annotate contrib/hgfixes/fix_bytes.py @ 11747:40d5633889bb

hgfixes: add a fixer to convert plain strings to bytestrings

This patch implements a 2to3 fixer that converts all plain strings in a python
source file to byte strings syntax. Example:

foo = 'Normal string'

would become

foo = b'Normal string'

The motivation behind this fixer can be found in
http://selenic.com/pipermail/mercurial-devel/2010-June/022363.html or, in other
words: the current hg source assumes that _most_ strings are "meant" to be byte
sequences, so it makes sense to make the convertion implemented by this patch.

As mentioned above, not all mercurial modules want to use strings as bytes,
examples include i18n (which uses unicode), and demandimport (in py3k, module
names are normal strings, thus unicode, and there's no need for a convertion).
Therefore, these modules are blacklisted in the fixer. There are also a few
functions that can take only unicode arguments, thus the convertion shouldn't
be done for those.

"""Fixer that changes plain strings to bytes strings."""

import re

from lib2to3 import fixer_base
from lib2to3.pgen2 import token
from lib2to3.fixer_util import Name
from lib2to3.pygram import python_symbols as syms

_re = re.compile(r'[rR]?[\'\"]')

# XXX: Implementing a blacklist in 2to3 turned out to be more troublesome than
# blacklisting some modules inside the fixers. So, this is what I came with.

blacklist = ['mercurial/demandimport.py',
             'mercurial/i18n.py',
            ]

def isdocstring(node):
    def isclassorfunction(ancestor):
        symbols = (syms.funcdef, syms.classdef)
        # if the current node is a child of a function definition, a class
        # definition or a file, then it is a docstring
        if ancestor.type == syms.simple_stmt:
            try:
                while True:
                    if ancestor.type in symbols:
                        return True
                    ancestor = ancestor.parent
            except AttributeError:
                return False
        return False

    def ismodule(ancestor):
        # Our child is a docstring if we are a simple statement, and our
        # ancestor is file_input. In other words, our child is a lone string in
        # the source file.
        try:
            if (ancestor.type == syms.simple_stmt and
                ancestor.parent.type == syms.file_input):
                    return True
        except AttributeError:
            return False

    def isdocassignment(ancestor):
        # Assigning to __doc__, definitely a string
        try:
            while True:
                if (ancestor.type == syms.expr_stmt and
                    Name('__doc__') in ancestor.children):
                        return True
                ancestor = ancestor.parent
        except AttributeError:
            return False

    if ismodule(node.parent) or \
       isdocassignment(node.parent) or \
       isclassorfunction(node.parent):
        return True
    return False

def shouldtransform(node):
    specialnames = ['__main__']

    if node.value in specialnames:
        return False

    ggparent = node.parent.parent.parent
    sggparent = str(ggparent)

    if 'getattr' in sggparent or \
       'hasattr' in sggparent or \
       'setattr' in sggparent or \
       'encode' in sggparent or \
       'decode' in sggparent:
           return False

    return True

class FixBytes(fixer_base.BaseFix):

    PATTERN = 'STRING'

    def transform(self, node, results):
        if self.filename in blacklist:
            return
        if node.type == token.STRING:
            if _re.match(node.value):
                if isdocstring(node):
                    return
                if not shouldtransform(node):
                    return
                new = node.clone()
                new.value = 'b' + new.value
                return new