bdiff: give slight preference to appending lines
[This change could be folded into the previous changeset to minimize the repo
churn ...]
The general preference to matches in the middle of bdiff ranges helps getting
balanced recursion and efficient computation. But, as previous changes have
shown, it might also give diffs that seems "obviously wrong".
To mitigate that: If the best match on the A side starts at the beginning of
the bdiff range, don't aim for the middle-most B side match but for the
earliest.
This will make the matches balanced (by both sides being "early") even though
the bisection will be less balanced. Still, this case only apply if the *best*
and middle-most match was fully unbalanced on the A side. Each recursion will
thus even in this worst case reduce the problem significantly and we are not
re-introducing the problem that was fixed in f1ca249696ed.
The bundle size for 4.0 (hg bundle --base null -r 4.0 x.hg) happens to go from
22806817 to 22807275 bytes - a 0.002% increase.
This make the recent test-bdiff.py changes give a more pretty output ... but
they no longer show that the recursion is around middle matches (because it in
these cases isn't).
from __future__ import absolute_import, print_function
import struct
from mercurial import (
bdiff,
mpatch,
)
def test1(a, b):
d = bdiff.bdiff(a, b)
c = a
if d:
c = mpatch.patches(a, [d])
if c != b:
print("bad diff+patch result from\n %r to\n %r:" % (a, b))
print("bdiff: %r" % d)
print("patched: %r" % c[:200])
def test(a, b):
print("test", repr(a), repr(b))
test1(a, b)
test1(b, a)
test("a\nc\n\n\n\n", "a\nb\n\n\n")
test("a\nb\nc\n", "a\nc\n")
test("", "")
test("a\nb\nc", "a\nb\nc")
test("a\nb\nc\nd\n", "a\nd\n")
test("a\nb\nc\nd\n", "a\nc\ne\n")
test("a\nb\nc\n", "a\nc\n")
test("a\n", "c\na\nb\n")
test("a\n", "")
test("a\n", "b\nc\n")
test("a\n", "c\na\n")
test("", "adjfkjdjksdhfksj")
test("", "ab")
test("", "abc")
test("a", "a")
test("ab", "ab")
test("abc", "abc")
test("a\n", "a\n")
test("a\nb", "a\nb")
#issue1295
def showdiff(a, b):
print('showdiff(\n %r,\n %r):' % (a, b))
bin = bdiff.bdiff(a, b)
pos = 0
q = 0
while pos < len(bin):
p1, p2, l = struct.unpack(">lll", bin[pos:pos + 12])
pos += 12
if p1:
print('', repr(a[q:p1]))
print('', p1, p2, repr(a[p1:p2]), '->', repr(bin[pos:pos + l]))
pos += l
q = p2
if q < len(a):
print('', repr(a[q:]))
showdiff("x\n\nx\n\nx\n\nx\n\nz\n", "x\n\nx\n\ny\n\nx\n\nx\n\nz\n")
showdiff("x\n\nx\n\nx\n\nx\n\nz\n", "x\n\nx\n\ny\n\nx\n\ny\n\nx\n\nz\n")
# we should pick up abbbc. rather than bc.de as the longest match
showdiff("a\nb\nb\nb\nc\n.\nd\ne\n.\nf\n",
"a\nb\nb\na\nb\nb\nb\nc\n.\nb\nc\n.\nd\ne\nf\n")
print("done")
def testfixws(a, b, allws):
c = bdiff.fixws(a, allws)
if c != b:
print("*** fixws", repr(a), repr(b), allws)
print("got:")
print(repr(c))
testfixws(" \ta\r b\t\n", "ab\n", 1)
testfixws(" \ta\r b\t\n", " a b\n", 0)
testfixws("", "", 1)
testfixws("", "", 0)
print("done")
print("Nice diff for a trivial change:")
showdiff(
''.join('<%s\n-\n' % i for i in range(5)),
''.join('>%s\n-\n' % i for i in range(5)))
print("Diff 1 to 3 lines - preference for appending:")
showdiff('a\n', 'a\n' * 3)
print("Diff 1 to 5 lines - preference for appending:")
showdiff('a\n', 'a\n' * 5)
print("Diff 3 to 1 lines - preference for balanced recursion:")
showdiff('a\n' * 3, 'a\n')
print("Diff 5 to 1 lines - preference for balanced recursion:")
showdiff('a\n' * 5, 'a\n')