contrib/byteify-strings.py

wireprotov2: change how revisions are specified to changesetdata

Right now, we have a handful of arguments for specifying the revisions
whose data should be returned. Defining how all these arguments
interact when various combinations are present is difficult.

This commit establishes a new, generic mechanism for specifying
revisions. Instead of a hodgepodge of arguments defining things, we
have a list of dicts that specify revision selectors. The final set
of revisions is a union of all these selectors.

We implement support for specifying revisions based on:

* An explicit list of changeset revisions
* An explicit list of changeset revisions plus ancestry depth
* A DAG range between changeset roots and heads

If you squint hard enough, this problem has already been solved by
revsets. But I'm reluctant to expose revsets to the wire protocol
because that would require servers to implement a revset parser.
Plus there are security and performance implications: the set
of revision selectors needs to be narrowly and specifically tailored
for what is appropriate to be executing on a server. Perhaps there
would be a way for us to express the "parse tree" of a revset
query, for example. I'm not sure. We can explore this space another
time. For now, the new mechanism should bring sufficient flexibility
while remaining relatively simple.

The selector "types" are prefixed with "changeset" because I plan
to add manifest and file-flavored selectors as well. This will enable
us to e.g. select file revisions based on a range of changeset
revisions.

Differential Revision: https://phab.mercurial-scm.org/D4979

#!/usr/bin/env python3
#
# byteify-strings.py - transform string literals to be Python 3 safe
#
# Copyright 2015 Gregory Szorc <[e-mail]>
#
# 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 argparse
import contextlib
import errno
import os
import sys
import tempfile
import token
import tokenize

def adjusttokenpos(t, ofs):
    """Adjust start/end column of the given token"""
    return t._replace(start=(t.start[0], t.start[1] + ofs),
                      end=(t.end[0], t.end[1] + ofs))

def replacetokens(tokens, opts):
    """Transform a stream of tokens from raw to Python 3.

    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.
    """
    sysstrtokens = set()

    # 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 _ensuresysstr(j):
        """Make sure the token at j is a system string

        Remember the given token 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(("'", '"')):
            sysstrtokens.add(st)

    coldelta = 0  # column increment for new opening parens
    coloffset = -1  # column offset for the current line (-1: TBD)
    parens = [(0, 0, 0)]  # stack of (line, end-column, column-offset)
    for i, t in enumerate(tokens):
        # Compute the column offset for the current line, such that
        # the current line will be aligned to the last opening paren
        # as before.
        if coloffset < 0:
            if t.start[1] == parens[-1][1]:
                coloffset = parens[-1][2]
            elif t.start[1] + 1 == parens[-1][1]:
                # fix misaligned indent of s/util.Abort/error.Abort/
                coloffset = parens[-1][2] + (parens[-1][1] - t.start[1])
            else:
                coloffset = 0

        # Reset per-line attributes at EOL.
        if t.type in (token.NEWLINE, tokenize.NL):
            yield adjusttokenpos(t, coloffset)
            coldelta = 0
            coloffset = -1
            continue

        # Remember the last paren position.
        if _isop(i, '(', '[', '{'):
            parens.append(t.end + (coloffset + coldelta,))
        elif _isop(i, ')', ']', '}'):
            parens.pop()

        # 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 and t not in sysstrtokens:
            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 adjusttokenpos(t, coloffset)
                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 adjusttokenpos(t, coloffset)
                continue

            # String literal. Prefix to make a b'' string.
            yield adjusttokenpos(t._replace(string='b%s' % t.string),
                                 coloffset)
            coldelta += 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:
                    _ensuresysstr(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:
                        _ensuresysstr(argidx)

            # It changes iteritems/values to items/values as they are not
            # present in Python 3 world.
            elif opts['dictiter'] and fn in ('iteritems', 'itervalues'):
                yield adjusttokenpos(t._replace(string=fn[4:]), coloffset)
                continue

        # Looks like "if __name__ == '__main__'".
        if (t.type == token.NAME and t.string == '__name__'
            and _isop(i + 1, '==')):
            _ensuresysstr(i + 2)

        # Emit unmodified token.
        yield adjusttokenpos(t, coloffset)

def process(fin, fout, opts):
    tokens = tokenize.tokenize(fin.readline)
    tokens = replacetokens(list(tokens), opts)
    fout.write(tokenize.untokenize(tokens))

def tryunlink(fname):
    try:
        os.unlink(fname)
    except OSError as err:
        if err.errno != errno.ENOENT:
            raise

@contextlib.contextmanager
def editinplace(fname):
    n = os.path.basename(fname)
    d = os.path.dirname(fname)
    fp = tempfile.NamedTemporaryFile(prefix='.%s-' % n, suffix='~', dir=d,
                                     delete=False)
    try:
        yield fp
        fp.close()
        if os.name == 'nt':
            tryunlink(fname)
        os.rename(fp.name, fname)
    finally:
        fp.close()
        tryunlink(fp.name)

def main():
    ap = argparse.ArgumentParser()
    ap.add_argument('-i', '--inplace', action='store_true', default=False,
                    help='edit files in place')
    ap.add_argument('--dictiter', action='store_true', default=False,
                    help='rewrite iteritems() and itervalues()'),
    ap.add_argument('files', metavar='FILE', nargs='+', help='source file')
    args = ap.parse_args()
    opts = {
        'dictiter': args.dictiter,
    }
    for fname in args.files:
        if args.inplace:
            with editinplace(fname) as fout:
                with open(fname, 'rb') as fin:
                    process(fin, fout, opts)
        else:
            with open(fname, 'rb') as fin:
                fout = sys.stdout.buffer
                process(fin, fout, opts)

if __name__ == '__main__':
    main()