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# __init__.py - Startup and module loading logic for Mercurial.
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#
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# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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from __future__ import absolute_import
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import sys
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# Allow 'from mercurial import demandimport' to keep working.
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import hgdemandimport
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demandimport = hgdemandimport
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__all__ = []
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# Python 3 uses a custom module loader that transforms source code between
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# source file reading and compilation. This is done by registering a custom
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# finder that changes the spec for Mercurial modules to use a custom loader.
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if sys.version_info[0] >= 3:
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import importlib
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import importlib.abc
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import io
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import token
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import tokenize
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class hgpathentryfinder(importlib.abc.MetaPathFinder):
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"""A sys.meta_path finder that uses a custom module loader."""
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def find_spec(self, fullname, path, target=None):
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# Only handle Mercurial-related modules.
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if not fullname.startswith(('mercurial.', 'hgext.', 'hgext3rd.')):
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return None
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# don't try to parse binary
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if fullname.startswith('mercurial.cext.'):
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return None
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# third-party packages are expected to be dual-version clean
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if fullname.startswith('mercurial.thirdparty'):
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return None
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# zstd is already dual-version clean, don't try and mangle it
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if fullname.startswith('mercurial.zstd'):
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return None
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# pywatchman is already dual-version clean, don't try and mangle it
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if fullname.startswith('hgext.fsmonitor.pywatchman'):
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return None
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# Try to find the module using other registered finders.
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spec = None
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for finder in sys.meta_path:
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if finder == self:
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continue
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spec = finder.find_spec(fullname, path, target=target)
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if spec:
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break
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# This is a Mercurial-related module but we couldn't find it
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# using the previously-registered finders. This likely means
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# the module doesn't exist.
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if not spec:
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return None
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# TODO need to support loaders from alternate specs, like zip
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# loaders.
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loader = hgloader(spec.name, spec.origin)
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# Can't use util.safehasattr here because that would require
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# importing util, and we're in import code.
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if hasattr(spec.loader, 'loader'): # hasattr-py3-only
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# This is a nested loader (maybe a lazy loader?)
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spec.loader.loader = loader
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else:
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spec.loader = loader
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return spec
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def replacetokens(tokens, fullname):
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"""Transform a stream of tokens from raw to Python 3.
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It is called by the custom module loading machinery to rewrite
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source/tokens between source decoding and compilation.
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Returns a generator of possibly rewritten tokens.
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The input token list may be mutated as part of processing. However,
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its changes do not necessarily match the output token stream.
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REMEMBER TO CHANGE ``BYTECODEHEADER`` WHEN CHANGING THIS FUNCTION
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OR CACHED FILES WON'T GET INVALIDATED PROPERLY.
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"""
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futureimpline = False
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# The following utility functions access the tokens list and i index of
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# the for i, t enumerate(tokens) loop below
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def _isop(j, *o):
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"""Assert that tokens[j] is an OP with one of the given values"""
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try:
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return tokens[j].type == token.OP and tokens[j].string in o
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except IndexError:
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return False
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def _findargnofcall(n):
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"""Find arg n of a call expression (start at 0)
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Returns index of the first token of that argument, or None if
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there is not that many arguments.
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Assumes that token[i + 1] is '('.
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"""
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nested = 0
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for j in range(i + 2, len(tokens)):
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if _isop(j, ')', ']', '}'):
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# end of call, tuple, subscription or dict / set
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nested -= 1
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if nested < 0:
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return None
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elif n == 0:
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# this is the starting position of arg
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return j
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elif _isop(j, '(', '[', '{'):
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nested += 1
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elif _isop(j, ',') and nested == 0:
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n -= 1
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return None
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def _ensureunicode(j):
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"""Make sure the token at j is a unicode string
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This rewrites a string token to include the unicode literal prefix
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so the string transformer won't add the byte prefix.
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Ignores tokens that are not strings. Assumes bounds checking has
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already been done.
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"""
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st = tokens[j]
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if st.type == token.STRING and st.string.startswith(("'", '"')):
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tokens[j] = st._replace(string='u%s' % st.string)
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for i, t in enumerate(tokens):
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# Convert most string literals to byte literals. String literals
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# in Python 2 are bytes. String literals in Python 3 are unicode.
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# Most strings in Mercurial are bytes and unicode strings are rare.
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# Rather than rewrite all string literals to use ``b''`` to indicate
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# byte strings, we apply this token transformer to insert the ``b``
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# prefix nearly everywhere.
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if t.type == token.STRING:
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s = t.string
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# Preserve docstrings as string literals. This is inconsistent
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# with regular unprefixed strings. However, the
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# "from __future__" parsing (which allows a module docstring to
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# exist before it) doesn't properly handle the docstring if it
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# is b''' prefixed, leading to a SyntaxError. We leave all
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# docstrings as unprefixed to avoid this. This means Mercurial
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# components touching docstrings need to handle unicode,
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# unfortunately.
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if s[0:3] in ("'''", '"""'):
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yield t
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continue
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# If the first character isn't a quote, it is likely a string
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# prefixing character (such as 'b', 'u', or 'r'. Ignore.
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if s[0] not in ("'", '"'):
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yield t
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continue
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# String literal. Prefix to make a b'' string.
