tests/test-rust-discovery.py

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

from __future__ import absolute_import
import unittest

from mercurial import policy

PartialDiscovery = policy.importrust('discovery', member='PartialDiscovery')

try:
    from mercurial.cext import parsers as cparsers
except ImportError:
    cparsers = None

# picked from test-parse-index2, copied rather than imported
# so that it stays stable even if test-parse-index2 changes or disappears.
data_non_inlined = (
    b'\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01D\x19'
    b'\x00\x07e\x12\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff'
    b'\xff\xff\xff\xff\xd1\xf4\xbb\xb0\xbe\xfc\x13\xbd\x8c\xd3\x9d'
    b'\x0f\xcd\xd9;\x8c\x07\x8cJ/\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    b'\x00\x00\x00\x00\x00\x00\x01D\x19\x00\x00\x00\x00\x00\xdf\x00'
    b'\x00\x01q\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\xff'
    b'\xff\xff\xff\xc1\x12\xb9\x04\x96\xa4Z1t\x91\xdfsJ\x90\xf0\x9bh'
    b'\x07l&\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
    b'\x00\x01D\xf8\x00\x00\x00\x00\x01\x1b\x00\x00\x01\xb8\x00\x00'
    b'\x00\x01\x00\x00\x00\x02\x00\x00\x00\x01\xff\xff\xff\xff\x02\n'
    b'\x0e\xc6&\xa1\x92\xae6\x0b\x02i\xfe-\xe5\xbao\x05\xd1\xe7\x00'
    b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01F'
    b'\x13\x00\x00\x00\x00\x01\xec\x00\x00\x03\x06\x00\x00\x00\x01'
    b'\x00\x00\x00\x03\x00\x00\x00\x02\xff\xff\xff\xff\x12\xcb\xeby1'
    b'\xb6\r\x98B\xcb\x07\xbd`\x8f\x92\xd9\xc4\x84\xbdK\x00\x00\x00'
    b'\x00\x00\x00\x00\x00\x00\x00\x00\x00'
)


class fakechangelog(object):
    def __init__(self, idx):
        self.index = idx


class fakerepo(object):
    def __init__(self, idx):
        """Just make so that self.changelog.index is the given idx."""
        self.changelog = fakechangelog(idx)


@unittest.skipIf(
    PartialDiscovery is None or cparsers is None,
    "rustext or the C Extension parsers module "
    "discovery relies on is not available",
)
class rustdiscoverytest(unittest.TestCase):
    """Test the correctness of binding to Rust code.

    This test is merely for the binding to Rust itself: extraction of
    Python variable, giving back the results etc.

    It is not meant to test the algorithmic correctness of the provided
    methods. Hence the very simple embedded index data is good enough.

    Algorithmic correctness is asserted by the Rust unit tests.
    """

    def parseindex(self):
        return cparsers.parse_index2(data_non_inlined, False)[0]

    def repo(self):
        return fakerepo(self.parseindex())

    def testindex(self):
        idx = self.parseindex()
        # checking our assumptions about the index binary data:
        self.assertEqual(
            {i: (r[5], r[6]) for i, r in enumerate(idx)},
            {0: (-1, -1), 1: (0, -1), 2: (1, -1), 3: (2, -1)},
        )

    def testaddcommonsmissings(self):
        disco = PartialDiscovery(self.repo(), [3], True)
        self.assertFalse(disco.hasinfo())
        self.assertFalse(disco.iscomplete())

        disco.addcommons([1])
        self.assertTrue(disco.hasinfo())
        self.assertFalse(disco.iscomplete())

        disco.addmissings([2])
        self.assertTrue(disco.hasinfo())
        self.assertTrue(disco.iscomplete())

        self.assertEqual(disco.commonheads(), {1})

    def testaddmissingsstats(self):
        disco = PartialDiscovery(self.repo(), [3], True)
        self.assertIsNone(disco.stats()['undecided'], None)

        disco.addmissings([2])
        self.assertEqual(disco.stats()['undecided'], 2)

    def testaddinfocommonfirst(self):
        disco = PartialDiscovery(self.repo(), [3], True)
        disco.addinfo([(1, True), (2, False)])
        self.assertTrue(disco.hasinfo())
        self.assertTrue(disco.iscomplete())
        self.assertEqual(disco.commonheads(), {1})

    def testaddinfomissingfirst(self):
        disco = PartialDiscovery(self.repo(), [3], True)
        disco.addinfo([(2, False), (1, True)])
        self.assertTrue(disco.hasinfo())
        self.assertTrue(disco.iscomplete())
        self.assertEqual(disco.commonheads(), {1})

    def testinitnorandom(self):
        PartialDiscovery(self.repo(), [3], True, randomize=False)


if __name__ == '__main__':
    import silenttestrunner

    silenttestrunner.main(__name__)