similar: compare between actual file contents for exact identity
Before this patch, similarity detection logic (for addremove and
automv) depends entirely on SHA-1 digesting. But this causes incorrect
rename detection, if:
- removing file A and adding file B occur at same committing, and
- SHA-1 hash values of file A and B are same
This may prevent security experts from managing sample files for
SHAttered issue in Mercurial repository, for example.
https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html
https://shattered.it/
Hash collision itself isn't so serious for core repository
functionality of Mercurial, described by mpm as below, though.
https://www.mercurial-scm.org/wiki/mpm/SHA1
This patch compares between actual file contents after hash comparison
for exact identity.
Even after this patch, SHA-1 is still used, because it is reasonable
enough to quickly detect existence of "(almost) same" file.
- replacing SHA-1 causes decreasing performance, and
- replacement of it has ambiguity, yet
Getting content of removed file (= rfctx.data()) at each exact
comparison should be cheap enough, even though getting content of
added one costs much.
======= ============== =====================
file fctx data() reads from
======= ============== =====================
removed filectx in-memory revlog data
added workingfilectx storage
======= ============== =====================
# __init__.py - Startup and module loading logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import
import imp
import os
import sys
import zipimport
from . import (
policy
)
__all__ = []
modulepolicy = policy.policy
# Modules that have both Python and C implementations. See also the
# set of .py files under mercurial/pure/.
_dualmodules = set([
'mercurial.base85',
'mercurial.bdiff',
'mercurial.diffhelpers',
'mercurial.mpatch',
'mercurial.osutil',
'mercurial.parsers',
])
class hgimporter(object):
"""Object that conforms to import hook interface defined in PEP-302."""
def find_module(self, name, path=None):
# We only care about modules that have both C and pure implementations.
if name in _dualmodules:
return self
return None
def load_module(self, name):
mod = sys.modules.get(name, None)
if mod:
return mod
mercurial = sys.modules['mercurial']
# The zip importer behaves sufficiently differently from the default
# importer to warrant its own code path.
loader = getattr(mercurial, '__loader__', None)
if isinstance(loader, zipimport.zipimporter):
def ziploader(*paths):
"""Obtain a zipimporter for a directory under the main zip."""
path = os.path.join(loader.archive, *paths)
zl = sys.path_importer_cache.get(path)
if not zl:
zl = zipimport.zipimporter(path)
return zl
try:
if modulepolicy in policy.policynoc:
raise ImportError()
zl = ziploader('mercurial')
mod = zl.load_module(name)
# Unlike imp, ziploader doesn't expose module metadata that
# indicates the type of module. So just assume what we found
# is OK (even though it could be a pure Python module).
except ImportError:
if modulepolicy == 'c':
raise
zl = ziploader('mercurial', 'pure')
mod = zl.load_module(name)
sys.modules[name] = mod
return mod
# Unlike the default importer which searches special locations and
# sys.path, we only look in the directory where "mercurial" was
# imported from.
# imp.find_module doesn't support submodules (modules with ".").
# Instead you have to pass the parent package's __path__ attribute
# as the path argument.
stem = name.split('.')[-1]
try:
if modulepolicy in policy.policynoc:
raise ImportError()
modinfo = imp.find_module(stem, mercurial.__path__)
# The Mercurial installer used to copy files from
# mercurial/pure/*.py to mercurial/*.py. Therefore, it's possible
# for some installations to have .py files under mercurial/*.
# Loading Python modules when we expected C versions could result
# in a) poor performance b) loading a version from a previous
# Mercurial version, potentially leading to incompatibility. Either
# scenario is bad. So we verify that modules loaded from
# mercurial/* are C extensions. If the current policy allows the
# loading of .py modules, the module will be re-imported from
# mercurial/pure/* below.
if modinfo[2][2] != imp.C_EXTENSION:
raise ImportError('.py version of %s found where C '
'version should exist' % name)
except ImportError:
if modulepolicy == 'c':
raise
# Could not load the C extension and pure Python is allowed. So
# try to load them.
from . import pure
modinfo = imp.find_module(stem, pure.__path__)
if not modinfo:
raise ImportError('could not find mercurial module %s' %
name)
mod = imp.load_module(name, *modinfo)
sys.modules[name] = mod
return mod
# Python 3 uses a custom module loader that transforms source code between
# source file reading and compilation. This is done by registering a custom
# finder that changes the spec for Mercurial modules to use a custom loader.
if sys.version_info[0] >= 3:
from . import pure
import importlib
import io
import token
import tokenize
class hgpathentryfinder(importlib.abc.MetaPathFinder):
"""A sys.meta_path finder that uses a custom module loader."""
