[PATCH 2 of 3 RFC] py3kcompat: added a "compatibility layer" for py3k

[Renato Cunha]

# HG changeset patch
# User Renato Cunha <renatoc at gmail.com>
# Date 1280854368 10800
# Node ID 6f03bc4c53e5d9fa072923bf1beb29c4e9aa8531
# Parent  11660a9463432288abd71f7b11ea8890683d2954
py3kcompat: added a "compatibility layer" for py3k

This patch adds some ugly constructs. The first of them is bytesformatter, a
function that formats strings like when '%' is called. The main motivation for
this function is py3k's strange behavior:

>>> 'foo %s' % b'bar'
"foo b'bar'"
>>> b'foo %s' % b'bar'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for %: 'bytes' and 'bytes'
>>> b'foo %s' % 'bar'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for %: 'bytes' and 'str'

In other words, if we can't format bytes with bytes, and recall that all
mercurial strings will be converted by a fixer, then things will break badly if
we don't take a similar approach.

The other addition with this patch is that the os.environ dictionary is
monkeypatched to have bytes items. Hopefully this won't be needed in the
future, as python 3.2 might get a os.environb dictionary that holds bytes
items.

diff --git a/contrib/hgfixes/fix_bytes.py b/contrib/hgfixes/fix_bytes.py
--- a/contrib/hgfixes/fix_bytes.py
+++ b/contrib/hgfixes/fix_bytes.py
@@ -13,6 +13,7 @@
 # blacklisting some modules inside the fixers. So, this is what I came with.
 
 blacklist = ['mercurial/demandimport.py',
+             'mercurial/py3kcompat.py', # valid python 3 already
              'mercurial/i18n.py',
             ]
 
diff --git a/mercurial/py3kcompat.py b/mercurial/py3kcompat.py
new file mode 100644
--- /dev/null
+++ b/mercurial/py3kcompat.py
@@ -0,0 +1,65 @@
+# py3kcompat.py - compatibility definitions for running hg in py3k
+#
+# Copyright 2010 Renato Cunha <renatoc at gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+import os, builtins
+
+from numbers import Number
+
+def bytesformatter(format, args):
+    '''Custom implementation of a formatter for bytestrings.
+
+    This function currently relias on the string formatter to do the
+    formatting and always returns bytes objects.
+
+    >>> bytesformatter(20, 10)
+    0
+    >>> bytesformatter('unicode %s, %s!', ('string', 'foo'))
+    b'unicode string, foo!'
+    >>> bytesformatter(b'test %s', 'me')
+    b'test me'
+    >>> bytesformatter('test %s', 'me')
+    b'test me'
+    >>> bytesformatter(b'test %s', b'me')
+    b'test me'
+    >>> bytesformatter('test %s', b'me')
+    b'test me'
+    >>> bytesformatter('test %d: %s', (1, b'result'))
+    b'test 1: result'
+    '''
+    # The current implementation just converts from bytes to unicode, do
+    # what's needed and then convert the results back to bytes.
+    # Another alternative is to use the Python C API implementation.
+    if isinstance(format, Number):
+        # If the fixer erroneously passes a number remainder operation to
+        # bytesformatter, we just return the correct operation
+        return format % args
+    if isinstance(format, bytes):
+        format = format.decode('utf-8', 'surrogateescape')
+    if isinstance(args, bytes):
+        args = args.decode('utf-8', 'surrogateescape')
+    if isinstance(args, tuple):
+        newargs = []
+        for arg in args:
+            if isinstance(arg, bytes):
+                arg = arg.decode('utf-8', 'surrogateescape')
+            newargs.append(arg)
+        args = tuple(newargs)
+    ret = format % args
+    return ret.encode('utf-8', 'surrogateescape')
+builtins.bytesformatter = bytesformatter
+
+# Create bytes equivalents for os.environ values
+for key in list(os.environ.keys()):
+    # UTF-8 is fine for us
+    bkey = key.encode('utf-8', 'surrogateescape')
+    bvalue = os.environ[key].encode('utf-8', 'surrogateescape')
+    os.environ[bkey] = bvalue
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+