mercurial/node.py

dirstate: change placeholder hash length to 20 bytes

Previously the new-node placeholder hash for manifests generated from the
dirstate was a 21byte long string of "!" characters. Normal hashes are only 20
bytes long.  This makes it complicated to implement more efficient manifest
implementations which rely on the hashes being fixed length.

Let's change this hash to just be 20 bytes long, and rely on the astronomical
improbability of an actual hash being 20 "!" bytes in a row (just like we rely
on no hash ever being the nullid).

A future diff will do this for added and modified dirstate markers as well, so
we're putting the new newnodeid in node.py so there's a common place for these
placeholders.

# node.py - basic nodeid manipulation for mercurial
#
# Copyright 2005, 2006 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import binascii

# This ugly style has a noticeable effect in manifest parsing
hex = binascii.hexlify
bin = binascii.unhexlify

nullrev = -1
nullid = b"\0" * 20
nullhex = hex(nullid)

# Phony node value to stand-in for new files in some uses of
# manifests.
newnodeid = '!' * 20

wdirnodes = set((newnodeid,))

# pseudo identifiers for working directory
# (they are experimental, so don't add too many dependencies on them)
wdirrev = 0x7fffffff
wdirid = b"\xff" * 20

def short(node):
    return hex(node[:6])