tests/svn-safe-append.py

rebase: calculate ancestors for --base separately (issue5420)

Previously, the --base option only works with a single "branch" - if there
is one changeset in the "--base" revset whose branching point(s) is/are
different from another changeset in the "--base" revset, "rebase" will error
out with:

  abort: source is ancestor of destination

This happens if the user has multiple draft branches, and uses "hg rebase -b
'draft()' -d master", for example. The error message looks cryptic to users
who don't know the implementation detail.

This patch changes the logic to calculate the common ancestor for every
"base" changeset separately so we won't (incorrectly) select "source" which
is an ancestor of the destination.

This patch should not change the behavior where all changesets specified by
"--base" have the same branching point(s).

A new situation is: some of the specified changesets could be rebased, while
some couldn't (because they are descendants of the destination, or they do
not share a common ancestor with the destination). The current behavior is
to show "nothing to rebase" and exits with 1.

This patch maintains the current behavior (show "nothing to rebase") even if
part of the "--base" revset could be rebased. A clearer error message may be
"cannot find branching point for X", or "X is a descendant of destination".
The error message issue is tracked by issue5422 separately.

A test is added with all kinds of tricky cases I could think of for now.

#!/usr/bin/env python

from __future__ import absolute_import

__doc__ = """Same as `echo a >> b`, but ensures a changed mtime of b.
Without this svn will not detect workspace changes."""

import os
import sys

text = sys.argv[1]
fname = sys.argv[2]

f = open(fname, "ab")
try:
    before = os.fstat(f.fileno()).st_mtime
    f.write(text)
    f.write("\n")
finally:
    f.close()
inc = 1
now = os.stat(fname).st_mtime
while now == before:
    t = now + inc
    inc += 1
    os.utime(fname, (t, t))
    now = os.stat(fname).st_mtime