mercurial/encoding.py

parsers: add a function to efficiently lowercase ASCII strings

We need a way to efficiently lowercase ASCII strings. For example, 'hg status'
needs to build up the fold map -- a map from a canonical case (for OS X,
lowercase) to the actual case of each file and directory in the dirstate.

The current way we do that is to try decoding to ASCII and then calling
lower() on the string, labeled 'orig' below:

    str.decode('ascii')
    return str.lower()

This is pretty inefficient, and it turns out we can do much better.

I also tested out a condition-based approach, labeled 'cond' below:

    (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c

'cond' turned out to be slower in all cases. A 256-byte lookup table with
invalid values for everything past 127 performed similarly, but this was less
verbose.

On OS X 10.9 with LLVM version 6.0 (clang-600.0.51), the asciilower function
was run against two corpuses.

Corpus 1 (list of files from real-world repo, > 100k files):
orig:   wall 0.428567 comb 0.430000 user 0.430000 sys 0.000000 (best of 24)
cond:   wall 0.077204 comb 0.070000 user 0.070000 sys 0.000000 (best of 100)
lookup: wall 0.060714 comb 0.060000 user 0.060000 sys 0.000000 (best of 100)

Corpus 2 (mozilla-central, 113k files):
orig:   wall 0.238406 comb 0.240000 user 0.240000 sys 0.000000 (best of 42)
cond:   wall 0.040779 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)
lookup: wall 0.037623 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)

On a Linux server-class machine with GCC 4.4.6 20120305 (Red Hat 4.4.6-4):

Corpus 1 (real-world repo, > 100k files):
orig:   wall 0.260899 comb 0.260000 user 0.260000 sys 0.000000 (best of 38)
cond:   wall 0.054818 comb 0.060000 user 0.060000 sys 0.000000 (best of 100)
lookup: wall 0.048489 comb 0.050000 user 0.050000 sys 0.000000 (best of 100)

Corpus 2 (mozilla-central, 113k files):
orig:   wall 0.153082 comb 0.150000 user 0.150000 sys 0.000000 (best of 65)
cond:   wall 0.031007 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)
lookup: wall 0.028793 comb 0.030000 user 0.030000 sys 0.000000 (best of 100)

SSE instructions might help even more, but I didn't experiment with those.

# 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, parsers
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 }
    >>> len(d) # no collision
    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'
    """

    try:
        try:
            # make sure string is actually stored in UTF-8
            u = s.decode('UTF-8')
            if encoding == 'UTF-8':
                # fast path
                return s
            r = u.encode(encoding, "replace")
            if u == r.decode(encoding):
                # r is a safe, non-lossy encoding of s
                return r
            return localstr(s, r)
        except UnicodeDecodeError:
            # we should only get here if we're looking at an ancient changeset
            try:
                u = s.decode(fallbackencoding)
                r = u.encode(encoding, "replace")
                if u == r.decode(encoding):
                    # r is a safe, non-lossy encoding of s
                    return r
                return localstr(u.encode('UTF-8'), r)
            except UnicodeDecodeError:
                u = s.decode("utf-8", "replace") # last ditch
                return u.encode(encoding, "replace") # can't round-trip
    except LookupError, k:
        raise error.Abort(k, hint="please check your locale settings")

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(k, hint="please check your locale settings")

# 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 string for display in the local encoding"
    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 getcols(s, start, c):
    '''Use colwidth to find a c-column substring of s starting at byte
    index start'''
    for x in xrange(start + c, len(s)):
        t = s[start:x]
        if colwidth(t) == c:
            return t

def trim(s, width, ellipsis='', leftside=False):
    """Trim string 's' to at most 'width' columns (including 'ellipsis').

    If 'leftside' is True, left side of string 's' is trimmed.
    'ellipsis' is always placed at trimmed side.

