mercurial/strutil.py

scmutil: abort if an empty revision is given to revpair()

When using 'extdiff --patch' to check the changes in a rebase, 'precursors(x)'
evaluated to an empty set because I forgot the --hidden flag, so the other
revision was used as the replacement for the empty set.  The result was the
patch for the other revision was diffed against itself, and the tool saying
there were no differences.  That's misleading since the expected diff args were
silently changed, so it's better to bail out.

The other uses of scmutil.revpair() are commands.diff and commands.status, and
it doesn't make sense to allow an empty revision there either.  The code here
was suggested by Yuya Nishihara.

# strutil.py - string utilities for Mercurial
#
# Copyright 2006 Vadim Gelfer <[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

def findall(haystack, needle, start=0, end=None):
    if end is None:
        end = len(haystack)
    if end < 0:
        end += len(haystack)
    if start < 0:
        start += len(haystack)
    while start < end:
        c = haystack.find(needle, start, end)
        if c == -1:
            break
        yield c
        start = c + 1

def rfindall(haystack, needle, start=0, end=None):
    if end is None:
        end = len(haystack)
    if end < 0:
        end += len(haystack)
    if start < 0:
        start += len(haystack)
    while end >= 0:
        c = haystack.rfind(needle, start, end)
        if c == -1:
            break
        yield c
        end = c - 1