[PATCH 1 of 6 foldmap-in-C] encoding: define an enum that specifies what normcase does to ASCII strings

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1427872870 25200
#      Wed Apr 01 00:21:10 2015 -0700
# Node ID 42a1040af0c362b38ce45fc71e065d1769902c79
# Parent  37a2b446985f2ef77b9690a0548c8630828b7412
encoding: define an enum that specifies what normcase does to ASCII strings

For C code we don't want to pay the cost of calling into a Python function for
the common case of ASCII filenames. However, while on most POSIX platforms we
prefer to normalize filenames by lowercasing them, on Windows we uppercase
them. We define an enum here indicating the direction that filenames should be
normalized as. Some platforms (notably Cygwin) have more complicated
normalization behavior -- we add a case for that too.

In upcoming patches we'll also define a fallback function that is called if the
string has non-ASCII bytes.

This enum will be replicated in the C code to make foldmaps. There's
unfortunately no nice way to avoid that -- we can't have encoding import
parsers because of import cycles. One way might be to have parsers import
encoding, but accessing Python modules from C code is just awkward.

The name 'normcaseasciispecs' was chosen to indicate that this is merely
an integer that specifies a behavior, not a function. The name was pluralized
since in upcoming patches we'll introduce 'normcaseasciispec' which will be one
of these values.

diff --git a/mercurial/encoding.py b/mercurial/encoding.py
--- a/mercurial/encoding.py
+++ b/mercurial/encoding.py
@@ -354,6 +354,19 @@ def upper(s):
     except LookupError, k:
         raise error.Abort(k, hint="please check your locale settings")
 
+class normcaseasciispecs(object):
+    '''what a platform's normcase does to ASCII strings
+
+    This is specified per platform, and should be consistent with what normcase
+    on that platform actually does.
+
+    lower: normcase lowercases ASCII strings
+    upper: normcase uppercases ASCII strings
+    other: the fallback function should always be called'''
+    lower = -1
+    upper = 1
+    other = 0
+
 _jsonmap = {}
 
 def jsonescape(s):