def find_spec(self, fullname, path, target=None):
# Only handle Mercurial-related modules.
if not fullname.startswith(('mercurial.', 'hgext.', 'hgext3rd.')):
return None
# This assumes Python 3 doesn't support loading C modules.
if fullname in _dualmodules:
stem = fullname.split('.')[-1]
fullname = 'mercurial.pure.%s' % stem
target = pure
assert len(path) == 1
path = [os.path.join(path[0], 'pure')]
# Try to find the module using other registered finders.
spec = None
for finder in sys.meta_path:
if finder == self:
continue
spec = finder.find_spec(fullname, path, target=target)
if spec:
break
# This is a Mercurial-related module but we couldn't find it
# using the previously-registered finders. This likely means
# the module doesn't exist.
if not spec:
return None
if fullname.startswith('mercurial.pure.'):
spec.name = spec.name.replace('.pure.', '.')
# TODO need to support loaders from alternate specs, like zip
# loaders.
spec.loader = hgloader(spec.name, spec.origin)
return spec
def replacetokens(tokens, fullname):
"""Transform a stream of tokens from raw to Python 3.
It is called by the custom module loading machinery to rewrite
source/tokens between source decoding and compilation.
Returns a generator of possibly rewritten tokens.
The input token list may be mutated as part of processing. However,
its changes do not necessarily match the output token stream.
REMEMBER TO CHANGE ``BYTECODEHEADER`` WHEN CHANGING THIS FUNCTION
OR CACHED FILES WON'T GET INVALIDATED PROPERLY.
"""
futureimpline = False
# The following utility functions access the tokens list and i index of
# the for i, t enumerate(tokens) loop below
def _isop(j, *o):
"""Assert that tokens[j] is an OP with one of the given values"""
try:
return tokens[j].type == token.OP and tokens[j].string in o
except IndexError:
return False
def _findargnofcall(n):
"""Find arg n of a call expression (start at 0)
Returns index of the first token of that argument, or None if
there is not that many arguments.
Assumes that token[i + 1] is '('.
"""
nested = 0
for j in range(i + 2, len(tokens)):
if _isop(j, ')', ']', '}'):
# end of call, tuple, subscription or dict / set
nested -= 1
if nested < 0:
return None
elif n == 0:
# this is the starting position of arg
return j
elif _isop(j, '(', '[', '{'):
nested += 1
elif _isop(j, ',') and nested == 0:
n -= 1
return None
def _ensureunicode(j):
"""Make sure the token at j is a unicode string
This rewrites a string token to include the unicode literal prefix
so the string transformer won't add the byte prefix.
Ignores tokens that are not strings. Assumes bounds checking has
already been done.
"""
st = tokens[j]
if st.type == token.STRING and st.string.startswith(("'", '"')):
tokens[j] = st._replace(string='u%s' % st.string)
for i, t in enumerate(tokens):
# Convert most string literals to byte literals. String literals
# in Python 2 are bytes. String literals in Python 3 are unicode.
# Most strings in Mercurial are bytes and unicode strings are rare.
# Rather than rewrite all string literals to use ``b''`` to indicate
# byte strings, we apply this token transformer to insert the ``b``
# prefix nearly everywhere.
if t.type == token.STRING:
s = t.string
# Preserve docstrings as string literals. This is inconsistent
# with regular unprefixed strings. However, the
# "from __future__" parsing (which allows a module docstring to
# exist before it) doesn't properly handle the docstring if it
# is b''' prefixed, leading to a SyntaxError. We leave all
# docstrings as unprefixed to avoid this. This means Mercurial
# components touching docstrings need to handle unicode,
# unfortunately.
if s[0:3] in ("'''", '"""'):
yield t
continue
# If the first character isn't a quote, it is likely a string
# prefixing character (such as 'b', 'u', or 'r'. Ignore.
if s[0] not in ("'", '"'):
yield t
continue
# String literal. Prefix to make a b'' string.
yield t._replace(string='b%s' % t.string)
