So what's the status of this now?

changeset:   10294:d1cd09bb4d18
branch:      stable
parent:      10284:b08ffd27dfc8
user:        Matt Mackall <mpm@selenic.com>
date:        Thu Jan 28 22:45:46 2010 -0600
summary:     copies: fix issue1994

In main, but it breaks lots of tests.

This is definitely specific to rebase and how it fiddles with ancestry. The
patch that fixes your rebase case breaks a bunch of tests in the test suite.

Also, in your test case, this should -not- appear:

  local changed dd/a which remote deleted
 use (c)hanged version or (d)elete? c

..because remote didn't delete the file, it renamed it. The new code detects
the rename(!), but detects it as being a divergent rename (both sides
renaming it from its original name) because it's not following the "virtual
history" that rebase tries to impose on the merge.

@mpm: it works with your patch. The test output is slightly modified into:
"""
ERROR: /Users/pmezard/dev/mercurial/hg/hg-pmezard/tests/test-rebase-copies
output changed
--- /Users/pmezard/dev/mercurial/hg/hg-pmezard/tests/test-rebase-copies.out 
+++ /Users/pmezard/dev/mercurial/hg/hg-pmezard/tests/test-rebase-copies.err 
@@ -4,6 +4,7 @@
 1 files updated, 0 files merged, 1 files removed, 0 files unresolved
 created new head
 1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+merging dd/a
  local changed dd/a which remote deleted
 use (c)hanged version or (d)elete? c
 adding branch
!
Failed test-rebase-copies: output changed
# Ran 1 tests, 0 skipped, 1 failed.
"""
but that's probably better anyway.

Try this:

diff -r 08a0f04b56bd mercurial/copies.py
--- a/mercurial/copies.py	Mon Jan 25 00:05:27 2010 -0600
+++ b/mercurial/copies.py	Mon Jan 25 01:14:41 2010 -0600
@@ -154,7 +154,7 @@
                 break # no merge needed, quit early
             c2 = ctx(of, m2[of])
             cr = related(oc, c2, ca.rev())
-            if of == f or of == c2.path(): # non-divergent
+            if cr and (cr.path() == f or cr.path == c2.path()): # non-divergent
                 copy[f] = of
                 of = None
                 break

tonfa: Yes, it takes an hg st for one user from 10min to 3sec, while your
optimization didn't help.

By the way, is the improvement from eb243551cbd8 justified on default (I 
pushed a speed up, just not on stable):

changeset:   9991:a7d11deb47dd
user:        Benoit Boissinot <benoit.boissinot@ens-lyon.org>
date:        Thu Dec 03 01:01:49 2009 +0100
summary:     revlog: add fast path to ancestor

To reproduce, run the attached test script before and after:


changeset:   10262:eb243551cbd8
branch:      stable
user:        Matt Mackall <mpm@selenic.com>
date:        Tue Jan 19 22:20:05 2010 -0600
files:       mercurial/context.py mercurial/copies.py
description:
copies: speed up copy detection

On some large repos, copy detection could spend > 10min using
fctx.ancestor() to determine if file revisions were actually related.
Because ancestor must traverse history to the root to determine the
GCA, it was doing a lot more work than necessary. With this
replacement, same status -r a:b takes ~3 seconds.