tests/svn-safe-append.py

copies: follow copies across merge base without source file (issue6163)

As in the previous patch, consider these two histories:

  @  4 'rename x to y'
  |
  o  3 'add x again'
  |
  o  2 'remove x'
  |
  | o  1 'modify x'
  |/
  o  0 'add x'

  @  4 'rename x to y'
  |
  o  3 'add x again'
  |
  | o  2 'modify x'
  | |
  | o  1 'add x'
  |/
  o  0 'base'

We trace copies from the 'modify x' commit to commit 4 by going via
the merge base (commit 0). When tracing file 'y' (_tracefile()) in the
first case, we immediately find the rename from 'x'. We check to see
if 'x' exists in the merge base, which it does, so we consider it a
valid copy. In the second case, 'x' does not exist in the merge base,
so it's not considered a valid copy. As a workaround, this patch makes
it so we also attempt the check in mergecopies's base commit (commit 1
in the second case). That feels pretty ugly to me, but I don't have
any better ideas.

Note that we actually also check not only that the filename matches,
but also that the file's nodeid matches. I don't know why we do that,
but it was like that already before I rewrote mergecopies(). That
means that the rebase will still fail in cases like this (again, it
already failed before my rewrite):


  @  4 'rename x to y'
  |
  o  3 'add x again with content X2'
  |
  o  2 'remove x'
  |
  | o  1 'modify x to content X2'
  |/
  o  1 'modify x to content X1'
  |
  o  0 'add x with content X0'

Differential Revision: https://phab.mercurial-scm.org/D6604

#!/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 stat
import sys

if sys.version_info[0] >= 3:
    text = os.fsencode(sys.argv[1])
    fname = os.fsencode(sys.argv[2])
else:
    text = sys.argv[1]
    fname = sys.argv[2]

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