('out.tar.gz', 'wb') as gzipf:
    with tarfile.open(fileobj=gzipf, mode='w') as tf:
        tf.add('t')

$ python3 t.py 
$ mypy t.py
t.py:7: error: Argument "fileobj" to "open" has incompatible type "GzipFile"; expected "Optional[IO[bytes]]"
Found 1 error in 1 file (checked 1 source file)
$ mypy --version
mypy 0.812

presumably fileobj should use a Protocol of some shape ?

[hauntsaninja]

I think this just got fixed in #5099

[asottile]

appears not fixed:

$ mypy --custom-typeshed-dir /tmp/typeshed/ t.py 
t.py:7: error: Argument "fileobj" to "open" has incompatible type "GzipFile"; expected "Optional[IO[bytes]]"
Found 1 error in 1 file (checked 1 source file)
$ mypy --version
mypy 0.820+dev.675ae1afc8a5b0a9a515292c7e9d6bc2a38887be
$ git -C ../typeshed/ rev-parse HEAD
7d4ecf7f0a64cbfab59e54c8df1d5c53bcd9b9a1

[emmatyping]

It looks like #5170 fixed GzipFile, but not tarfile.

[JelleZijlstra]

As discussed the PR doesn't fix this issue, which is about tarfile.open. We still need to convert tarfile.open to overloads + IO protocols.

[max-muoto]

We should be able to close this out now @JelleZijlstra.