contrib/fuzz/manifest_corpus.py

wireprototypes: make `baseprotocolhandler` methods abstract

The documentation says it's an abstract base class, so let's enforce it.  The
`typing.Protocol` class is already an ABC, but it only prevents instantiation if
there are abstract attrs that are missing.  For example, from `hg debugshell`:

    >>> from mercurial import wireprototypes
    >>> x = wireprototypes.baseprotocolhandler()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class baseprotocolhandler with abstract method name
    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     pass
    ...
    >>> x = fake()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class fake with abstract method name

That's great, but it doesn't protect against calling non-abstract methods at
runtime, rather it depends on the protocol type hint being added to method
signatures or class attrs, and then running a type checker to notice when an
instance is assigned that doesn't conform to the protocol.  We don't widely use
type hints yet, and do have a lot of class hierarchy in the repository area,
which could lead to surprises like this:

    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     @property
    ...     def name(self) -> bytes:
    ...         return b'name'
    ...
    >>> z = fake()
    >>> z.client()
    >>> print(z.client())
    None

Oops.  That was supposed to return `bytes`.  So not only is a bad/unexpected
value returned, but it's one that violates the type hints (since the base
client() method will be annotated to return bytes).  With this change, we get:

    >>> from mercurial import wireprototypes
    >>> class fake(wireprototypes.baseprotocolhandler):
    ...     @property
    ...     def name(self) -> bytes:
    ...         return b'name'
    ...
    >>> x = fake()
    Traceback (most recent call last):
      File "<console>", line 1, in <module>
    TypeError: Can't instantiate abstract class fake with abstract methods
        addcapabilities, checkperm, client, getargs, getpayload, getprotocaps, mayberedirectstdio

So this looks like a reasonable safety harness to me, and lets us catch problems
by running the standard tests while the type hints are being added, and pytype
is improved.  We should probably do this for all Protocol class methods that
don't supply a method implementation.

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",
    )