encoding: add localstr class to track UTF-8 version of transcoded strings

This allows UTF-8 strings to losslessly round-trip through Mercurial

mercurial/encoding.py

@@ -1,103 +1,146 b''
 # 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
-            return u.encode(encoding, "replace")
+            if u == 'UTF-8':
+                return localstr(s, u.encode(encoding, "replace"))
+            else:
+                return localstr(u.encode('UTF-8'),
+                                u.encode(encoding, "replace"))
         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")
+    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.
 ambiguous = os.environ.get("HGENCODINGAMBIGUOUS", "narrow")
 
 def colwidth(s):
     "Find the column width of a UTF-8 string for display"
     d = s.decode(encoding, 'replace')
     if hasattr(unicodedata, 'east_asian_width'):
         wide = "WF"
         if ambiguous == "wide":
             wide = "WFA"
         w = unicodedata.east_asian_width
         return sum([w(c) in wide and 2 or 1 for c in d])
     return len(d)
 

tests/test-doctest.py

@@ -1,20 +1,20 b''
 # this is hack to make sure no escape characters are inserted into the output
 import os
 if 'TERM' in os.environ:
     del os.environ['TERM']
 import doctest
 
 import mercurial.changelog
 doctest.testmod(mercurial.changelog)
 
 import mercurial.dagparser
 doctest.testmod(mercurial.dagparser, optionflags=doctest.NORMALIZE_WHITESPACE)
 
 import mercurial.match
 doctest.testmod(mercurial.match)
 
-import mercurial.url
-doctest.testmod(mercurial.url)
+import mercurial.encoding
+doctest.testmod(mercurial.encoding)
 
 import hgext.convert.cvsps
 doctest.testmod(hgext.convert.cvsps)