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yield t._replace(string='b%s' % t.string)
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continue
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# Insert compatibility imports at "from __future__ import" line.
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# No '\n' should be added to preserve line numbers.
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if (t.type == token.NAME and t.string == 'import' and
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all(u.type == token.NAME for u in tokens[i - 2:i]) and
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[u.string for u in tokens[i - 2:i]] == ['from', '__future__']):
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futureimpline = True
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if t.type == token.NEWLINE and futureimpline:
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futureimpline = False
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if fullname == 'mercurial.pycompat':
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yield t
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continue
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r, c = t.start
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l = (b'; from mercurial.pycompat import '
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b'delattr, getattr, hasattr, setattr, xrange, '
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b'open, unicode\n')
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for u in tokenize.tokenize(io.BytesIO(l).readline):
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if u.type in (tokenize.ENCODING, token.ENDMARKER):
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continue
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yield u._replace(
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start=(r, c + u.start[1]), end=(r, c + u.end[1]))
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continue
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# This looks like a function call.
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if t.type == token.NAME and _isop(i + 1, '('):
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fn = t.string
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# *attr() builtins don't accept byte strings to 2nd argument.
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if (fn in ('getattr', 'setattr', 'hasattr', 'safehasattr') and
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not _isop(i - 1, '.')):
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arg1idx = _findargnofcall(1)
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if arg1idx is not None:
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_ensureunicode(arg1idx)
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# .encode() and .decode() on str/bytes/unicode don't accept
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# byte strings on Python 3.
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elif fn in ('encode', 'decode') and _isop(i - 1, '.'):
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for argn in range(2):
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argidx = _findargnofcall(argn)
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if argidx is not None:
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_ensureunicode(argidx)
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# It changes iteritems/values to items/values as they are not
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# present in Python 3 world.
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elif fn in ('iteritems', 'itervalues'):
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yield t._replace(string=fn[4:])
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continue
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# Emit unmodified token.
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yield t
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# Header to add to bytecode files. This MUST be changed when
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# ``replacetoken`` or any mechanism that changes semantics of module
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# loading is changed. Otherwise cached bytecode may get loaded without
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# the new transformation mechanisms applied.
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BYTECODEHEADER = b'HG\x00\x0a'
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class hgloader(importlib.machinery.SourceFileLoader):
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"""Custom module loader that transforms source code.
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When the source code is converted to a code object, we transform
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certain patterns to be Python 3 compatible. This allows us to write code
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that is natively Python 2 and compatible with Python 3 without
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making the code excessively ugly.
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We do this by transforming the token stream between parse and compile.
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Implementing transformations invalidates caching assumptions made
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by the built-in importer. The built-in importer stores a header on
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saved bytecode files indicating the Python/bytecode version. If the
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version changes, the cached bytecode is ignored. The Mercurial
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transformations could change at any time. This means we need to check
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that cached bytecode was generated with the current transformation
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code or there could be a mismatch between cached bytecode and what
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would be generated from this class.
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We supplement the bytecode caching layer by wrapping ``get_data``
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and ``set_data``. These functions are called when the
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``SourceFileLoader`` retrieves and saves bytecode cache files,
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respectively. We simply add an additional header on the file. As
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long as the version in this file is changed when semantics change,
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cached bytecode should be invalidated when transformations change.
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The added header has the form ``HG<VERSION>``. That is a literal
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``HG`` with 2 binary bytes indicating the transformation version.
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"""
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def get_data(self, path):
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data = super(hgloader, self).get_data(path)
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if not path.endswith(tuple(importlib.machinery.BYTECODE_SUFFIXES)):
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return data
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# There should be a header indicating the Mercurial transformation
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# version. If it doesn't exist or doesn't match the current version,
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# we raise an OSError because that is what
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# ``SourceFileLoader.get_code()`` expects when loading bytecode
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# paths to indicate the cached file is "bad."
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if data[0:2] != b'HG':
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raise OSError('no hg header')
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if data[0:4] != BYTECODEHEADER:
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raise OSError('hg header version mismatch')
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return data[4:]
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def set_data(self, path, data, *args, **kwargs):
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if path.endswith(tuple(importlib.machinery.BYTECODE_SUFFIXES)):
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data = BYTECODEHEADER + data
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return super(hgloader, self).set_data(path, data, *args, **kwargs)
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def source_to_code(self, data, path):
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"""Perform token transformation before compilation."""
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buf = io.BytesIO(data)
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tokens = tokenize.tokenize(buf.readline)
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data = tokenize.untokenize(replacetokens(list(tokens), self.name))
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# Python's built-in importer strips frames from exceptions raised
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# for this code. Unfortunately, that mechanism isn't extensible
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# and our frame will be blamed for the import failure. There
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# are extremely hacky ways to do frame stripping. We haven't
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# implemented them because they are very ugly.
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return super(hgloader, self).source_to_code(data, path)
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# We automagically register our custom importer as a side-effect of
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# loading. This is necessary to ensure that any entry points are able
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# to import mercurial.* modules without having to perform this
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# registration themselves.
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if not any(isinstance(x, hgpathentryfinder) for x in sys.meta_path):
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# meta_path is used before any implicit finders and before sys.path.
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sys.meta_path.insert(0, hgpathentryfinder())
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