$ hg init empty-repo

  $ cd empty-repo

Flags on revlog version 0 are rejected

  >>> with open('.hg/store/00changelog.i', 'wb') as fh:

  ...     fh.write(b'\x00\x01\x00\x00') and None

  $ hg log

  abort: unknown flags (0x01) in version 0 revlog 00changelog.i!

  [255]

Unknown flags on revlog version 1 are rejected

  >>> with open('.hg/store/00changelog.i', 'wb') as fh:

  ...     fh.write(b'\x00\x04\x00\x01') and None

  $ hg log

  abort: unknown flags (0x04) in version 1 revlog 00changelog.i!

  [255]

Unknown version is rejected

  >>> with open('.hg/store/00changelog.i', 'wb') as fh:

  ...     fh.write(b'\x00\x00\x00\x02') and None

  $ hg log

  abort: unknown version (2) in revlog 00changelog.i!

  [255]

  $ cd ..

Test for CVE-2016-3630

  $ hg init

  >>> open("a.i", "wb").write(

  ... b"""eJxjYGZgZIAAYQYGxhgom+k/FMx8YKx9ZUaKSOyqo4cnuKb8mbqHV5cBCVTMWb1Cwqkhe4Gsg9AD

  ... Joa3dYtcYYYBAQ8Qr4OqZAYRICPTSr5WKd/42rV36d+8/VmrNpv7NP1jQAXrQE4BqQUARngwVA=="""

  ... .decode("base64").decode("zlib"))

     rev linkrev nodeid       p1           p2

       0       2 99e0332bd498 000000000000 000000000000

       1       3 6674f57a23d8 99e0332bd498 000000000000

  >>> from mercurial import revlog, vfs

  >>> tvfs = vfs.vfs(b'.')

  >>> tvfs.options = {b'revlogv1': True}

  >>> rl = revlog.revlog(tvfs, b'a.i')

  >>> rl.revision(1)

  mpatchError('patch cannot be decoded',)