view mercurial/pure/bdiff.py @ 46779:49fd21f32695

revlog: guarantee that p1 != null if a non-null parent exists

This change does not affect the hashing (which already did this
transformation), but can change the log output in the rare case where
this behavior was observed in repositories. The change can simplify
iteration code where regular changesets and merges are distinct
branches.

Differential Revision: https://phab.mercurial-scm.org/D10150

# bdiff.py - Python implementation of bdiff.c
#
# Copyright 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.

from __future__ import absolute_import

import difflib
import re
import struct


def splitnewlines(text):
    '''like str.splitlines, but only split on newlines.'''
    lines = [l + b'\n' for l in text.split(b'\n')]
    if lines:
        if lines[-1] == b'\n':
            lines.pop()
        else:
            lines[-1] = lines[-1][:-1]
    return lines


def _normalizeblocks(a, b, blocks):
    prev = None
    r = []
    for curr in blocks:
        if prev is None:
            prev = curr
            continue
        shift = 0

        a1, b1, l1 = prev
        a1end = a1 + l1
        b1end = b1 + l1

        a2, b2, l2 = curr
        a2end = a2 + l2
        b2end = b2 + l2
        if a1end == a2:
            while (
                a1end + shift < a2end and a[a1end + shift] == b[b1end + shift]
            ):
                shift += 1
        elif b1end == b2:
            while (
                b1end + shift < b2end and a[a1end + shift] == b[b1end + shift]
            ):
                shift += 1
        r.append((a1, b1, l1 + shift))
        prev = a2 + shift, b2 + shift, l2 - shift

    if prev is not None:
        r.append(prev)

    return r


def bdiff(a, b):
    a = bytes(a).splitlines(True)
    b = bytes(b).splitlines(True)

    if not a:
        s = b"".join(b)
        return s and (struct.pack(b">lll", 0, 0, len(s)) + s)

    bin = []
    p = [0]
    for i in a:
        p.append(p[-1] + len(i))

    d = difflib.SequenceMatcher(None, a, b).get_matching_blocks()
    d = _normalizeblocks(a, b, d)
    la = 0
    lb = 0
    for am, bm, size in d:
        s = b"".join(b[lb:bm])
        if am > la or s:
            bin.append(struct.pack(b">lll", p[la], p[am], len(s)) + s)
        la = am + size
        lb = bm + size

    return b"".join(bin)


def blocks(a, b):
    an = splitnewlines(a)
    bn = splitnewlines(b)
    d = difflib.SequenceMatcher(None, an, bn).get_matching_blocks()
    d = _normalizeblocks(an, bn, d)
    return [(i, i + n, j, j + n) for (i, j, n) in d]


def fixws(text, allws):
    if allws:
        text = re.sub(b'[ \t\r]+', b'', text)
    else:
        text = re.sub(b'[ \t\r]+', b' ', text)
        text = text.replace(b' \n', b'\n')
    return text