    >>> ellipsis = '+++'
    >>> from mercurial import encoding
    >>> encoding.encoding = 'utf-8'
    >>> t= '1234567890'
    >>> print trim(t, 12, ellipsis=ellipsis)
    1234567890
    >>> print trim(t, 10, ellipsis=ellipsis)
    1234567890
    >>> print trim(t, 8, ellipsis=ellipsis)
    12345+++
    >>> print trim(t, 8, ellipsis=ellipsis, leftside=True)
    +++67890
    >>> print trim(t, 8)
    12345678
    >>> print trim(t, 8, leftside=True)
    34567890
    >>> print trim(t, 3, ellipsis=ellipsis)
    +++
    >>> print trim(t, 1, ellipsis=ellipsis)
    +
    >>> u = u'\u3042\u3044\u3046\u3048\u304a' # 2 x 5 = 10 columns
    >>> t = u.encode(encoding.encoding)
    >>> print trim(t, 12, ellipsis=ellipsis)
    \xe3\x81\x82\xe3\x81\x84\xe3\x81\x86\xe3\x81\x88\xe3\x81\x8a
    >>> print trim(t, 10, ellipsis=ellipsis)
    \xe3\x81\x82\xe3\x81\x84\xe3\x81\x86\xe3\x81\x88\xe3\x81\x8a
    >>> print trim(t, 8, ellipsis=ellipsis)
    \xe3\x81\x82\xe3\x81\x84+++
    >>> print trim(t, 8, ellipsis=ellipsis, leftside=True)
    +++\xe3\x81\x88\xe3\x81\x8a
    >>> print trim(t, 5)
    \xe3\x81\x82\xe3\x81\x84
    >>> print trim(t, 5, leftside=True)
    \xe3\x81\x88\xe3\x81\x8a
    >>> print trim(t, 4, ellipsis=ellipsis)
    +++
    >>> print trim(t, 4, ellipsis=ellipsis, leftside=True)
    +++
    >>> t = '\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa' # invalid byte sequence
    >>> print trim(t, 12, ellipsis=ellipsis)
    \x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa
    >>> print trim(t, 10, ellipsis=ellipsis)
    \x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa
    >>> print trim(t, 8, ellipsis=ellipsis)
    \x11\x22\x33\x44\x55+++
    >>> print trim(t, 8, ellipsis=ellipsis, leftside=True)
    +++\x66\x77\x88\x99\xaa
    >>> print trim(t, 8)
    \x11\x22\x33\x44\x55\x66\x77\x88
    >>> print trim(t, 8, leftside=True)
    \x33\x44\x55\x66\x77\x88\x99\xaa
    >>> print trim(t, 3, ellipsis=ellipsis)
    +++
    >>> print trim(t, 1, ellipsis=ellipsis)
    +
    """
    try:
        u = s.decode(encoding)
    except UnicodeDecodeError:
        if len(s) <= width: # trimming is not needed
            return s
        width -= len(ellipsis)
        if width <= 0: # no enough room even for ellipsis
            return ellipsis[:width + len(ellipsis)]
        if leftside:
            return ellipsis + s[-width:]
        return s[:width] + ellipsis

    if ucolwidth(u) <= width: # trimming is not needed
        return s

    width -= len(ellipsis)
    if width <= 0: # no enough room even for ellipsis
        return ellipsis[:width + len(ellipsis)]

    if leftside:
        uslice = lambda i: u[i:]
        concat = lambda s: ellipsis + s
    else:
        uslice = lambda i: u[:-i]
        concat = lambda s: s + ellipsis
    for i in xrange(1, len(u)):
        usub = uslice(i)
        if ucolwidth(usub) <= width:
            return concat(usub.encode(encoding))
    return ellipsis # no enough room for multi-column characters

def asciilower(s):
    '''convert a string to lowercase if ASCII

    Raises UnicodeDecodeError if non-ASCII characters are found.'''
    s.decode('ascii')
    return s.lower()

asciilower = getattr(parsers, 'asciilower', asciilower)

def lower(s):
    "best-effort encoding-aware case-folding of local string s"
    try:
        s.decode('ascii') # throw exception for non-ASCII character
        return s.lower()
    except UnicodeDecodeError:
        pass
    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
    except LookupError, k:
        raise error.Abort(k, hint="please check your locale settings")

def upper(s):
    "best-effort encoding-aware case-folding of local string s"
    try:
        s.decode('ascii') # throw exception for non-ASCII character
        return s.upper()
    except UnicodeDecodeError:
        pass
    try:
        if isinstance(s, localstr):
            u = s._utf8.decode("utf-8")
        else:
            u = s.decode(encoding, encodingmode)

        uu = u.upper()
        if u == uu:
            return s # preserve localstring
        return uu.encode(encoding)
    except UnicodeError:
        return s.upper() # we don't know how to fold this except in ASCII
    except LookupError, k:
        raise error.Abort(k, hint="please check your locale settings")

