--- a/mercurial/filemerge.py	Mon Apr 19 20:30:31 2010 +0200
+++ b/mercurial/filemerge.py	Mon Apr 19 20:41:53 2010 +0200
@@ -135,6 +135,9 @@
     if not fco.cmp(fcd.data()): # files identical?
         return None
 
+    if fca == fco: # backwards, use working dir parent as ancestor
+        fca = fcd.parents()[0]
+
     ui = repo.ui
     fd = fcd.path()
     binary = isbin(fcd) or isbin(fco) or isbin(fca)

--- a/tests/test-inotify	Mon Apr 19 20:30:31 2010 +0200
+++ b/tests/test-inotify	Mon Apr 19 20:41:53 2010 +0200
@@ -82,7 +82,7 @@
 echo c >> a
 hg st
 
-hg up 0
+HGMERGE=internal:local hg up 0
 hg st
 
 HGMERGE=internal:local hg up

--- a/tests/test-inotify.out	Mon Apr 19 20:30:31 2010 +0200
+++ b/tests/test-inotify.out	Mon Apr 19 20:41:53 2010 +0200
@@ -44,7 +44,6 @@
 A h
 R h/h
 M a
-merging a
 1 files updated, 1 files merged, 2 files removed, 0 files unresolved
 M a
 3 files updated, 1 files merged, 0 files removed, 0 files unresolved

--- a/tests/test-merge-local.out	Mon Apr 19 20:30:31 2010 +0200
+++ b/tests/test-merge-local.out	Mon Apr 19 20:41:53 2010 +0200
@@ -24,16 +24,20 @@
 use 'hg resolve' to retry unresolved file merges
 merging zzz1_merge_ok
 merging zzz2_merge_bad
-2 files updated, 2 files merged, 3 files removed, 0 files unresolved
+warning: conflicts during merge.
+merging zzz2_merge_bad failed!
+2 files updated, 1 files merged, 3 files removed, 1 files unresolved
+use 'hg resolve' to retry unresolved file merges
 --- a/zzz1_merge_ok
 +++ b/zzz1_merge_ok
-+new first line
 +new last line
 --- a/zzz2_merge_bad
 +++ b/zzz2_merge_bad
 +another last line
++=======
 M zzz1_merge_ok
 M zzz2_merge_bad
+? zzz2_merge_bad.orig
 # local merge with conflicts
 merging zzz1_merge_ok
 merging zzz2_merge_bad
@@ -43,18 +47,23 @@
 use 'hg resolve' to retry unresolved file merges
 merging zzz1_merge_ok
 merging zzz2_merge_bad
-2 files updated, 2 files merged, 3 files removed, 0 files unresolved
+warning: conflicts during merge.
+merging zzz2_merge_bad failed!
+2 files updated, 1 files merged, 3 files removed, 1 files unresolved
+use 'hg resolve' to retry unresolved file merges
 --- a/zzz1_merge_ok
 +++ b/zzz1_merge_ok
-+new first line
 +new last line
 --- a/zzz2_merge_bad
 +++ b/zzz2_merge_bad
 +another last line
 +=======
++=======
 +new last line
++=======
 M zzz1_merge_ok
 M zzz2_merge_bad
+? zzz2_merge_bad.orig
 # local merge without conflicts
 merging zzz1_merge_ok
 4 files updated, 1 files merged, 2 files removed, 0 files unresolved

--- a/tests/test-up-local-change.out	Mon Apr 19 20:30:31 2010 +0200
+++ b/tests/test-up-local-change.out	Mon Apr 19 20:41:53 2010 +0200
@@ -48,8 +48,7 @@
 update: a 2/2 files (100.00%)
 picked tool 'true' for a (binary False symlink False)
 merging a
-my a@802f095af299+ other a@33aaa84a386b ancestor a@33aaa84a386b
- premerge successful
+my a@802f095af299+ other a@33aaa84a386b ancestor a@802f095af299
 0 files updated, 1 files merged, 1 files removed, 0 files unresolved
 changeset:   0:33aaa84a386b
 user:        test