mercurial/encoding.py

i18n: calculate terminal columns by width information of each characters

neither number of 'bytes' in any encoding nor 'characters' is
appropriate to calculate terminal columns for specified string.

this patch modifies MBTextWrapper for:

  - overriding '_wrap_chunks()' to make it use not built-in 'len()'
    but 'encoding.colwidth()' for columns of string

  - fixing '_cutdown()' to make it use 'encoding.colwidth()' instead
    of local, similar but incorrect implementation

this patch also modifies 'encoding.py':

  - dividing 'colwith()' into 2 pieces: one for calculation columns of
    specified UNICODE string, and another for rest part of original
    one. the former is used from MBTextWrapper in 'util.py'.

  - preventing 'colwidth()' from evaluating HGENCODINGAMBIGUOUS
    configuration per each invocation: 'unicodedata.east_asian_width'
    checking is kept intact for reducing startup cost.

# encoding.py - character transcoding support for Mercurial
#
#  Copyright 2005-2009 Matt Mackall <[e-mail]> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import error
import unicodedata, locale, os

def _getpreferredencoding():
    '''
    On darwin, getpreferredencoding ignores the locale environment and
    always returns mac-roman. http://bugs.python.org/issue6202 fixes this
    for Python 2.7 and up. This is the same corrected code for earlier
    Python versions.

    However, we can't use a version check for this method, as some distributions
    patch Python to fix this. Instead, we use it as a 'fixer' for the mac-roman
    encoding, as it is unlikely that this encoding is the actually expected.
    '''
    try:
        locale.CODESET
    except AttributeError:
        # Fall back to parsing environment variables :-(
        return locale.getdefaultlocale()[1]

    oldloc = locale.setlocale(locale.LC_CTYPE)
    locale.setlocale(locale.LC_CTYPE, "")
    result = locale.nl_langinfo(locale.CODESET)
    locale.setlocale(locale.LC_CTYPE, oldloc)

    return result

_encodingfixers = {
    '646': lambda: 'ascii',
    'ANSI_X3.4-1968': lambda: 'ascii',
    'mac-roman': _getpreferredencoding
}

try:
    encoding = os.environ.get("HGENCODING")
    if not encoding:
        encoding = locale.getpreferredencoding() or 'ascii'
        encoding = _encodingfixers.get(encoding, lambda: encoding)()
except locale.Error:
    encoding = 'ascii'
encodingmode = os.environ.get("HGENCODINGMODE", "strict")
fallbackencoding = 'ISO-8859-1'

class localstr(str):
    '''This class allows strings that are unmodified to be
    round-tripped to the local encoding and back'''
    def __new__(cls, u, l):
        s = str.__new__(cls, l)
        s._utf8 = u
        return s
    def __hash__(self):
        return hash(self._utf8) # avoid collisions in local string space

def tolocal(s):
    """
    Convert a string from internal UTF-8 to local encoding

    All internal strings should be UTF-8 but some repos before the
    implementation of locale support may contain latin1 or possibly
    other character sets. We attempt to decode everything strictly
    using UTF-8, then Latin-1, and failing that, we use UTF-8 and
    replace unknown characters.

    The localstr class is used to cache the known UTF-8 encoding of
    strings next to their local representation to allow lossless
    round-trip conversion back to UTF-8.

    >>> u = 'foo: \\xc3\\xa4' # utf-8
    >>> l = tolocal(u)
    >>> l
    'foo: ?'
    >>> fromlocal(l)
    'foo: \\xc3\\xa4'
    >>> u2 = 'foo: \\xc3\\xa1'
    >>> d = { l: 1, tolocal(u2): 2 }
    >>> d # no collision
    {'foo: ?': 1, 'foo: ?': 2}
    >>> 'foo: ?' in d
    False
    >>> l1 = 'foo: \\xe4' # historical latin1 fallback
    >>> l = tolocal(l1)
    >>> l
    'foo: ?'
    >>> fromlocal(l) # magically in utf-8
    'foo: \\xc3\\xa4'
    """

    for e in ('UTF-8', fallbackencoding):
        try:
            u = s.decode(e) # attempt strict decoding
            r = u.encode(encoding, "replace")
            if u == r.decode(encoding):
                # r is a safe, non-lossy encoding of s
                return r
            elif e == 'UTF-8':
                return localstr(s, r)
            else:
                return localstr(u.encode('UTF-8'), r)

        except LookupError, k:
            raise error.Abort("%s, please check your locale settings" % k)
        except UnicodeDecodeError:
            pass
    u = s.decode("utf-8", "replace") # last ditch
    return u.encode(encoding, "replace") # can't round-trip

def fromlocal(s):
    """
    Convert a string from the local character encoding to UTF-8

    We attempt to decode strings using the encoding mode set by
    HGENCODINGMODE, which defaults to 'strict'. In this mode, unknown
    characters will cause an error message. Other modes include
    'replace', which replaces unknown characters with a special
    Unicode character, and 'ignore', which drops the character.
    """

    # can we do a lossless round-trip?
    if isinstance(s, localstr):
        return s._utf8

    try:
        return s.decode(encoding, encodingmode).encode("utf-8")
    except UnicodeDecodeError, inst:
        sub = s[max(0, inst.start - 10):inst.start + 10]
        raise error.Abort("decoding near '%s': %s!" % (sub, inst))
    except LookupError, k:
        raise error.Abort("%s, please check your locale settings" % k)

# How to treat ambiguous-width characters. Set to 'wide' to treat as wide.
wide = (os.environ.get("HGENCODINGAMBIGUOUS", "narrow") == "wide"
        and "WFA" or "WF")

def colwidth(s):
    "Find the column width of a UTF-8 string for display"
    return ucolwidth(s.decode(encoding, 'replace'))

def ucolwidth(d):
    "Find the column width of a Unicode string for display"
    eaw = getattr(unicodedata, 'east_asian_width', None)
    if eaw is not None:
        return sum([eaw(c) in wide and 2 or 1 for c in d])
    return len(d)

def lower(s):
    "best-effort encoding-aware case-folding of local string s"
    try:
        if isinstance(s, localstr):
            u = s._utf8.decode("utf-8")
        else:
            u = s.decode(encoding, encodingmode)

        lu = u.lower()
        if u == lu:
            return s # preserve localstring
        return lu.encode(encoding)
    except UnicodeError:
        return s.lower() # we don't know how to fold this except in ASCII