continue
# Insert compatibility imports at "from __future__ import" line.
# No '\n' should be added to preserve line numbers.
if (t.type == token.NAME and t.string == 'import' and
all(u.type == token.NAME for u in tokens[i - 2:i]) and
[u.string for u in tokens[i - 2:i]] == ['from', '__future__']):
futureimpline = True
if t.type == token.NEWLINE and futureimpline:
futureimpline = False
if fullname == 'mercurial.pycompat':
yield t
continue
r, c = t.start
l = (b'; from mercurial.pycompat import '
b'delattr, getattr, hasattr, setattr, xrange, open\n')
for u in tokenize.tokenize(io.BytesIO(l).readline):
if u.type in (tokenize.ENCODING, token.ENDMARKER):
continue
yield u._replace(
start=(r, c + u.start[1]), end=(r, c + u.end[1]))
continue
# This looks like a function call.
if t.type == token.NAME and _isop(i + 1, '('):
fn = t.string
# *attr() builtins don't accept byte strings to 2nd argument.
if (fn in ('getattr', 'setattr', 'hasattr', 'safehasattr') and
not _isop(i - 1, '.')):
arg1idx = _findargnofcall(1)
if arg1idx is not None:
_ensureunicode(arg1idx)
# .encode() and .decode() on str/bytes/unicode don't accept
# byte strings on Python 3.
elif fn in ('encode', 'decode') and _isop(i - 1, '.'):
for argn in range(2):
argidx = _findargnofcall(argn)
if argidx is not None:
_ensureunicode(argidx)
# It changes iteritems to items as iteritems is not
# present in Python 3 world.
elif fn == 'iteritems':
yield t._replace(string='items')
continue
# Emit unmodified token.
yield t
# Header to add to bytecode files. This MUST be changed when
# ``replacetoken`` or any mechanism that changes semantics of module
# loading is changed. Otherwise cached bytecode may get loaded without
# the new transformation mechanisms applied.
BYTECODEHEADER = b'HG\x00\x08'
class hgloader(importlib.machinery.SourceFileLoader):
"""Custom module loader that transforms source code.
When the source code is converted to a code object, we transform
certain patterns to be Python 3 compatible. This allows us to write code
that is natively Python 2 and compatible with Python 3 without
making the code excessively ugly.
We do this by transforming the token stream between parse and compile.
Implementing transformations invalidates caching assumptions made
by the built-in importer. The built-in importer stores a header on
saved bytecode files indicating the Python/bytecode version. If the
version changes, the cached bytecode is ignored. The Mercurial
transformations could change at any time. This means we need to check
that cached bytecode was generated with the current transformation
code or there could be a mismatch between cached bytecode and what
would be generated from this class.
We supplement the bytecode caching layer by wrapping ``get_data``
and ``set_data``. These functions are called when the
``SourceFileLoader`` retrieves and saves bytecode cache files,
respectively. We simply add an additional header on the file. As
long as the version in this file is changed when semantics change,
cached bytecode should be invalidated when transformations change.
The added header has the form ``HG<VERSION>``. That is a literal
``HG`` with 2 binary bytes indicating the transformation version.
"""
def get_data(self, path):
data = super(hgloader, self).get_data(path)
if not path.endswith(tuple(importlib.machinery.BYTECODE_SUFFIXES)):
return data
# There should be a header indicating the Mercurial transformation
# version. If it doesn't exist or doesn't match the current version,
# we raise an OSError because that is what
# ``SourceFileLoader.get_code()`` expects when loading bytecode
# paths to indicate the cached file is "bad."
if data[0:2] != b'HG':
raise OSError('no hg header')
if data[0:4] != BYTECODEHEADER:
raise OSError('hg header version mismatch')
return data[4:]
def set_data(self, path, data, *args, **kwargs):
if path.endswith(tuple(importlib.machinery.BYTECODE_SUFFIXES)):
data = BYTECODEHEADER + data
return super(hgloader, self).set_data(path, data, *args, **kwargs)
def source_to_code(self, data, path):
"""Perform token transformation before compilation."""
buf = io.BytesIO(data)
tokens = tokenize.tokenize(buf.readline)
data = tokenize.untokenize(replacetokens(list(tokens), self.name))
# Python's built-in importer strips frames from exceptions raised
# for this code. Unfortunately, that mechanism isn't extensible
# and our frame will be blamed for the import failure. There
# are extremely hacky ways to do frame stripping. We haven't
# implemented them because they are very ugly.
return super(hgloader, self).source_to_code(data, path)
# We automagically register our custom importer as a side-effect of loading.
# This is necessary to ensure that any entry points are able to import
# mercurial.* modules without having to perform this registration themselves.
if sys.version_info[0] >= 3:
_importercls = hgpathentryfinder
else:
_importercls = hgimporter
if not any(isinstance(x, _importercls) for x in sys.meta_path):
# meta_path is used before any implicit finders and before sys.path.
sys.meta_path.insert(0, _importercls())