_jsonmap = {}

def jsonescape(s):
    '''returns a string suitable for JSON

    JSON is problematic for us because it doesn't support non-Unicode
    bytes. To deal with this, we take the following approach:

    - localstr objects are converted back to UTF-8
    - valid UTF-8/ASCII strings are passed as-is
    - other strings are converted to UTF-8b surrogate encoding
    - apply JSON-specified string escaping

    (escapes are doubled in these tests)

    >>> jsonescape('this is a test')
    'this is a test'
    >>> jsonescape('escape characters: \\0 \\x0b \\t \\n \\r \\" \\\\')
    'escape characters: \\\\u0000 \\\\u000b \\\\t \\\\n \\\\r \\\\" \\\\\\\\'
    >>> jsonescape('a weird byte: \\xdd')
    'a weird byte: \\xed\\xb3\\x9d'
    >>> jsonescape('utf-8: caf\\xc3\\xa9')
    'utf-8: caf\\xc3\\xa9'
    >>> jsonescape('')
    ''
    '''

    if not _jsonmap:
        for x in xrange(32):
            _jsonmap[chr(x)] = "\u%04x" %x
        for x in xrange(32, 256):
            c = chr(x)
            _jsonmap[c] = c
        _jsonmap['\t'] = '\\t'
        _jsonmap['\n'] = '\\n'
        _jsonmap['\"'] = '\\"'
        _jsonmap['\\'] = '\\\\'
        _jsonmap['\b'] = '\\b'
        _jsonmap['\f'] = '\\f'
        _jsonmap['\r'] = '\\r'

    return ''.join(_jsonmap[c] for c in toutf8b(s))

def toutf8b(s):
    '''convert a local, possibly-binary string into UTF-8b

    This is intended as a generic method to preserve data when working
    with schemes like JSON and XML that have no provision for
    arbitrary byte strings. As Mercurial often doesn't know
    what encoding data is in, we use so-called UTF-8b.

    If a string is already valid UTF-8 (or ASCII), it passes unmodified.
    Otherwise, unsupported bytes are mapped to UTF-16 surrogate range,
    uDC00-uDCFF.

    Principles of operation:

    - ASCII and UTF-8 data successfully round-trips and is understood
      by Unicode-oriented clients
    - filenames and file contents in arbitrary other encodings can have
      be round-tripped or recovered by clueful clients
    - local strings that have a cached known UTF-8 encoding (aka
      localstr) get sent as UTF-8 so Unicode-oriented clients get the
      Unicode data they want
    - because we must preserve UTF-8 bytestring in places such as
      filenames, metadata can't be roundtripped without help

    (Note: "UTF-8b" often refers to decoding a mix of valid UTF-8 and
    arbitrary bytes into an internal Unicode format that can be
    re-encoded back into the original. Here we are exposing the
    internal surrogate encoding as a UTF-8 string.)
    '''

    if isinstance(s, localstr):
        return s._utf8

    try:
        s.decode('utf-8')
        return s
    except UnicodeDecodeError:
        # surrogate-encode any characters that don't round-trip
        s2 = s.decode('utf-8', 'ignore').encode('utf-8')
        r = ""
        pos = 0
        for c in s:
            if s2[pos:pos + 1] == c:
                r += c
                pos += 1
            else:
                r += unichr(0xdc00 + ord(c)).encode('utf-8')
        return r

def fromutf8b(s):
    '''Given a UTF-8b string, return a local, possibly-binary string.

    return the original binary string. This
    is a round-trip process for strings like filenames, but metadata
    that's was passed through tolocal will remain in UTF-8.

    >>> m = "\\xc3\\xa9\\x99abcd"
    >>> n = toutf8b(m)
    >>> n
    '\\xc3\\xa9\\xed\\xb2\\x99abcd'
    >>> fromutf8b(n) == m
    True
    '''

    # fast path - look for uDxxx prefixes in s
    if "\xed" not in s:
        return s

    u = s.decode("utf-8")
    r = ""
    for c in u:
        if ord(c) & 0xff00 == 0xdc00:
            r += chr(ord(c) & 0xff)
        else:
            r += c.encode("utf-8")
    return r